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    Insights and Perspectives
    • The Role of Soil in the Formation of Plant Biodiversity and Its Research Significance

      CAI Zucong

      2022,59(1):1-9, DOI: 10.11766/trxb202106170314

      Abstract:

      Soil scientists well know the role of biological factor as one of the five major natural factors driving soil formation and evolution, but they rarely ask about the role of soil in the origin and evolution of plants. I believe that the origin and evolution process of land plants is essentially an adaptation process to the soil environment. It means that the soil environment has a "mold effect" on the formation and evolution of the plants. The diversity of soil environments in profile thickness and layer configuration, physical, chemical and biological properties provides a basis of the formation of the plant diversity. Since plant roots grow in the soil, by absorbing nutrients from the soil to meet their growth demands, the role of soil environment on the formation of plant characteristics is mainly reflected in the genetic characteristics of plant root phenotype, nutritional physiology and resistant physiology to the stress of soil environments. Soil-plant diversity builds diverse habitats for different types of organisms and plays a key role in the formation and maintenance of biodiversity. Protecting the diversity of soil environment is crucial for biodiversity protection, and the key is to protect the heterogeneity of soil environment. In order to enhance crop yields, the cultivation processes of cropland soils are, in essence, the homogenization processes of soil properties, hence, it is not conducive to biodiversity protection. It is of great significance to trace the soil environment in which crops originate, understand the crop genetic characteristics formed by the originated soil environment for the crop allocation, breeding, and crop nutrient management, and so on. However, the research requires not only rich knowledge in soil science, but also rich knowledge in other disciplines, particularly in molecular genetics. Therefore, conducting research in the field will expand research fields of soil science, re-understand the importance of soil resources, and promote the cross-integration of soil science and other disciplines.

    Reviews and Comments
    • Research on Salt-affected Soils in China: History, Status Quo and Prospect

      YANG Jingsong, YAO Rongjiang, WANG Xiangping, XIE Wenping, ZHANG Xin, ZHU Wei, ZHANG Lu, SUN Ruijuan

      2022,59(1):10-27, DOI: 10.11766/trxb202110270578

      Abstract:

      Taking salt-affected soils and salt-affected habitat as the main research objects, salt-affected soil research is a field focusing on genesis and evolution process of salt-affected soils and salinization, on impact and mechanism of environmental factors and human activities on salinization, and on theory and technology of salt-affected soils management, improvement and utilization. With huge area and a wide variety, salinization has prominent impact on agricultural production and ecological environment in China. On salt-affected soil research, the theories and technical methods proposed by Chinese scientists, such as "water and salt regulation", "water and salt balance", "salt-free fertile layer" and "obstacle reduction", have played a positive role in developing agricultural production, improving land productivity, ensuring food security and expanding cultivated land resources. Recently, China has made positive progress and achievements in monitoring the evolution process of soil salinization and multi-source data fusion, simulation and scale expansion of soil water and salt transport process, nutrient circulation-loss control-efficiency increase of salt-affected farmland, ecological reduction of saline obstacles, microbial remediation of saline obstacles, optimal management of irrigation and drainage of saline farmland and safe utilization of marginal water. It is suggested to carry out theoretical and technical research on efficient and safe water use theory and technology for precise salt control of salt-affected soils, green reduction and health conservation of soil salinity barriers, expansion of nutrient storage capacity of saline farmland, carbon increase and emission reduction, coupling response and collaborative adaptation of soil salinization and regional ecology. We should strive to expand the theoretical research and develop new technology for agriculture resources, ecology, environment and other industries and fields, and play more important role in the country's agricultural upgrading, food security, cultivated land security, ecological security and high-quality development. This paper reviews the development process of salt-affected soils research in China and the relationship between domestic and foreign research, systematically analyzes the characteristics and progress of recent salt-affected soils related research, and puts forward the research prospect of salt-affected soils in China in combination with the frontier hotspots and national needs of relevant research at home and abroad.

    • New Perspectives about Health Risk Assessment of Soil Heavy Metal Pollution-Origin and Prospects of Probabilistic Risk Analysis

      YANG Shiyan, LIU Xingmei, XU Jianming

      2022,59(1):28-37, DOI: 10.11766/trxb202009120516

      Abstract:

      Health hazard assessment of soil heavy metal pollution is the paramount premise of soil environmental risk management. Probabilistic risk assessment (PRA) that upholds the idea of uncertainty and variability of characterization has opened up new perspectives about health risk assessment of soil heavy metal pollution. In order to strengthen the theoretical cognition of PRA and to promote in-depth application of PRA in the field of soil heavy metals exposure risk assessment, this paper systematically elaborated the theoretical basis and connotation evolution of PRA, with the aid of the bibliometric and integrating analysis methods, and compared PRA with the traditional deterministic risk assessment (DRA), with emphases on dynamics of its application and development and trends and directions of the research on PRA in future. The research indicates that being an important supplement to DRA, PRA is an integration of a set of concepts and technologies that include both variability and uncertainty into the environment risk assessment. It has broken through the limit of the traditional conservative single-point risk estimation, and is applicable to fine assessment of the risk of soil heavy metals exposure to human health. However, the current PRA framework fails to explain clearly the definition of parameter boundaries and uncertainty handling of exposure scenarios, thus leading to arguments over its accuracy, applicability and resource costs. Another challenge originates from its integration with source apportionment and biomarkers analysis of soil heavy metals and development towards a multi-media, multi-receptor and multi-scale PRA framework. It is, therefore, essential for us to unfold in-depth research on PRA from the aspects of theoretical basis, technology and practical application, so as to enhance the policy implications in drafting benchmarks and developing management systems of soil environment risks.

    • Advancement in Researches on Technical Systems and Modes for Risk Management and Control of Contaminated Sites at Home and Aborad

      LI Xiaonuo, CHEN Weiping, Lü Sidan

      2022,59(1):38-53, DOI: 10.11766/trxb202010120569

      Abstract:

      With risk management as basic principle, sustainable remediation and safe utilization of contaminated sites has become an urgent environmental and developmental issue worldwide. To promote the application of rapid, economical and effective risk management and control technologies at the early stage of the soil pollution prevention and control drive in China, while specifying attributes of the broad and narrow connotations of risk management and control of contaminated sites, the paper elaborated systematically the technical theory, engineering implementation and applicable conditions of the risk management technologies in narrow connotation, including engineering control, institutional control and monitored natural attenuation, analyzed the risk management and control systems in developed countries, with reference to the risk management and control mode supported by the technical system and policy system established on the reality of the soil environmental management in China. In the end, aiming at the problems of weak foundation, unsound system and insufficient technical support of the risk management and control system in China, the authors put forth an overall layout of "prevention-control-remediation-management" for risk management and control of contaminated sites in consistence with the idea of green sustainability and the theory of life cycle management, which is expected to be of great practical significance to promotion of application of the technology and improvement of the risk management level.

    • The Abiotic and Biotic Transformation Processes of Soil Iron-bearing Minerals and Its Interfacial Reaction Mechanisms of Heavy Metals: A Review

      HU Shiwen, LIU Tongxu, LI Fangbai, SHI Zhenqing

      2022,59(1):54-65, DOI: 10.11766/trxb202010300268

      Abstract:

      Iron (Fe) minerals are widely distributed in soil and are an important component of soils, which play an important role in regulating soil health, pollutant behavior, and element biogeochemical cycles. These minerals are of great importance since they can influence many key chemical processes. For instance, they can affect the bioavailability and toxicity of heavy metals via a series of physical and chemical processes, such as physical encapsulation, adsorption, complexation, and co-precipitation. Additionally, soil organic substances can affect the transformation of iron minerals and lead to changes in the structure and surface properties of the products. Besides, the resultant products of such interactions have been reported to show a varied affinity for heavy metals and demonstrate contrasting effects on the environmental behaviors of heavy metals. In this review, we considered the following three points:(i) the effect of reaction pH, reaction temperature, and the added ferrous iron activity and concentrations on the abiotic transformation rates, degree, and pathways; (ii) the influence of soil root exudates such as oxalate acid, citric acid, and phenols on the accumulation, reduction, nucleation, dissolution and coprecipitation of Fe oxides; and lastly (iii) the surface complexation, and redox reactions of heavy metals at iron minerals-water interface. Here, the influence of iron mineral transformation on (a) the distribution of heavy metals, (b) the reaction process and molecular mechanism of heavy metals at the interface of iron mineral-organic matter, and (c) the use of kinetic models to evaluate and predict the environmental behavior of heavy metals is given in detail. It was observed that the ferrous oxidation is mediated by anaerobic photoautotrophic ferric oxidizing bacteria, and the bacteria affect the iron oxidation process through nitrate-reducing ferrous oxidation and biomineralization. Also, iron-reducing bacteria influence the iron reduction process primarily through chelating reagents, redox-active electron shuttling substances, and the c-type cytochrome of the outer membrane. Additionally, soil organic matters (e.g., fulvic acids and humic acids) can affect the aggregation and stability of soil aggregates. They can interact with iron minerals packaged in soil aggregates by electrostatic attraction, coordination exchange, van der Waals force, hydrophobic interaction, and hydrogen bonding, thereby affecting the biotic and abiotic transformation process of iron minerals. Nevertheless, this study can only serve as a reference for detail understanding of iron mineral-organic matter-heavy metal dynamic interaction mechanism at the microscale and the interaction molecular mechanisms of heavy metal at the soil multi-component interface. We suggest that future researchers should provide (i) an in-depth analysis revealing the molecular mechanism of the soil heavy metals environmental behavior under the dynamic interaction of iron minerals, soil organic matter and microorganisms, (ii) a clear picture of the soil interfacial reaction processes and mechanism at the atomic and molecular level, and (iii) a path for developing an in-situ dynamic monitoring method and technology for soil-water interface reaction process in the microscale, simulating the complex biogeochemical reactions, and predicting and assessing the trend of heavy metals in the complex natural environment by coupled kinetics models.

    • Progress of Impact of Plant Domestication on Composition and Functions of Microbiome

      SUN Mingxue, SONG Chunxu

      2022,59(1):66-78, DOI: 10.11766/trxb202006090210

      Abstract:

      The plant microbiome plays crucial roles in nutrient acquisition, growth and health of plants, and has the potential to reduce dependence of the crops on fertilizers and pesticides. Plant domestication shows a significant impact on composition and functions of the microbiome. However, the mechanisms underlying this process are not well understood. Here, the paper is presented to summarize impacts of the variation of the plant in cultivar and genotype, root exometabolite and habitat, while the plants are being domesticated on composition and functions of the microbiome. Multifaceted comparison shows:(1) that domestication affects microbial diversity significantly and most of the plant microbial communities decrease in diversity during domestication; wild crops might attract more microbial communities that are beneficial to the resistance of pathogenic bacteria:and variation of the plant in cultivar and genotype affects composition of the rhizosphere microbiome and symbiotic relationship of the microbiome with the plant; (2) that changes in root exometabolite affect nutrient acquisition of the microbes and domestication weakens chemical defense of the plant; (3) Relative to the microbiome in the soil of croplands, the one in the virgin soil habitat is composed of more diverse and unique microbes. To sum up, the change in the plant rhizosphere microbiome is the result of the comprehensive interactions of multiple factors during the plant domestication process. Revealing the impacts of plant domestication on functions of the microbiome and restoring the beneficial plant-microbe connections and properties that may have got lost during plant domestication, can facilitate the development of new microbiome-based breeding strategies.

    Research Articles
    • Pedogenetic Characteristics and Paleoenvironment Significance of Mesozoic Paleosols in Sichuan Basin

      LI Jun, HUANG Chengmin, WEN Xingyue, YUE Zhihui

      2022,59(1):79-91, DOI: 10.11766/trxb202004300208

      Abstract:

      [Objective] Detailed inversion of paleoclimates facilitates a better understanding of variation of the climate in the history and provides a basis for predicting future changes triggered by human activities in climate. Paleosol, formed on the Earth's surface during its geological period, is a direct record of the information about the terrestrial environmental conditions when it was formed. Quite a volume of paleosols are found developed within the Mesozoic strata across the Sichuan Basin and they may serve as an important terrestrial archive available for the research on global or regional deep-time paleoclimate.[Method] In this paper, a total of four hundred and thirteen deep-time paleosol profiles were identified in the Mesozoic strata of the Sichuan Basin, southwest China based on the pedogenic characteristics of paleosols. Of the paleosol profiles, observations and analyses were performed for their morphology, micromorphology, mineral composition, particle size composition and geochemical properties, for summarization of their pedogenic characteristics, for researches on their classification, and for discussion of their environmental significance as indicators.[Result] These profiles with distinct pedogenic features, such as presence of root traces and/or animal burrows, accumulation of pedogenic carbonate nodules, vertical variation of color, and development of soil horizons and soil structures, could be sorted into four different types of paleosols (i.e., Paleosol A, Paleosol B, Paleosol C, and Paleosol D). All the paleosol horizons are predominantly composed of quartz and calcite in mineralogy with minor proportions of feldspar, muscovite, illite and/or smectite. And content of the minerals varies with type of the paleosol. The paleosols are obviously lower than their corresponding modern ones in TOC and vary in a similar trend. And moreover, the two are basically consistent in element composition, and do not differ much in geochemical weathering index, leaching index, clayeyness, salinization index, and barium/strontium ratio, which indicate that the paleosols vary in chemical weathering degree with geological period and type of the soil.[Conclusion] According to the standards of the Chinese Soil Taxonomy, the paleosols, observed within the Mesozoic strata of the Sichuan Basin, are analogous to the four orders of modern soil, that is, Primosols, Cambosols, Aridosols, and Argosols, and the proportion of the last is relatively low. The development of the different types of paleosols indicates that the environment of the Sichuan Basin experienced repeated alternations between aridity and humidity during the Mesozoic Era, however, it was mainly under semi-arid and arid weathers.

    • Application of Seismic Refraction Tomography in Stratigraphic Division of Critical Zones in Red Soil Area

      ZHONG Chen, SONG Xiaodong, YANG Shunhua, ZHANG Ganlin

      2022,59(1):92-104, DOI: 10.11766/trxb202008080247

      Abstract:

      [Objective] It is of great significance to identify structure of the critical zones (CZs) of the earth for better understanding the geochemical, ecological and hydrological processes occurring in the CZs. However, previous studies relied mainly on borehole drilling and profiles, which is far from enough to help draw a full picture of the underground structure of the CZs. To overcome this problem, in this study, attempts were made to combine borehole drilling with the seismic refraction tomography (SRT) method to test if the seismological method can effectively detect the structure of CZs of highly weathered regolith.[Method] To that end, case studies were carried out of the Sunjia Catchment of Yingtan and the terraces of slat bedrock along the Yangtze River in Changsha. The study areas are both located in the red soil region, but different in bedrock composition. The bedrock is red sandstone in the Sunjia Catchment and sedimentary slate in the terraces along the Yangtze River. Ten seismic lines were arranged in the two study areas, and each had a detection depth ranging between 25~30 m. In addition, a total of 13 boreholes were drilled in the two study areas. In the field investigation recognition capability and error range of the SRT method were evaluated.[Result] Results show:SRT can effectively discern propagation velocity of p-wave at different depths in the CZs, and determine depth of key interfaces. In Yingtan, the identified lower boundary of the Overburden layer varies in the range of 3.0~5.2 m, with root mean square error (RMSE) being 1.7 m, and the identified bedrock surface does in the range between 8.2 and 22.0 m, with RMSE being 7.0 m. In Changsha, the identified lower boundary of the first layer falls in the range of 8.1~13.2 m, with RMSE being 2.4 m, and the identified bedrock surface does between 18.8 and 22.9 m, with RMSE being 0.9 m. The prediction is in good agreement with the drilling observation. The seismic wave travels at 2400 m/s in red sandstone and at 2 000 m·s-1 in sedimentary slate. Under flat terrain the overburden and bedrock are stable, while under sloping terrain, the overburden is thick on the top slope, and gets thinner on the mid slope. Landfills reduce the precision of seismograph in predicting underground structure for they have great impacts on the structure of the overburden layer, but not much on the structure of the deep underground. Groundwater in aquifers makes the overburden of the critical zones divided with the seismic refraction method tend to be thinner.[Conclusion] The longitudinal wave traveling through the subterranean layers of the CZs varies in velocity with the layer, which is the key to identification of the structural layers of the CZs by seismograph. SRT can not only improve the efficiency of field investigations, but also advance the development of the CZ three-dimensional mapping.

    • Influence of Soil Erosion on the Obstacle Factors of Cultivated Layer in Purple Sloping Farmland

      JIANG Na, SHI Dongmei, ZENG Xiaoying, YE Qing, ZHANG Jianle, LI Huidan

      2022,59(1):105-117, DOI: 10.11766/trxb202011090401

      Abstract:

      [Objective] Purple soil sloping farmland is an important cultivated land resource in the upper reaches of the Yangtze River. Therefore, clarifying the change characteristics and main obstacle factors influencing purple soil sloping farmland under different erosion degrees is important.[Method] In a cultivated layer of sloping farmland, five erosion degrees (0, 5, 10, 15, 20 cm) were set up in situ. The cultivated layer quality index (CLQI) and obstacle degree (Mij) were calculated by selecting 10 quality indexes, including bulk density, total porosity, saturated hydraulic conductivity, soil compactness, soil shear strength, organic matter, total nitrogen, total phosphorus, pH and cation exchange capacity. Thus, the change characteristics of cultivated layer quality and obstacle degree under different erosion degrees were quantitatively evaluated.[Result] Soil erosion destroyed the structure of the cultivated layer, resulting in deterioration of cultivated layer quality index. Total porosity, saturated hydraulic conductivity, shear strength, cation exchange capacity, total nitrogen and total phosphorus decreased with the increase of erosion degree, while bulk density and soil compaction increased with the increase of erosion degree. The order of obstacle degree from cultivated layer quality was soil compaction (17.04%) > saturated hydraulic conductivity (15.83%) > total nitrogen (11.49%) > organic matter (11.47%) > total phosphorus (10.73%). The main obstacle factors of cultivated layer quality were soil compaction, saturated hydraulic conductivity, total nitrogen, organic matter and total phosphorus. The effect of soil erosion and management measures on soil compaction was significant (P < 0.01) while the effect of management measures on organic matter and saturated hydraulic conductivity was extremely significant (P < 0.01). Also, the interaction between soil erosion and management measures had a significant (P < 0.05) effect on saturated hydraulic conductivity and organic matter.[Conclusion] The main obstacles of cultivated layer types of purple soil sloping farmland can be divided into soil nutrient-poor obstacle and soil acidification obstacle. All the findings above can provide a theoretical basis for quality control of purple soil sloping farmland.

    • Effects of Temperature on Soil Atterberg Limit in Soil of Collapsing Gully Wall in the Hilly Granitic Region of South China

      ZHANG Yue, ZHAO Dongfeng, ZHENG Qinmin, LIN Jinshi, JIANG Fangshi, HUANG Bifei, GE Hongli, HUANG Yanhe

      2022,59(1):118-128, DOI: 10.11766/trxb202007300287

      Abstract:

      [Objective] Collapsing gully, one of the most serious soil erosion problems in the tropical and subtropical areas of South China, occurs mainly in the hilly red soil regions as triggered off by the interaction of runoff and gravity. A collapsing gully generally consists of five parts:an upper catchment, a collapsing wall, a colluvial deposit, a scour channel, and an alluvial fan. Stability of a collapsing gully wall determines the scale of the collapsing gully and the volume of the colluvial deposit. Rainfall and temperature not only determine weathering rate of soils, but also affect the mechanical state of granite red soils. Liquid and plastic limits are the most commonly tested mechanical indices. However, few studies have been reported about investigation of the effects of temperature on soil Atterberg limits in collapsing gullies.[Method] In this study, soil samples were collected from the three soil layers in a soil profile, i.e. red soil layer, sandy soil layer and detritus layer, of a typical collapsing gully located in Anxi County, Fujian Province. The soil profile was subdivided into three soil layers in the light of their colors and structures. Four levels of temperature (15, 25, 40 and 60℃) were set to investigate their effects on soil liquid and plastic limits and soil bound water content.[Result] The red soil layer was found to be the highest in soil liquid limit, plastic limit and plastic index and followed by the sandy soil layer and the detritus layer. Liquid and plastic limits positively and linearly related to contents of fine clay, organic matter and iron oxide. When temperature rose from 15℃ to 40℃, soil liquid and plastic limits in the three soil layers all decreased, as well as the soil bound water content. When temperature rose from 40℃ to 60℃, soil plastic limit increased in the red soil layer and the detritus layer, and soil liquid limit increased in the red soil layer and sandy soil layer. The effect of temperature on soil bound water content was consistent with the changes in soil liquid and plastic limits.[Conclusion] The soil liquid limit of the detritus layer is approximate to its saturated water content, and decreases gradually with the rising soil temperature. In the case of high temperature and heavy rain in summer in this region, flow deformation is the most likely to occur in the detritus layer, which might be one of the main reasons causing the collapse of a collapsing gully wall.

    • Hydraulic Characteristics of Rills of Non-eroded and Eroding on Saturated Purple Soil

      TAO Tingting, CHEN Xiaoyan, CHEN Shiqi, HAN Zhen, LI Yanhai, GU Xiaojie, YE Hongming

      2022,59(1):129-138, DOI: 10.11766/trxb202005280259

      Abstract:

      [Objective] Rill hydraulics is an important dynamic factor affecting slope soil erosion. Rill morphology affects flow dynamics characteristics at all erosion stages, and further on development and morphology evolution of rill erosion.[Method] Scouring experiments were conducted on flumes packed with saturated purple soil for determination of runoff velocity in non-eroded and eroding rill, relative to flow discharge (2, 4, and 8 L·min-1) and slope gradient (5°, 10°, 15°, and 20°). The electrolyte pulse boundary model method was used to measure rill flow velocity (V), On such a basis, calculation was done of the hydraulic parameters of rills of non-eroded and eroding (including mean flow depth (h), Reynolds number (Re), Froude number (Fr), Darcy-Weisbach friction coefficient (f) and Manning roughness coefficient (n)), and then comparison was made of the hydraulic characteristics between the rills of the two states.[Result] Results show that the flow velocity in the rills of non-eroded state (VN) ranged from 0.170 to 0.778 m·s-1, and that in the rills of eroding state (VE) did from 0.156 to 0.619 m·s-1. VN varied with flow discharge to the power of 0.524 and with slope gradient to the power of 0.601, while VE varied with flow discharge to the power of 0.474 and with slope gradient to the power of 0.530, and their determination coefficient was 0.910 and 0.905, respectively. The mean flow depth of the rills of non-eroded state (hN) ranged from 0.078 to 0.413 cm, and that of the rills of eroding state (hE) did from 0.107 to 0.450 cm. hN varied with flow discharge to the power of 0.502 and with slope gradient to the power of -0.505, while hE varied with flow discharge to the power of 0.558 and with slope gradient to the power of -0.415, and their determination coefficients were both 0.942. When the flow discharge was 2 L·min-1, Re was < 500, and when the flow discharge was 4 or 8 L·min-1, Re varied between 500 and 2 000. Fr was always >1 regardles of working conditions, and ranged from 1.237 to 6.026 in the rills of non-eroded (FrN), and from 1.079 to 4.274 in the rills of eroding state (FrE). f ranged from 0.079 to 0.856, n did from 0.011 to 0.035, fN (in the rills of non-eroded state) did from 0.079 to 0.592, and fE (in the rills of eroding state) did from 0.156 to 0.856.[Conclusion] The parameter h is positively related to flow discharge in the power function, but negatively to the slope gradient. The influences of flow discharge and slope gradient on V decrease in all the rills regardless of state, and that of the former on h increases, while that of the latter on h decreases. The flow regime is dominated by transition flow and rarely by laminar flow, all belonging to rapids. Re does not differ much between rills different in state; FrEremaints almost a constant while approaching 1; f varies as affected by the interaction between V and h, in which V is the dominant one in the rill of non-eroded state, while h is in the other rills. During the development of the rills from the non-eroded state to the eroding state, V decreases, while h increases, so that Re increases, Fr decreases, and both f and n increase, and the erosion of the rills of eroding state caused by rill flow is lower than that of the rills of non-eroded state in intensity. This is because variation of the rills in morphology promotes energy dissipation, which in turn retards rill flow, reduces flow velocity, but increases the mean flow depth, thus eventually leading to changes in flow regime and resistance. All the findings in this study may hopefully help determine hydraulic characteristics of saturated purple soils with rills different in state and be of certain reference value to the establishment of a physical model for researches on soil erosion.

    • Distribution and Application of Soil Electrical Resistivity in Slope Land and Dam Land in the Loess Region

      LIU Chenggong, JIA Xiaoxu, ZHAO Chunlei, SHAO Mingan

      2022,59(1):139-147, DOI: 10.11766/trxb202004260196

      Abstract:

      [Objective] Soil moisture is one of the most important factors for plant growth and solute transport in arid and semi-arid areas. An accurate and effective measurement of profile soil moisture is a critical issue of soil hydrology. The technology of electrical resistivity tomography (ERT) based on soil electrical properties provides a new geophysical method for measuring soil moisture content in the profile, which has been widely applied in the studies of soil water dynamics, groundwater recharge and root-water interactions in many regions in the world. However, little is known yet about the applicability of ERT to monitoring soil moisture or groundwater in the loess area, and the lack of information on profile soil resistivity (ρ) as affected by land use inhibits progress of the research on hydro-geophysics. This study was conducted to (1) explore characteristics of profile ρ, as affected by land use and slope position, in slope land and dam land in the northern part of the Loess Plateau, (2) determine effects of slope position and land use type on ρ and (3) examine applicability of ERT to monitoring soil moisture and groundwater dynamics in the loess area.[Method] Profile ρ in slope lands and dam land, different in land use type (including cropland, natural grassland, artificial grassland and caragana shrubland) was measured with a high-density ERT (Advanced Geosciences, Inc.) in the Liudaogou catchment in the northern part of the Loess Plateau. Variation of profile ρ with land use type and slope position was analyzed with ANOVA.[Results] Results show that land use type and slope position had significant effects on ρ in slope land. In terms of mean profile ρ, lands different in land use type followed an order of caragana shrubland > artificial grassland > natural grassland > cropland. Furthermore, mean profile ρ was the lowest in the bottom of the slope, followed by the middle and top of the slope. These findings suggest that profile ρ was closely related to soil moisture condition. Profile ρ in the dam land exhibited obvious horizontal and vertical variation in distribution. Vertically, ρ displayed a curve of high-low-high from the top to the deep loess layer, and the upper boundary of the low-resistance zone was consistent with the table of shallow groundwater in the dam land, while horizontally, profile ρ was closely related to land use type and geological position. Compared with the head dam land, the tail dam land had a low-resistance zone significantly thicker and penetrating the high-resistance zone in the shallow soil layer, which may be ascribed to crops' lower water consumption.[Conclusion] Spatial distribution of profile ρ varies significantly with land use type and slope position in the loess area. The geophysical method of ERT is recommended for monitoring and studying spatial and temporal characteristics of dry and wet conditions of soil profiles different in land use type, as well as shallow groundwater dynamics in the loess area of China. It can also be used to study relationships between precipitation, vegetation, soil moisture and groundwater, particularly for areas thick in sediment deposits.

    • Spatial Distribution of Shajiang Content in Shajiang Black Soil of Huaibei Plain and Its Influencing Factors

      CHEN Yueming, GAO Lei, ZHANG Zhongbin, GUO Zichun, SHAO Fangrong, PENG Xinhua

      2022,59(1):148-160, DOI: 10.11766/trxb202004280202

      Abstract:

      [Objective] Shajiang black soil (Vertisol), one of the major soil types in China with low or medium productivity, is mainly distributed in the Huaibei plain. As the name suggests, in soil configuration, the soil is composed of a black soil layer and a Shajiang layer, with the former overlaid with the latter. Although the black soil layer is dark in color, it is very low in organic matter content (< 1%). "Shajiang", a special kind of calcareous concretion, is a major component and a typical feature of Shajiang black soil. The presence of Shajiang leads to high heterogeneity of the soil and significantly influences physical and chemical properties of the soil, thus restraining root growth and crop yield. Shajiang is a byproduct of soil-forming process, and shows high spatial variability. However, little is yet known about spatial distribution of Shajiang and its driving factors in the Huaibei Plain. The objective of this study was to investigate spatial distribution of Shajiang its driving factors in the Plain.[Method] Based on the classical statistics and geo-statistics, this study selected two bands of Shajiang black soil, typical of the area, extending from west to east and from north to south in the plain for investigation of contents of Shajiang in the 0~100 cm soil layer, therein. Meanwhile, soils in the 0~20 cm soil layer were sampled for analysis of physico-chemical properties. Besides, topographic and climate data of the sampling sites were collected too. The west-east band extended from Shangcai County in Henan Province to Sixian County in Anhui Province (360 km long, and a total of 35 samples collected), and the north-south band did from Luyi County in Henan Province to Huaiyuan County in Anhui Province (195 km long and a total of 29 samples collected).[Result] (1) the two bands showed a general increasing trend from west to east and from north to south, separately in Shajiang content, but a decreasing one in depth of their burial; (2) Shajiang content increased with soil depth in both bands, and peaked in the 20~60 cm soil layer. The analysis of particle size composition of Shajiang shows that the 2~5 mm fraction of Shajiang accounted for 40%~44% of the total; (3) Similar to Shajiang content in variation trend, increasing from west to east and from north to south in the two bands, the proportion of montmorillonite, MAT and MAP increased too, but MAE and elevation did reversely. However, the content of total calcium only showed a decreasing trend from north to south in the north-south band; and (4) Pearson correlation analysis shows that Shajiang content was positively related to montmorillonite content (r=0.321, P < 0.01), MAP (r=0.416, P < 0.01), and MAT (r=0.369, P < 0.01), but negatively to total calcium content (r=-0.279, P < 0.05), elevation (r=-0.387, P < 0.01), and MEA (r=-0.392, P < 0.01). Principal component analysis shows that topography (37.4%) and climate conditions (38.4%) were factors more important than soil properties affecting Shajiang content (24.1%).[Conclusion] Therefore, it can be concluded that Shajiang content in the Huaibei Plain is mainly regulated by topography, climate conditions and soil properties together, thus forming a spatial distribution pattern of "low in the northwest, and high in the southeast".

    • Inversion of Leaf Area Index in Winter Wheat by Merging UAV LiDAR with Multispectral Remote Sensing Data

      NIU Yujie, LI Xiaopeng, ZHANG Jiabao, MA Donghao, JI Jingchun, XUAN Kefan, JIANG Yifei, WANG Chunfen, DENG Haodong, LIU Jianli

      2022,59(1):161-171, DOI: 10.11766/trxb202007130239

      Abstract:

      [Objective] In order to further tap the potential of unmanned aerial vehicle (UAV) carried LiDAR to monitor crop growth and to explore effect of merging UAV LiDAR with multispectral data in inversing leaf area index (LAI) in winter wheat, this study was carried out.[Method] In this study, with the aid of UAV LiDAR scanners and visible-near infrared multispectral cameras, UAV LiDAR point cloud and multispectral data of the winter wheat at the booting stage in experiment zone were collected. From the data, four LiDAR point cloud structure parameters, i.e., three-dimensional volumetric parameters (BIOVP), mean plant height (Hmean), 75 percentile plant height (H75) and laser penetration index (LPI), and six vegetation indices, i.e., NDVI, SAVI, MCARI, TVI, NDRE and RVI were extracted. Then correlation analysis was performed of these parameters for screening suitable modeling parameters. With the aid of the multiple linear regression (MLR) and the partial least squares regression (PLSR), a LAI inversion model was constructed through merging the LiDAR point cloud structure parameters with vegetation indices as input parameters of the model. In applying the MLR method, the two vegetation indices, NDVI and SAVI, that are the most closely correlated with the field-observed LAI and the two point cloud structure parameters, H75 and BIOVP, that are the most closely correlated with the field-observed LAI, were used as input parameters of the model. While in adopting the PLSR method, the number of principal components in modeling was determined in the light of the result of the cross-validation. Before modeling, the experimental dataset had been randomly divided into a modeling set (n=32) and a validation set (n=16) at a ratio of 7:3 in all treatments. A LAI inversion model was built up based on the modeling dataset and then the validation dataset was used to evaluate effect of the model. Meanwhile, in order to determine whether the inversion with the LiDAR point cloud data merged with the multispectral data was better than that based on multispectral data alone, LAI inversion models were constructed using the same modeling method with vegetation indices as input parameters of the model only.[Result] The evaluation of the model using the coefficient of determination (R2) and the root mean square error (RMSE) shows that the inversion model using the LiDAR point cloud data merged with the multispectral data well reflect the LAI in winter wheat, with R2 of the modeling set being all > 0.900 and RMSE being < 0.400 and R2 of the validation set being all > 0.800, and RMSE being < 0.500. In addition, no matter whether using MLR or PLSR, the models with the LiDAR point cloud data and vegetation indices (MLR:R2=0.901, RMSE=0.480; PLSR:R2=0.909, RMSE=0.445 (n=16)) are all superior to the models using vegetation indices only (MLR:R2=0.897, RMSE=0.492; PLSR:R2=0.892, RMSE=0.486 (n=16)).[Conclusion] In conclusion, although the LAI data in this research were too scattered, leading to insignificant difference between models in comparison, it could still be seen that the addition of UAV LiDAR data could make up for the defect of using the multispectral data alone that insufficient information could be extracted along the vertical direction of the crop, and improve accuracy of the inversion of LAI in winter wheat. Therefore, the model with UAV LiDAR data merged with multispectral data is a superior means for inversion of LAI in winter wheat and even other crops smaller in plant type.

    • In Vitro Test-based Study on Health Risks of Arsenic in Typical Soils of China and Their Influencing Factors

      CHEN Xiaochen, HUANG Zhenjia, CHEN Yuqing, YAO Congcong, ZHANG Jianyu, DIAO Guowang, YUAN Ching, XU Kaiqin, LIU Xianhua

      2022,59(1):172-182, DOI: 10.11766/trxb202005140100

      Abstract:

      [Objective] This study aimed at accurate assessment of health risks of arsenic (As) in typical soils of China and comprehensive investigation of their influencing factors, based on oral bioaccessibility/bioavailability of soil As.[Method] Samples of five typical soils of the country, i.e. red soil, black soil, cinnamon soil, brown soil and yellow soil, were collected and prepared into As-contaminated samples by spiking As at 600 mg·kg-1. After one-month aging, bioaccessibility/bioavailability of soil As in the gastrointestinal tract of a human being were studied, and its health risk was evaluated by means of in vitro test (PBET-UF model). Besides, from the perspective of soil properties (soil basic physicochemical properties and As fractions), influencing factors of As bioaccessibility/bioavailability were explored and variation of As bioaccessibility/bioavailability with the soil analyzed.[Result] Results show that As bioaccessibility/bioavailability significantly varied between soils, as As bioaccessibility ranged from 37.2% to 71.8% in the gastric phase and from 49.0% to 73.3% in the small intestinal phase, while As bioavailability in the small intestinal phase ranged from 48.6% to 72.1%. It was indicated that from the stomach to the small intestine soil As was gradually dissolved by digestive fluids, and almost all the dissolved As in the small intestine could pass through the specific ultrafiltration membrane used to simulate small intestinal epithelium. Also, health risks of soil As through oral ingestion significantly varied with the soil. Based on the estimated As bioaccessibility in the gastric phase, carcinogenic and non-carcinogenic risks of As in the five soils varied in the range of 4.28×10-4~8.26×10-4and in the range of 14.86~28.69, respectively; and based on the estimated As bioavailability in the small intestinal phase, they did in the range of 5.59×10-4~8.30×10-4and in the range of 19.40~28.81, respectively. The carcinogenic risk and non-carcinogenic risk was two orders and one order of magnitude respectively higher than their respective acceptable limit. In addition, correlation analysis shows that between bioaccessibility/bioavailability of soil As was significantly related to certain soil properties.[Conclusion] Oral bioaccessibility/bioavailability of soil As is significantly and positively related to soil pH, migration coefficientS and migration coefficientW, but negatively to content of free Fe and Al oxides. Migration coefficientS is the main influencing factor determining bioaccessibility of soil As in the gastric phase, whereas soil pH is in the small intestinal phase. Although free Fe and Al oxides in the soils are not the determining factors directly affecting bioaccessibility/bioavailability of soil As in the gastric phase, they form new minerals with As, thus reducing the activity and consequent bioaccessibility/bioavailability of soil As. It is expected that all the findings in this study may contribute positively to making future field investigations of soil environmental quality of China more in line with the reality, and consummation of the methodologies for health risk assessment of heavy metal (loid) -contaminated soil.

    • Effect of Reductive Soil Disinfestation Mitigating Adverse Factors for Growth of Replanted Longya Lily (Lilium brownii var. viridulum)

      XIA Qing, LUO Chen, ZENG Liangbin, ZHANG Jinbo, CAI Zucong, ZHAO Jun

      2022,59(1):183-193, DOI: 10.11766/trxb202007220410

      Abstract:

      [Objective] Longya Lily (Lilium brownii var. viridulum) is a perennial herb aboriginal of Longhui County, Shaoyang City, Hunan Province, with edible and medicinal values. It is of great significance to sustain cultivation of the crop for farmers' income and local economic development. However, soil borne diseases and weeds are the two key adverse factors affecting growth of replanted Longya Lily, and hence threatening stability and development of the local Lily industry. Reductive soil disinfestation (RSD) refers to a technology of pre-planting soil treatment designed to effectively eliminate soil-borne pathogens, degrade allelochemicals, and improve soil physicochemical properties, etc., but how much RSD could control weeds and soil weed seed bank is still unclear. Therefore, this study was oriented to explore effects of RSD on soil borne pathogens and weed seed bank in Longya Lily fields.[Method] A field experiment, designed to have three treatments, i.e. CK (control without soil treatment); MO[RSD incorporated with 6 t·hm-2liquid organic material (C/N 21)]; SB[RSD incorporated with 15 t·hm-2 solid organic material (C/N 94)], was conducted in a field planted with Longya Lily for one year. Real-time PCR was used to determine populations of the bacteria, fungi and soil-borne pathogens in the soil. Species of the weeds in the field were identified and density and biomass of the weeds were recorded.[Result] Results show that RSD effectively suppressed Fusarium oxysporum, Fusarium solani and Rhizoctonia solani, and significantly lowered the proportion of genus Fusarium in the fungal community as compared to CK, with disinfestation efficacy up to 98.8%. Furthermore, RSD also effectively inhibited germination of most of the weeds in the soil weed seed bank, and significantly reduced density and biomass of the weeds in the field, by 94.1%~96.0% and 71.0%~94.7%, respectively. And treatment MO was higher than treatment SB in weed control effect. In addition, RSD significantly changed structure and reduced diversity, richness and dominance of the weed community.[Conclusion] Therefore, it can be concluded that RSD can significantly reduce soil borne pathogens, weeds and other adverse factors in the field of replanted Longya Lily. It is a promising agricultural measure with the potential to reduce the occurrence of both soil borne diseases and weed infestation. The findings in this study could provide a theoretical basis and certain technical support for reducing the use of pesticide and realizing sustainable development of the green agriculture.

    • Effects of Rapeseed/Wheat-Rice Rotation and Fertilization on Soil Nutrients and Distribution of Aggregate Carbon and Nitrogen

      ZHANG Shuntao, REN Tao, ZHOU Xiangqi, FANG Yating, LIAO Shipeng, CONG Rihuan, LU Jianwei

      2022,59(1):194-205, DOI: 10.11766/trxb202004090091

      Abstract:

      [Objective] In China, upland-paddy rotation systems are mainly distributed in the Yangtze River Basin, with rapeseed-rice (RR) and wheat-rice (WR) rotations being the main systems. It was noticed that rice productivity varied with the rotation system. Therefore, a long-term experiment, designed to have different treatments concerning rotation system and fertilization pattern, was carried out. The study aimed to explore differences in soil nutrients and distribution of aggregate carbon and nitrogen between RR and WR rotations and between different fertilization methods. It is hoped that the study may providing a scientific basis for optimizing the paddy-upland rotation systems and the fertilization methods as well in the rapeseed-wheat interlaced area of the middle reaches of the Yangtze River.[Method] The field experiment was designed to have two treatments in rotation system (i.e., RR and WR) and three treatments in fertilization, i.e., CK (no fertilization), NPK (chemical fertilization), and NPK+S (chemical fertilization combined with straw returning). Soil samples were collected from the 0-20cm soil layer of each treatment after harvest of the upland crops of the fourth year for analysis of physical and chemical properties, such as soil organic matter, nutrient content, porosity, distribution and stability of soil aggregates, and contribution rate of soil aggregate organic carbon and nitrogen to the soil total.[Result] Compared with WR, RR was 13.1%-19.2% and 18.8%-59.5% higher in content of soil organic matter and available phosphorus when fertilized. Treatment NPK+S was 28.1% than CK and 29.2% higher than Treatment NPK in content of soil total nitrogen. In the group of Treatment NPK, Treatment RR was significantly or 8.1% (in CK) and 10.3% (in Treatment NPK) higher and 11.7% and 10.5%, respectively, higher than Treatment WR in total porosity and capillary porosity. In the group of fertilization treatments (either NPK or NPK+S), Treatment WR was significantly higher than Treatment RR in mean weight diameter (MWD) and geometric mean diameter (GMD) of the water-stable soil aggregates and content of water-stable macroaggregate (WSMA), and in contribution rate of large-sized soil aggregates to total organic carbon and total nitrogen as well. In terms of soil organic matter and nutrient contents the fertilization treatments displayed an order of CK < NPK < NPK+S, and Treatments NPK and NPK+S were significantly higher than CK in soil aggregate stability and contribution rate of large-sized aggregates to total organic carbon and total nitrogen, regardless of rotation patterns. In the group of Treatment WR, Treatment NPK + S was significantly higher than CK and NPK in soil total porosity and capillary porosity, while in the group of Treatment RR, no significant difference was observed in soil porosity between different fertilizer treatments.[Conclusion] All the findings show that under the rapeseed-rice rotation system, application of chemical fertilizer combined with straw returning can increase contents of soil organic matter and soil nutrients, improve bulk density and porosity of the soil, and stabilize soil aggregate structure. Hence, the combination of rapeseed-rice rotation and application of NPK coupled with straw returning could be deemed as an important measure to achieve sustainable development of rice fields.

    • Effects of Mortierella on Nutrient Availability and Straw Decomposition in Soil

      NING Qi, CHEN Lin, LI Fang, ZHANG Congzhi, MA Donghao, CAI Zejiang, ZHANG Jiabao

      2022,59(1):206-217, DOI: 10.11766/trxb202006020213

      Abstract:

      [Objective] Saprophytic fungi can convert complex organic substances into available components, which is closely related to soil nutrient availability and carbon (C) sequestration. Mortierella has been reported to be substantially enhanced after long-term fertilization in agricultural soils. Studies in the past demonstrated that some species of Mortierella did make important contributions to soil nutrient transformation and availability, and were able to degrade hemicellulose, cellulose and lignin, and hence could directly affect straw decomposition and alter nutrient status of the soil. Furthermore, Mortierella species show great ability to excrete a large volume of polyunsaturated fatty acids, which contained abundant C sources, thus altering the soil microhabitat. It was therefore, presumed that Mortierella inoculants could affect soil microbial communities in part by changing their nutrient uptake, thus indirectly influencing soil nutrient transformation and availability in the soil. However, empirical evidence of the effects of Mortierella inoculants on the soil microbial communities under planting conditions is seldom available. The objective of this study was to explore how indigenous strains of Mortierella affect soil nutrient availability during the process of straw decomposition.[Method] Two strains of Mortierella (Mortierella alpina and Mortierella elongata) were isolated from two types of agricultural soils (red soil and Shajiang black soil) that had been applied with organic manure for decades. A pot experiment, designed to have three treatments, i.e. no inoculation (Control); inoculation with Mortierella alpina (Ma); and inoculation with Mortierella elongata (Me), and three replicates for each treatment, was conducted with the two soils packed in the pots separately and incorporated with straw. Availability of C, nitrogen (N) and phosphorus (P) and activities of β-glucosidase, N-acetyl-β-glucosaminidase and phosphatase were determined. Chemical C structure of the residual straw and bacterial community composition in the soil was analyzed with the aid of the solid state 13C-nuclear magnetic resonance (13C-NMR) spectroscopy and the technique of 16S rRNA gene amplicon sequencing, respectively.[Result] In red soil, Treatment Ma increased the content of soil available P by 29.0%, while Treatment Me did the content of soil available N and the activity of β-glucosidase by 15.5% and 81.3%, respectively. In Shajiang black soil, both Mortierella treatments notably increased the content of soil available N and the activity of β-glucosidase. In addition, Treatment Ma significantly increased the activity of phosphatase, while Treatment Me did the content of dissolved organic C and soil available P by 16.2% and 11.5%, respectively. In red soil, Mortierella inoculants inhibited straw decomposition and significantly altered composition and metabolic functions of the bacterial community, while in Shajiang black soil, they promoted straw degradation but had little effect on bacterial community structure. Ochrobactrum, Achromobacter and Streptomyces were the most influential taxa contributing to differences in bacterial community between the treatments and the control in red soil. Network analysis showed that the interactions between soil microbes were more complex connectedness in red soil than in Shajiang black soil. Lysobacter, Stenotrophomonas, Pantoea, Phyllobacteriaceae and Solirubrobacterales were identified as the keystone taxa in red soil, while Comamonadaceae, Lysobacter, Cytophagaceae and Serpens flexibilis were in Shajiang black soil. These keystone taxa acted as decomposers or biocontrol agents, and played important roles in maintaining microbial interactions and in potential processes of straw decomposition.[Conclusion] The present study has demonstrated that Mortierella alpina and Mortierella elongata can improve soil C, N and P availability and associated enzyme activities, and provide evidence of roles of indigenous strains of Mortierella strains on straw decomposition and nutrient transformation in agricultural soils.

    • Effects of Nitrogen Deficiency on Microbial Community Structure in Rhizosphere Soil of Wheat

      XIONG Yi, ZHENG Lu, SHEN Renfang, LAN Ping

      2022,59(1):218-230, DOI: 10.11766/trxb202005080225

      Abstract:

      [Objective] Rhizosphere microorganisms play an essential role in the process of nutrients absorbing in crops. To improve nitrogen utilization efficiency in wheat production, it is of great significance to study effects of nitrogen deficiency on structure of the microbial community in the rhizosphere of wheat.[Method] Soil samples were collected from a nitrogen-depleted wheat field of Lou soil, which is typical of the Guanzhong Region, Shaanxi Province for a rhizobox experiment. The experiment was designed to have two treatments, one applied with nitrogen fertilizer at a normal rate (150 mg·kg-1) and the other with no nitrogen fertilizer to the wheat growing in the rhizoboxes. Soil microbial communities in the rhizosphere, near-rhizosphere and non-rhizosphere were analyzed with the technique of 16S rRNA gene amplicon high-throughput sequencing for comparison between the two treatments in soil microbial diversity and community structure in these sections of the rhizoboxes.[Result] Results show that the content of soluble inorganic nitrogen in the soil played a leading role in triggering changes in microbial community diversity and community structure. Compared with normal nitrogen supply, soil microbial community has higher α diversity index under nitrogen deficiency. The abundance of microorganisms, such as Firmicutes, Gracilibacteria, Candidatus Jorgensenbacteria and Elusimicrobia, was negatively related to soil nitrate content. Nitrososphaeria an ammonia-oxidizing class of archaea, was a critical node of the microbial co-occurrence network affected by nitrogen deficiency. Nitrogen deficiency induced a series of microbial metabolic processes, such as mRNA synthesis, glycolysis, peroxides, and phosphoinositol metabolism. Nitrosospira and Nitrospirae contributed the most to accuracy of the random forest classifier, and can be used as biomarker for prediction of nitrogen supply level in soil.[Conclusion] To sum up, the effects of nitrogen deficiency on diversity, community structure, and metabolic function of the soil microbes in the rhizosphere were significant, and more than the rhizosphere effect. It is helpful for the exploration of plant growth-promoting rhizobacteria and provides some theoretical basis for reducing the nitrogen fertilizer application and improving the utilization efficiency of nitrogen fertilizer in wheat production.

    • Effects of Paddy Periphyton Biofilms on Rice Germination and Seedling Growth Relative to Paddy Ecosystems

      SUN Rui, SUN Pengfei, WU Yonghong

      2022,59(1):231-241, DOI: 10.11766/trxb202004190180

      Abstract:

      [Objective] Periphyton is ubiquitously distributed in paddy fields, directly affecting nutrient cycles and their bio-availabilities. However, no study regarding effects of periphyton on rice growth has been reported.[Method] In this study, model paddy ecosystems with three types of soils were simulated under controlled conditions to investigate the effects of periphyton on rice seed germination and seedling growth.[Result] Results show that periphyton of three types of soils was mainly composed of Proteobacteria, Cyanobacteria and Bacteroidetes, while the diversity of periphyton of the three soils was significantly different, and that grown in soil from Yanbian (YBP) had the highest OTU number and Chao1 index. Furthermore, there were significant differences in carbon metabolic activity among the three periphyton (P<0.05). The Pearson correlations indicated that periphyton composition and diversity was positively correlated with soil pH, TP, TOC and Mn contents (P<0.05). The carbon metabolism activity of YBP was the highest during the whole growth period, while that of soil from Yingtan (YTP) was the lowest. The presence of periphyton greatly increased the germination index of rice seed (by maximally 18%), and α-amylase activity in the presence of periphyton was increased significantly (P<0.05). Besides, the periphyton covering on paddy soil surface from Yanbian (YBP) significantly promote shoot length and its biomass (P<0.05). The Pearson correlations indicated that seed germination and survival rate was positively correlated with periphyton chemical properties.[Conclusion] To summarize, this study indicates that the presence of periohyton biofilm during seed germination period was propitious for rice growth. Results of this study provided an insight into understanding the periphyton-plant relationships with different soil-types and also new approaches to controlling plant phenology by regulating the growth of periphyton.

    • Effect of Planting System on Fertilization-induced Variation of Soil Denitrification Potential and Its Microbial Mechanism

      WANG Haicui, LIU Zhaodong, LI Dandan, LIU Kailou, HUANG Qinghai, ZHAO Bingzi, ZHANG Jiabao

      2022,59(1):242-252, DOI: 10.11766/trxb202009250539

      Abstract:

      [Objective] Soil denitrification potential (SDP) is generally higher in paddy field than in upland field. However, as the effect of fertilization on SDP in paddy field and upland field varies with climatic and soil type, accuracy of its assessment is often affected by external conditions.[Method] In this study, two adjacent fields, one paddy field and one upland field, both derived from the same parent material of Quaternary red clay, in a long-term field experiment were selected for exploration of effect of fertilization regime on SDP and its association with abundances of functional genes (narG, nirS, nirK, and nosZ) and community composition of nirS-type denitrifiers with the aid of in-lab incubation, real-time quantitative polymerase chain reaction (qPCR), and high-throughput sequencing technology.[Result] In the paddy field, compared with Treatment NPK, Treatment NP and PK was significantly or 33.01% and 23.57%, respectively, higher in SDP, while Treatment NK was 35.76% lower in SDP. The effects of Treatments NP and NK were related to the abundance of nirS gene, and the changes in content of soil available P (AP) and N:P ratio, while that of Treatment PK was associated with the community composition of nirS-type denitrifiers (Azospira sp. NC3H-14). In the upland field, compared with Treatment NPK, Treatment NP, NK and P was 13.94%, 26.51%, and 25.41%, respectively, higher in SDP. The effects of Treatments NK and P were significantly related to the abundance of narG gene and of nirS-type denitrifiers (Azospira sp. NC3H-14 and Ideonella sp. NC3L-43b for NK treatment; Azospira sp. NC3H-14, Rhodanobacter sp. D206a, Rubrivivax gelatinosus for P treatment). The content of amorphous iron oxide (Feo) was probably the main factor affecting the abundance of narG gene.[Conclusion] The above listed findings indicate that planting system affects the effect of fertilization on SDP. The variation of SDP in paddy field is mainly attributed to nirS-type denitrifiers, while that in upland field primarily to the abundance of functional gene and the community compostion of nirS-type denitrifiers.

    • Dissimilatory Nitrate Reduction to Ammonium Coupled to Fe2+ Oxidation in Paddy Soils as Affected by Oxygen Presence and Carbon Addition

      WU Min, LI Jinfang, WEI Zhijun, LI Chenglin, XIA Yongqiu, SHAN Jun, YAN Xiaoyuan

      2022,59(1):253-262, DOI: 10.11766/trxb202007100382

      Abstract:

      [Objective] Dissimilatory nitrate reduction to ammonium (DNRA), a biological pathway converting NO3- to NH4+, provides ammonium for rice uptake and microbial immobilization, resulting in N retention in paddy soils. Recently, the coupling between DNRA and Fe2+oxidation has been reported occurring in freshwater lake or estuary sediments. However, so far little has been reported on this process in paddy soil, and its potential key factors are practically unknown.[Method] Using 15N-tracing technique in combination with membrane inlet mass spectrometer (MIMS), an in-lab incubation experiment was performed to investigate the process of DNRA coupled to Fe2+ oxidation as affected by oxygen presence and carbon addition in two types of paddy soils (CS and TY).[Result] Results showed that the process of DNRA coupled to Fe2+ oxidation was found in both paddy soils, where the potential rate of DNRA increased from N 0.36-0.38 to 0.81-2.35 nmol·g-1·h-1 with Fe2+ addition rising from 0 to 800 μmol·L-1. At the concentration of 800 μmol·L-1 Fe2+, potential rate of DNRA was significantly higher in CS soil than that in TY soil, which was in consistence with differences between the two tested soils in nrfA gene abundance. Effect of oxygen presence and/or lactic acid addition on the process of DNRA coupled to Fe2+ oxidation varied in the two tested paddy soils. In TY soil, regardless of singly or in combination applied, oxygen presence and lactic acid addition significantly promoted potential rate of DNRA at varying Fe2+concentrations. In CS soil, single oxygen presence or lactic acid addition significantly increased potential rate of DNRA at the concentration of 500 μmol·L-1 Fe2+, whereas, at the concentration of 800 μmol·L-1 Fe2+, either lactic acid singly applied or in combination with oxygen significantly decreased potential rate of DNRA.[Conclusion] Findings of this study suggest that the process of DNRA coupled to Fe2+ oxidation occurs in paddy soils and may be affected by presence of oxygen and carbon addition. Further studies are needed to deepen understanding of this process by including more types of soil and comprehensively evaluating the effects of environmental parameters and soil properties on the process.

    • Impacts of Plantation of Winter Green Manure Crops on Soil Nitrification in Paddy Soil

      GAO Songjuan, ZHOU Guopeng, CAO Weidong

      2022,59(1):263-273, DOI: 10.11766/trxb202004050150

      Abstract:

      [Objective] Utilization of green manure crops in winter is an effective practice to maintain high and stable yields in paddy fields in South China, and plays an important role in N management in the rice cropping system. Nitrification is a key process in N cycling and is highly related to N utilization of crops and to N leaching loss as well. Since nitrification process is a potential N loss pathway, it is worthwhile to study impacts of cultivation and incorporation of green manure crops on nitrification process and ammonia oxidizing microorganisms in paddy soil.[Method] A pot experiment having three crops a year, that is, green manure crop, early rice and later rice, was conducted in alkaline paddy soil and designed to have four treatments, i.e. winter fallow-double cropping rice (WF), milk vetch-double cropping rice (MV), ryegrass-double cropping rice (RG) and rape-double cropping rice (RP). Nitrification potential (NP) and recovered nitrification potential (RNP) of the soil in the pots were measured. Relative contributions of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) to RNP were explored using specific bacterial inhibitors (Kanamycin and Spectinomycin). Abundances of AOA and AOB were measured using the amoA gene-based real-time quantitative PCR method.[Result] Treatments MV and RG increased the N uptake of early rice and late rice, respectively. Plantation of winter green manure crops, no matter what, significantly lowered NP at the pre-transplanting, tillering and jointing stages of early rice. The NP at the jointing stage of early rice was the highest in Treatment WF, reaching up to 56.15 mg×kg-1×d-1. Compared to Treatment WF, the other three treatments were all higher in NH4+-N, and lower in NO3--N at most of the sampling stages. Soil NO3--N was significantly and positively related to NP. Compared to Treatment WF, all the green manure treatments were higher in copy numbers of AOA and AOB amoA genes at most of the sampling stages, especially the former, which was much higher than the latter. However, AOB was a dominating contributor to RNP at all the sampling stages, contributing relatively 61.02%-82.37%. The abundance of amoA genes had nothing to do with the contributions of AOA and AOB to nitrification. Utilization of green manure crops increased relative contribution of AOB to RNP (RNPAOB) at the tillering stage of early rice, but decreased that of AOA to RNP (RNPAOA) at the pre-transplanting and jointing stages of early rice. Soil properties were significantly related to nitrification process, especially soil pH, NH4+-N and NO3--N. Application of winter green manure crops decreased soil pH in alkaline soil, which may be one of the main causes of the practice inhibiting nitrification.[Conclusion] Application of winter green manure crops reduces soil NP, which is consistent with the variation of soil NO3--N, suggesting that the practice may mitigate the risk of NO3--N leaching loss. Therefore, it plays an important role in N management in paddy soil.

    • Strategies for Soil Microbes Utilizing Exogenous Substrates in Ultisol Based on Nucleic Acid Stable Isotope Probing Technique

      WANG Xinxin, LIU Yan, ZHANG Wei, ZHOU Xuhui, HE Hongbo, ZHANG Xudong

      2022,59(1):274-284, DOI: 10.11766/trxb202008100445

      Abstract:

      [Objective] The input of exogenous active carbon (C) substrate strongly affects the growth of soil microorganisms. However, so far little knowledge is available about dynamic responses of soil microorganisms (bacteria and fungi) to the input of exogenous active carbon substrate and functional traits of the microorganisms in utilizing the substrate and their relationships with community structure of the microorganisms.[Method] Hence, an experiment was carried out using 13C-glucose as substrate in Ultisol for incubation of soil microorganisms (bacteria and fungi), which were sampled periodically for analysis with the aid of DNA-based stable isotope probing and high-throughput pyrosequencing techniques to explore dynamic traits of the microorganisms utilizing the carbon of glucose relative to species.[Result] It was found that in utilizing the substrate, the bacterial and fungal communities followed the r/K selection strategy in evolution from bacteria to fungi. Among the bacterial community, copiotrophic bacteria, like Proteobacteria and Actinobacteria, were higher than oligotrophic phyla, like Acidobacteria and Chloroflexi, in activated substrate utilization capacity. Different from bacteria in utilization of substrates, fungi, like Ascomycota and Basidiomycota, were low in selectivity and able to utilize both labile C and native soil organic matter.[Conclusion] Hence, bacteria retain their intrinsic life-history strategies controlled by their copiotrophic or oligotrophic natures, regardless of increase in C availability. Fungi can utilize a wide range of substrates and labile C input can induce copiotrophic Ascomycota to utilize heterogeneous recalcitrant C, thus accelerating decomposition of native soil C.

    • The Effect of Long-term Fertilization on the Abundance and Composition of Ammonia-oxidizing Archaea and Bacteria in Paddy Soil Profiles

      TIAN Meijie, GUO Junli, LI Juan, GE Tida, TANG Haiming, HE Zhili, LIU Yi

      2022,59(1):285-296, DOI: 10.11766/trxb202007140240

      Abstract:

      [Objective] Nitrification is a critical process of the nitrogen cycle which is driven by ammonia-oxidizing archaea (AOA) and bacteria (AOB). It has been observed that long-term fertilization affect soil properties and nitrifying microbial community in paddy soils. However, the effect of long-term fertilization on the community structure of AOA and AOB along the depth in paddy soils has been given little attention.[Method] From a long-term experiment on fertilization management of a paddy field in Ningxiang, Hunan Province, we selected four treatments; no fertilization (CK), straw organic fertilizer (ST), organic-inorganic fertilizer (OM), and inorganic fertilizer (NPK), and used real-time fluorescent quantitative PCR and Illumina MiSeq sequencing technology to analyze the soil properties, and abundance and composition of AOA and AOB in the soil layers (0-10 cm, 10-20 cm, 20-30 cm, 30-40 cm).[Result] ST, OM and NPK treatments increased the contents of soil organic carbon, total nitrogen, available phosphorus and the nitrification potential in each soil layer, but decreased soil pH. The contents of soil organic carbon, total nitrogen, alkali hydrolyzable nitrogen, available phosphorus, and the nitrification potential decreased with an increase in soil depth, while the pH value showed an opposite trend. Importantly, NPK had a more significant effect on soil acidification (0-20 cm) compared to the other fertilizers. The AOB abundance in the control (no fertilization) treatment was higher than AOA abundance, with the ratio of AOB/AOA abundance in the range 9.24-29.19. Also, the application of fertilizers promoted the growth of AOA, with the AOA/AOB abundance ratio in the range 0.77-31.28. Long term application of fertilizers enriched the proportion of Nitrosocosmicus in AOA population and Nitrosolobus in AOB population. Redundancy analysis showed that available phosphorus and pH had a significant impact on the composition of AOA and AOB communities, with interpretive degrees of 31.5% and 46.7%, respectively. This indicated that available phosphorus and pH were the key factors driving the succession of AOA and AOB community structure. Additionally, the vertical distribution characteristics of AOA and AOB were affected by different fertilization measures and soil layers.[Conclusion] Long term fertilization can acidify paddy soil and change the main executor of ammonia oxidation in the nitrification process. Variations in carbon, nitrogen, phosphorus and pH along the paddy soil depth induced the observed changes in AOA and AOB abundance and community composition and then affected the nitrification ability of soil. This study can serve as a theoretical basis for improving nitrogen use efficiency and reducing greenhouse gas emission.

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      • Effects of Drying and Oxidation Stage on the Forms and Availability of Cd and As in the Soil-rice System

        ZHANG Yuting, ZHU Qihong, HUANG Daoyou, TIAN Yingbing, XU Chao, ZHU Hanhua, HE Lei, WANG Wei, ZHANG Quan

        DOI: 10.11766/trxb202105190264

        Abstract:

        【Objective】The chemical behavior of cadmium (Cd) and arsenic (As) in paddy soils is opposite to the change in biological efficiency. This presents serious challenges to the simultaneous control of Cd and As pollution in rice. Previous studies have found that continuous flooding of Cd polluted fields can reduce the bioavailability of Cd while reducing soil water content can mitigate the bioavailability of As. However, the forms and availability of Cd and As in the soil-rice system under the process of drying (oxidation) remain unclear. 【Method】In this study, continuous sampling during the process of drying (days 0, 3, 5, and 7 of the drying process) under tillering period of rice in a pot experiment was carried out. At the same time the soil samples were analyzed for pH, Eh, soluble organic carbon, available Cd and As, and the different forms of Cd and As. Also, the plant samples were analyzed for Fe plaque in the rice roots and Cd and As concentration in the rice tissues. 【Result】 The results showed that: during the process of drying, the Cd concentration in all parts of rice tissues increased with a reduction in water content, and the Cd concentrations in roots and shoots were increased by 109% and 183%, respectively, under the second drying stage (drying for 5 days) compared with the control treatment (P < 0.05). The concentration of As in rice roots decreased firstly and then increased with the reduction of water content. Compared with the control treatment, the concentration of As in rice roots was decreased by 41.96 mg·kg-1 (P < 0.05). Also, the shoot As concentration was decreased by 12% and 18%, respectively, under the second and third stages of drying (drying for 5 and 7 days) (P < 0.05). The Cd, As and Fe concentrations in the Fe plaque increased by 96%, 16% and 16%, respectively (P < 0.05). With the decrease of soil water content, soil Eh, soil soluble organic carbon, and soil available Cd extracted by DTPA were increased, but soil pH, soil available As, and soil available Fe extracted by DTPA were decreased. In addition, reducing soil water content promoted the transformation of residual Cd to acid extractable and reducible Cd, resulting in the increase of oxidizable As concentration. It was also observed that when the soil moisture content was 33.6%, the bioavailable Cd and As concentration remained relatively low. 【Conclusion】Reasonable water management practices can reduce the bioavailability of Cd and As in soil. This is due to the changing soil Eh, pH, soluble organic carbon and available Fe, and the promotion of adsorption and fixation of Cd and As by the Fe plaque. However, it is worth noting that while exploring water management methods to reduce the bioavailability of Cd and As, the growth and development of rice cannot be ignored. Our study contributes to the wealth of knowledge aimed at improving the remediation of Cd and As contaminated soils.

      • Study of the Water Infiltration Processes using ERT and TDR in Layered Soils

        LIN Qing, XU Shaohui

        DOI: 10.11766/trxb202104280227

        Abstract:

        【Objective】Soil water is the link between surface water and groundwater,and the carrier of solute transport in soil, which plays a key role in the Soil-Plant-Atmosphere Continuum (SPAC) system. The movement of soil water is a very complex process, especially in the layered structure. Heterogeneity of texture and pore of layered soil changes hydraulic characteristics at the interface of the soil layer, and thus the soil water movement and solute transport differ significantly from that in homogeneous soil.【Method】To fully understand the process of soil water movement, infiltration was evaluated using electrical resistivity tomography (ERT) in soil with a stratified profile. A field infiltration test was performed on an 8.7-m-long transect and successive measurements using ERT allowed determining resistivity changes as infiltration progressed. In the meantime, the soil water content was measured by time domain reflectometry (TDR) at the point scale, and the quantitative relationship was established between resistivity and water content. In addition, the soil water contents derived by ERT were validated with the soil water content derived by the drying method. 【Result】Results showed that the Multi-electrode resistivity method can fairly monitor the process of soil water movement, identify the depth of water infiltration, 90 cm in our study, and quantitatively retrieve the profile water content. The movement of soil water is mainly vertical downward with a weak horizontal flow. A good correlation between resistivity and soil moisture measurements revealed the capability of resistivity measurements to infer soil moisture spatial and temporal variability with root mean square error (RMSE) equal to 0.042 cm3·cm-3 for loam and 0.041 cm3·cm-3 for clay loam. However, when the soil water content was lower than 0.15 cm3 cm-3, the electrical resistivity changed greatly with the increase in water content, while the soil water content was higher, the resistivity did not change significantly with water content. When the soil water reached the interface (~30 cm) between loam and clay loam, the soil water did not immediately move to the lower layer. According to the established relationship between resistivity and water content, it is estimated that at the soil interface, when the mass moisture content reached 0.136 g·g-1 at the upper layer of the soil, the water infiltrated the lower layer. Unexpectedly, abnormally increased resistivity appeared under the area of the soil water infiltration, which was presumably caused by the significant difference in resistivity of soil adjacent layers during the infiltration process. 【Conclusion】 In comparison with TDR, the resistivity method gives information integrated on a greater volume of soil and the measurements are easier and quicker to be carried out without disturbing the soil. Therefore, this method can be considered as an alternative tool to be employed for qualitative and quantitative soil moisture monitoring in the field. Also, this study provides a new method for quantitative analysis of the movement of soil water at a layered interface.

      • Effect of Reduced Nitrogen Fertilization on Nitrogen Runoff Loss and Apparent Balance on Red-soil Dry Slope Peanut Land

        ZHENG Wenqi, TAN Wenfeng, LIU Zhao, WANG Lingyun, ZHENG Haijin

        DOI: 10.11766/trxb202101110019

        Abstract:

        【Objective】Severe soil erosion and water leakage on dry slopes of red soils are a common phenomenon that results in significant nitrogen loss. These occurrences cause nitrogen imbalance and subsequent yield losses. This study aimed to explore the effects of different levels of reduced nitrogen fertilization on crop yield and nitrogen loss characteristics. 【Method】Randomized field trials comprising of five nitrogen treatments in three replicates were set up in peanut fields located in the dry slopes of northern Jiangxi characterized by red soils. The five treatments were 100% nitrogen application rate (N100%, pure nitrogen application of 180 kg·hm-2), 1/6 (N1/6), 1/3 (N1/3), 1/2 (N1/2), and zero (N0) nitrogen application rates. 【Result】The peanut yield and plant nitrogen uptake of N1/2 and N1/6 treatments were insignificantly lower than those of the N100% treatment (P>0.05). Besides, N1/6 and N1/2 treatments had no significant differences in agronomic characteristics such as the main stem length, plant height, crown width, number of full fruits, and the number of original branches (P>0.05). N1/6, N1/3, N1/2, and N0 treatments significantly reduced the average total nitrogen (TN) concentration in the surface runoff by 14.36%, 26.35%, 14.01%, and 21.34%, respectively, compared to the N100% treatment (P<0.05). Also, N1/3, , N1/2,, and N0 treatments reduced the average TN concentration in the leakage compared to the N100% treatment. However, the average increase in TN leakage concentration in the N1/6 treatment was not significantly different from that of the N100% treatment (P>0.05). The nitrogen output from the peanut planting system ranged between 34.95 and 93.98kg·hm-2. Nitrogen losses from runoff and leakage ranged between 38.31% and 70.50%, while other apparent nitrogen losses such as gaseous losses ranged between 29.50% and 60.63%. 【Conclusion】This finding affirmed the significance ofin nitrogen loss through runoff and leakage. Non-nitrogen treatment on newly reclaimed land reduced the soil inorganic nitrogen while reduced-nitrogen fertilization increased the soil inorganic nitrogen by up to 31.44%. Thus, rReduced nitrogen fertilization could, therefore, maintain a constant soil fertility level. Based on the comprehensive production goals, environmental impacts, and soil fertility, 90 kg·hm-2 is the recommended nitrogen application rate for peanuts planted in dry slope land with red soils.

      • An Intelligent Model of Cultivated Land Quality Evaluation Based on Random Forest and Its Application

        WANG Li, ZHOU Yong, LI Qing, XU Tao, ZUO Qian, WU Zhengxiang, LIU Jingyi

        DOI: 10.11766/trxb202012030670

        Abstract:

        【Objective】Constructing a scientific and quantitative quality-assessment model for cultivated land is important for understanding cultivated land quality, and can provide a theoretical basis and technical support for formulating rational and effective management policies and realizing the sustainable use of cultivated land resources. To accurately reflect on the systematic, complex, and differential characteristics of cultivated land quality, this study aimed to explore an intelligent cultivated land quality assessment method that avoids the subjectivity of determining indicator weights while improving assessment accuracy. 【Method】In this study, taking Xiangzhou in Hubei Province of China as the study area, 14 indicators were selected from four dimensions—terrain, soil conditions, socioeconomics, and the ecological environment—to build a comprehensive assessment index system for cultivated land quality. A total of 1,590 representative cultivated land quality samples in Xiangzhou were selected, of which 1,110 were used as training samples, 320 as test samples, and 160 as validation samples. Three models of entropy weight (EW), back propagation neural network (BPNN), and random forest (RF) were selected for training, and the assessment results of cultivated land quality were output through simulations to compare the assessment accuracy of the three methods to verify the reliability and superiority of the RF model. In addition, the distribution pattern of cultivated land quality grades in Xiangzhou in 2018 was also analyzed in this study. 【Result】 The results are summarized as follows: (1) The overall quality of cultivated land in Xiangzhou was better, with a larger area of second- and third-grade farmland, accounting for 54.63%, and the grades conformed to a positive distribution trend. From the distribution point of view, the spatial distribution of cultivated land quality in Xiangzhou was unbalanced, influenced by the topography and socioeconomic development level and showing an obvious geographical differentiation pattern, with overall characteristics of high in the north-central area and low in the southern area. The distribution of cultivated land quality grades also varied widely among towns. (2) The RF model for cultivated land quality assessment required fewer parameters and could simulate the complex relationships between indicators more accurately and analyze each indicator’s contribution to cultivated land quality scientifically. (3) In terms of the average quality index of farmland, RF > BPNN > EW. The spatial patterns of the quality index from RF and BPNN were similar, and both were significantly different from EW. (4) Compared to BPNN and EW, RF had a higher data mining ability and training accuracy, and its assessment result was the best. The coefficient of determination (R2) was 0.8145, the mean absolute error (MAE) was 0.009, and the mean squared error (MSE) was 0.012. 【Conclusion】 The findings in this study showed that RF was more suitable for the quality assessment of cultivated land with complex nonlinear characteristics. This study enriches and improves the index system and methodological research of cultivated land quality assessment at the county scale, and provides a theoretical basis for achieving a threefold production pattern of cultivated land quantity, quality, and ecology in Xiangzhou, while also serving as a reference for the evaluation of cultivated land quality in similar regions.

      • Estimation of Soil Environmental Carrying Capacity and Its Application in the Determination of Remediation Target in Contaminated Sites

        DING Shoukang, WANG Meie, WANG Yujun, LI Xiaonuo, CHEN Weiping

        DOI: 10.11766/trxb202102090088

        Abstract:

        【Objective】It is important to study the soil environmental carrying capacity for soil pollution prevention and control in “The Action Plan for Prevention and Treatment of Soil Pollution”. Application of the estimation model of soil environmental carrying capacity could greatly improve the science content of the method of remediation target determination. 【Method】Taking an abandoned chemical site in Jiangsu Province as a case study, the spatial distribution and health risk assessment of three target pollutants (i.e. mercury, hexachlorobenzene, and chlorobenzene) were analyzed based on soil sampling and investigation in the site. The environmental carrying capacities and remediation target values for the pollutants were estimated using the soil environmental carrying capacity model. 【Result】 The results revealed that more than half of the sites had soil mercury and hexachlorobenzene excessing their risk screening values, with about 17% for chlorobenzene. The spatial distributions of all three pollutants were mainly dependent on the distribution of the sources and manufacturing processes. Importantly, a serious non-carcinogenic risk is suggested for mercury and chlorobenzene, while a serious carcinogenic risk for hexachlorobenzene. Results of the soil environmental carrying capacity estimation suggested that, under a normal scenario and taking the risk screening value as soil quality standard, there were areas in the site having an environmental carrying capacity for all three pollutants less than zero. This indicated that the contamination of those areas excessed the soil environmental carrying capacities. Under an optimistic scenario and taking the risk controlling value as soil quality standard, the whole site had environmental carrying capacities for all three pollutants greater than zero. This suggested that the site can contain more pollutants.【Conclusion】 The remediation target values calculated by the soil carrying capacity estimation model were 1.8 to 1.9 times higher than the corresponding risk screening and control values. This was due to the coefficient calibration during the processes of risk emergence, soil adsorption, and fixation of pollutants in the carrying capacity model. The results in this study can provide scientific and technical support for the development and application of soil environmental carrying capacity.

      • Analyses and Corrections of Formula Errors in Soil Soluble Salt and Its Components Calculation

        YUAN Jinhua, QIAO Wandekua, E Shengzhe, CHE Zongxian

        DOI: 10.11766/trxb202102180101

        Abstract:

        【Objective】There are many errors in soil soluble salt and its component formula in published professional books. However, this has not attracted enough attention and no corrections have been made. Such published data may induce wrong results in soil soluble salt and its components calculation and subsequently wrong judgments in the classification or grading of saline-alkali soils.【Method】12 professional books published during 2000~2020 and containing 9 indexes (soil soluble salt, CO32?, HCO3?, SO42?, Cl?, K+, Na+, Ca2+, Mg2+) were selected for use in deriving their formulas based on related concepts, theoretical basis, experimental principles and experimental methods.【Result】Results suggested that there were 68 total errors using the 9 indexes. Among the 9 indexes, HCO3? recorded the highest frequency of errors, i.e. 11 times and accounted for 16.2%. It is followed by Ca2+ which recorded 10 times in total and accounted for 14.7% while soil soluble salt and Cl? recorded the lowest, i.e. 4 times in total (5.88%). Based on analyses of the characteristics of errors with the 9 indexes, the errors were found to occur as five different aspects categorized as coefficient 2, conversion coefficient, formula, reference and formula unstandard. Out of the five categories, conversion coefficient recorded the highest frequency of errors, i.e. 31 times in total (45.6%); followed by formula at 13 times (19.1%) and the coefficient 2 with the lowest of 4 times (5.88%).【Conclusion】 Errors in soil soluble salt and its component formula were discovered in published data and corrective measures were applied accordingly. The characteristics and causes of errors in calculating the formula of soil soluble salt and its components were suggested. Also, our results suggest reference values for the corrections of relevant formula.

      • Influence of Land Use Changes on Evolution of Different K Forms in Purple Paddy Soils

        LI Xiuzhi, HU Conyue, YANG Fan, HAN Guangzhong

        DOI: 10.11766/trxb202106290334

        Abstract:

        【Objective】Significant changes have recently taken place in the agricultural planting structure of the purple paddy soil area. These changes have profoundly affected the form and dynamic balance of soil potassium. Thus, understanding the impact of land-use changes on the evolution characteristics of different forms of potassium in purple paddy soil is of great significance to regional potassium management and environmental protection. 【Method】In this paper, we analyzed the dynamic characteristics and influencing factors of different forms of potassium in the purple paddy soil after abandonment, dry farming and conversion to fish ponds, using the time series method. 【Result】The results showed that abandonment and dry farming reduced the water-soluble potassium content of purple paddy soil, and conversion to fish ponds increased the water-soluble potassium content of purple paddy soil. Abandonment, dry farming and conversion to fish ponds could all increase the exchangeable potassium and non-exchangeable potassium content of purple paddy soil. Both the increasing magnitude and rate are highest for dry farming, intermediate for abandonment, and smallest for fish farming. 【Conclusion】In the purple paddy soil, potassium in different forms reached a general balance after 5 years of fish farming or 12 years after abandonment. However, after 20 years of dry farming, the different forms of potassium in the soil did not reach a general balance. The results also showed that the release of mineral potassium in purple paddy soil was relatively fast in the natural state. After the land-use changes, there were complex connections between the occurrence and dynamic balance of purple paddy soil, the loss of soil organic matter, and the transformation of soil clay minerals, which needs further research.

      • Metastable Equilibrium Adsorption of Alkali Metal Ions on the Surface of Montmorillonite and Its Specific Effects

        DU Wei, HU Feinan, XU Chenyang, LI Xiong, Lü Jialong

        DOI: 10.11766/trxb202105210265

        Abstract:

        【Objective】Metastable equilibrium is an important theoretical paradigm to describe the characteristics and extent of the actual reaction equilibrium in ion-exchange adsorption. This study aimed to theoretically derive the metastable equilibrium model of ion adsorption, establish the mathematical relationship between ion equilibrium adsorption amount and activation energy, and discuss the specific effect of alkali metal ion metastable equilibrium adsorption. 【Method】Using miscible displacement technology combined with the ion adsorption kinetic model and based on surface electrostatic field theory, the metastable equilibrium adsorption of K+, Na+, and Li+ on the surface of saturated Cs+-montmorillonite was investigated. The theoretical model was verified by carrying out adsorption kinetics experiments of K+, Na+, and Li+ on the Cs+-montmorillonite surface. 【Result】(1) Significant metastable equilibrium characteristics were observed during K+, Na+, and Li+ adsorption onto the surface of Cs+-montmorillonite saturated samples, and the adsorption activation energy (energy barrier) of exchange ions came from the desorption process of adsorbed Cs+; (2) Strong ion polarization caused by the surface electrostatic field resulted in specific effect of metastable equilibrium adsorption of each ion under the same ion concentration condition; (3) The metastable equilibrium of ion adsorption was affected by both ion concentration and specific ion effects, and the ion equilibrium adsorption capacity was proportional to the ion adsorption rate. 【Conclusion】The adsorption equilibrium of alkali metal ion at the montmorillonite surface is a metastable equilibrium rather than a real equilibrium. The presence of ionic metastable adsorption equilibrium should be attributed to the restraint of activation energies to ion adsorption kinetics. Also, the different polarization effects of alkali metal ions lead to different activation energies of each system, which further triggers the specific effect of ion metastable equilibrium adsorption.

      • Research Progress on the Environmental Behavior of Heavy Metals in Soil Tracing by Stable Isotopes

        ZHANG Miaoyue, YIN Wei, WANG Yi, YANG Wenjun, TANG Yetao, QIU Rongliang

        DOI: 10.11766/trxb202101180694

        Abstract:

        With the revolutionary breakthrough of high-precision mass spectrometry represented by multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), the research on stable isotopes has been developed by leaps and bounds. Heavy metal stable isotopes have become an effective tool to trace the circulation of heavy metals in soils, showing great application potential in identifying pollution sources, analyzing key processes, and tracking environmental behaviors. Based on the basic concept of isotopes, this paper systematically introduces the applications in using heavy metal stable isotopes to trace the source and fate of heavy metals in the soil environment, the transport and transformation of heavy metals in soil-plant system, and the environmental behaviors of metal nanoparticles. Processes influencing heavy metal stable isotope fractionation, such as redox, precipitation, dissolution, adsorption and desorption, complexation reaction, and biological action, are further summarized. Finally, the research outlook for the applications of tracing heavy metal environmental behavior by heavy metal stable isotopes is proposed, which plays a significantly important role in the prevention, control, and remediation of metal contamination in soil.

      • High-resolution Digital Mapping of Soil Organic Carbon at Small Watershed Scale Using Landform Element Classification and Assisted Remote Sensing Information

        WEI Yuchen, LU Xiaoli, ZHU Changda, ZHANG Xiuxiu, PAN Jianjun

        DOI: 10.11766/trxb202103120140

        Abstract:

        【Objective】 Soil organic carbon (SOC) is an important indicator of soil fertility and plays a fundamental role in the terrestrial ecosystem carbon cycle. As one of the primary environmental factors in digital soil mapping (DSM), landform elements are irreplaceable in predicting SOC. The purpose of this study was to simulate the complex and nonlinear relationship between SOC and environmental variables and evaluate the importance of each variable to accuracy in SOC mapping. 【Method】We applied machine learning techniques to map SOC content in a small watershed (1: 25000) of Huangmei Town, Jurong City using high-resolution landform elements classification maps known as geomorphons, digital elevation model (DEM) derivatives, optical and synthetic aperture radar (SAR) remote sensing data. The performance of all geomorphon (GM) variables under different hyperparameter settings was evaluated to predict SOC content. Three machine-learners including bagged classification and regression tree (Bagged CART), random forest (RF) and Cubist were used to construct predictive models of SOC content based on 74 soil samples and different combinations of environmental covariates. Model A, Model B, and Model D included only GM variables, DEM derivatives, and remote sensing variables, respectively. Model B was a combination of GM data and DEM derivatives, while Model E included all predictor variables. The performance of these models was evaluated based on a 10-fold cross-validation method by four statistical indicators. Concordance index (C index), root mean square errors (RMSE), bias and coefficient of determination (R2) of the three models were worked out for evaluation of the accuracy of their predictions. The best model was screening-out for mapping SOC in the study area based on the raster datasets of all environmental variables. 【Result】Overall, the Cubist model performed better than RF and Bagged CART, and these models yielded similar spatial distribution patterns of SOC, i.e. an ascending trend from the northern hilly area to the southern flatter land of the study area. Our results showed that more accurate predictions of SOC content were provided with the introduction of GM variables than individual DEM derivatives. The GM map with 20 cells search radius (L) and 5° flatness threshold (t) showed the highest relative importance within four GM variables in three models. The Cubist E model that functioned based on GM landform elements classification variables, DEM derivatives and remote sensing variables was much better than the others in performance and could explain most of the spatial heterogeneity of SOC (R2 = 0.53). Also, the prediction accuracy changed with and without the GM predictors with the R2 for estimating SOC content using the Cubist model increasing by 14.3%. The SOC contents of the hilly region predicted with the Cubist E model ranged from 5.65 to 13.31 g·kg-1. In addition, topographic variables were the main explanatory variables for SOC predictions and the multi-resolution index of valley bottom flatness (MRVBF) and elevation were assigned as the two most important variables. 【Conclusion】The Cubist model that functions based on GM variables, DEM derivatives, as well as remote sensing variables, is a promising approach to predicting the spatial distribution of SOC in hilly regions at a small watershed scale. The results of this study illustrate the potential of GM landform elements classification data as input when developing SOC prediction models.

      • Responses of Soil Carbon Pool of Abandoned Grassland on the Loess Plateau to Two-years Warming and Increased Precipitation

        WANG Xing, ZHONG Zekun, WANG Jiayi, JIAN Junnan, YANG Gaihe, REN Chengjie, HAN Xinhui

        DOI: 10.11766/trxb202106120307

        Abstract:

        【Objective】Global climate change has had a huge impact on the carbon pool of terrestrial ecosystems, and the changes in average temperature and precipitation patterns pose severe challenges to the management of terrestrial carbon pools. This is especially serious in the Loess Plateau where the ecological environment is fragile. Therefore, understanding the changes of different fractions of soil organic carbon pool and the stability of this carbon pool under the background of the warming and humid climate of the Loess Plateau is of great significance. This will be of importance in the sustainable development of the carbon pool in fragile ecological areas and the evaluation of regional ecological benefits.【 Method】In this study, natural abandoned grassland in the loess hilly region was taken as the research object. Soil warming and increased precipitation were artificially simulated and the changes in vegetation community, soil carbon fractions content and distribution, carbon pool stability index under warming (W), precipitation (P50%) and their interactions (WP50%) were analyzed. 【Result】The results showed that: (1) P50% significantly increased the vegetation Gleason richness index, W and WP50% significantly reduced the Gleason richness index(P < 0.05)and the leaf organic carbon content under the WP50% was significantly higher than the control treatment. Both P50% and WP50% treatments reduced the Shannon-wiener diversity index and pielou evenness index. (2) Soil organic carbon (SOC), acid hydrolyzable organic carbon (AHC), easily oxidizable carbon(EOC), dissolved organic carbon(DOC)content and their distribution ratio of the two sampling years under P50% were significantly higher than the control treatment. Also, warming based on P50% can further increase soil EOC, microbial biomass carbon(MBC)content and distribution ratio. However, only the soil MBC showed a significant difference compared with the control under W treatment. Recalcitrant organic carbon (ROC) presents an opposite trend to AHC. The correlation analysis showed that there was a significant correlation between soil total organic carbon and each active carbon fractions(P < 0.05). (3) The soil carbon pool activity (CA), carbon pool activity index (CAI), and carbon pool management index (CPMI) under WP50% treatment were higher than other treatments. The sensitivity index of AHC and MBC was relatively high under the treatment of climate change.【Conclusion】In summary, the total organic carbon, the content and distribution ratio of active fractions of organic carbon, and the stability of the carbon pool in abandoned grassland of the loess-hilly area will be significantly improved under background warming and humid climate. This will contribute to the healthy development of the carbon pool. From a sensitivity point of view, AHC and MBC can be used as early important indicators of changes in soil organic carbon under warm and humid climates in the future. This study provides a theoretical and scientific basis for research on climate change and carbon pool management in fragile ecological areas.

      • Research Progress and Perspective on the Pollution Process and Abatement Technology of Herbicides in Black Soil Region in Northeastern China

        REN Wenjie, TENG Ying, LUO Yongming

        DOI: 10.11766/trxb202107090354

        Abstract:

        Herbicides are important inputs in the agricultural chain of production required for the improved productivity of black soil granary. Nevertheless, the high-frequency and high-intensity application of herbicides in the black soil region in northeastern China might lead to their residual accumulation in soil. Thus, this affects the growth of after reap crops and becomes the bottleneck of crop rotation and planting structure adjustment. Therefore, research on the herbicide pollution process and key abatement technologies are of great scientific significance to ensure green sustainable development of agriculture in the black soil region. This paper systematically analyzed the research progress and development trend on herbicide pollution process and abatement technology in the black soil region. The scientific and technical problems existing in this research field was pointed out. Besides, we also put forward research ideas and key directions of herbicide pollution process and abatement technology in the black soil region in China, so as to promote the development of herbicide pollution and remediation theory and technology in the black soil region in China.

      • The subsequent effects of phosphorus fertilization in upland red soils and the underlying mechanisms

        Shi Wei, Zhang Limei, Wang Jinsong, Li Congping, Gu Chaoling, Zhao Huiyu

        DOI: 10.11766/trxb202106220680

        Abstract:

        The utilization efficiency of phosphorus fertilizer is generally low in agro-ecosystems as phosphorus is readily co-precipitated with iron and manganese oxyhydroxides, iron aluminides, or directly absorbed to the soil minerals, particularly in the red soil ecosystem. Thus, understanding the subsequent effects of phosphorus retained in the soil on soil ecological function and crop nutrient supply is of significance to guide the management of phosphorus fertilization. Based on a long-term fertilization experiment in red upland soil, this study investigated the effect of the conventional fertilization (CK) and short-term phosphorus fertilizer input (at rates of 0, 50, 100, 150 and 1 000 kg·hm-2, P2O5) on soil nutrients, soil nitrogen cycle process and crop yields after 27 years. We evaluated the relationship between these factors and the residual effect of phosphorus using the multivariate statistical analysis method. Short-term P fertilizer addition at a high rate (1 000 kg·hm-2, P1000) had no significant effects on soil total carbon (TC), total nitrogen (TN) and microbial biomass (MBC) compared to the conventional fertilization treatment (CK). Also, it significantly increased soil pH, nitrogen mineralization rate (Nmin), soil nitrogenase activity (SNA), and potential nitrification rate (PNR) (P < 0.05), while it significantly decreased the net N2O emission potential (NN2O) (P < 0.05). Compared with the low phosphorus dosage treatment (50, 100, 150 kg·hm-2), P1000 significantly increased soil available phosphorus (AP), Nmin, SNA, PNR and potential N2O production rate (PN2O) by 33.3%-76.4%, 88.2%-388.1%, 111.4%-4 826.3%, 22.6%-152.4% and 13.8%-78.9%, respectively (P < 0.05), but significantly decreased the net N2O emission potential by 64.6%-78.9% (P < 0.05). These results suggest that the application of a high dosage of phosphorus fertilizer has a strong residual effect on soil microbial activity and nitrogen processes even after 27 years. Spearman correlation analysis and redundancy analysis showed that AP and pH were the most important factors affecting soil microbial activities. Maize yield in the recent three years showed no significant difference among all treatments but was significantly positively correlated with TP, AP and pH. In comparison to low phosphorus treatments, P1000 treatments showed a promotion effect of 3%-23% on maize yield based on the historical yield data during 1991—2019. Our results reveal that the short-term application of a large amount of phosphorus fertilizer has significant positive effects on maintaining soil fertility, microbial activity, soil nitrogen cycle function activity and crop yield even after 27 years, owing to the promotion of soil pH and slow release of available phosphorus

      • Effects of loose soil samples, repacked soil columns and compactness on soil organic carbon mineralization

        Rong Hui, Fang Huan, Jiang Yuji, Zhao Xu, Peng Xinhua, Sun Bo, Zhou Hu

        DOI: 10.11766/trxb202104100187

        Abstract:

        【Objective】Soil organic carbon (SOC) mineralization is generally measured by laboratory incubation of loose soil samples. However, the structure of loose soil samples is of great difference from that of bulk soil samples. The relationship between SOC mineralization of loose soil samples and bulk soil samples is not clear. Soil samples close to field conditions can be obtained by repacking soil columns. Nevertheless, compactness can affect soil pore structure and may influence SOC mineralization. Therefore, this study aimed to evaluate whether it is accurate to represent SOC mineralization in the field by incubating loose soil samples and how compactness influences soil pore structure or SOC mineralization in repacked soil columns. 【Method】Soil samples were collected from a long-term field experimental site with treatments receiving different amount of pig manure. In our first incubation experiment, all of these soils were selected and two treatments were set up in each soil: loose soil samples and repacked soil columns. In the second incubation experiment, only one soil was used, and the soil was repacked into columns with four bulk densities, which were 1.1 (BD1.1), 1.3 (BD1.3), 1.5 (BD1.5) and 1.7 (BD1.7) g?cm-3. The samples of these two experiments were incubated for 57 d and 28 d, respectively. SOC mineralization was measured during incubation, and soil pore structure was quantified using X-Ray micro-computed tomography (μ CT) imaging. 【Result】At the end of incubation (57 d), the cumulative amount of SOC mineralization was significantly different between loose soil samples and repacked soil columns. The cumulative amount of SOC mineralization in the loose soil samples was about 4 times that of the repacked soil columns. In the second experiment, the total porosity decreased by 12.9%, 14.8% and 17.4%, respectively under BD1.3, BD1.5 and BD1.7 compared with BD1.1. In relative to BD1.1, the increase of compactness decreased macro-porosity by 19.0%, 65.5% and 88.5%, respectively under BD1.3, BD1.5 and BD1.7. In addition, the water-filled pore space (WFPS) increased from 36.4% to 91.8% and air-filled pore space (AFPS) decreased from 63.6% to 8.2%. At the end of incubation (28 d), the cumulative amount of SOC mineralization generally increased as bulk density increased up to 1.5 g?cm-3, after which there was a decrease. The regression analysis showed that there was a significant nonlinear relationship between the cumulative amount of SOC mineralization and total porosity, macro-porosity, WFPS and AFPS. The cumulative amount of SOC mineralization increased with increasing total porosity and macro-porosity until a level of 46% and 3.7% was respectively reached, afterwards it began to decline. Also, the relationship between the cumulative amount of SOC mineralization and WFPS and AFPS showed the same trend. The cumulative amount of SOC mineralization was the highest when WFPS was 66% or AFPS was 34%. 【Conclusion】Laboratory incubation using loose soil samples will overestimate the potential of SOC mineralization in the field, while a change of compactness will modify soil pore structure and subsequently affect SOC mineralization. There is a significant nonlinear relationship between the cumulative amount of SOC mineralization and porosity.

      • Effects of Key-stone Microbe Based on Co-occurrence Networks on Wheat Yield in the Soils with Straw Returning

        QIU Lili, LI Dandan, ZHANG Jiabao, ZHAO Bingzi ☨

        DOI: 10.11766/trxb202107200372

        Abstract:

        【Objective】The mechanism of the inconsistent effects of straw application on crop yield is still unclear, and the main reason may be related to the insufficient understanding of the effects of straw application on soil microbial community composition and its abundance changes on crop yield.【Method】A pot experiment to study the growth of wheat was carried out using red and yellow-cinnamon soils. Three levels of straw application were set for each soil, namely 0, 10 and 30 g·kg-1 soil (S0, S10, S30). Based on bacterial-fungal co-occurrence networks, the Path analysis model was used to evaluate the contribution of microbial ecological clusters, enzyme activities and chemical properties to wheat yield.【Result】The results showed that although the content of available nutrients, soluble organic carbon, microbial biomass carbon and enzyme activities (amylase, invertase, polyphenol oxidase, urease, acid phosphatase, dehydrogenase) increased significantly in both soils, the wheat yield increased with the increase in straw dosage in the red soil but decreased in yellow-cinnamon soil. Compared with S0, S10 and S30 treatments increased wheat grain yield and above-ground biomass by 33%~44% and by 73%~85% in the red soil; and decreased wheat grain yield and above-ground biomass by 22%~25% and by 55% in the yellow-cinnamon soil, respectively. The abundance of two key ecological clusters within the bacterial-fungal co-occurrence network, enzyme activities and soil chemical properties had positive effects on wheat yield in red soil while the abundance of two key ecological clusters had a larger positive effect on wheat yield in yellow-cinnamon soil. The straw application significantly increased the abundance of Aspergillus, a key microorganism positively correlated with wheat yield in red soil, while significantly decreased the abundance of Bacillus, Burkholderia, and Basidiobolus, which were positively correlated with wheat yield in yellow-cinnamon soil.【Conclusion】The combined effects of straw application, an increase in key microbial abundance, enzyme activities, and improvement of soil chemical properties was responsible for improving wheat yield in the red soil. In the yellow-cinnamon soil, the decrease in wheat yield was mainly related to lower key microbial abundance, whose effect was superior to the potential positive effects of improved soil chemical properties and enzyme activities. These results suggest that the change in the abundance of key microorganisms has an important influence on the variation of crop yield after straw returning.

      • Research Progresses on Soil Enzymes as Indicators of Soil Health and Their Responses to Heavy Metal Pollution

        TAN Xiangping, HE Jinhong, GUO Zhiming, WANG Ziquan, NIE Yanxia, YE Qing, HE Wenxiang, SHEN Weijun

        DOI: 10.11766/trxb202107240275

        Abstract:

        Soil enzymes play a vital role in the biogeochemical cycling of key elements, maintenance of animal and plant health, and decontamination of environmental pollution. The activities of soil enzymes can be applied in the environmental risk assessment of soil heavy metal pollution. However, the effects of heavy metals on soil enzyme activities varied with soil physicochemical and biological properties and the differences of research methods. Thus, these factors hinder the application of soil enzymes in the assessment of soil health and quality. This study systematically elaborates the eco-toxicological effects of heavy metal pollution on soil enzyme activities and the kinetic characteristics of soil enzyme catalytic reactions. We also constructed a conceptual diagram of soil enzymes in response to soil-heavy metals-microorganisms, proposed and discussed the future trends and directions in soil enzyme in the assessment of heavy metal pollution. Soil enzymes are potential biological indexes for the evaluation of soil heavy metal pollution, because the determination of soil enzyme activity is efficient and cheap, and soil enzyme activity is sensitive to heavy metal toxicity. However, soil enzyme activity may overestimate or underestimate the ecological toxicity of heavy metals as an individual indicator. Furthermore, there is no uniform standard on how to select soil enzyme as a general indicator to assess the toxicity of heavy metals in different soils. Also, it is difficult to establish a quantitative relationship between the ecological doses of heavy metals for soil enzyme activity and soil properties, which led to the arguments about its accuracy and applicability in the ecological risk of heavy metal pollution. Therefore, it is crucial to use new technologies and methods to uncover the reactive mechanisms of enzymes to heavy metal toxicity in different types of soils, and quantitatively analyze the relationship between soil properties and ecological doses of heavy metals based on kinetic parameters. This can strengthen the practical application of soil enzymes in the diagnosis of soil pollution by heavy metals.

      • Nitrate-Dependent and Photosynthetic Fe(II) Oxidation Processes in a Calcareous Paddy Soil

        CHEN Zhihuai, WANG Xugang, SUN Lirong, DONG Leheng, GUO Dayong, SHI Zhaoyong

        DOI: 10.11766/trxb202104010174

        Abstract:

        【Objective】Iron redox processes under anaerobic conditions are closely correlated to nitrogen cycling in soils. Both nitrate-dependent ferrous oxidation (NDFO) and photosynthetic ferrous oxidation (PFO) are crucial pathways of biological ferrous iron oxidation. However, whether NDFO occurs in calcareous paddy soils and its relation to PFO is still ambiguous. 【Method】 We collected soil samples from Mengjin County, Henan Province, within the middle and lower reaches of the Yellow River. The soil samples were made into slurries using 10 mmol?L-1 NO3-/NH4+ solution or water at the very beginning. Then the slurries were anaerobically incubated under darkness or illuminated. On the 7th day of the incubation, we injected 0.5 mL 70 mmol?L-1 NO3- or NH4+ into a part of those slurries made with water to adjust their external NO3- or NH4+ content to 10 mmol L-1. To assess the iron reduction, and ferrous oxidation, Fe(II) in the slurries was measured dynamically using the phenanthroline colorimetric method. To evaluate the nitrogen transformation, NO3- and NO2- were analyzed dynamically using an ion chromatograph equipped with an electrical conductivity detector, and NH4+ was measured after the incubation by 1 mol?L-1 KCl extraction-Kjeldahl method. To fractionate the PFO, O2 in the headspaces was determined dynamically using a portable fiber-optic trace oxygen meter. 【Result】The results showed that, though no apparent ferrous oxidation was observed, iron reduction rate decreased by 0.28 mg?g-1?d-1 and 0.33 mg?g-1?d-1. Also, the iron reduction rate constant was decreased by 0.15 d-1, and 0.17 d-1 in slurries under darkness with NO3- or NH4+ amended at the very beginning. Ferrous iron was oxidized by 2.21 mg?g-1 and 0.68 mg?g-1 in slurries with NO3- or NH4+ injected on the 7th day of the dark incubation and by 1.99 mg?g-1 in slurries incubated under light. In addition, Fe(II) in the slurries was negatively correlated to O2 in the headspace. Importantly, the reduction of NO3— to NH4+ occurred in the slurries with NO3- injected on the 7th day of dark incubation. 【Conclusion】 Ferrous oxidation caused by NDFO was observed in the calcareous paddy soil amended with 10 mmol?L-1 NO3- and incubated anaerobically under darkness. However, the oxidation could be inhibited since the ferric iron resulting from NDFO would be reduced rapidly when the NO3- becomes depleted. Both NDFO and PFO occurred in the calcareous paddy soil incubated under illumination and the PFO resulted in 1.99 mg?g-1 ferrous iron oxidized. Ferrous oxidation in soils under illumination was increased by 0.57 mg?g-1 when NO3- was injected. These results help to further understand the redox processes and the coupled nitrogen transformation in wetland soils.

      • Effects of Straw returning instead of Chemical Fertilizer on Crop Yield and Soil Fertility in Fluvo-aquic Soil

        ZHAO JinHua, CHEN Lin, Duan Yan, Zhang Congzhi, Ma Donghao, ZHANG JiaBao

        DOI: 10.11766/trxb202106230326

        Abstract:

        Abstract:【Objective】The excessive application of chemical fertilizers in China’s major grain-producing areas has led to a series of problems including the reduction of fertilizer utilization rate, soil quality degradation, and increase pollution risk,【Method】A field experiment was set up in the fluvo-aquic soil area of the Huang-Huai-Hai Plain to study the effects of straw returning combined with different proportions of nitrogen and phosphorus reduction on soil nutrients. Also, the effects of these amendments on crop yields, straw nutrient release, and soil microorganisms were studied to clarify the nutrient components of chemical fertilizers that can be replaced by straw returning without loss of crop yields and soil nutrients. Importantly, the microbial mechanism that promotes efficient utilization of straw nutrients and provides a basis for the implementation of chemical fertilizer reduction action was explored.【Result】The results showed that compared with conventional fertilization, a 30% reduction of nitrogen or 50% reduction of phosphorus had no significant effect on crop yield and soil nutrient content. The straw degradation rate reached 43.33% ~ 53.11% in the first season while the reduction of 30% nitrogen or 50% phosphorus could increase it by 12.40%, and the degradation rate reached 63.41% ~ 75.62% after two years. Nitrogen reduction by 100% significantly reduced the abundance, species richness and diversity of bacterial fungi, while phosphorus reduction had little effect. Nitrogen and phosphorus reductions by 30% and 50%, respectively, mainly increased the relative abundance of Gemmatimonadetes longimicrobiaceae and Proteobacteria nitrosomonadaceae in bacteria, increased the relative abundance of Chrytridiomycota GS13 class in fungi, and decreased the relative abundance of Ascomycota sordariomycetes and Mortierellomycota mortierellomycetes. Redundancy analysis showed that the main environmental factors affecting bacteria and fungi were soil organic carbon (SOC) and total nitrogen (TN). 【Conclusion】In conclusion, straw returning combined with nitrogen reduction by 30% or phosphorus reduction by 50% has the potential to maintain fertilizer use efficiency and stable yield in the medium and high yield fields of fluvo-aquic soil.

      • Status of Soil Phosphorus Pool and Environmental Risk Assessment in Rice-Oilseed rape Rotation Area in the Yangtze River Basin

        yanjinyao, guolixuan, wangkunkun, liaoshipeng, luzhifeng, congrihuan, lixiaokun, rentao, lujianwei

        DOI: 10.11766/trxb202108050327

        Abstract:

        The objective of this study was to clarify the status of soil phosphorus (P) pools in rice-oilseed rape rotation areas in the Yangtze River Basin, and assessed the risk of soil P leaching. Alse it aimed to provide a reference for reasonable phosphorus application in the rice-oilseed rape rotation system in the Yangtze River Basin. From April to May 2018, 247 soil samples of the cultivated layer after the oilseed rape harvest were collected in 14 provinces (cities/districts) around the Yangtze River Basin in typical rice-oilseed rape rotation regions to determine soil total phosphorus, available phosphorus (Olsen-P) and soluble phosphorus (CaCl2-P). With reference to soil total phosphorus and available phosphorus grading indexes, the current status of soil phosphorus abundance and deficiency in rice-oilseed rape rotation areas in the Yangtze River Basin was clarified, and the quantitative relationship between Olsen-P and CaCl2-P was established. According to the available phosphorus grading, 72 samples were selected for Hedley phosphorus fraction determination, and the distribution characteristics of soil phosphorus pool in rice-oilseed rape rotation were analyzed. The results showed that the average content of total phosphorus, available phosphorus and CaCl2-P in cultivated soils of rice-oilseed rape rotation area in the Yangtze River Basin were 0.62 g·kg-1, 23.2 mg·kg-1 and 0.49 mg·kg-1, respectively. There was no significant difference in total phosphorus between the upper, middle and lower reaches of the Yangtze River, and 48.6% of the total area was in a state of abundance. The lack and excess of soil available phosphorus coexist, accounting for 23.1% and 31.1%, respectively. The areas of soil available phosphorus deficiency and excess were concentrated in the middle and lower reaches of the Yangtze River, respectively. Also the soil phosphorus pool was dominated by inorganic phosphorus, accounting for an average of 82.2%. The average content of H2O-Pi, NaHCO3-Pi, NaOH-Pi, HCl-Pi, NaHCO3-Po, NaOH-Po and Residual-P pools were 10.8, 46.8, 115.6, 218.6, 22.3, 104.9 and 193.8 mg·kg-1, respectively. With an increase in soil available phosphorus levels, the contents of NaHCO3-Pi and NaOH-Pi increased significantly, and the stable phosphorus pools (HCl-Pi and Residual-P) were relatively stable. The relationship between Olsen-P and CaCl2-P conformed to the double-line model. When a change point appeard, the content of Olsen-P was 39.9 mg·kg-1 with a corresponding content of CaCl2-P of 0.6 mg·kg-1. Also, when the Olsen-P content was greater than 39.9 mg·kg-1, the risk of soil phosphorus leaching increased. Generally, the soil phosphorus content in the rice-oilseed rape rotation area in the Yangtze River Basin showed an upward trend and 13.0% of this area was at a high risk of phosphorus leaching. Also, the soil phosphorus mainly accumulated in stable phosphorus pools. Therefore, more attention should be paid to the rational application of phosphorus fertilizers, appropriately reduce phosphorus fertilizer input, and tap the potential of stable phosphorus pools in soils. Thus, this will reduce soil Olsen-P accumulation, environmental P loss in the rice-oilseed rape rotation system, and improve crop P fertilizer utilization.

      • The Soil Microbial Legacy Effects of Long-Term Gradient P Fertilization Based on the Analysis of Plant Growth, Nutrient Absorption, Soil Enzyme Activity and Mycorrhizal Characteristics

        Lang Ming, Zhang Chunyan, Zhang Junling

        DOI: 10.11766/trxb202104300231

        Abstract:

        【Objective】Long-term excessive phosphorus (P) application in intensive agro-ecosystem leads to P accumulation in soil. Whether there was a legacy effect on accumulated P in soil.【Method】This study was based on a long-term experiment (started in 2007) in North China Plain. The microorganisms with different P supply levels (from P2O5 0, 75, 300 kg hm-2, P0, P75, P300, respectively) in calcareous soil was selected as the research object. Pot microbial inoculation experiment was conducted to explore the soil microorganisms training with gradient P fertilization on plant growth, nutrition absorption, soil enzyme activities and mycorrhizal characteristics under two substrate P supply levels (0 mg · kg-1, 30 mg · kg-1, no P, + P, respectively).【Result】The type of inoculants (original inoculants, sterilization treatment) significantly affected the aboveground biomass and phosphorus uptake of plants. Inoculating original inoculants (P0, P75 and P300) significantly increased the aboveground biomass and P uptake of clover compared with sterilized inoculants under the condition of two substrate P levels, but there was no significant difference among the three original inoculants. The aboveground biomass of maize inoculated with original inoculants P300 was significantly higher than that in the treatments of P0 and P75. At the same time, the inoculant and substrate P supply level co-affected soil enzyme activities. Compared with P0 and P75 inoculants, P300 inoculant significantly decreased the peroxidase activities in the soil of clover under no P and + P conditions, and significantly increased the peroxidase and chitinase activities in the soil of maize under no P conditions. Also, compared with inoculating in original P0 and P300 inoculants, P75 inoculant significantly increased the activities of acid and alkaline phosphatase in maize soil under no P condition. In addition, the mycorrhizal colonization differed due to plant species. Compared with P0 and P75 inoculants, the colonization rate of arbuscular mycorrhizal fungi in clover root significantly reduced after inoculating with P300, but there was no significant difference among the three original inoculants in maize root.【Conclusion】The substrate P supply and plant species co-affect microorganisms training by accumulated P, suggesting that plant-microbial characteristics need to be considered in P fertilizer management.

      • The Spatial Variations of Saline-alkali Artificial Grassland on the Songnen Plain

        YANG Hongtao, AN Fenghua, ZHANG Lu, YANG Fan, WANG Zhichun

        DOI: 10.11766/trxb202010280601

        Abstract:

        【Objective】Grasslands in Songnen plain are propitious to the develop the mechanized-graziery due to its flat terrain and the climatic conditions, which influences by temperate continental monsoon climate. Moreover, influenced by the high plant coverage and diversity, black soil was developed, and the high quality forage species was dominated by Leymus chinensis in the past decades. However, the fragile eco-environment of Songnen grasslands could be impacted by the special topography, high salinity and shallow groundwater, and the parent material. Soil parameters are typically used to quantify the relationship between soil properties and forage yield and to identify the limiting factors of grassland productivity. Because of overgrazing and overdevelopment, the Songnen grasslands were degraded and salinized significantly. The husbandry was remarkable hindered by the low grassland productivity. The objectives of this study were: 1) to investigate the spatial variation characteristics of soil physical and chemical properties; 2) to estimate the spatial variation characteristics of vegetation community; 3) to explore the potential linkages between dry yield of alfalfa and soil physical and chemical properties. 【Method】 The artificial grassland locates at the Xinfawopeng village of Baicheng City, which covers an area of 600 m×450 m. The soil sample points were set by grid method, with the spacing of each neighbor sample points was 50 m. The soil samples were collected from alfalfa artificial grassland from by cutting rings and soil auger in October 2017 and May 2018 for detecting the soil physico-chemical properties, meanwhile, the forage samples were collected in a quadrat of 1 m2 (1 m×1 m). All the soil samples were air-dried, ground and then passed through a 2-mm sieve for chemical properties. The 1:5 of soil-water extracts were used to determining soil pH, EC, Na+, Ca2+, Mg2+, HCO3-, and CO32-. The spatial variations of soil properties, including soil mass water content (MWC), soil pH, EC, and total alkalinity (TA) were determined by classical statistics and geostatistics. Furthermore, the spatial variations of biological characteristics of artificial grassland, such as the Shannon-Wiener Index (SWI), dry yield (DY), shoot height (SH), and cover degree (CD) in the study area, were analyzed with classical statistics and geostatistics. 【Result】At the depth of 0 ~ 30 cm, very high spatial variability of the EC and TA were found, however, the pH and MWC showed moderate spatial variations; The biological properties of the grassland community showed high spatial variations. Results of multiple linear regression (MLR-step wise) suggested that the alfalfa dry biomass (DM) could be predicted by (DM) = 2699.73-276.496 pH (7.17< pH <9.76), which indicated that the soil pH influenced the alfalfa yield more than other soil properties. 【Conclusion】The above results indicated that the soil physico-chemical properties of artificial grasslands in western Songnen pain were high and moderate spatial variations, and the alfalfa could not tolerance the pH higher than 9.76.

      • Research on the Cross-Coloration Effect of Iron Oxides and Humus in Soil

        GUAN Yanxia, LU Jinmei, MA Rongjun, XING Dengchun, LONG Xiaoyong

        DOI: 10.11766/trxb202103200154

        Abstract:

        Soil color is an important index of soil classification, climate reconstruction and environmental remote sensing. Iron oxides and humus are the two major chromogenic components of soil, which dominate the spectral response characteristics of soil. 【Objective】This paper is based on the unclear cross-coloration effect of iron oxides and humus in soils and sediments.【Method】 We selected kaolinite as substrate, hematite (Hm) and goethite (Gt) as the representatives of iron oxides, humic acid (Ha) and fulvic acid (Fa) as the representatives of humus. The spectral characteristics, color changes and cross-interference characteristics of iron oxides and humus with different contents were discussed by high-resolution Diffuse Reflectance Spectrum (DRS). 【Result】It is found that in terms of the chromogenic effect of a single component, Hm is stronger than Gt, and Ha is stronger than Fa. The addition of humus has an obvious effect on the coloration of iron oxides, which usually reduces the Mean Reflectance, Value (V) and Chroma (C), and makes the Hue (H) yellowish. The anti-jamming ability of Hm is greater than that of Gt. The a* of Lab color system and the redness of DRS are sensitive to the change of Hm content. The b* of Lab color system and the yellowness of DRS are sensitive to the change of Gt content. They can be used as indices for the quantitative determination of soil iron oxides. However, the addition of Ha can lead to the underestimation of Hm and Gt, and the addition of Fa has less effect on the estimation depending on the contents of Hm and Gt. 【Conclusion】Based on this, the estimation formulas of Hm and Gt mixed with different contents of humic acids are given. It not only helps understand the color change of natural soils but also lays a foundation for iron oxide determination at a large scale based on remote sensing.

      • Research Progress on the Microstructure and Constituents of Fe-Mn Nodules in Soil

        WANG Yi, HUANG Laiming

        DOI: 10.11766/trxb202107130360

        Abstract:

        Ferromanganese concretions (or Fe-Mn nodules), as a specific type of soil neoformations, are formed during pedogenic processes. The structure of concentric rings in soil Fe-Mn nodules can be used to reconstruct paleoclimatic conditions and soil-forming environments. The constituents of soil Fe-Mn nodules can provide nutrients and energy for microbial metabolism that in turn affect the transformation, fixation and mobilization of soil nutrients and heavy metals. This article reviewed the research progresses on soil Fe-Mn nodules during the past several decades, including (i) the formation mechanism and process of Fe-Mn nodules and the associated influencing factors; (ii) differences in the microstructure and constituents of Fe-Mn nodules in different regions; and (iii) effects of Fe-Mn nodules on nutrient transformation and heavy metal sorption. Future research priorities include (a) study of the formation rates and environmental thresholds of Fe-Mn nodules during different stages of soil development; (b) establishment of the evolution models of Fe-Mn nodules in different soil-forming environments; and (c) elucidation of the mechanisms of stabilization and release of soil nutrients and heavy metals by Fe-Mn nodules. This will facilitate understanding of the pedogenic processes and elemental biogeochemical cycling in the Earth’s Critical Zone and provide a basis for quantitative evaluation of soil quality and function under changing environments.

      • The Indicators, Framework and Procedures for Soil Health: A Critical Review

        lixuanzhen, luoyongming, houdeyi

        DOI: 10.11766/trxb202105240270

        Abstract:

        Soil health has become a hot topic in soil science. Scientific assessment of soil health is fundamental to soil management and the achievement of sustainable development goals. Soil health assessment is challenging because of the multiple properties and ecosystem services. In this paper, the development of the concept and the traditional health assessment indicators, including physical, chemical and biological indicators, and their connotation were summarized. Also, the commonly used soil health assessment frameworks and their applicability were introduced while the general procedure of soil health assessment was summarized. This study also pointed out that the future soil health assessment in China should enhance the weight of carbon pool index, biological index and environmental index. Thus, the paper aims to lay a foundation for the establishment of a soil health assessment method that conforms to China"s national conditions.

      • Transport of Straw-derived Carbon in Black Soil and Cinnamon Soil and its Response to Nitrogen Fertilization

        CHEN Xianni, WU Shanwei, KOU Taiji, XU Pengfei, TAN Xiaohua, GUO Dayong

        DOI: 10.11766/trxb202105210059

        Abstract:

        【Objective】 A laboratory incubation was conducted to study the transport characteristics of soil native carbon (Cs) and straw-derived carbon (Cstr) after adding wheat straw and nitrogen fertilizer in black soil and cinnamon soil. 【Method】 There are four treatments: Control (soil only, no straw or nitrogen added), N (soil with nitrogen fertilization, 170 kg?hm-2), R (soil with straw addition, 8 580 kg?hm-2), RN (soil with nitrogen fertilizer 170 kg?hm-2 and straw addition 8 580 kg?hm-2). The wheat straw used was isotope 13C labeled. Soil samples were collected and fractionated into three different soil organic carbon fractions (light fraction-LF, occluded particulate organic carbon-OPOC, heavy fraction-HF) at 0, 180, 300 days. 【Result】 The results showed that the soil incubation was a carbon loss process of soil carbon mineralization. Nitrogen fertilization showed an inhibitory effect on carbon mineralization in both soils, and the effect in cinnamon soil was more significant in straw-added treatments compared to no straw-added treatments. The percentages of Cs loss in the two soils were ranked as HF>OPOC>LF. Straw application increased the percentage of Cs loss in HF from 2.83% to 5.53% (P<0.05) in black soil and decreased the percentage of Cs loss in OPOC from 1.86% to 0.82% (P<0.01) in cinnamon soil. Importantly, the Cstr in LF was gradually transferred to OPOC and HF, and the transfer became slower after 180 days. By the end of incubation (300 days), the total residual rate of Cstr in cinnamon soil showed no significant difference compared to that in black soil. The residual rate of Cstr in LF was 4.98%-8.52% in cinnamon soil and was significantly higher than that in black soil (1.71%-2.47%). Compared to R treatment, RN treatment almost doubled the residual rate of Cstr in LF of cinnamon soil. 【Conclusion】 The HF was the main source of Cs loss. Nitrogen fertilization inhibited carbon mineralization in the two soils. Straw addition exhibited a positive priming effect on the carbon mineralization of HF in black soil and an inhibitory effect on the mineralization of OPOC in cinnamon soil. The degradation degree of LF-Cstr in cinnamon soil was lower than that in black soil and could be limited by nitrogen application.

      • Evaluation of Phosphate Fertilizer Reduction on Annual Phosphorus Loss under Intensive Open-field Vegetable Production

        WANG Rui, SHI Weiming, LI Yilin

        DOI: 10.11766/trxb202102050078

        Abstract:

        【Objective】Intensive vegetable fields have been the priority control projects for phosphorus (P) loss in farming due to massive fertilization and flood irrigation, accounting for the highest proportion of P pollution from farmlands. Therefore, (i) quantifying the assessment of the annual P loss of vegetable fields, (ii) clarifying the reasonable threshold range of phosphate fertilization for vegetables, and (iii) controlling P migration and loss from vegetable fields through the source are of great significance for effectively reducing the environmental pressure caused by agricultural non-point source pollution. 【Method】A plot experiment in the Tai Lake Basin with conventional fertilization and phosphate fertilization reduction treatments was conducted in a perennial and open vegetable field. The one-year vegetable rotation experiments focused on clarifying the environmental threshold of P and annual P runoff loss characteristics. There were five treatments, conventional fertilization (CK), reduction of 20% (P-20), 30% (P-30), 50% (P-50), and 100% (P-100) based on conventional P fertilization. 【Result】 The environmental threshold of soil P in the tested vegetable fields was 78.9 mg?kg-1. During the whole experimental period, Olsen-P content in the soil surface of different treatments exceeded the leaching threshold. The results of annual total P (TP) runoff loss concentration in vegetable fields showed that with the decrease of phosphate fertilization input, the annual loss concentration of TP decreased. Also, dissolved P (DP) was the dominant form of P species, accounting for 50.1%~63.1%. Runoff loss loads of P showed seasonal characteristics, with the amount of P loss in a summer-autumn season (1.93~3.26 kg?hm-2), accounting for 59.2%~63.2% of the annual P loss flux. Based on the structural equation modeling (SEM), the amount of phosphate fertilizer had a direct and extremely significant effect on TP loss concentration. Furthermore, TP loss concentration had a positive and extremely significant impact on TP runoff loss load with a path coefficient of 0.97. The loss coefficients of P were between 1.36% and 3.33%, and the lowest loss coefficient was in the P-50 treatment. With a decreased amount of P applied, the reduction ratio of P runoff loss increased, and a P loss reduction rate of 41.5% was recorded in the P-100 treatment. Treatments of P-20 and P-30 had no significant yield reduction during a three-successive vegetable growth period in a year compared with CK. 【Conclusion】 Taking environmental risk and economic yield into consideration, it is appropriate to reduce between 20%~30% P fertilizer application based on conventional phosphate fertilizer rate for open vegetable fields in Tai Lake region.

      • Effects of Different Phosphorus Application Techniques on Phosphorus Availability in a Rape System in a Red Soil

        WANG Yikun, CAI Zejiang, FENG Gu

        DOI: 10.11766/trxb202104210207

        Abstract:

        【Objective】Phosphorus (P) is an indispensable nutrient needed for plant growth and development and P is deficient, especially in the red soil region of South China. However, the unsuitable application of P fertilizer results in low use efficiency of the fertilizer, ranging from 10% to 25% in the current season in the region. This could result in P surpluses in soils, and runoffs and is one of the important nonpoint source pollutions of aquatic habitats and other water resources. Thus, it is important to investigate a suitable P fertilization in the region to improve P use efficiency and sustain crop yields. 【Method】A field experiment was conducted at the Experimental Station of the Chinese Academy of Agricultural Sciences, Qiyang, Hunan Province, China. The effects of different phosphorus fertilizers (superphosphate, swine manure, calcium magnesium phosphate, monoammonium phosphate, diammonium phosphate), P application rates (conventional phosphorus application, phosphorus reduction 20%, phosphorus reduction 30%), and P combined with amendments (lime, calcium magnesium phosphate fertilizer combined with diammonium phosphate, or crop straw return) on phosphorus availability and crop growth in red soil were tested. 【Result】Of the different phosphorus fertilizers, swine manure induced the highest soil available phosphorus and aboveground biomass and P use efficiency in 2019. Also, under this treatment the crop yield in 2020 was significantly higher than that of other treatments. Compared with the control treatment, swine manure treatment significantly increased soil available phosphorus and aboveground biomass by 32% and 241%, respectively, in 2019, and by 73% and 510% in 2020. As P application rates decreased, the soil available P content was also significantly decreased. However there were no changes in rape seed yield, aboveground biomass, P use efficiency and phosphorus agronomy efficiency. Among them, 30% phosphorus reduction was the best treatment. Compared with a single application of calcium magnesium phosphate, the combined application of calcium magnesium phosphate and diammonium phosphate effectively improved crop yield, soil available phosphorus and phosphorus efficiency index to a certain extent. The treatment of calcium magnesium phosphate fertilizer + diammonium phosphate had the best effect on the crop yield, soil available phosphorus, phosphorus fertilizer cumulative use efficiency, phosphorus agronomic efficiency and soil phosphorus surplus. The addition of lime improved crop yield, soil available phosphorus and phosphorus fertilizer cumulative use efficiency , but did not reach a significant level as compared to superphosphate only treatment. There was a significant positive correlation between rape seed yield and soil available phosphorus. 【Conclusion】 From the above research results, we can conclude that the replacement of chemical phosphorus fertilizer by swine manure phosphorus could achieve the purpose of reducing application and increasing efficiency. Also the best amount of phosphorus fertilizer was a 30% reduction of conventional phosphorus application rate. The calcium magnesium phosphorus fertilizer as a P source should be applied combination with diammonium phosphate to supply P demand for crop growth in such weak acidic red soils.

      • Rhizosphere Communication and Its Effects on Improving Phosphorus Utilization in High-input Vegetable Production System: A Review

        LI Huimin, WANG Rui, ZHONG Yueming, SHI Weiming, LI Yilin

        DOI: 10.11766/trxb202007010354

        Abstract:

        Intensive vegetable production system with a high amount of phosphate fertilizer will cause phosphorus (P) resources waste and environmental risks caused by high accumulation of P in the soil. One of the effective methods to reduce P input and increase P use efficiency in vegetable fields is rhizosphere regulation, which could also improve P absorption and utilization by vegetables. This paper summarizes the major modules of rhizosphere communication, including plant-plant communication (vegetables intercropping root interactions), plant-microorganism communication (vegetable root and mycorrhizal fungi and rhizosphere bacteria interactions) and microorganism-microorganism communication (P solubilizing microorganism with rhizosphere microorganisms in vegetable fields) in promoting vegetable root development. Importantly, we discussed the mechanism(s) for activating soil accumulated P to increase the absorption and utilization of P by vegetables and its mechanism. In addition, different artificial regulation modules, such as increase P absorption and utilization of vegetables by applying P microbial fertilizer, and relieving the obstacles of continuous cropping of vegetables are discussed. Finally, the paper evaluated the direction of the rhizosphere communication in high-input systems to provided a theoretical basis for promoting the green and sustainable development of P fertilizer management in high-input vegetable planting systems.

      • Effects of Maize and Soybean Roots on Topsoil Shear Strength of Red Clay on Sloping Farmland in Central Yunnan

        ZHANG Liyun, DUAN Qingsong, FAN Maopan, YANG Yali, CHENG Weiwei, LI Yongmei

        DOI: 10.11766/trxb202012140689

        Abstract:

        【Objective】The area of sloping farmland in central Yunnan accounts for 61.14% of the total arable land area, and its sustainability is affected by serious soil erosion,so it is urgent to study the positive effects of the rational allocation of vegetation on the sloping land space on improving soil erosion and maintaining sustainable agricultural production.And 89.4% of the sloping farmland utilization in the province is planting crops, and maize and soybean are the main ones in summer. Previous studies have shown that the soil-fixing capacity of vegetation roots plays a significant role in soil and water conservation.This study was conducted to explore the soil-fixing effect of corn and soybean roots ,and provided a basis for the calculation of the soil-fixing ability of crop roots. It also provided a reference for the rational layout of crop planting to prevent soil erosion on slope farmland.【Method】In this study the field experiment was designed to have three treatments and a total of 9 experimental plots were set up, i.e.CK(Bare land) , MM(mono-maize)and SS (mono- soybean).The unconfined compression tests were used to determine the shear strength and stress-strain characteristics of rootless soil and root-soil composites of maize(Zea mays L.)and soybean(Glycine max L.)at mature stage. The WinRHIZO(Pro.2019) system was employed to analyze the root distribution and configuration characteristics. And then the relationship between shear strength and root parameters was studied.【Result】The results indicated that: ①Compared with rootless soil, the roots of maize and soybean could significantly enhance the shear strength of root-soil composite (P < 0.01), and the strength of the root-soil composites is increased by 117.65% and 71.91%, respectively;②The cohesion of two crop root-soil composites were significantly positively correlated with root length density, root surface area density, root volume density and root weight density (P <0.01). and the contribution of fine roots with D≤1mm to the cohesive force increment is greater than that of other diameter-level roots;③In the different root architecture traits, the number of root branches of maize is 45.44% higher than that of soybeans, and the root distribution of each diameter class is more even. The corn root-soil complex shows weak strain hardening characteristics when the root content increases. The crack propagation slows down and the lateral deformation decreases.【Conclusion】The root systems of the two crops could enhance the shear strength of the soil, but the different root structure types have different effects on the mechanical properties of the soil. The maize root system with more fine roots and more branches can effectively enhance the strength and restrain the deformation, so fibrous root maize is better than taproot soybeans in holding the surface soil. In the use of sloping farmland, it is possible to prevent soil erosion by rationally arranging fibrous root crops.

      • Enrichment Characteristics of Soil Ammonium Nitrogen in Ionic Rare Earth Mining Area

        XU Zhe, YANG Jinling, ZHANG Ganlin, ZHAO Yue, ZHOU Jun

        DOI: 10.11766/trxb202104140195

        Abstract:

        【Objective】The leaching agent (ammonium sulfate) causes residues of ammonium nitrogen in the soil of ionic rare earth mining area.This results in serious nitrogen pollution in the soil and water bodies and destroys the ecological environment in the mining area. It also endangers the health of the surrounding residents and restricts the mining of ionic rare earth ore. However, the ammonium nitrogen pollution situation in ionic rare earth tailings and its impact mechanism are still unclear. 【Method】In order to understand the enrichment characteristics of soil ammonium nitrogenin in the mining area and its influencing factors, we chose an in-situ leaching ionic rare earth mining area that has been closed for 4 years in Longnan County, Ganzhou City, Jiangxi Province. We sampled sites located on the different slopes of the hill. Soil samples were chosen from the soil surface to the bottom of the ore body, with a depth of 5.5 to 9.7 m. Ammonium nitrogenin and other soil properties in the soil were determined. 【Result】The results show that soil ammonium nitrogenin content in the mining area ranged from 2.32 to 1056.44 mg·kg-1, and was several times or even hundreds of times higher than in the natural and farmland soils. Ammonium nitrogenin in the mining layers with rare earth was higher than in the upper soil, and with wide the variations among different soil layers in the vertical direction. Also, soil ammonium nitrogenin content in the hill slope followed the sequence of top > bottom > middle slope. The correlation between soil ammonium nitrogen and the physicochemical properties of ionic rare earth tailings was observed to be different from the research conclusions of natural or farmland soil. Due to the supersaturation of ammonium in the soil, the distribution of ammonium nitrogenin is not directly controlled by soil basic physicochemical properties which have an important influence on the ammonium nitrogen adsorption, such as soil clay, cation exchange capacity, etc. 【Conclusion】The major factors observed to influence ammonium nitrogen are the depth and amount of leaching solution inputting, and the permeability changes caused by the soil structure. Mining facilities such as leaching liquid pools, liquid collecting ditch, etc, affect the surrounding soil ammonium nitrogenin content. Due to gravity, ammonium nitrogen will gradually migrates from the top to the middle and the bottom of the slope. This causes ammonium nitrogen to accumulate at the bottom of the slope over time. Under the leaching action of rainfall, a large amount of ammonium nitrogenin in mining area soil will continuously migrate to the surrounding soil and water, which will harm the ecological environment in the long run. The results of this study are of great significance for improving the migration process of soil nitrogen in ionic rare earth mining areas and guiding the treatment of ammonia nitrogen pollution.

      • A Comparitive Analysis of Boundary Layer Methods in Solving Convection-dispersion Equation of Solute Transport

        WANG Jiao, SHAO Ming’an

        DOI: 10.11766/trxb202009240537

        Abstract:

        【Objective】Understanding the behaviours of solute transport in soils is of great importance to agricultural management, resource utilitzation and environmental protection. Introducing boundary-layer theory to solve solute transport problems provides a simple and accurate alternative method to predict solute profile distribution and estimate transport parameters. Appropriate selection of boundary layer solutions requires an overall understanding of the characteristics of boundary layer solution accuracy under different conditions. 【Method】This study compared the accuracy of the polynomial solution, exponential solution, combined solution, logarithmic solution and small flux solution based on multiple parameter combinations. Solute front movement with time in soil column experiments was further used to evaluate the performance of boundary layer solutions for parameter estimation. 【Result】The accuracy of boundary layer solutions for predicting solute concentration profile increased first and then decreased with time. Comparison of different boundary layer solutions indicated that the cubic polynomial solution was optimal at the beginning while the exponential solution turned to be better afterwards for most cases. Importantly, the boundary layer methods performed better in estimating retardation factor than dispersion coefficient. The retardation factor obtained from boundary layer solutions was almost the same but with an exception of the small flux solution. The dispersion coefficient was greater than the breakthrough curve fitting method and varied between boundary layer solutions. The cubic polynomial and logarithmic solutions had a minimum error in the determination of the dispersion coefficient. 【Conclusion】Boundary layer solutions can be used to accurately predict solute profile distribution for the early stage of solute transport processes. Cubic and exponential solutions had better performance than other solutions. Neverthless, cubic and logarithmic solutions can be the first choice for estimating parameters.

      • Effects of Freeze-thaw Cycles and Soil Water Contents on Disintegration Characteristics of Brown Earth

        ZHU Longxiang, FAN Haoming, MA Renming

        DOI: 10.11766/trxb 202103020119

        Abstract:

        【Objective】 Undisturbed brown earth soils from 5~7 cm and 25~27 cm depths in the Shenyang area of China were collected for this research. The effects of freeze-thaw cycles and soil water contents on the disintegration characteristics of the soils were analyzed. 【Method】 Based on meteorological data and field observation, five freeze-thaw cycles were designed. The weighed water contents of the soil samples were regulated to 10%, 15%, 20%, 25% and 35%, respectively, and the disintegration process was measured. 【Result】 1) The soil disintegration had four phases, including the rapid water absorption phase, exponential disintegration phase, step disintegration phase, and disintegration completion phase. In the four phases, the exponential disintegration phase was regarded as the main disintegration process. Importantly, during the exponential disintegration phase, the soil sample collapsed continuously due to pulling or losing support. Also, the disintegration rate in the exponential disintegration phase and non-capillary water content showed similar behavior as the increasing freeze-thaw cycle. According to the two fitting surfaces, there was a most easily disintegrating soil water content in the range10%~15% in which the total disintegration rate was largest. When the water contents were 25% and 35%, all soil samples skipped the exponential disintegration phase and directly entered the step disintegration phase. The total disintegrations of 5~7 cm and 25~27 cm soils were very small under 35% soil water content, and was no more than 6.93% and 11.14%, respectively. 2) Over-consolidation was observed on soil samples with 10% and 15% water contents, and the polarization distribution of soil pores was accelerated under the freeze-thaw cycles. The disintegration rate of the exponential disintegration phase and non-capillary water content of both soil samples was increased after continuous freeze-thaw cycles. Under the freeze-thaw cycles, the structure of soil samples with 25% and 35% water contents was destroyed, soil pores were expanded with an internal settlement, and the water absorption capacity was reduced. 3) The pore difference of 25~27 cm soil sample was slightly larger, the control ability of electric double layer to free water was inhibited by the higher clay content, which resulted in a higher total disintegration rate. 【Conclusion】 The ability of soil to resist erosion from inside to outside was transformed into the ability from outside to inside under freeze-thaw cycles. All the findings may serve as a data basis for brown earth soil erosion research.

      • Research Progress of the Evolution Trends and Controls of Soil Organic Phosphorus Speciation during Natural Pedogenesis Based on Solution 31P Nuclear Magnetic Resonance

        LUO Yuanjun, HUANG Laiming, YUAN Dagang

        DOI: 10.11766/trxb202105060240

        Abstract:

        Soil organic phosphorus (Po) is an important phosphorus pool in soils. The forms, contents and bioavailability of Po change significantly with pedogenesis, which affects soil P supply, nutrient balance and ecosystem productivity. However, compared with inorganic phosphorus (Pi), previous studies paid less attention to Po, which was mainly attributed to the difficulty in the extraction, analysis and identification of different Po speciation. In recent years, the solution 31P nuclear magnetic resonance (31P NMR) spectroscopy was increasingly applied in pedology for characterizing Po compounds, providing a new way for quantitative analysis of Po forms and contents. This significantly improved our understanding of the transformation process of Po during long-term terrestrial ecosystem evolution. This paper systematically summarized the forms and properties of soil Po, and described the principle and procedures of solution 31P NMR spectroscopy for characterizing soil Po speciation. Then we reviewed the evolution trends and controls of different Po speciation during natural pedogenesis, and put forward several questions that need to be resolved in the future. Future research priorities include (i) determining the rates, pathways and thresholds of soil Po transformation during long-term soil evolution; (ii) elucidating the coupling relationship between Po and other nutrients such as C and N at different stages of soil evolution and the mechanisms of fixation and release of soil Po; and (iii) building a quantitative model of Po evolution in different types of soils. Providing solutions to the above questions can improve our understanding of the phosphorus biogeochemical cycle in Earth’s Critical Zone and provide a theoretical basis for nutrient management and regulation at different stages of soil evolution, and would promote sustainable utilization of soil resources.

      • Comparative Study on Ammonia Volatilization from Soil Surface and whole Shed in Solar Greenhouse

        ZHANG Zhaobei, LUO wei, BAI Xinlu, CHENG Yuzhen, CHEN Zhujun

        DOI: 10.11766/trxb202101280056

        Abstract:

        Abstract: 【Objective】Ammonia volatilization from solar greenhouses driven by excessive nitrogen input has received widespread attention in recent years. However, the ammonia volatilization emission of greenhouse system is mainly determined by soil surface ammonia volatilization. Greenhouses are semi-closed structures, as a result, a part of NH3 emitted from soil can be absorbed again by the plant canopy or dissolved in the greenhouse membrane water and returned to the soil. The volatilization of ammonia from soil surface can not accurately reflect the amount of ammonia discharged into the atmosphere by solar greenhouse. Therefore, ammonia volatilization from soil surface is difficult to accurately reflect the amount of ammonia emitted into the atmosphere by solar greenhouse.【Method】Experiment comprised four treatments: (i) no nitrogen input with conventional irrigation (N0+FI), (ii) conventional nitrogen input with conventional irrigation (FT+FI), (iii) optimum nitrogen input with conventional irrigation (OPT+FI), and (iv) optimum nitrogen input with optimum irrigation (OPT+OI). Ammonia volatilization losses were measured in three vegetables seasons (tomato-watermelon-tomato) using intermittent closed chamber ventilation method. The air volume mask (Kanomax 6570) was used to measure the gas flow at the vent, and the ammonia concentration at the vent was continuously monitored by pumping method. In this way, the loss rate and amount of ammonia volatilization were measured from the whole greenhouse, and losses were compared with the soil surface.【Result】The results showed that the ammonia volatilization rate peaked on the same day after greenhouse fertilization, and there was no significant difference between fertilized and unfertilized (control) after 7 days. During the three planting seasons, the ammonia volatilization under different nitrogen treatments were: 2.82-4.97 kg hm-2 , 6.59-9.97 kg hm-2 and 15.77-21.83 kg hm-2 , respectively, and the corresponding ammonia volatilization emission factors were 0.64%-1.50%, 3.11%-4.21% and 2.59%-3.90%, respectively. The trend of ammonia volatilization rate of the whole shed was basically consistent with that of the soil surface. The ammonia volatilization rate of the whole shed was 2.22 kg N hm-2 in the second quarter and N 2.92 kg hm-2 in the third quarter, which accounted for 13.38%-33.69% of the ammonia volatilization from the soil surface, and the ammonia volatilization coefficient was only 0.46%-1.48%, which was much lower than the ammonia volatilization from the soil surface.【Conclusion】Thus, it is concluded that the ammonia volatilization from solar greenhouse will be overestimated when only taking the soil surface ammonia volatilization into consideration. Measuring ammonia volatilization based on the whole solar greenhouse system is thus recommended in future studies.

      • A Review of Responses of Soil Nitrous Oxide Emissions to Nitrogen Input in Forest Ecosystems

        zheng xiang, Liu Qi, Cao min min, ji xiao fang, fang wan li, jiang jiang

        DOI: 10.11766/trxb202105150258

        Abstract:

        Rising nitrous oxide (N2O) concentrations in the atmosphere have exacerbated global warming. Forest soil plays a vital role in regulating atmospheric N2O concentration. The effect of nitrogen (N) input on the N2O fluxes of forest soil has attracted much attention. However, the response mechanism of forest soil N2O emissions to N input, especially the regulatory effects of plants and microorganisms on N2O flux, has not been systematically studied. Therefore, this article reviews how N input affects forest soil N2O emissions through forest vegetation (root N absorption, litter decomposition, and formation of arbuscular mycorrhizal) and soil microorganisms (microbial biomass and community composition). The results show that the competitive N uptake of plants can reduce the promotion of N input on N2O emissions. Importantly, the magnitude of its effect may mainly depend on the state of the soil "N saturation". Plant litter mainly affects N2O emissions of forest soil under the background of N input through nutrient return and the release of secondary metabolites during the decomposition process. The former has a promoting effect and the latter has an inhibitory effect. The arbuscular mycorrhiza mainly regulates forest soil N2O fluxes by absorbing available N and water, promoting the formation of aggregates, and changing the N2O-related functional gene community. Nitrogen input leads to soil acidification or nutrient limitation, which can reduce microbial biomass and/or influence the composition of microbial communities, and then affects N2O emissions. Nitrogen input also affects different production pathways of N2O, which is regulated by soil moisture, the concentration of N2O substrates, and the abundance of functional genes associated with soil N2O emissions (AOB、 AOA、nirK、 nirS and nosZ). In the future model predictions, plant N absorption, litter decomposition, mycorrhiza and N2O production pathways can be fully incorporated into the model to improve the accuracy of model predictions, and provide a scientific basis for formulating forest management policies and greenhouse gas abatement measures under the background of global change.

      • Dynamics and Prediction of Soil Salinization Parameters under the Amelioration of Heavy Coastal Saline- alkali Land

        XIE Xuefeng, PU Lijie, SHEN Hongyun, WU Tao, ZHU Ming, HUANG Sihua

        DOI: 10.11766/trxb202101240043

        Abstract:

        【Objective】Soil salinization is one of the main types of land degradation, which seriously inhibits the improvement of soil quality and the growth and grain yield of crops. Reclamation of coastal land is increasingly being used as a means of raising agricultural productivity and improving food security in China. Determining the importance of potential influencing factors of soil salinization parameters and thus predicting their concentrations are important for formulating targeted control measures to improve soil quality and crop yield in tidal flat reclamation areas.【Method】In this study, six treatments including control (CK), organic manure (OM), polyacrylamide plus organic manure (PAM+OM), straw mulching plus organic manure (SM+OM), buried straw plus organic manure (BS+OM), and bio-organic manure plus organic manure (BM+OM) were applied to explore the effect of different reclamation treatments on different soil parameters. The effect of all treatments on soil salt content (SSC), pH, sodium adsorption ratio (SAR), and exchange sodium percentage (ESP) was analyzed and the main factors affecting the degree of soil salinization were identified. Thereafter, the multi-linear regression model (MLR), BP artificial neural network model (BP-ANN), and random forest model (RF) were conducted to predict the soil salinization parameters (SSC, pH, SAR, and ESP) using covariates, such as air temperature, precipitation, evaporation, wind speed, soil water content, soil temperature, and soil bulk density.【Result】The results indicated that the concentration of SSC, SAR, and ESP gradually increased, while the pH gradually decreased during the oat growing stage. All reclamation treatments effectively reduced the level of surface soil salinization. Among them, SM+OM treatment had the best inhibition effect on SSC, whereas BM+OM treatment had the best inhibition effect on soil pH, SAR and ESP. Besides, both meteorological parameters and soil properties had a significant impact on the level of surface soil salinization during the amelioration of coastal saline-alkali land. Additionally, the RF model performed much better than BP-ANN and MLR as it revealed a much higher coefficient of determination (R2) and Nash-Sutcliffe efficiency (NSE), and lower root mean square error (RMSE) than BP-ANN and MLR model.【Conclusion】The above results indicate that the reclamation treatments can effectively inhibit soil evaporation, improve soil structure, increase soil water holding capacity, and thus reduce the salinization level of surface soil. Our results also suggest that the RF model is a more powerful modeling approach in predicting soil salinization dynamics of coastal saline-alkali land due to its advantages in handling the nonlinear and hierarchical relationships between soil salinization parameters and covariates, and insensitivity to overfitting and the presence of noise in the data. Thus, our findings could provide a reference for predicting the soil salinization parameters in areas with similar environmental conditions.

      • Mechanisms in Plant Growth Promotion by Novel Bio-organic Fertilizer Containing Sorbitol

        FANG Dan, ZHU Mingzhu, WEI Mengyu, YANG Yuting, XUE Chao, SHEN Qirong

        DOI: 10.11766/trxb202012040672

        Abstract:

        【Objective】In this study, a novel bio-organic fertilizer was designed by adding sorbitol, which is one of the preferred carbon sources for the functional strain Bacillus amyloliquefaciens SQR9, to the normal bio-organic fertilizer rich in strain SQR9 (2×108 CFU?g-1). The plant growth promotion effect was evaluated. The mechanism for elevation of plant growth promotion effect of the normal bio-organic fertilizer by sorbitol addition was studied. 【Method】The effect of this novel bio-organic fertilizer on cucumber growth, soil biological and chemical properties was evaluated by pot experiments. The effect of sorbitol on plant growth promotion and stimulating IAA (indole-3-acetic acid) production by strain SQR9-gfp was investigated by culturing experiment using Arabidopsis. 【Result】The pot experiment showed that the application of this novel bio-organic fertilizer could promote cucumber growth by increasing the soil nutrient availability and the colonization of strain SQR9-gfp. The addition of sorbitol could promote IAA production by strain SQR9-gfp. Comparing to the wild type Arabidopsis, the plant growth promotion effect of sorbitol addition vanished on the IAA insensitive mutant Arabidopsis pin2. 【Conclusion】These results suggest that the application of this novel bio-organic fertilizer can promote plant growth. The addition of sorbitol can promote IAA production by SQR9-gfp and this is one of the mechanisms through which the novel bio-organic fertilizer boosted plant growth.

      • Research on the Characteristics of Preferential Flow Movement Along Varied Hillslopes Covered with Different Vegetation in the Three Gorges Reservoir Area

        LIU Muxing, SONG Xingmin, LU Shiguo, ZHANG Hailin, YI Jun

        DOI: 10.11766/trxb202102230616

        Abstract:

        【Objective】Studying the effects of topographic position, vegetation cover, and soil property on the characteristics of preferential flow in mountainous areas can enrich research content of hillslope hydrology, and further reveal the mechanism of forestland in soil and water conservation.【Method】Dye tracing experiments using Brilliant blue solution combined with photographed images analysis were carried out in the Dalaoling forestland of the Three Gorges area to explore the transport features of preferential flow along with soil vertical profile and lateral section. Six hillslope sites were selected to conduct dye tracing experiments, including the upslope and downslope covered by evergreen forest (EG), secondary deciduous forest mixed with shrubs (SDFS), and deforested pasture (DP), respectively. Several parameters were analyzed to demonstrate stained feathers along with vertial profile or lateral hillslope, including stained area ratio (SAR), stained path number (SPN), distribution of different preferential flow paths width and lateral flow length along the slope.【Result】Results indicated that: (1) Larger stained area ratio and more stained path number were observed in upper soil horizon than deeper soil horizon. Compared among different vegetation covers, the largest SAR was observed in SDFS, followed by DP and EG, which were 44.2%, 36.1%, and 35.3% at 0-60 cm depth, respectively. While average SPN in SDFS, EG, and DP was 43, 19, 15 at 0-60 cm depth, respectively. For different topographic positions, larger SAR was identified in upslope sites (41.5%) than in downslope sites (35.6%), while upslope sites had less SPN (23) than downslope sites (28) at 0-60 cm depth. Deeper percolated depth was identified at SDFS sites than that of other sites, which showed abundant stained paths even at 60-110 cm depth, while few paths were found at this horizon for EG and DP sites. (2) The stained area at six sites were dominated by preferential flow paths with 1-10 cm width and >10 cm width, which account for 82.8% of the total stained area. Homogeneous matrix flow and heterogeneous matrix fingering flow were mainly distributed at 0-30 cm depth, while other preferential flow patterns were mainly observed at deeper soil horizons. (3) Compared with EG and SDFS sites, more lateral flow appeared at DP sites showing stained patches extended 50 cm distance along the downslope direction, while only 10-20 cm distance extending was observed at other sites. 【Conclusion】Vegetation types and topographic position affected water infiltration processes through controlling soil properties and affecting water flow paths. Forestland sites had a better ecohydrological function in water conservation than deforested land, as the vertical flow process at DP was inhibited by the plowing hardpan. These led to more lateral flow at the shallow horizon and had more risks triggering a surface runoff. The practices of deep ploughing and reforestation can enrich root channels and benefit soil and water conservation.

      • Research on Spatio-temporal Heterogeneity of Soil Electrical Conductivity in Cotton Field Based on Electromagnetic Induction Technology

        FENG Chunhui, LIU Xinlu, JI Wenjun, WU Jialin, LIU Weiyang, PENG Jie

        DOI: 10.11766/trxb202010170576

        Abstract:

        【Objective】Characterizing spatial and temporal variability of soil salinity at field and landscape scales is important for a variety of agronomic and environmental concerns. In arid regios, soil salt content and its distribution position in the profile are important factors for the calculation of the irrigation quota of salinized soil. Due to the strong spatial variability of soil salinity content, the guiding value of soil surface salinization information for quota irrigation is very limited. A three-dimensional visualization study of the distribution and content of salinity in the soil profile is of great significance to the fixed irrigation of saline soil. The objective of this study was to evaluate apparent electrical conductivity (ECa) directed soil sampling as a basis for monitoring management-induced Spatio-temporal change in soil salinity. 【Method】A soil salinity assessment study was conducted on an 18 hm2 saline-sodic field in Alar’s Agricultural Science and Technology Park from March to November 2018. The study evaluated the three-dimensional spatio-temporal change that had occurred as a result of irrigation with drainage water over that period. Using geospatial electromagnetic induction(EMI) measurements of ECa and a spatial response surface sampling design 18 soil profile sites were selected and they reflected the ECa measurements every time. At each site soil profile samples were taken at 0.2 m intervals to a depth of 1 m and analyzed for electrical conductivity of the saturation extract (ECe). Also, the soil apparent conductivity data of four different periods and the electrical conductivity data of soil profile samples collected synchronously were analyzed. The inversion model between measured and apparent conductivity of different soil layers in the soil profile was constructed by the multiple linear regression method. Furthermore, the 3D visualization of soil salinity was realized by using 3D-IDW and the spatial and temporal changes of soil salinity in cotton field under mulch drip irrigation of Xinjiang were studied.【Result】The results showed that there was a good correlation between the apparent conductivity and the measured conductivity. The determination coefficient (R2) of the measured conductivity inversion model based on the apparent conductivity data was between 0.82 and 0.99. The results of 3D-dimensional data statistics of soil electrical conductivity showed that the distribution characteristics and content of soil salinity in different periods are quite different. These differences were attributed to human factors such as irrigation, film mulching and uncovering, and natural factors such as air temperature, evaporation and groundwater level. Also, the distribution type of soil salinity in March was uniform and the electrical conductivity range of the 0-100cm soil profile was 0.78 to 0.88 dS•m-1. The salinity in June and October was mainly concentrated in 0~20 cm and the electrical conductivity was 3.32 to 5.28 dS•m-1, respectively. Also, the electrical conductivity of 20~100 cm was 0.99~1.36 to 0.95~1.70 dS•m-1, respectively. In July, the salinity was mainly concentrated in 0~40 cm, and the conductivity in 0-40cm was 2.25~2.45 dS•m-1 while the conductivity of 40~100 cm was 0.87~0.93 dS•m-1. 【Conclusion】An assessment of three-dimensional spatio–temporal changes in soil salinity was conducted to provide a preliminary evaluation of the sustainability of irrigation quota on the Agricultural Science and Technology Park to ascertain its potential as an alternative for drainage water disposal. The results of this study can be used as guidance for accurate irrigation application in cotton fields.

      • Molecular Phylogeny Suggests a Key Role of ATPase Genes on Evolutionary Adaption of Soil Ammonia-oxidizing Thaumarchaeota to Acid Stress

        Song Yuxiang, Wang Baozhan, Qin Hua, Kuang Lu, Tang Xiufeng, Wang Xinxin, Jia Zhongjun

        DOI: 10.11766/trxb202101310062

        Abstract:

        Abstract: 【Objective】Molecular ecology studies have found that the DNA sequences of ammonia oxidizing archaea commonly found in neutral/alkaline soils also exist in acidic soils. Our recent research has found that neutral ammonia oxidizing archaea may have acquired acid tolerance through V-ATPase adaptive evolution. Or acidophilic physiological growth ability. However, it is not clear whether this phenomenon is universal.【Method】Aiming at the acid soils of 5 masson pine plantations (15 years, 24 years, 45 years, 55 years, and 63 years) with different planting years as the research object, 736 billion base pairs were obtained through deep metagenomic sequencing to reconstruct the ammonia oxidation Archaea AOA ammonia monooxygenase amoA gene and ATPase gene, to study the eosinophilic mechanism of AOA in different ecological types of ammonia oxidizing archaea.【Result】Results showed that the phylogenetic analysis based on the amoA gene found that AOA mainly included the acidophilic Ca. Nitrosotaleales ecotype and the alkaline Nitrososphaerales ecotype. Ecotype AOA (Nitrososphaerales) with neutral pH exists in all acid forest soils, and the ATPase is mainly V-ATPase, and its classification results and changes are the same as the amoA gene, indicating that ATPase may be AOA in masson pine forest soil that adapts to acid stress The mechanism of molecular evolution. With the increase of forest age, the abundance of Ca. Nitrosotaleales first decreased and then increased, while the abundance of Nitrososphaerales first increased and then decreased. Available potassium is an important environmental factor that significantly affects the structure of AOA community.【Conclusion】These results indicate that plantation plantation is likely to promote the differentiation of acidic AOA populations, and the Nitrososphaerales ecotype that has not yet been purely cultivated may have played an important role in the in-situ soil nitrification process of Masson pine forest.

      • Effects of Adding Woody Peat and Bentonite on Physical and Chemical Properties of Eroded and Degraded Black Soil

        ZHAO Xu, FAN Jun, WANG Xi, FU Wei

        DOI: 10.11766/trxb202101150028

        Abstract:

        【Objective】Black land is a valuable land resource, which plays an important role in ensuring food security in the northeast region of China. In order to slow down the erosion and degradation of black soil farmland and improve farmland fertility, new soil management practices need to be developed. 【Method】In this study, woody peat and bentonite were added to a typical eroded and degraded black land. The saturated hydraulic conductivity, air permeability and relative gas diffusion, water holding capacity, organic carbon content and crop yield were evaluated by the combination of indoor simulation and field in-situ observation. 【Result】The results showed that: under indoor conditions, (1) adding 2% or 4% woody peat decreased the saturated hydraulic conductivity by 14.3% or increased it by 9.9%, increased the air permeability by 18.9% or 4.1%, increased the relative gas diffusion by 15.5% or 6.6%, increased the organic carbon content by 39.4% or 71.5%, and increased the yield of potted maize by 2.0 times or 1.9 times respectively; (2) adding 1% bentonite decreased the saturated hydraulic conductivity, air permeability and relative gas diffusion by 63.2%, 55.3% and 7.6%, and increased the organic carbon content and yield of potted maize by 1.0% and 1.1 times, respectively; (3) adding 2% or 4% woody peat and 1% bentonite decreased the saturated hydraulic conductivity by 65.8% or 73.1%, decreased the air permeability by 33.2% or 32.8%, increased the relative gas diffusion by 0.2% or 4.7%, increased the organic carbon content by 37.8% or 70.6%, and increased the yield of potted maize by 1.9 times or 1.5 times. The saturated hydraulic conductivity, relative gas diffusion, organic carbon content and soybean yield increased by 75.0%, 32.0%, 36.1% and 43.2% respectively, and the air permeability decreased by 45.2% when woody peat was added to the eroded farmland. Also, the saturated hydraulic conductivity, air permeability and relative gas diffusion decreased by 39.1%, 44.4% and 44.0% respectively, while the organic carbon content and soybean yield increased by 3.6% and 4.2%, respectively, when bentonite was added to the eroded farmland. Even though there was no significant difference in organic carbon content and soybean yield; the soil saturated hydraulic conductivity, relative gas diffusion, organic carbon content and soybean yield increased by 134.4%, 28.0%, 36.0% and 26.3% respectively, and the air permeability decreased by 38.2% when woody peat and bentonite was added to the eroded farmland. The addition of woody peat and bentonite could improve the water holding capacity of black land soils, and bentonite can retard the decomposition of organic carbon. 【Conclusion】In general, the mixed addition of woody peat and bentonite has the best effect, which can effectively improve the soil aeration permeability, water holding capacity, organic carbon content and crop yield, and also help to accumulate organic carbon in the soil. It is an effective measure to rapidly improve the degraded black soil.

      • Analysis of Soil Microbial Community Structure via Integrated High-throughput Absolute Abundance Quantification (iHAAQ) Method

        WANG Changyi, LOU Jun, YAN Kang, WANG Haizhen, XU Jianming

        DOI: 10.11766/trxb202010200588

        Abstract:

        【Objective】The high-throughput sequencing technology can easily access the species varieties and the relative abundance of a microbial community. Nevertheless, the relative abundance cannot fully reflect the microbial quantities when using it to evaluate the community. On the other hand, the absolute abundance which is one of the essential parameters for describing a microbial community structure in ecology has been ignored. The absolute abundance can be calculated by integrated high-throughput absolute abundance quantification (iHAAQ); which combines high-throughput sequencing and quantitative PCR (qPCR). Both relative and absolute abundances are essential parameters for describing a microbial community structure in ecology. The relative abundance could describe and evaluate the relationship of specific taxa with others in the same sample, while the absolute abundance as a constant parameter is more suitable for describing and evaluating the quantitative variations of specific taxa in a sample or among samples. Thus, this study aimed to provide a comprehensive and in-depth analysis of soil microbial community through the relative and absolute abundances of the archaeal, bacterial, and eukaryotic (fungi) domains of microorganisms (described as three-domain microorganisms).【Method】Based on data of soil microbial community in the studies of banana panama disease, the reclaimed sandy agricultural ecosystem and microbial inhibitor, the absolute abundances of archaea, bacteria and fungi in three papers were obtained by iHAAQ. Then the absolute and relative abundances of three-domain microorganisms were further calculated. The α- and β-diversity analyses of archaea, bacteria, fungi and three-domain microorganisms were conducted according to their relative and absolute abundances, respectively.【Result】The results showed that: (1) Compared to archaea and fungi, the bacteria dominated the soil microbial community with higher species varieties and absolute abundance. Meanwhile, the lack of absolute abundance parameters might lead to the misunderstanding of the microbial community. (2) The α-diversity indexes calculated by relative and absolute abundances were the same, while the β diversity indexes were different. (3) In the research of banana panama disease and reclaimed sandy agricultural ecosystem, PCoA results of three-domain microorganisms and bacteria were relatively similar, which indicated that the community structures of three-domain microorganisms were mainly affected by bacteria in these two studies. But no similar results were found in the research of microbial inhibitors.【Conclusion】The iHAAQ method can be applied to the studies that perform high-throughput sequencing and qPCR analyses, simultaneously. It is of great ecological significance to study the three-domain microbial community with the species varieties, relative and absolute abundances obtained by the iHAAQ method, and it should be encouraged for future research.

      • Effects of Different Treatments with Straw Returning on Arbuscular Mycorrhizal Fungal Community and Corn Phosphorus Utilization Efficiency

        HU Kaijie, LUAN Lu, ZHENG Jie, LI Jing, XUE Jingrong, SUN Bo, JIANG Yuji

        DOI: 10.11766/trxb202103280167

        Abstract:

        【Objective】Arbuscular mycorrhizal fungi (AMF) can form a symbiotic structure with 80% of plants, and play important roles in the nutrient cycling of the plant-soil system. As a typical soil in south China, red soils are facing numerous challenges including rapid acidification, low phosphorus availability, and the degradation of soil microbiome functioning. Straw returning has been proposed as an effective method to improve the fertility of red soils. In order to improve and control the degradation of red soil, we studied the effect of the AMF community in the rhizosphere on corn phosphorus utilization efficiency in a typical red soil.【Method】In this study, we performed a long-term field experiment by returning straw with equal carbon content in the Red Soil Agroecosystem Experiment Station of the Chinese Academy of Sciences in Yingtan, Jiangxi Province. Five fertilization treatments were set up, including no fertilization (CK), conventional NPK (N), NPK with straw (NS), NPK with straw and pig manure (NSM), and NPK with straw biochar (NB). High-throughput sequencing was used to estimate the diversity and structure of the rhizosphere AMF community in driving plant growth and phosphorus utilization efficiency under the different treatments.【Result】The results showed that soil properties were significantly affected after treatments with straw. The NSM treatment increased significantly the contents of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and available phosphorus (AP), as well as the acid phosphomonoesterase (ACP) and alkaline phosphomonoesterase (ALP) activities. Treatments with straw significantly promoted the diversity and modified the structure of the rhizosphere AMF community. Glomus and Paraglomus were the two dominant genera in the AMF community. The diversity and structure of the AMF community were mainly affected by SOC. Corn yield and phosphorus utilization efficiency were the highest under the NSM treatment. Also, phosphate utilization efficiency was primarily affected by AP, TP, SOC, TN, the diversity and composition of the AMF community, and ACP activity.【Conclusion】The composition of the AMF community in the rhizosphere may regulate the phosphorus activation, corn productivity, and phosphorus utilization efficiency under all three treatments with straw. Our results highlight the importance of the rhizosphere AMF community in strengthening soil health and crop productivity.

      • Several Problems about Dynamic Chamber Technique in Determining Ammonia Volatilization from Rice Fields

        TIAN Yuhua, YIN Bin, ZENG Ke, ZHAO Xu

        DOI: 10.11766/trxb202012310721

        Abstract:

        【Objective】Ammonia emitted from agricultural fields has led to significant adverse effects on air, soil and water environment. To evaluate the fate of applied nitrogen fertilizers, guide the rational application of nitrogen (N) fertilizers and eliminate the adverse environmental effects caused by ammonia volatilization (AV), it is important to measure AV in field conditions. The dynamic chamber method is commonly used in determining AV from rice fields. However, there are still some drawbacks associated with this method. These limitations lead to the incomparability between different research results and thus affect the systematic analysis and assessment of regional ammonia emissions from farmland.【Method】In this study, the effects of the air exchange rate, time of the measurement, characteristics of the dynamic chamber, types of air-washing device, and the difference between vacuum pumping and natural wind environment on AV were studied. 【Result】 Results showed that AV increased with the increase of air exchange rate. Overall, there were three stages during the increase of AV which was linearly correlated with the logarithm of the air exchange rate. The diurnal variation of AV was different between the period of rapid hydrolysis of the applied urea and the period after rapid hydrolysis of urea. As for the types of air-washing device, AV values measured with the spherical porous and straight through types were 25.6% and 8.5% lower than that measured with disk porous type, respectively. The larger the inner diameter and the lower the height of the gas phase of the dynamic chamber are, the lower the ammonia volatilization is. Volatilized ammonia absorbed by two gas washing bottles in series is only 88.6% of that absorbed by the single gas washing bottle. The evaporation within the dynamic chamber increased with the air exchange rate. Although the amount of surface water loss within the container which was ventilated via vacuum pumping was similar to that under the natural ventilation environment, AV of the former container is relatively low. This indicates that the process of AV is affected to some extent by the vacuum pump and air-washing system. 【Conclusion】It is obvious that the influencing factors such as air exchange rate, measurement period during the rapid hydrolysis of applied urea, characteristics of the dynamic chamber, and the air-washing device should all be considered in measuring AV. The transparent dynamic chamber (diameter 15 cm) connected with a separate flowmeter and only one gas-washing bottle, containing gas-washing holes on the side of the disk or the end side of the straight rod, airflow rate of 15?20 L?min-1, and the gas phase height of 5?8 cm are recommended to be employed in measuring ammonia volatilization from rice fields.

      • Effects of Water-nitrogen Interaction on Greenhouse Gas Emissions in a Paddy Soil

        CAO Kaixun, ZHAO Kun, JIN Wangfeifei, ZHU Tongyun, SHAN Xinliang, MEI Hang, ZHU Liyang, QIAN Lili, WANG Feng, XIAO Xin

        DOI: 10.11766/trxb202011250646

        Abstract:

        【Objective】In order to study the effects of water management-nitrogen fertilizer on greenhouse gas (CH4, N2O and CO2) emission and soil physicochemical properties.【Method】Two irrigation modes including controlled irrigation (C1) and normal irrigation (C2), and three nitrogen application levels (low nitrogen, N1; medium nitrogen, N2 and high nitrogen, N3) were set up under a long-term pilot plot. 【Result】 The results showed that compared with normal irrigation, controlled irrigation significantly reduced the cumulative emissions of CH4 and N2O by 43.12% and 23.53%, respectively. Under normal irrigation, the contents of soil ammonium nitrogen in low nitrogen, medium nitrogen and high nitrogen treatments were 35.26, 38.90 and 35.20 mg?kg-1, respectively, while those under controlled irrigation were 33.08, 34.30 and 42.40 mg?kg-1, respectively. Under the condition of controlled irrigation, CO2 emission was higher than that of conventional irrigation and increased with the increase of nitrogen application level. According to the overall analysis of the Greenhouse Effect, the GWP (global warming potential) of 0.55 t?hm-2 under controlled irrigation was much lower than that of 0.82 t?hm-2, under conventional irrigation, while the GWP of 0.65 t?hm-2 under N2 treatment was much lower than that of 0.74 t?hm-2 under N1 treatment and 0.67 t?hm-2 under N3 treatment. The coupling of water and nitrogen was the main factor affecting N2O emission from the paddy field, and under medium and high concentration of nitrogen application, the contribution of N2O emission from the paddy field to the Greenhouse Effect was greater than that of CH4. 【Conclusion】Therefore, the application of controlled irrigation combined with reduced nitrogen fertilizer can effectively decrease the emissions of greenhouse gases, maintain a high level of soil ammonium nitrogen in paddy soil, which is of great significance for improving soil fertility quality and developing sustainable agriculture.

      • Interfacial Reactions between As(V) and Cd(II) Co-adsorption onto Various Mineral Surfaces

        HUANG Minxue, GUAN Yufeng, SU Zixian

        DOI: 10.11766/trxb202101140027

        Abstract:

        【Objective】pH is the most important environmental factor influencing the reactivity of heavy metals on mineral surfaces. The purpose of this study was to investigate the interfacial reactions between As(V) and Cd(II) adsorption/co-adsorption onto different mineral surface excluding the interference of pH.【Method】Three different minerals: Al2O3, TiO2, and kaolin, were chosen and passed through 100-mesh sieve. The experiments for As(V) and Cd(II) adsorption onto the different minerals were conducted in serum bottles (Effective volume = 2 mL) at pH 6.0. The bottles containing 0.02-1 mmol?L-1 As(V), 0.02-1 mmol?L-1 Cd(II), 28 mmol?L-1 4-Morpholineethanesulfonic acid sodium salt (MES), 100 mmol?L-1 NaCl and 2.0 mg of mineral powders were placed on a rotator at 200 r?min-1 and 25 oC. Batch studies were conducted to assess the adsorption kinetics, adsorption isotherm and the influence of molar ratio of As(V) and Cd(II) on the extent of As(V)and Cd(II) adsorption.【Result】The adsorption kinetics showed that As(V) and Cd(II) adsorbed onto different mineral interfaces followed the pseudo-second-order kinetics model, and chemical adsorption was the rate-controlling steps. Furthermore, the normalized adsorption capacities of Cd(II) and As(V) were ranked as TiO2 > Al2O3 > kaolin. The adsorption abilities of As(V) and Cd(II) were enhanced by the co-existing Cd(II) and As(V). Specifically, the addition of As(V) promoted the adsorption of Cd(II) onto Al2O3, while the addition of Cd(II) enhanced As(V) adsorption onto TiO2. The synergistic effect of As(V) and Cd(II) co-adsorption was mainly controlled by the electrostatic adsorption and the ternary complex formation. Moreover, with the increase of Cd(II)/As(V) concentration ratio, the regulation mechanism of Cd(II) adsorption gradually changed from the electrostatic adsorption to the synergy of the formation of interfacial - As(V) - Cd(II) ternary complex and electrostatic adsorption, and then changed to the formation of surface precipitate. Importantly, with the increase of As(V)/Cd(II) concentration ratio, the key regulation mechanism changed from adsorption controlling to surface precipitation controlling. 【Conclusion】Electrostatic adsorption, formation of interfacial - As(V) - Cd(II) ternary complex, and surface precipitation were the critical mechanisms controlling the interfacial reactions between As(V) and Cd(II) adsorption onto various mineral surfaces at various ratios.

      • The Effects of Litters and Phosphorus Addition on Soil Carbon Priming Effect in Pinus massoniana Forest

        MEI Kongcan, CHEN Yuehmin, FAN Yuexin, ZHOU Jiacong, ZHANG Qiufang, CHENG Lei, ZENG Quanxin, XU Jianguo, YUAN Xiaochun, CUI Juyan, LIU Yuanyuan

        DOI: 10.11766/trxb202101130025

        Abstract:

        【Objective】 Priming effect (PE) plays a critical role in the storage and turnover of soil organic carbon (SOC) in forest ecosystems. The intensity and direction of the priming effect, induced by litters, usually depend on the availability of limited nutrient (e.g., phosphorus, P), especially in subtropical highly weathered forest soils. However, how P and litters addition affect the soil priming effect in this region is not clear. This study aimed to investigate the effects of litter and phosphorus addition on SOC mineralization and priming effects in subtropical low-phosphorus soils and to provide a theoretical basis for the study of the carbon cycle in forest ecosystems in this region. 【Method】 Three kinds of 13C-labeled litters (Pinus massoniana, Michelia macclurei and Liquidambar formosana) and P (KH2PO4) were added to P. massoniana forest soil. Soil incubation of treated and control soils was conducted for 35 days in the laboratory. The physical and chemical properties, microbial properties and priming effect of the soils were determined after incubation. 【Result】 The results showed that the addition of the three kinds of litters significantly increased the soil native SOC mineralization, and produced a positive priming effect. The intensity of priming effect performance for P. massoniana > M. macclurei > L. formosana. In addition, litters addition decreased the content of available nitrogen (AN), but increased microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP), and β-glucosidase (βG) and acid phosphatase (ACP) activities. P addition alone significantly enhanced SOC mineralization, and the available phosphorus (AP), dissolved organic carbon (DOC), microbial biomass carbon (MBC), MBN, and MBP were also increased. Compared with the addition of litters alone treatment, the M. macclurei and L. formosana litters combined with P addition significantly reduced the priming effect and ACP activity. Linear regression analysis revealed that the cumulative priming effect was correlated negatively with soil AP, MBN and MBP content, whereas it was positively correlated with ACP activities. 【Conclusion】The addition of litters stimulated microbial growth and as such promoted SOC mineralization and produced a positive priming effect. Also, the intensity of priming was mainly related to the quality of litters. Although P addition alone increased SOC mineralization, the influence of P added with litters on soil priming effect was dependent on the litter types; with low-quality litter having a lower soil priming effect.

      • Current research progress and prospects of cultivated and grassland soil health - A review

        SI Shaocheng, WU Yucheng, LI Yuan, TU Chen, FU Chuancheng, LUO Yongming

        DOI: 10.11766/trxb202104090063

        Abstract:

        Soil is an essential component of the Earth"s critical zone, offering series of essential ecosystem services (i.e. agricultural production, plant growth, animal habitat, biodiversity, carbon sequestration, and environmental quality). Soil stands for a nexus of the whole natural ecosystem. Enhancing soil health is vital to achieving sustainable development goals; therefore, scientific researchers have paid much attention to that over the world. Cultivated land and grassland are currently the most extensive land-use types on the Earth, accounting for 12% and 26% of the ice-free land, respectively. Also, these two crucial components consist of the Mountain-River-Forest-Farmland-Lake-Grass System theory. Therefore, keeping up the soil health status of these two land-use patterns has significant meaning for holding the whole natural ecosystem healthy and achieving sustainable development goals. In recent decades, the research focusing on the soil health of these two land-uses types is progressive worldwide. China is also relatively vibrant in this research field; however, the achievements have not made a difference. Additionally, a unified soil health assessment system has not yet been established at the national level. In this paper, firstly, the connotation and evolution of "soil health" was sorted out comprehensively. Then, focusing on the cultivated land and grassland, we highlighted the recent hotpots and advances in soil health globally. Secondly, we outlined several soil health assessment systems in different countries and sketched out series of fundamental works on soil health maintenance in China. Finally, we pointed out the new insights in the future to improve soil ecosystem functions and maintain the soil health of cultivated and grassland soils in China.

      • Characteristics of Enhanced Microbial Thermogenic Functions in Hyperthermophilic Composting

        CUI Peng, AI Chaofan, LIAO Hanpeng, ZHOU Shungui

        DOI: 10.11766/trxb202102050077

        Abstract:

        【Objective】Hyperthermophilic composting (hTC) exhibits significant advantages during organic solid waste treatment such as nitrous oxide mitigation, nitrogen retention, antibiotic resistance genes removal compared with those of conventional composting (cTC). Such advantages are closely linked with hyperthermophilic temperatures However, the reason for extremely high composting temperature remains unclear. 【Method】Here, by using PICRUSt (physiological investigation of communities by reconstruction of unobserved states), the variations in microbial function during hTC and cTC using chicken manure were studied. The reason for the extremely high composting temperature in hTC was explored. 【Result】Results show that the composting temperature could reach up to 80oC and last for more than 5 days in hTC. hTC exhibited significant differences in both the composition of the microbial community and their metabolic pathways abundance during the hyperthermophilic stage. The abundances of thermogenesis related metabolic pathways (such as energy metabolism, carbohydrate metabolism) and aerobic respiration chain-related genes (such as NADH dehydrogenase gene, succinate dehydrogenase gene) were significantly increased during the hyperthermophilic stage (P<0.05). Furthermore, the abundance of the enriched metabolic pathways and functional genes was significantly correlated with the temperature variation of hTC (P < 0.05). Random forest regression models comparing the predicted to actual composting temperatures found strong correlations in both treatments (for hTC, adjusted R2 =0.96; for cTC, adjusted R2 =0.97). The model indicated that the abundances of K03943 (NADH dehydrogenase flavoprotein 2), k15862 (cytochrome c oxidase cbb3-type subunit I/II) and k05580 (NADH-quinone oxidoreductase subunit I) were the most important factors affecting the composting temperature in hTC. By comparison, the highest composting temperature of cTC was below 70oC, and the abundance of metabolic pathways and functional genes related to heat production was significantly negatively correlated with compost temperature (P<0.05).【Conclusion】Our results suggest that the hTC community might metabolize organic matter more rapidly by significantly increasing the abundance of functional genes related to the aerobic respiration chain, thus increasing the rate of ATP synthesis and generating more metabolic heat.

      • Succession of Microbial Community in Typical Black Soil under Different Land Use Pattern

        HAN Xiaozeng, FU Yuhao, JIA Zhongjun, TIEDJE James M.

        DOI: 10.11766/trxb202103040128

        Abstract:

        【Objective】To explore the succession of soil microbial community structure and its environmental driving mechanism under different land use pattern, soil samples were collected from plots in a long-term (32 years) field experiment station in the black soil region of Northeast China. 【Method】 The long-term field experiment was started on different land usage in the National Field Research Station of Agro-Ecosystem of Chinese Academy of Sciences in 1985. The experiment was designed with three treatments and three replicates, i.e. bareland (vegetation removed), cropland (crop rotation without fertilizer), and grassland (natural meadow vegetation). Soil samples were collected for analysis from the 0~20 cm soil layer in October 2017. Soil microbe was determined by the Illumina high-throughput sequencing technology on MiSeq platform. 【Result】The soil organic matter was 52.07 g?kg-1, 54.83 g?kg-1 and 61.54 g?kg-1 in the treatments of bareland, cropland and grassland, respectively. Compared to the bareland, the soil organic matter increased by 8.0% and 27.5% in the cropland and grassland, respectively. The available nitrogen, phosphorus and potassium also increased significantly in cropland and grassland. At the same time, the total abundance of microbe increased from 2.25×107 copies?g-1 dry soil to 8.08×107 copies?g-1 dry soil and 1.69×108 copies?g-1 dry soil in the three treatments, respectively. The abundance of microbe increased by 2.58 times and 6.51 times in cropland and grassland, respectively. At the phylum level, dominant microbe were Proteobacteria, Actinobacteria, and Acidobacteria, whose relative abundances were more than 19% and with no significant differences in the three treatments (P > 0.05). The 54 of 228 microbial genera detected showed significant differences (P < 0.05) among the three treatments, and most of them showed relatively low abundance. The genera of Gemmatimonas, Rhodoplanses, Arenimonas showed significant differences and higher abundance in the three treatments. The redundancy analysis showed that soil properties were the main environmental driving force for the differentiation of microbial community structure, including cation exchange capacity, total nitrogen, organic matter, available nitrogen, available phosphorus and available potassium. Network analysis showed that Granulicella had the strongest association with soil properties and other microbial genera, suggesting that this genus can be used as an indicator to assess changes in the black soil. 【Conclusion】 The vegetation cover was an key factor for the succession of soil microbial communities. Research should thoroughly explore the functions and agricultural environmental significance of microbe under in-situ conditions in black soil in the future, to provide theoretical references for maintaining the virtuous cycle of nutrient and developing sustainable agricultural ecological management models.

      • Soil Phosphorus Pool Evolution and Environmental Risk Prediction of Paddy Soil in the Taihu Lake Region

        WANG Yu, YUAN Jiahui, CHEN Hao, CHEN Guanglei, ZHAO Hongmeng, XU Lingying, ZHAO Xu, WANG Shenqiang

        DOI: 10.11766/trxb202012160696

        Abstract:

        【Objective】Agricultural sustainable development and aquatic ecological environment security are faced with numerous challenges. As a non-renewable resource, phosphorus (P) is an essential element for crop growth, but has the potential to cause water eutrophication. Disparities in P management such as fertilizer or manure and the harvested crop P removal result in a massive variation of P imbalances in agricultural systems. Phosphorus loss is mainly affected by the form and availability of soil P. 【Method】Therefore, in this paper, considering strong spatial differentiation characteristics of soil P pools and availability, the soils of typical flood and drought rotation farmlands were selected. The farmlands were located in the Taihu Lake Region in the lower reaches of the Yangtze River. In detail, 319 farmland soil samples and 83 wheat samples were collected based on the systematic random point distribution method. The spatial differences of soil phosphorus fractionations and crop P uptake were analyzed. 【Result】 Compared with the results of the second national soil survey and the survey in 2009, soil total P (TP) and available P (Olsen-P) increased significantly in the Taihu Lake Region. Soil Olsen-P concentration in Changshu and Yixing city ranged between 2.19-112.5 mg?kg-1 and 5.21-109.7 mg?kg-1, respectively. The average concentration was 37.6 mg?kg-1 and 29.8 mg?kg-1, which increased by 24.6 mg?kg-1 and 7.9 mg?kg-1 ??in contrast to 2009. The concentration of available P exceeded 10 mg?kg-1 of 93.1% of soil samples, and 65.2% of the total soil samples had more than 20 mg?kg-1, which indicated that most of the paddy soil P pool was in surplus. Furthermore, we analyzed soil P availability using the biologically-based P (BBP) method, and found that CaCl2-P, Citrate-P, Enzyme -P and HCl-P had a significant positive correlation with Olsen-P (P<0.001). This indicates that those four P forms were all available sources of soil P. We also found a notable relationship between soil TP and Olsen-P (P<0.001) or crop TP (P<0.01) concentration. Meanwhile, the correlation analysis of CaCl2-P and Olsen-P indicated the breakpoint of environmental risk, which was 30 mg?kg-1. 【Conclusion】In view of the strong spatial differences of soil phosphorus pools in this region, it is suggested to focus on the efficient utilization of soil phosphorus in the regional nutrient management and environmental protection. The results are expected to provide basic data support for increasing P use efficiency as well as agricultural non-point source pollution control in the Taihu Lake Region.

      • Study on Suitability Zoning of Biochar-based Organic Fertilizer Application in Bijie Tobacco Growing Area

        ZHANG Zhongqi, PENG Huawei, WANG Meiyan, SHI Xuezheng, SUN Weixia

        DOI: 10.11766/trxb202011270652

        Abstract:

        【Objective】The role of biochar-based organic fertilizers in improving soil fertility and health, in general, has gained a lot of attention in recent times. It is the premise of scientific fertilization to make clear which planting areas are suitable for applying biochar-based organic fertilizer and which areas are not.【Method】Based on 2 059 soil samples in Bijie tobacco planting area of Guizhou Province, this study analyzed the distribution characteristics of soil pH and the spatial changes of soil properties, such as organic matter, available calcium, available magnesium, clay content and cation exchange capacity (CEC). Based on the overall consideration of soil pH and soil acid-base buffer potential, the suitability grade of biochar-based organic fertilizer application in the Bijie tobacco planting area was obtained. 【Result】The results showed that the average pH value of all sampling points in Bijie tobacco growing area was 6.5, which was weakly acidic. The average pH values of Dafang County, Qixingguan District and Weining County were only 6.2, 6.3 and 6.3, respectively, while those of Zhijin County, Jinsha County and Qianxi County were more than 7.0. The contents of organic matter, available calcium and magnesium, clay and CEC in tobacco planting soils in different counties were different, which led to the differences of soil acid-base buffer index between different counties. In all counties, the comprehensive index of acid buffer in Dafang and Weining was 0.96, while that in Zhijin was 1.23. Generally, there was a positive correlation between the pH value and the buffering potential of each parent rock soil type. The pH value of sandstone coarse bone soil and yellow soil was lower, and the value of the acid-base buffering potential index was also smaller. Also, the value of carbonate limestone soil with higher pH value was higher than that of other soil types. The suitability grade of biochar-based organic fertilizer calculated by pH value and acid-base buffer composite index showed that except for the purple soil of sand shale, the soil types derived from sandstone and sand shale were the most suitable application grade, and it was very necessary to apply a biochar-based organic fertilizer to improve soil pH value in these soil types. Carbonate and calcareous soils were not suitable for the application, which indicates that biochar-based organic fertilizer is not suitable for the two soil types without changing the current soil pH and acid-base buffer potential. The remaining soil types from other parent rocks belong to the suboptimal grade, and a certain amount of biochar-based organic fertilizer should be applied to these soil types to moderately increase the pH value, to keep the soil pH in a better state.【Conclusion】From the township level, the town numbers of key application, general application, and unsuitable application grades were 82, 144, and 32 respectively. The key application towns of biochar-based organic fertilizer were mainly concentrated in Weining County, Zhijin County, and Hezhang County. The towns with general application grade were more, and most of them were distributed in Dafang County and Qixingguan District. The unsuitable application towns for biochar-based organic fertilizer are mainly concentrated in Qianxi County and Jinsha County. This study fully considered the effects of soil pH value and acid-base buffer potential on the suitability of biochar-based organic fertilizer, and identified the key application, general application and unsuitable application towns in the Bijie tobacco planting area. This study provides a scientific basis for the accurate application of biochar-based organic fertilizer in the Bijie tobacco planting area and also enriches the research connotation of soil management division in the tobacco planting area.

      • A Coupled Amidation - Liquid Chromatography Technique for Detecting Low Molecular Monocarboxylic Acid in Pedosphere Samples with High Sensitivity

        CHEN Hong, TANG Haoye, ZHONG Ming, LIU Xiaodong, WANG Ruhai, YU Yuanchun

        DOI: 10.11766/trxb202103080130

        Abstract:

        【Objective】Formic, acetic, propionic and butyric acid exist widely in the natural ecological environment, but their contents are usually low. Thus, their accurate qualitative and quantitative determination is often hindered by impurities in the sample matrix. 【Method】Using the coupling amidation method, low molecular monocarboxylic acids (LMMAs) can form new derivatives with high sensitivity to ultraviolet (UV) light. This was achieved by incorporating the indole group into LMMAs’ structure, which made it possible for the low-level LMMAs to be detected by high-performance liquid chromatography with diode array detector (HPLC-DAD) under a specific wavelength UV light with high response. As a result, we observed the accurate determination of LMMAs. Through experimentations, we propose the following steps: first, a suitable amount of sample and MES (2-Morpholinoethanesulfonic Acid) aqueous solution were added into a small bottle with the reaction system adjusted to about pH≈5.5. This was followed by the addition of EDC (1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride) aqueous solution. After 20 minutes of cross-linking reaction, a suitable amount of NHS (N-Hydroxy succinimide) aqueous solution was added to promote coupling reactions. After an appropriate period, a tryptamine aqueous solution (containing acetonitrile) was added into the reaction system for amidation overnight. This was followed by the addition of ultrapure water to a certain volume and prepared for determination. 【Result】The experimental results showed that for an optimized observation, the mole ratio of MES:EDC:NHS:tryptamine:carboxylic acid should be maintained at about 10:7:3:7:1 around and after 45 minutes of coupled reaction and the addition of tryptamine aqueous solution for amidation. The detection limit for the four organic acids in this method was from 0.008 to 0.046 mg·L-1, and the linear correlation coefficient R2 of the standard working curve was around 0.991~0.998. The average recovery rate range was 85.9%~123%, and the precision of the method ranged between 1.69%~8.41%, which meets the requirements of organic analysis. 【Conclusion】The actual sample test results showed that the data of the derivation method and the direct method were the same. However, compared with the HPLC direct detection method, the derivation-HPLC method could correct the positive error caused by the impurities in complex samples, and improve the detection rates of low concentration monocarboxylic acid samples. So the qualitative and quantitative results of the derivation-HPLC method were more reliable.

      • Study of Soil Organic Carbon Sequestration Rate and Potential of Farmland Soil in Fujian Province Based on the Large Scale Soil Database

        WU Shirong, QIU Longxia, CHEN Hanyue, FAN Xieyu, XING Shihe, ZHANG Liming

        DOI: 10.11766/trxb202012040671

        Abstract:

        【Objective】Farmland soil organic carbon pool is one of the most important soil carbon pools and its sequestration and emission have a huge impact on global climate change. It is essential to estimate the soil carbon sequestration rate and potential of farmland soils accurately for managing soil fertility and the ecological environment. Fujian Province is characterized by a large population and small land use and strong spatial heterogeneity of soil. It is of great significance to identify the dynamic evolution trend of soil organic carbon and future carbon sequestration potential of cultivated land in this region for formulating the national strategy of "carbon neutrality" and food security in subtropical regions of China.【Method】This study covered five counties including Minhou, Pucheng, Tongan, Wuping and Yongding, located in different geographical locations in Fujian Province. Soil attributes data based on the data of field measurements at 30,211 sampling sites in 1980 and 15,948 sampling sites in 2008,scattered in these five counties were analyzed. The 1980 soil spatial database was digitized during the Second Soil Survey 1:50 000 soil map and the 2008 soil spatial database was extracted from the annual 1:50 000 land-use status map. Through ArcGIS software and the Ordinary Kriging method, we related the soil spatial data and soil attributes to obtain a high-precision farmland soil database. Based on the most detailed soil database of 1:50 000 at the regional scale, we used the biogeochemical process model DNDC (DeNitrification and Decomposition) to simulate the organic carbon changes in these five counties from 1980 to 2009 and to get predicted value from 2010 to 2039. Also, we estimated the soil carbon sequestration rate and potential of farmland soil in the province by the method of scaling up. 【Result】 Results show that the carbon sequestration amount of the cultivated land in Fujian Province from 1980 to 2009 was 7.37 Tg, and the carbon sequestration potential from 2010 to 2039 was 7.04 Tg. The average annual carbon sequestration rate for the two periods was 190 kg·hm-2 and 176 kg·hm-2, respectively. Among them, paddy soil and saline paddy soil showed the highest carbon sequestration rate in soil type and soil subgroup, respectively, and was greater than 175 kg hm-2 in different periods. The carbon sequestration rate of the red soil group and soil subgroup was the lowest, with an average rate between -29~3 kg·hm-2. Generally, the total carbon sequestration of paddy soil was higher than 6.5 Tg in different periods, accounting for more than 92% of the province""s total carbon sequestration, which is the key to formulating carbon sequestration and emission reduction measures in the future.【Conclusion】 Results of this study indicate that the cultivated soil in Fujian province showed a weak "carbon sink" effect from 1980 to 2009 and 2010 to 2039. This indicates that the current farmland management measures in this area are conducive for carbon sequestration of cultivated soil and should continue to be promoted. Meanwhile, due to the high variability in soil properties, the soil organic carbon (SOC) change in Fujian province was strongly influenced by soil type, soil subgroup and soil genus. Therefore, in future "carbon sink" policy formulation, it is necessary to formulate corresponding management measures for specific soil types.

      • Root Water Source of Pinus sylvestris L. var. Mongholica Litv. and Influencing Factors in the Southeastern Part of Mu Us Sandy Land, China

        PEI Yanwu, HUANG Laiming, SHAO Mingan, lI Ronglei, ZHNAG Yinglong

        DOI: 10.11766/trxb202011060608

        Abstract:

        Water shortage is the main limiting factor for vegetation restoration and desertification control in the arid region of northwestern China. 【Objective】Investigation of the root water source and influencing factors of typical plants used for desertification control can provide a basis for scientific sand control and efficient water use in the region.【Method】Pinus sylvestris L. var. mongholica Litv. (P. sylvestris) is an evergreen coniferous tree of the Pinus genus. It is widely used in wind sheltering and sand fixation in the north of China because of its strong root system and ecological adaptability. In this study, the hydrogen and oxygen isotope composition (δ2H and δ18O) of plant xylem water and its potential water sources (precipitation, soil water and groundwater) were measured monthly from June to November 2018 in an artificial P. sylvestris forest (18~20 a). The experiment was carried out in the Gechougou watershed in the southeastern part of Mu Us Sandy Land. The dynamic changes and controls of root water sources were studied by the multiple linear mixed models. 【Result】Our results showed that the range of δ2H was −69.95‰ ~ −49.25 ‰, −144.81‰~−6.60‰, −83.62‰~−48.57 ‰ and −65.63‰ ~ −53.65 ‰ for xylem water, precipitation, soil water and groundwater, respectively. Also, the range of δ18O was −8.77‰~−8.21‰, −18.86‰~−2.07‰, −9.45‰~−6.54‰ and −9.97‰~−8.26‰, respectively, during the period monitored (June–November). The weighted mean values of δ2H and δ18O in soil water were between the precipitation and groundwater due to the influence of precipitation infiltration and groundwater recharge. Rainfall amount, soil water content and groundwater level in the rainy season (July–September) were 24.80~90.10 mm, 3.36%~8.40% and 5~15 cm higher than that in the dry season (June, October, November). Iso-source model predicted that P. sylvestris mainly used the nearly saturated layer water (>90 cm) (15.40%) and groundwater (70.10%) in June. However, from July to September, the root used water source mainly came from the active and stable soil layer (<80 cm) (61.03%) with the increase in rainfall. Compared with the rainy season (July–September), the contribution of the nearly saturated layer (>70 cm) and groundwater to the root water source increased by 5.82%~28.00% and 20.64%~23.30% in October and November when precipitation decreased. During the detection periods, the average ratio of absorption and utilization by P. sylvestris root from the active layer, stable layer, nearly saturated layer and groundwater were 21.48%, 31.13%, 16.42% and 30.98%, respectively. The dependence on groundwater for P. sylvestris was significantly higher than that of other soil layers, which may be prejudice to survival under extreme drought environments in the future.【Conclusion】The soil water content was positively correlated with the root water absorption of P. sylvestris. The uplift and decline of groundwater level significantly changed the position of the nearly saturated soil layer, and then affected the absorption and utilization ratio of P. sylvestris from different potential water sources. Therefore, the root water source of artificial P. sylvestris forest was affected by both supply-consumption dynamics of soil water and seasonal fluctuation of groundwater level. This study provides a useful method that identified the absorption and utilization ratio of water by plants from different potential water resources, which will be significant for vegetation restoration in the Mu Us Sandy Land soil-plant ecosystems.

      • The Effects of Combined Application of Algae and Bacteria on Paddy Soil Phosphorus Availability and Microbial Community

        ZHANG Huijie, LIU Junzhuo, WU Yonghong

        DOI: 10.11766/trxb202103240159

        Abstract:

        【Objective】Phosphorus is a major element essential for biological growth, but its bioavailability and utilization efficiency in soil are low. Microorganisms play important roles in soil phosphorus cycling. In recent decades, phosphate solubilizing bacteria and microalgae have been widely used as biofertilizers, with great effects on soil phosphorus cycling and the composition and activity of microbial communities. Nevertheless, the combined effects of microalgae and bacteria have been given little attention. This study aimed to explore the effects of the combined application of Bacillus megaterium and Chlorella vulgaris on phosphorus availability and the microbial community in paddy soil. 【Method】In this study, a laboratory cultivation experiment was carried out by using Bacillus megaterium, Chlorella vulgaris, and paddy soils from Jurong, Jiangsu, China, with four treatments, including the application of Chlorella vulgaris alone (A), application of Bacillus megaterium alone (B), combined application of Bacillus megaterium and Chlorella vulgaris (A+B) and the control without application of Bacillus megaterium or Chlorella vulgaris (CK). Specifically, we measured soil pH, contents of Olsen-P, total organic carbon (TOC), and total nitrogen (TN). Also, we determined the soil microbial community composition and diversity using 16S and 18S rRNA gene amplification high-throughput sequencing and characterized the metabolic heat release of soil microorganisms using microthermal analysis.【Result】After 30 days of culture, the soil Olsen-P content of combined application of Bacillus megaterium and Chlorella vulgaris (A+B, 15.92 mg·kg-1) was significantly higher than that of the control and Chlorella vulgaris alone (A: 14.46 mg·kg-1, CK: 14.61 mg·kg-1), with an increase of 9.0% compared to the control (14.61 mg·kg-1). The combined application of Bacillus megaterium and Chlorella vulgaris also significantly increased the pH, TN and TOC contents of paddy soil. The relative abundance of Bacillus in the soil of the combined application of Bacillus megaterium and Chlorella vulgaris (1.70%) increased by 27.9% compared to that applied with Bacillus megaterium alone (1.33%), and the relative abundance of Chlorella in Chlorophyta of the combined application of Bacillus megaterium and Chlorella vulgaris (3.14%) increased by 3.18% compared to that applied with Chlorella vulgaris alone (3.04%). Also, the combined application of Bacillus megaterium and Chlorella vulgaris significantly increased the metabolic activity and proliferation rate of soil microorganisms. 【Conclusion】This study showed that the combined application of Bacillus megaterium and Chlorella vulgaris significantly improved the availability of P in paddy soils and the activity of soil microorganisms. This provides practical information for the development and utilization of algae and bacteria-based compound biofertilizers, and a new perspective for improving the phosphorus availability in paddy soils and for alleviating the accumulation of P and reducing environmental risks.

      • Metagenomic Analysis of the Viral Community Patterns and Functions of Farmland soil in the Black Soil Region of Northeast China

        RUAN Chujin, XIONG Guangzhou, NIU Xinyao, CHEN Guowei, WU Hanqing, MA Zechao, ZHU Kun, LIU Ying, WANG Gang

        DOI: 10.11766/trxb202104230215

        Abstract:

        [Objective]Viruses exist almost everywhere on Earth. They can infect humans, animals, plants, fungi, and even bacteria, and thus play critical roles in the biogeochemical cycling of elements and energy. Knowledge of the viruses’ community patterns and genomic information is key for proper understanding of their crucial ecological functions. This study aims to quantify the viral community patterns and functions in a farmland black soil of Northeast China and analyze their potential roles in soil ecosystems. [Method]The metagenome sequences of the viruses were obtained based on metagenomics sequencing technology and were analyzed individually for functional gene analysis, host prediction, and genome assembly of viral Contigs. A bioinformatics software was employed to analyze the diversity patterns of the viruses. [Result]The results showed that the majority of the viruses in the farmland black soil belonged to Caudovirales (59.38%) and Herpesvirales (2.56%) orders. This consisted of 29 families, with Siphoviridae and Microviridae representing the top two abundant families and accounting for about 44.48% and 20.53%, respectively. Gene annotation analysis revealed that soil viruses may actively contribute to numerous biogeochemical cycling processes, including nitrogen compounds metabolism, catabolism, biosynthesis, methylation, multi-organism metabolism, cellular metabolism, primary metabolism, nucleobase-containing small molecules metabolism, and organic substance metabolism, etc. Additional analysis showed that the virus hosts could be classified into 35 genera that belong to 5 phyla. [Conclusion]With these quantitative measurements, this study provides necessary information towards advancing the virus gene database of the black soil and its ecological functions.

      • Competitive adaptation mechanism of soil archaea and marine archaea under different pH and oxygen conditions

        xiongxumei, zhouxue, guojia, jiazhongjun, jiangxianjun

        DOI: 10.11766/trxb202101220668

        Abstract:

        Abstract:【Objective】pH and oxygen were the key limiting factors for the ammonia oxidation activity of archaea. The law of competition and adaptation of different archaea ecotypes (soil archaea and marine archaea) to pH and oxygen in complex soils are still unclear.【Method】Ammonia-oxidizing archaea (AOA) was selected as the marine archaea Group1.1a-associated with acid forest soil with pH = 5.40, and the active ammonia-oxidizing archaea were selected as the soil archaea Group 1.1b-associated with alkaline paddy soil with pH = 8.02. After adjusting the pH and oxygen concentration of the mixed soil, a stable isotopic probe microcosm indoor culture experiment was set up to analyze the intensity of soil nitrification. Also, quantitative PCR and 454 high-throughput sequencings were employed to study the effect of different pH and oxygen conditions on the number of soil ammonia-oxidizing archaea and bacteria and also the types of active ammonia-oxidizing microorganisms present.【Result】Compared with zero time, the contents of nitrate nitrogen and ammonium nitrogen had no change at pH3.8; At pH6.0 and 7.6, nitrate nitrogen content increased by 23 times and 19 times, respectively, and the ammonium nitrogen content decreased significantly.The results show that after the soil samples were mixed, there was no nitrification at pH 3.8, while strong nitrification occurred at pH 6.0 and 7.6. Also, the nitrification in a high-oxygen environment was stronger than that in a low-oxygen environment.After substrate culture, the number of oxidizing archaea was increased significantly ; DNA-SIP shows that the active ammonia oxidizing archaea with pH 6.0 and 7.6 were almost all soil archaea Group 1.1b.【Conclusion】 This study reveals that pH rather than oxygen is the main factor affecting nitrification. Although oxygen also has a certain effect on nitrification; in neutral and alkaline soil, soil archaea lineage has greater activity in high O2 and low O2 environment and have more adaptive capacity than marine lineage.

      • An improved apparatus driven by gravity for streaming potential measurement of simulated soil

        Li Zhongyi, LIU Fangming, WU Jinwen, Xu renkou, Xie deti

        DOI: 10.11766/trxb202101130023

        Abstract:

        【Objective】Theoretically, surface electrochemical properties of bulk soil can be well characterized by streaming potential measurement. Since the streaming potential measurement is usually adopted to measure the zeta potential of charged solid with large size (e.g. bulk soil). Nevertheless, commercial streaming potential apparatus is cumbersome to operate and expensive. This limits the application and development of streaming potential measurement in soil research.【Method】In this study, a laboratory-made streaming potential apparatus was developed to measure the zeta potential of simulated bulk soil. Packed quartz grains and Fe oxide-coated quartz grains column were used to mimic the porous structure and surface electrochemical characteristics of bulk soil. The zeta potentials of quartz grains in NaCl electrolytes with different ionic strength (0.01, 0.05, 0.1, 0.5, 1.0, 2.0, and 5.0 mmol?L-1)were measured by the streaming potential measurement. Also, using this self-made streaming potential apparatus, we measured the zeta potentials of quartz grains and Fe oxide-coated quartz grains in electrolytes with same ionic strength (20 μS ?cm-1) but different pHs (4.4, 5.2, 6.1, 6.6, 6.9, 7.7, and 8.0). In addition, the zeta potentials of colloidal quartz in different pH’s electrolytes measured by traditional electrophoresis measurement was used to verify the accuracy of the streaming potential measurement.【Result】The results showed that, with increasing ionic strength, the zeta potential of quartz grains measured by steaming potential measurement became less negative due to compression of the diffusion layer of the electric double layers on charged solid surfaces at higher electrolyte concentrations. Similarly, with increasing electrolyte pH, the zeta potentials of both quartz and Fe oxide-coated quartz grains measured by steaming potential measurement decreased because of the greater deprotonation effect of functional groups on the surface of quartz and Fe oxide-coated quartz grains. When Fe oxide was adsorbed on the quartz surface, the zeta potential of Fe oxide-coated quartz grains was higher than that of uncoated quartz grains. This was because of charge neutralization between positively charged Fe oxide and negatively charged quartz grains. The measured IEP (isoelectric point) of the Fe oxide-coated quartz grains was between the IEPs of quartz grains and Fe hydroxide. There was a good consistency between the zeta potentials of quartz grains measured by streaming potential and the zeta potentials of quartz colloids measured by electrophoresis measurement.【Conclusion】The results obtained by using the laboratory-made streaming potential measurement apparatus are consistent with the theoretical prediction and electrophoresis measurement. Also, the structure of the laboratory-made streaming potential apparatus is simple, its operation is convenient, and the cost to build this apparatus is low compared to commercial apparatus. Thus, the streaming potential measuring apparatus used in this study can be used as a powerful tool to conduct studies in the field of soil electrochemistry.

      • Characteristics of Rhizosphere Microbial Communities in a Disease-suppressive Soil of Tomato Bacterial Wilt and its Disease-suppressive Transmission Mechanism

        LIU Hong, DONG Yuanhua, SHEN Minchong, SUN Feifei, WANG Xia, LIU Jingping, LI Jiangang

        DOI: 10.11766/trxb202101200037

        Abstract:

        Microorganisms in the rhizosphere play an important role in the process of plants resistance to soil-borne diseases. 【Objective】 This study investigated the characteristics of rhizosphere microbial community and the mechanism of microbial community assembly in disease-conductive soil and disease-suppressive soil in a tomato-cultivated field. 【Method】Real-time quantitative PCR was applied to detect the pathogen density in disease-conductive rhizosphere soil and disease-suppressive rhizosphere soil. Also, the distinction of tomato rhizosphere soil microbial community diversity, composition, structure, and assembly processes based on zero model were analyzed through high-throughput sequencing of 16S rRNA gene amplicon. 【Result】The results showed that, compared to disease-conductive soil, there was a significantly lower disease index of tomato bacterial wilt in disease-suppressive soils (disease index in disease-conductive soil and disease-suppressive soil were 47.5 and 22.5, respectively). The rhizosphere bacterial communities in disease-suppressive soils were characterized with higher alpha diversity, more abundant beneficial microorganisms, such as Actinobacteria, Firmicutes, Bacillaceae, and Streptomycetaceae, lower abundance of Ralstonia solanacearum (disease suppression pathogenic bacteria in rhizosphere soil samples of abundances decreased by 12.22 times) and accompanied with more stochastic processes. This shows that the adaptability of disease-suppressive soil to pathogenic disease stress is stronger than that of disease-conductive soil. To test the transmitability of inhibition properties of disease-suppressive soil, the disease-conductive soil and disease-suppressive soil were mixed in a certain proportion to form three treatments; disease-conductive soil alone (D10H0), a mixture of disease-conductive soil and disease-suppressive soil with a mass ratio of 1:1 (D5H5), and disease-suppressive soil alone (D0H10). It was observed that with the increase in the proportion of disease-suppressive soil, the disease index of tomato bacterial wilt gradually decreased (the disease index in D10H0, D5H5, and D0H10 were 41.67, 29.17, and 16.67, respectively). While the diversity of bacterial alpha gradually increased, the abundance of Firmicutes, Streptomyces, and Bacillaceae increased significantly. Also, the dominant role of the stochastic and random processes was strengthened. 【Conclusion】Disease stress had a significant effect on the alpha diversity, composition, structure, and community assembly process of the tomato rhizosphere microbial community. The disease-suppressive soil can recruit more beneficial microorganisms through plant roots to resist pathogenic disease stress.

      • Influences of long-term different N application rates on straw decomposition and bacterial community structure in a fluvo-aquic soil

        lijingwang, chenlin, madonghao, zhangcongzhi, zhangjiabao

        DOI: 10.11766/trxb202103150145

        Abstract:

        【【Objective】The problems caused by excessive nitrogen (N) application in agriculture has been of growing concern, but the soil mineral N level and its effect on straw decomposition after long-term N application remain unclear. 【Method】We used a fluvo-aquic soil treated for 14 years (2005-2018) with N at the rates of 0 (N0), 150 (N1), 190 (N2), 230 (N3) and 270 (N4) kg N ha-1 yr-1, and conducted a 50-day laboratory incubation experiment with and without straw addition. Soil CO2 emission was determined during the incubation, soil mineral N (nitrate and ammonium nitrogen), dissolved organic carbon (DOC), microbial biomass carbon (MBC) were measure before and after the incubation, and the bacterial community structure was determined using amplicon sequencing of the 16S rRNA genes. 【Result】The results showed that soil mineral N content and straw decomposition efficiency increased with increasing N application rates and the bacterial community composition was significantly (P < 0.05) influenced by N application rates. The network analysis revealed that the co-occurrence pattern among species within the bacterial community during straw decomposition changed with the N application level, and the negative association among bacterial communities was strengthened under a high N application level. At the same time, the dominant position of Proteobacteria was weakened and that of Acidobacteria was enhanced. 【Conclusion】 The relationship among soil mineral N content, bacterial community structure and species changed with the difference of long-term N application level. The results of this study provide guidelines for the use of straws to amend soils under N application.

      • Soil nitrogen supply and retention capacity determine the effect and utilization rate of nitrogen fertilizer in paddy field.

        Yang Binggeng, Cai Siyuan, Liu Yujuan, Xu Lingying, Wang Yu, Peng Xianlong, Zhaoxu, Yan Xiaoyuan

        DOI: 10.11766/trxb202104070181

        Abstract:

        Wuchang and Changshu are the representative production areas of high-quality japonica single-cropping rice in Northeast and East of China, respectively. However, the amount of nitrogen (N) fertilizer required to maintain a high yield in Wuchang is usually much lower than that in Changshu, but the agronomic use efficiency of fertilizer N (AE) is higher than that in Changshu. Different hydrothermal conditions, crop varieties, farmland managements and soil types in these two places make it difficult to identify what causes such regional differences. To explore soil factors" influence on NUE, black paddy soil (BS) and gleyed paddy soil (WS) were collected from the two rice fields. There were three N treatments as follows: no N treatment (CK), low N rate and high N rate (150 and 300 kg N·hm-2 with 15N urea). A rice pot experiment was carried out in Changshu National Agro-Ecosystem Observation and Research Station to compare the rice yield, NUE, and total N loss between the two soils. The characteristics of N mineralization in the two paddy soils were also studied through a three-week indoor anaerobic incubation experiment. The results suggested that the rice yield, agronomic fertilizer N use efficiency and above-ground N uptake of BS were better than that of WS among these N treatments under the same climate, rice variety and management levels. The NUE of BS was higher than that of WS by about 20.0-28.7%. However, the 15N recovery efficiency of BS was only higher than that of WS by about 5.56-8.01%. Although the above-ground N uptake by rice increased after N addition in two soils, the N increment of BS from the soil source was 95%-215% higher than that of WS. Also, the increment of N taken up from the priming effect (difference of above-ground plant N uptake derived from the soil between CK and the corresponding N application treatments) of BS was 173-354 mg·pot-1 and 88-113 mg·pot-1 for WS. This observation was consistent with the results that the net soil N mineralization amount of BS was 0.95-2.49 times higher than that of WS after N application in the anaerobic incubation experiment. Thus, this result indicated that the N application had a greater priming effect on the increase of N supply in BS soil. Also, the total loss of 15N fertilizer in WS soil was significantly higher than that of BS with the increase of N application rate in the pot experiment. Overall, the high yield and NUE of BS may be related to the fact that N fertilizer could provide a greater priming effect and maintain a higher soil N retention level. However, the rice yield of WS depended more on the N fertilizer input due to its lower priming effect of N fertilizer and had a weaker ability to retain fertilizer N. Thus, the soil is an important factor influencing the difference in agronomic use efficiency of fertilizer N and N use efficiency in paddy fields.

      • Research on Anaerobic Microbial Degradation of Polycyclic Aromatic Hydrocarbons Under Different Reducing Conditions: Analysis Based on Bibliometrics

        ZHU Yanjie, HEYan, XU Jianming

        DOI: 10.11766/trxb202102060081

        Abstract:

        【Objective】Polycyclic aromatic hydrocarbons (PAHs) are a kind of persistent organic pollutants that exist widely in various environmental media. As one of the most important ways to eliminate PAHs pollution in the environment, microbial degradation has been widely studied in the past few decades. Many of the polluted environmental media may undergo anaerobic states or remain in anaerobic states, e.g. paddy soils, bottom soils, wetlands, sediments, water. However, existing studies mainly focused on the aerobic environment and paid less attention to the anaerobic environment. Considering the current situation, this study systematically and comprehensively illustrates the research status of anaerobic microbial degradation of PAHs. 【Method】The core collection database of Web of Science was used as the data source to conduct a bibliometric analysis of published literature in this field, with the aid of two pieces of software, VOSviewer and CiteSpace. The main contents of the bibliometric analysis included the year of publication, disciplines, keywords frequencies, keywords co-occurrence and most cited papers. In addition, by classifying different electron acceptors based on their reducing sequence, this paper discussed the research progress regarding anaerobic microbial degradation of PAHs in denitrification, metal ion reducing, sulfate reducing and methanogenesis conditions, respectively, with a focus on typical degrading microbes and mechanisms. On this basis, the existing theoretical gaps and future development trends in the field of PAHs anaerobic microbial degradation in the soil were discussed emphatically.【Result】The results showed that since 1991, the number of studies in this field showed the trend of fluctuating growth but was still relatively small on the whole, and most of them only focused on low-ring PAHs, especially naphthalene. Among the four different reducing systems, denitrification and sulfate reducing systems were studied more extensively, while less attention was paid to metal ion reducing and methanogenesis systems. Most significantly, the majority of mechanical studies remained at a relatively superficial level, without exposing the biological mechanisms of PAHs anaerobic microbial degradation and the interactions between functional microbes. Emerging technologies have not been commonly used in this field. Most studies were based on pure culture or environmental media such as water and sediment, but few were based on soil system. 【Conclusion】As a result, there are still many theoretical gaps in the understanding of anaerobic microbial degradation of PAHs in the soil at present. Soil is the main site for the confluence and accumulation of PAHs in the environment. In the future, researchers should try to combine Compound-specific Stable Isotope Analysis(CSIA), DNA-stable isotope probing(DNA-SIP), Omics and other emerging technologies with traditional research methods to explore the mechanisms of PAHs anaerobic microbial degradation in the soil from a variety of different aspects, and verify the applicability of existing theories and experience to the soil, so as to fill the current theoretical gaps and promote the microbial remediation of PAHs pollution in anaerobic soil.

      • Application of Laser-Induced Breakdown Atomic Spectroscopy in Soil Analysis

        MA Fei, ZHOU Jianmin, DU Changwen

        DOI: 10.11766/trxb202012100679

        Abstract:

        Soil analysis is the tool for understanding the soil. However, the conventional chemical analysis methods have been difficult to meet the requirements of mass information deprived from modern soil science. Laser-induced breakdown spectroscopy (LIBS) is one of the novel tools which reflects the elements atomic peaks in the soil with the advantages of less pre-processing, rapid, in situ, real-time and multielement monitoring. Moreover, each spectrum was recognized as a fingerprint of soil sample due to its unique characteristic. The current study aimed to provide a critical review of LIBS in soil analytical studies. Firstly, the principle of LIBS, the main factors in spectral recording and the chemometrics methods for spectra processing were introduced; then the applications in qualitative and quantitative soil analysis during the last decade were elaborated. Some of the soil analysis recorded with LIBS include soil identification, prediction of soil nutrients; soil heavy elements detection, and soil elements distribution studies at nano- and mesoscale. Lastly, the main challenges of the LIBS techniques in soil analysis were discussed and we highlighted the prospects and application of LIBS in future research.

      • Influence of Storage Conditions on 15N Isotopic Compostion of Gas and Liquid Samples

        Wen Teng

        DOI: 10.11766/trxb202011300661

        Abstract:

        Abstract: 【Objective】15N isotope techniques have been widely used in investigating soil and water nitrogen transformation. The 15N isotopic composition of NO3-, NH4+ and N2O are key data for this type of study. These gas or liquid samples are usually stored before their concentrations or before 15N abundance are determined. Nevertheless, improper storage processes may induce changes in these samples. However, the effect of storage conditions on the 15N isotopic composition of the gas or liquid samples has not been well defined. 【Method】The influence of storage container, temperature, sample pretreatment, time and other factors on the 15N abundance of gaseous and liquid samples were studied in this paper. 【Result】The stable storage time of N2O samples in aluminum foil air bags is very short, and its δ15N values significantly changed after 10-day storage. Also, the δ15N values were stable in a screw-top vacuum vial + butyl septa and clamp headspace vial + butyl septa for about 200 days. For soil extracts with natural abundance, the δ15N values of NO3- kept stable for about 10 days when refrigerated at 4℃ and frozen at -20 ℃, but its δ15N values of NH4+ remained stable for about 60 days and no more than 10 days when frozen at -20 ℃ and refrigerated at 4 ℃, respectively. Besides, for 15N enriched soil extracts, the 15N abundance of NO3- was stable for about 160 days, while the 15N abundance of NH4+ was only stable for about 30 days in -20 ℃ and less than 10 days in 4 ℃. For river samples, δ15N values of NO3- and NH4+ were only stable for about 10 days no matter whether the samples were refrigerated at 4 ℃ or frozen at -20 ℃.【Conclusion】Our results highlight the importance of storage conditions on 15N abundance of gas and liquid samples, and provides scientific guidance for proper storage conditions when adopting 15N isotope techniques.

      • Intercropping with Maize Influences Arbuscular Mycorrhizal Network Formation and Pepper Phytophthora Blight Suppression in Facility Sheds

        LIU Yifan, HOU Shaowei, HU Junli, CAI Peng, LI Minghui, WU Fuyong, LIN xiangui

        DOI: 10.11766/trxb202102280112

        Abstract:

        【Objective】Arbuscular mycorrhizal (AM) fungi have the potential for biocontrol of soil-borne diseases, e.g., pepper (Capsicum annuum L.) Phytophthora blight. However, the mass production and wide application of AM fungi have not been achieved due to the difficulties associated with in vitro cultivation. Therefore, it would be of great significance if the disease suppression function of soil indigenous AM fungi can be exploited.【Method】In the Pepper Science Park of Shizhu County, Chongqing city, plot experiments in a facility shed were carried out to investigate the effects of intercropping with maize (Zea mays L.) on indigenous AM fungal propagation and pepper Phytophthora blight suppression.【Result】Compared with the control (i.e., mono-cropping of pepper), intercropping with maize significantly increased not only the root mycorrhizal colonization rate of pepper, the rhizosphere AM fungal abundance, and soil phosphatase activity, but also the total nutrient (N, P, and K) acquisition amounts by the two crop species per plot. In contrast, intercropping with maize significantly decreased not only the incidence and severity of pepper Phytophthora blight but also the P acquisition amount and the fruit biomass per pepper plant. Compared to the treatment with the same row distances as control (SRD), the intercropping system which had the same ridge widths as control (SRW) and a relatively higher planting density, induced significantly higher (i) root mycorrhizal colonization rates with both crops, (ii) maize yield per plot, and (iii) total nutrient acquisition amounts by the two crop species per plot. Furthermore, the pepper Phytophthora blight incidence was significantly lower in the intercropping system with SRW than with SRD. 【Conclusion】In facility sheds, intercropping with maize may enhance the suppression of pepper Phytophthora blight by soil indigenous AM fungi via promoting their propagation and thus colonization on pepper roots. Also, the intercropping system with SRW has a relatively higher economic benefit compared to SRD.

      • Research Progress on Accumulation, Turnover and Stabilization of Microbial Residues in Soil

        ZHANG Bin, CHEN Qi, DING Xueli, HE Hongbo, ZHANG Xudong

        DOI: 10.11766/trxb202012270705

        Abstract:

        Microorganisms are the engine driving the biogeochemical cycling of soil elements and play an important role in the transformation of soil organic matter (SOM). They decompose SOM and release CO2 into the atmosphere through mineralization on the one hand and transform SOM into their cell components through assimilation on the other hand. These cell components can be accumulated in the soil as microbial residues after their death. There is increasing recognition that microbial residues are important precursors of SOM formation and contribute significantly to long-term SOM stabilization. Therefore, this paper calls for scientists to pay more attention and study the role of microbial residues in the accumulation, turnover and stabilization of SOM, and possible underlying mechanisms. To achieve this objective, this paper first explains the processes of how microorganisms continuously produce microbial residues in soils via assimilation and emphasizes the extent to which microbial residues contribute to soil stable carbon (C) pool. Subsequently, this paper introduces the (i) quantification of microbial residues using amino sugar analysis, (ii) conversion of amino sugar data into microbial residue C data to account for the proportion of microbial-derived C in soil organic C and (iii) distinction of original- and newly-formed microbial residues with isotopic labelling techniques to indicate the turnover of microbial residues in soil. Furthermore, this paper summarizes the key external factors influencing the accumulation and turnover of microbial residues. These factors include: (1) nutrition management that can directly influence substrate availability for soil microorganisms and consequently the production and accumulation of microbial residues, even though soil fungi and bacteria may respond differently to substrate addition; (2) tillage practices which generally reduce the accumulation of microbial residues through the destruction of fungal hyphae and breakdown of soil aggregates; (3) land-use change that can permanently impact the contribution of microbial-derived C to soil organic C; and (4) climate change factors which include temperature elevation, elevated CO2 concentration and nitrogen deposition. The fourth section of this paper summarizes the potential stabilization mechanisms of microbial residues in soil, which include chemical protection by attaching to soil mineral surfaces, physical protection by occluding in soil aggregates and delayed decomposition due to the chemical structure of microbial residues. In the last section, some perspectives are provided for the scientific issues that need to be further studied regarding microbial residue contribution to SOM: (a) combine microbial residues with living microbial communities to link with the processes of microbial assimilation from both instantaneous and continuous perspectives; (b) explore the distribution process and stabilization mechanism of microbial residues with soil minerals; (c) investigate the accumulation and turnover of microbial residues in subsurface soils as soil physicochemical properties and microbial community composition change substantially with increase in depth. These discussions will provide a clue to clarify the role of microbial anabolism driving and involving SOM formation and stabilization as well as the underlying relationship between SOM turnover and microbial process in terrestrial ecosystem.

      • Micromorphological Evidence on the Pedogenic Characteristics and Reticulated Mechanism of Aggradation Red Earth

        WANG Linyi, ZHU Lidong, YU Hongmei, LI Fengquan, CHEN Tianran, JIA Jia, MA Zhenzhen, ZHANG Zhongping, ZHANG Hangjia

        DOI: 10.11766/trxb202011240643

        Abstract:

        【Objective】The aggradation red earth sediment is widely distributed on terraces in the middle and lower reaches of the Yangtze River, especially in the piedmont of Lushan Mountain in China. Their sequences haves well recorded the weathering history during Quaternary in South China. Therefore, the objectives of this research were to (1) investigate the micromorphological characteristics of aggradation red earth sequence and (2) reveal the paleosol pedogenic environment.【Method】The research profile was L-HH (29°32 "07.88 "N, 116°04" 19.53"E, H=87 m) at the eastern piedmont of Lushan Mountain. Nine undisturbed samples were collected from the different pedogenic unit and made into thin sections, which were observed by plane polarized (PPL) and crossed polarized light (XPL) using Zeiss Axio Lab. A1 polarizing microscope in the laboratory. A total of 159 bulk samples were collected along with the profile at 5~6cm intervals. Moreover, particle size, chroma, susceptibility and geochemical data of the 159 bulk samples were measured.【Result】L-HH profile can be divided into reticular red soil unit(RRS), reticulated yellowish-brown soil unit(RYB) and yellowish-brown soil unit(YBS) from the bottom up. The soil matrix under Fe-impregnation was mainly composed of clay and colloid, the content of which is up to 50%~70%. The fragments included quartz, plagioclase and muscovite, while the secondary mineral was mostly illite and vermiculite. Also, heavy minerals that were observed included apatite, zircon, rutile and tourmaline. These results suggest in general that the soil units have a moderate-strong degree of chemical weathering. However, there were differences in detail among different units. The voids types of RRS are dominated by large linear channels with good connectivity and smooth wall. Also, the pedological features were mainly composed of coating, ferromanganese nodules, and diffuse concentric rings. Additionally, the illuvial coating developed along the voids wall and formed interbedded layers. Mn-coating was mostly superposed on the Fe-coating, and some pores were filled with the coating. Besides, part of the illuvial Fe-clay coating had a decolorization phenomenon. Thus, the pedogenic environment of RRS was characterized by strong summer monsoon,high soil moisture content, and increased seasonal climate contrast. Furthermore, the voids types of RYB were dominated by vughs, chamber voids and well-connected channels. Fe-Mn features were abundant in the soil matrix. The types of pedological features were rich with Fe masses, ferromanganese nodules and rhizospheric concentric iron-rings scattered in the matrix. The brown-red or grey-black flaky coating was developed repeatedly along the voids wall, and the deposition thickness was increased. Also, the soil moisture decreased, but the alternation between dry and wet was still significant. This, indicated a warm and dry environment. The voids types of YBS were dominated by plane voids, chamber voids, irregular voids, and vughs. Also, the voids’ wall was rough and the channel connection was poor. The pedological features mainly included diffused coating. A thin Fe-illuvial coating was found on some voids wall. During this period, the temperature and moisture conditions became worse. The climate was dry and cool, and the winter monsoon was strengthened. Also, changes of environmental proxies along the profile strongly supported the results of soil micromorphology. From the bottom up, the soil moisture content decreased continuously, and the climate tended to be dry and cool. The micromorphological characteristics support the view that the reticulation process was controlled by iron differentiation. Moreover, the micromorphological characteristics also showed that soil voids and plant roots accelerated the process of reticulation.【Conclusion】The findings in this study demonstrate that there is a significant correspondence between soil micromorphological characteristics and environmental proxies in the L-HH profile. This is an important indicator for interpreting the pedogenic environment of red earth, monsoon evolution signal. and the reticulated mechanism.

      • The Effects of Iron Oxide Phases Distribution on Aggregate Stability of Ferrisol Along a Subtropical Slope Derived from Granite

        XING Dengchun, CHEN Jing, BAO Haipeng, LONG Xiaoyong

        DOI: 10.11766/trxb202009170519

        Abstract:

        【Objective】 Iron oxides are sensitive to the pedogenic environment and an important cement of soil aggregates. The differentiation of iron oxide phases occurs at multiple scales in natural systems, which may affect the formation and stability of soil aggregates. This study aimed to explore the differentiation of iron phases, including total iron (Fet), free Fe-oxide (Fed), amorphous Fe-oxide (Feo), hematite (Hm), and goethite (Gt) at the hillslope, profile and aggregate scales and evaluate their effects on the stability of soil aggregates. 【Method】 A topo-sequence of Ferrisol, derived from granite in the hilly area of central Fujian Province, was fractionated into aggregates using wet-sieving and pipette methods. Fed and Feo in bulk soils and different aggregates were extracted with the citrate-bicarbonate-dithionite (CBD) solution and the acid ammonium oxalate (AAO) solution, respectively. Diffuse reflectance spectroscopy (DRS) was applied to determine Hm and Gt content. The percentage of water-stable aggregate (WSA) and the mean weight diameter (MWD) were evaluated. 【Result】 At the hillslope scale, the Fed and Fed/Fet in bulk soils decreased, while the Feo and Feo/Fed increased downslope. Meanwhile, the Hm and Hm/(Hm+Gt) significantly declined, while the Gt kept a little variation downslope. At the profile scale, the upper layers generally possessed higher contents of Fed and Gt, as well as lower levels of Feo and Hm in contrast to the deeper layers. At the aggregate scale, Fed, Feo and Gt were enriched in micro-aggregates. The contents of Hm were comparable in the micro- and macro-aggregates, while Hm/(Hm+Gt) increased with the aggregate size. Micro-aggregates were the main components, but the >0.25 mm macro-aggregates dominated the aggregate stability along the hillslope. The WSA of 0.5 ~ 0.25 mm and 1 ~ 0.5 mm aggregates were significantly positively correlated with Feo and Feo/Fed respectively, and the WSA of 2 ~ 1 mm macro-aggregate was significantly positively correlated with the Hm and Hm/(Hm+Gt). 【Conclusion】 The iron oxides demonstrated significant differentiation from hillslope scale to aggregate scale. The soil aggregate stability in the top-slope and bottom-slope profiles were higher than those in the transitional profiles due to the upslope enrichment of Hm and downslope enrichment of Feo along the hillslope.

      • Long-term Straw Mulching Affects Rice and Wheat Yields, Soil Nitrogen Fractions, and Microbial Community under a No-till System

        ZHOU Zijun, ZENG Xiangzhong, SHANGGUAN Yuxian, QIN Yusheng, TU Shihua, HE Mingjiang, LI Lijun

        DOI: 10.11766/trxb202011190522

        Abstract:

        【Objective】Conservation tillage has attracted increasing attention over recent decades due to its benefits in improving soil quality. A 12-year fixed field experiment was conducted to assess the effects of long-term straw mulching on yields of rice and wheat, soil nitrogen fractions and microbial community with soil layers under a no-till system in Southwestern China.【Method】Two treatments, no-till without straw mulch (NT) and no-till with straw mulch (NTS), were used for the experiment. The soil was sampled at 0-5, 5-10, 10-20, and 20-30 cm soil layers. Soil total nitrogen (TN) and labile nitrogen fractions, including particulate organic nitrogen (PON), microbial biomass nitrogen (MBN), NH4+-N, NO3–-N, and dissolved organic nitrogen (DON) were analyzed. Soil microbial community was determined using phospholipid fatty acid (PLFA) analyses. Crop yields were measured from September in 2013 to May in 2018.【Result】The results showed that compared to the NT treatment, the NTS treatment significantly increased wheat yield by 6.49%, with negligible effects on rice yield. The NTS treatment increased the contents of soil TN at 0-5 cm soil layer, NH4+-N and NO3–-N at 0-5 cm layer, PON at 0-5 and 5-10 cm layers, and DON at 0-5 and 10-20 cm layers but not MBN content. Also, the NTS increased the DON/TN ratio at 0-5 and 10-20 cm layers rather than the ratios of other labile nitrogen fractions to TN. Soil total microbial PLFA and bacterial PLFA were higher in the NTS than in the NT treatment. Additionally, fungal and actinobacterial PLFA were comparable between the two treatments, leading to a lower fungal/bacterial ratio in the NTS. Principal component analysis revealed that the soil microbial community at 20–30 cm layer was separated from the other three soil layers, and soil microbial communities of NTS treatments were generally separated from NT treatments along the first principal component axis. Furthermore, redundancy analysis demonstrated that soil MBN, TN, and ratio of particulate organic carbon to PON were key factors in shaping soil microbial community. Soil TN, labile nitrogen fractions, and microbial PLFA fractions decreased with increased soil layers, irrespective of straw mulching status.【Conclusion】Straw mulching should be recommended to no-till systems in Sichuan province, Southwestern China because it leads to effective improvements in soil nitrogen contents, wheat yields, and soil total microbial PLFA.

      • Optimization of Soil Microbial Activation of Inorganic Phosphorus in Tobacco-maize Rotation under Long-term Combined Application of Organic and Inorganic Fertilizers

        WANG Yaqi, LIU Jing, GOU Jianyu, YUAN Ling

        DOI: 10.11766/trxb202008100448

        Abstract:

        【Objective】Mixed culture technology of soil suspension and culture medium, high-throughput sequencing, and conventional analysis methods were used to study the influence of long-term fertilization on inorganic phosphorus (P) mobilization in soil. 【Method】Soil samples were collected from the plots of a 15-year-long experiment regarding crop cultivation and fertilization in Zunyi City, China. The treatments included (i) fallow soil (Control), (ii) consecutive flue-cured tobacco cultivation plus the application of only chemical fertilizers (C-CF), (iii) consecutive flue-cured tobacco cultivation plus the application of chemical fertilizers in combination with manures (C-CFM), (iv) flue-cured tobacco-maize rotation plus the application of only chemical fertilizers (R-CF), and (v) flue-cured tobacco-maize rotation plus the application of chemical fertilizers in combination with manures (R-CFM). The soil collected from the long-term fertilization test site was divided into two parts. A part of the soil sample was used for the mixed culture technology of soil suspension and culture solution. The method involved preparing the soil suspension (soil:sterile water = 1:100) and then diluting it to 10-5 with sterile water. 200 ?L diluent was taken and inoculated into NBRIP (National Biological Research Institute phosphate growth medium) solid medium with Ca3(PO4)2, FePO4 and AlPO4 as phosphorus sources. After incubation at 30 °C for 2 days, the number of colonies with a phosphorus dissolving circle was observed. Then, another 200 ?L 1:100 soil suspension was taken and inoculated in 50 ml NBRIP liquid medium with Ca3(PO4)2, FePO4 and AlPO4 as phosphorus sources for 16 days. At 12, 24, 48, 72, 96, 120 and 144 hours after inoculation, the culture medium was drawn, and the pH, soluble inorganic phosphorus content, and organic acid content were determined. The other part of soil samples was sent to Meggie Biological Company for high-throughput sequencing to study the effect of long-term fertilization on the relative abundance of enzyme synthesis pathway related to organic acid synthesis. 【Result】The number of cultivable microorganisms (bacteria, fungi, actinomycetes and inorganic phosphate bacteria) in flue-cured tobacco-maize rotation, application of organic fertilizer and Control soil increased, and the population diversity increased. When the soil suspension was inoculated in a microbial culture medium, the content of available phosphorus was higher in the flue-cured tobacco-maize rotation than in consecutive flue-cured tobacco cultivation. Also, the available phosphorus was higher in the application of chemical fertilizers in combination with manures and Control than when only chemical fertilizers were applied; among which R-CFM was the highest and C-CF was the lowest. In the mixture, hydrogen ions were significantly correlated with dissolved Ca3(PO4)2, and organic acids were significantly correlated with dissolved FePO4 and AlPO4. This indicates that compared with pure culture technology of phosphorus-mobilizing microbes, soil suspension culture can not only reflect the phosphorus-mobilizing characteristics of microorganisms but also be closer to the complex phosphorus solubilization status of soil microbial flora. In high-throughput sequencing, the relative abundance of the synthetic pathways of citrate (Si)-synthase, protein glucose dehydrogenase and malate synthase in the soil of R-CFM was significantly higher than that of other treatments. 【Conclusion】 Optimal crop cultivation and scientific fertilization are conducive to the activation of soil inorganic phosphorus, and R-CFM can be promoted as a flue-cured tobacco demonstration cultivation model for widespread promotion in Zunyi tobacco areas. Soil suspension culture can be used as an extension of pure microbial liquid culture as (a) it is closer to the complex phosphorus solubilization status of soil microbial flora, (b) effectively characterizes the ability of PMM to activate inorganic phosphorus, and (c) supplements the deficiencies of pure microbial liquid culture technology. The difference in the relative abundance of enzyme synthesis pathways related to the synthesis of organic acids also explains the reason for rational crop rotation and combined application of chemical fertilizers and manures to promote the activation of soil inorganic phosphorus from the perspective of molecular biology.

      • The Effect of Controlled Release of Urea Coated with Natural Rubber and Biochemical Inhibitor on Soil Nitrogen Supply and Winter Wheat Growth

        QI Zenglian, HE Mingrong, DAI Xinglong, DONG Yuanjie

        DOI: 10.11766/trxb202012010592

        Abstract:

        【Objective】The purposes of this research were to (i) reduce or slow down the release and conversion rate of nitrogen, (ii) increase the utilization rate of nitrogen, (iii) increase the yield of wheat, and (iv) reduce environmental pollution.【Method】We applied the coating technology and inhibitor addition technology at the same time to prepare a new type of dual controlled release urea. For preparation, the coating material of the controlled release fertilizer was natural rubber while the inhibitors used were urease inhibitor (NBPT, n-butyl thiophosphoric triamide) and nitrification inhibitor (DMPP, 3,4-dimethylpyrazole phosphate). According to the different inhibitors added, four kinds of new natural rubber coated urea were prepared: uncoated (CRU1), NBPT coating (CRU2), DMPP coating (CRU3), and (NBPT+DMPP) combined coating (CRU4). The microstructure of natural rubber coated urea was observed by a scanning electron microscope (SEM). The slow-release characteristics of urea nitrogen were determined using a hydrostatic release test. The effects of NBPT and DMPP in controlling nitrogen conversion were determined by soil culture test. Also, we designed field experiments to verify the effects of the four controlled-release urea on soil nitrogen supply and winter wheat growth. 【Result】Natural rubber was used as a membrane material to prepare controlled-release fertilizers, with good film-forming properties, smooth surface and obvious nutrient channels in the profile. When loaded in still water, the controlled release period of natural rubber coated controlled-release fertilizer reached 60 days. Compared with urea (U) treatment, all controlled-release fertilizers significantly reduced the ammonia volatilization rate in the soil and postponed the peak ammonia volatilization days. Also, CRU1, CRU2, CRU3, and CRU4 significantly increased the continuous nitrogen supply capacity of the soil and increased the yield of wheat under 10% nitrogen reduction relative to U treatment. CRU4 was better than adding NBPT and DMPP alone in reducing soil urease activity during the growth period of winter wheat, inhibiting the conversion of soil NH4+-N to NO3--N, and reducing soil ammonia volatilization. Relative to U treatment, winter wheat production of CRU1, CRU2, CRU3, and CRU4 increased by 16.96%, 21.46%, 17.37% and 25.90%, respectively. 【Conclusion】CRU4 demonstrated the strongest continuous nitrogen supply capacity when applied in soil and the best increase in winter wheat yield. This result indicates that the new controlled-release urea prepared by combining natural rubber and inhibitor-coated urea controlled the dissolution of urea and delayed the urea conversion process. Under the condition of a 10% reduction in nitrogen application rate, the yield of winter wheat can still be significantly increased.

      • Effects of Different Land-use Types on Physical and Chemical Properties of Coastal Saline-alkali Soils in Shandong Province

        LI Shan, YANG Yuechao, YAO Yuanyuan, LIU Yan, ZHANG Shugang, ZHANG Yanpeng

        DOI: 10.11766/trxb202008310491

        Abstract:

        【Objective】The problems of high salinity, low nutrient and poor soil structure in the coastal saline-alkali area of Shandong province seriously affect the development of agricultural production. Therefore, the effective development and utilization of the soils in this region are of great importance to its agricultural production and income.【Method】In this study, the four land-use types (wasteland, grassland, cultivated land and forest land) in Kenli County of Dongying City were taken as the research objects, and the effects of different land-use types on the basic physical and chemical properties and aggregate stability of coastal saline-alkali soils were evaluated.【Result】The results showed that (i) the electrical conductivity (EC) and water-soluble K+ and Na+ contents in wasteland > cultivated land > grassland > forest land, with EC and Na+ content of wasteland being significantly higher than those from other sampling plots; (ii) the total nitrogen (N) and total organic carbon content (SOC) of the soils in forest land > grassland > cultivated land > wasteland, with SOC in the 0.25~2 mm water-stable aggregates being the highest; (iii) the mechanical stability mean weight diameter (MWD) and the mechanical stability aggregate content of > 0.25 mm particle diameter (R0.25) were significantly lower in forest land than those of other sampling plots; (iv) the water stability mean weight diameter (WMWD) and the water stability aggregate content of > 0.25 mm particle size (WR0.25) in wasteland were significantly lower than those in other sampling plots; and (v) the percentage of aggregate destruction (PAD) in wasteland > cultivated land > grassland > forest land. Additionally, results of the surface and internal scanning electron microscopy (SEM) of the 2 mm water-stable aggregates in grassland, cultivated land and forest land showed relatively obvious particles, pores, and adhesive materials. Furthermore, the Pearson correlation analysis showed that mechanical composition was significantly correlated with MWD and R0.25 while PAD was significantly correlated with soil water soluble Na+ content and SOC of 0.25~2 mm water-stable aggregate soil.【Conclusion】Different land-use types have different effects on soil physical, chemical, and mechanical properties. The grassland and forest land use types have significant ameliorating effects on the physical and chemical properties of coastal saline soil while forest land use has higher carbon reserves and aggregate water stability, but lower mechanical stability. The results of this study can provide references for the rational planning and sustainable development of land use in the coastal saline-alkali area.

      • Low pH Stress Induces the Accumulation of ROS By Increasing Production of Nitrate Reductase-Dependent NO in Rice Root Tips

        SUN Liming, MA Jianfeng, SHEN Renfang

        DOI: 10.11766/trxb202102070085

        Abstract:

        【Objective】 Low pH stress is one of the major factors limiting crop production on acidic soils. It often coexists with metal ion toxicity and this makes it difficult to explore directly the effect of pH in acidic soils. So far, the mechanisms of low pH stress in rice is poorly understood. 【Method】Two rice varieties with different low pH tolerance, Kasalath (low pH-tolerant) and Jinguoyin (low pH-sensitive), were selected to (i) study the relationship between low pH stress and the accumulation of nitric oxide (NO) and reactive oxygen species (ROS), and (ii) explore the regulatory relationship between NO and ROS under low pH stress. 【Result】Low pH caused the accumulation of NO and ROS in the root tips of Jinguoyin, but there was no significant change in Kasalath. The NO scavenger cPTIO reduced NO and ROS accumulation in root tips of Jinguoyin. Feedback inhibitor of nitrate reductase Gln significantly reduced NO content in the root tips of Jinguoyin under low pH, while L-NAME, a nitric oxide synthase inhibitor, did not affect NO content in the root tips of Jinguoyin. Low pH significantly increased the expression of nitrate reductase genes NIA1, NIA2 and NIA3 in Jinguoyin, and also increased the activity of nitrate reductase.【Conclusion】Low pH stress of Jinguoyin was related to the NO-mediated ROS accumulation. The NO signal generated under low pH stress is mainly synthesized by nitrate reductase through increasing the expression of NIA1 and NIA2.

      • Desorption of sulfamethoxazole in a soil-microplastics mixture system

        Jiaqing Wang, Ben Yu, Shaofeng Ma, Yiyang Chen, Yongming Luo, Haibo Zhang

        DOI: 10.11766/trxb202101220038

        Abstract:

        Both microplastics and antibiotics are emerging environmental contaminants which has been of concerned widely. Desorption of antibiotics from a sulfamethoxazole spiked soil in the presence of five difference microplastics was studied using batch equilibrium desorption experiments. Meanwhile, the factors that affected desorption behavior in such a system was revealed. The results indicated that the desorption rate of sulfamethoxazole declined significantly and a slow desorption phase could be observed from 10 h to 48 h in the experiment after addition of polyethylene and polystyrene microplastics. At the same time the equilibrium desorbed concentration of sulfamethoxazole in the solution declined significantly (p<0.05) as well in the presence of polyethylene and polyvinyl chloride microplastics. The influence of sodium and calcium ions on sulfamethoxazole desorption from the soil was not affected by the addition of microplastics. However, influence of fulvic acid on sulfamethoxazole desorption was mitigated after addition of microplastics in general. The decline of the sulfamethoxazole desorption could be negligible with elevated concentration of the fulvic acid.

      • Advances in the Indicator System and Evaluation Approaches of Soil Health

        ZHANG Jiangzhou, LI Yizan, LI Ying, ZHANG Junling, ZHANG Fusuo

        DOI: 10.11766/trxb202102150097

        Abstract:

        Healthy soil is the key to healthy food production and maintenance of the multifunctionality of the soil ecosystem. It is also the cornerstone of agriculture green development. Identifying the status of soil health and systematically carrying out soil health diagnosis is the basis of cultivating healthy soil and improving soil productivity. However, in the past, a large number of indicators and evaluations have been developed based on an individual soil function (e.g. soil productivity), while other soil functions were largely ignored. Soil biological indicators are still underrepresented in soil health assessment, and the dynamic monitoring of soil processes is not sufficiently conducted. In pursuit of sustainable development goals and with the requirement of agriculture green development, the indicator system and evaluation approaches of soil health have been greatly improved. Thus, the establishment of multi-objective coordinated soil health assessment has become the hotspot and the frontier. This paper summarizes the selection principle in the indicator system of soil health. The importance of soil biological indicators in soil health evaluation are analyzed. The advances, advantages, disadvantages and application areas of the Chinese soil health assessment method, Cornell Comprehensive Assessment of Soil Health, New Zealand SINDI, the framework of Soil Navigator, Soil Management Assessment Framework are expounded. Finally, the pathways to improve the soil health evaluation system are put forward. It is necessary to build a big data platform for integrated soil-crop management based on the regional ecological conditions. A multi-objective coordinated soil health assessment for different regions and crop systems should be established through the participation of multi-actors with the development of soil biological indicators. A long-term and whole-process dynamic monitoring system should be established in combination with rapid testing and intelligent information technologies. This will provide important support for agriculture green development.

      • The Responses of Active Cellulose-degrading Bacterial Community to Different Fertilization in Paddy Soils as Revealed by Magnetic Nanoparticle-mediated Isolation Method

        RONG Nan, ZHANG Jianwei, BAO Yuanyuan, HE Shiying, FENG Youzhi, LIN Xiangui

        DOI: 10.11766/trxb202011270598

        Abstract:

        Magnetic nanoparticle-mediated isolation (MMI) method is a promising technology for separating functional microbes from complex microbiota. In this study, we employed the MMI method to recover metabolically active cellulose decomposers from paddy soils with a 28-year history of different fertilization regimes (chemical fertilizers; termed NPK afterwards), organic amendments (OM), and without fertilization (CK)). Our findings suggest that compared to no fertilization, fertilization increased the number and activity of microorganisms, thereby facilitating cellulose degradation. These active cellulose-degrading bacterial phylotypes mainly belong to Bacteroides and Firmicutes at the phylum level, and further to Porphyromonadaceae and Paenibacillaceae at the family level. Also, we found that fertilization increased community stability, partly by decreasing interspecies dependency. Furthermore, OM fertilization increased the numbers of potential ecological function,which makes it more effective than NPK fertilization. These results were consistent with our previous conclusions based on DNA-SIP technology, suggesting that MMI is a powerful approach to recover active cellulose decomposers from a complex microbial community. Above all, these results would deepen our understanding of keystone straw decomposers in paddy soils and their shifts in response to different fertilizations.

      • The Effect of Sodium Carboxymethyl Cellulose on Water Movement and Soil Hydraulic Parameters of Loamy Sand

        SHAN Yuyang, MA Chenguang, WANG Quanjiu, LI Xiaoju, TAO Wanghai, ZHANG Jihong, SU Lijun

        DOI: 10.11766/trxb202012070675

        Abstract:

        【Objective】Scientific use of sodium carboxymethyl cellulose (CMC) to achieve water conservation and salt control is of great significance for the improvement of coastal sandy saline-alkali soil. It is therefore important to clarify the influence of CMC on the water movement law of coastal soil sand by evaluating the effect of CMC concentration on soil hydraulic parameters.【Method】In this study, a one-dimensional vertical infiltration experiment was carried out to study the effects of different CMC application amounts (0, 0.1, 0.2, 0.4, 0.6 g?kg-1) on the infiltration characteristics, water distribution, and soil hydraulic parameters.【Result】The results showed that the final cumulative infiltration increased by 4.90%~15.17%, and the infiltration time to reach the preset wetting front depth increased by 61.90%~604.73% with the increase of CMC application. The adsorptivity S in the Philip infiltration model decreased from 0.685 cm?min-0.5 to 0.256 cm?min-0.5 and the parameter KsSf in the Green-Ampt model decreased from 0.633 cm2?min-1 to 0.096 cm2?min-1 with CMC application. The S and the average soil water diffusivity could be described by a quadratic polynomial and exponential function, respectively. Soil water content increased by 0.7%~3.7% because CMC enhanced the soil water holding capacity. Additionally, the retention water content θr, saturated water content θs, and air-entry α reciprocal were positively correlated with the amount of CMC, and inversely proportional to the saturated water conductivity Ks and shape coefficient n. CMC induced a moderate variation to Ks and α, and a minor variation to θr, θs, and n.【Conclusion】This study can provide a valuable theoretical reference for rational use of CMC for the improvement of coastal saline-alkali soil.

      • Soil Erosion Characteristics of Different Soil and Rock Mosaic Slopes Under the Condition of Successive Rainfalls

        FAN Chunhua, ZHAO Longshan, LI Kaifeng, QIAN Xiaohe

        DOI: 10.11766/trxb202011020606

        Abstract:

        【Objective】The discontinuity of natural rainfall makes the influence of successive rainfalls on soil erosion different from that of single rainfall on slope erosion. Under the condition of not disturbing the slope after rainfall, the soil erosion characteristics of different soil and rock mosaic slopes in karst area under conditions of successive rainfalls were explored. 【Method】Using the method of artificial rainfall simulation, the soil erosion characteristics of three types of soil and rock mosaic slopes (i.e., FE, rock fully embedded in the soil layer, not exposed to the surface; PE, rock partly embedded in the soil layer, exposed to the surface; RC, rock not embedded in the soil layer, covering the surface) were studied under four rainfall conditions (24 h interval). The test slope was 25°, and the rainfall intensity was 50 mm·h-1. The rainfall lasted for 90 min. 【Result】Results showed that (1) with the increase of rainfall events, the surface runoff of FE, PE and RC increased, while the interflow and the underground runoff increased first and then decreased. In the first two rainfall scenarios, the surface runoff of three types of soil rock mosaic slope had no obvious regularity, but in the last two rainfall, the surface runoff was PE > FE > RC; (2) with the increase of rainfall events, the FE, PE and RC surface sediment yield increased. In addition to the first rainfall, the surface sediment yield in the last three rainfalls was PE > FE > RC. Also, the sediment yield of PE surface was 1.04-4.82 times that of the FE and RC surfaces, respectively; (3) with an increase of rainfall events, under the influence of early rainfall, the soil moisture content increased, and the runoff time of surface runoff and interflow in subsequent events was advanced by 5-16 min. 【Conclusion】Under successive rainfalls, the rock embedding in the soil has the effect of increasing the surface runoff and sediment yield. These results provide a scientific basis for further understanding the response of soil and water loss process to climate change on karst rocky desertification slope.

      • Effects of Prevention and Control Measures of Soil Erosion on Molecular Ecological Network of Soil Microbial Community in Pinus massoniana Plantation

        LI Zhongwu, NIE Xiaodong, XIAO Linhui, Shen Zhigao

        DOI: 10.11766/trxb202008220475

        Abstract:

        【Objective】 Prevention and control measures of soil erosion can restore forest vegetation and improve soil quality, and hence affect the soil microbial community structure. Soil microbes play an important role in soil substance recycling. Thus, it is of great significance to explore changes in soil biochemical processes and to study the effects of typical prevention and control measures of soil erosion on the interactions between soil microbial community. Ecological network analysis can be used to reveal microbial interactions and microbial network structure. However, it is still unclear how prevention and control measures of soil erosion affect the microbial interaction network in Pinus massoniana plantation. There are few researches exploring soil microbial interactions and the changes in environmental factors caused by agricultural engineering measures and vegetation planting. 【Method】 In this paper, a one-year field experiment was carried out in Pinus massoniana plantation of the Institute of Soil and Water Conservation of Shaoyang City (111°22′E, 27°03′N), Hunan Province, China. The experiment was designed to have three treatments, one for digging fish-scale pits and planting grass, one for digging fish-scale pits and planting grass and shrubs and another for a control check without any measure; three replicates were conducted for each treatment. One year later, soil samples were collected from the three treatments, separately, for analysis of soil physicochemical properties and DNAs. The 16S rRNA and 18S rRNA Illumina MiSeq high-throughput sequencing technology was used to determine the soil microbial community structure under different treatments, and the random matrix method was used to construct the microbial network. 【Result】After implementation of prevention and control measures of soil erosion, soil microbial community composition changed as the relative abundance of Chloroflexi significantly decreased and that of Proteobacteria and Acidobacteria significantly increased. Ecological network analysis showed that the total nodes, total links, average connective degree, and the modularity of the microbial network increased. This indicated an increase in the microbial network scale and complicated microbial interactions. Three microbial networks were dominated by negative interactions (60.59%~67.49%), and the competition between species was strengthened after the implementation of the two measures. Parts of the microbial communities of Chloroflexi, Actinobacteria, and Proteobacteria played an important connecting role in the microbial network of the study area. Also, some key microbial communities with low relative abundance (< 1%) played a key role in the establishment of the microbial network. The average path distance of microbial networks became longer after the implementation of the measures. This means that the response rate of microbial action slowed down and the stability of the community structure was improved. Additionally, the measure of digging fish-scale pits and planting grass and shrubs was more effective than digging fish-scale pits and planting grass. Soil bulk density (R2 = 0.465, P < 0.05), pH (R2 = 0.377, P < 0.05), soil organic matter (R2 = 0.383, P < 0.05), and total nitrogen (R2 = 0.545,P < 0.01)had significant influence on bacterial community structure while soil water content (R2 = 0.485, P < 0.05) had a significant influence on fungal community structure. 【Conclusion】After implementation of prevention and control measures of soil erosion (i) soil microbial community structure changed, (ii) the microbial network scale, interaction and stability increased, and (iii) the competition within soil microbial communities became more intensive.

      • Biological Effect of Trichoderma-enriched Biofertilizers on Cabbage Cultivation in Coastal Saline Soil

        YU Ya’nan, WU Haiyan, WANG Panxing, DING Mingyue, MA Xingcong, JIANG Siqi, SHEN Qirong

        DOI: 10.11766/trxb202009100511

        Abstract:

        【Objective】The area of coastal saline soil is recognized as an important land resource with utilization value for agriculture. However, coastal mudflat area is usually characterized by poor plant growth and low microbial activity due to its high salinity suppressing most crops via the high osmotic stress, nutrient deficiency, toxicity and poor physical soil conditions. Soil microbes like Trichoderma spp. play a significant role in assisting plants to tolerate salinity stress. The present study aimed to investigate the effect of two Trichoderma-enriched bio-organic fertilizers on the yield and quality of cabbages (Brassica oleracea L.) grown in coastal saline soil as well as their effect on soil nutrient availabilities. 【Method】Field and pot experiments were carried out with eight treatments: 100% chemical fertilizer (CF), 30% bio-organic fertilizer plus 70% chemical fertilizer, 60% bio-organic fertilizer plus 40% chemical fertilizer, 100% bio-organic fertilizer (without chemical fertilizers), and using the non-fertilization treatment as the control (CON). The two bio-organic fertilizers were respectively prepared with strains of Trichoderma guizhouense NJAU 4742 (which is commercially available in China as a plant-growth-promoting agent) and T. arenarium 1A131 (which was previously isolated from saline mudflat of Dafeng, Jiangsu). The nutrient load of the seven fertilization treatments was set up to equal in the aspect of the contents of total N, P and K. 【Result】Results obtained from both the field and pot experiments demonstrated that there was no significant difference in the effect of the two bio-organic fertilizers. Compared to the non-fertilized control (CON) and the full chemical fertilization (CF), 30% or 60% bio-organic fertilizer significantly increased the contents of nitrate N and available P in soil. The treatment of 60% bio-organic fertilizer plus 40% chemical fertilizer influenced the cabbage growth by significantly (P <0.05) promoting the biomass of shoot and roots, and the chlorophyll content (shown by the SPAD values) in leaves. Among the fertilization treatments, application of 60% bio-organic fertilizer plus 40% chemical fertilizer resulted in the significantly highest yield and best quality of cabbage heads (with increased sugar and vitamin C contents, and less nitrate accumulation, P < 0.05). Moreover, principal component analysis (PCA) demonstrated that the significantly better plant growth effect did not correspond to the variation of soil nutrients. Rather, it may be related to the loaded microbes which were previously reported to be able to promote plant growth via producing phytohormones and activating the local microbiome. 【Conclusion】Application of 60% bio-organic fertilizer combined with 40% chemical fertilizer, which allows the roots to develop to the maximum in such a saline ecosystem, is the optimized fertilization regime to cultivate cabbages in saline agriculture in coastal mud flats. Besides, compared to the nutrient load from the fertilizers, the function of the Trichoderma strains was found to be more directly linked to the plant-beneficial effect of this fertilization regime. The biological effect from the applied strains did not significantly rely on the origination of a specific strain. Moreover, the requirement of applying a local saline soil strain to the saline agriculture was not fully addressed here at least not in this study, and thus, needs further investigations.

      • Accumulation of Trace Element and Organic Functional Groups in Different Size Fractions of a Loess Topsoil After Long-term Micronutrient Fertilization

        HU Yaxian, GUO Shengli

        DOI: 10.11766/trxb202012290640

        Abstract:

        【Objective】 Trace elements are of vital importance in crop growth. Long-term application of micronutrient fertilizers may affect the distribution of the elements in farmland soil, therefore influencing crop yield and soil organic carbon composition. To explore the accumulations of trace elements in different size fractions of loess soil, we collected topsoils from field plots after 35 years of fertilization with Zn, Mn, and Cu. 【Method】 All the soil samples from the treated plots and control plots (CK) were fractionated into ≥250, 250-125, 125-63, 63-20, and ≤20 μm. The element contents, availability, and soil organic carbon content (SOC) were determined and compared. Also, the types and contents of organic functional groups in different size classes were determined using Fourier Transform Infrared (FTIR) spectrometer. 【Result】 The results show that the content of SOC in the treated plots was at a low level (6-12 g?kg-1) and was not significantly improved after applying Zn, Mn, and Cu fertilizers. Nevertheless, the three trace elements were enriched to different degrees: Zn and Cu fertilizers significantly increased the total contents of Zn and Cu (the degree of enrichment was above 10% and 100% respectively), but no evident Mn enrichment was observed under Mn fertilizer treatment (the degree of Mn was within 10%). The highest concentrations of Zn, Cu, and Mn were observed in the ≤20 μm fractions, but SOC stability in this fraction was the lowest, ranging between 0.30-0.32. This was mainly because of the greater content of the unstable functional group C-O, but lower contents of C=O, C=N, and C=C that were positively correlated with the recalcitrance of SOC. The functional groups (C-O, C=O, C=N) were positively associated with the accumulation of Cu in the soil. Also, the inconsistent relationships of Zn, Mn, and functional groups observed in the loess soil in this study suggest that the governing principals in this study were distinct from previous reports based on SOC-rich soils. 【Conclusion】Findings in this study suggest that long-term application of micronutrient fertilizers did not significantly change the content of organic carbon or organic carbon composition in the topsoil of our study area. Nevertheless, it enhanced the accumulation of Zn, Mn, and Cu in the micro-aggregates to varying degrees. This is affected by the total organic carbon, the content of organic functional groups, and the type and efficiency of elements adsorption together.

      • Effects of Different Ameliorative Measures on the Enzyme Activities of Quaternary Red Soil

        ZHAO Jing, WANG Yanan, ZENG Xibai, WEN Jiong, WEN Yunjie, WU Cuixia, ZHENG Zhong

        DOI: 10.11766/trxb202008100444

        Abstract:

        【Objective】Red soil is one of the important soil types in China. Its low fertility is a problem for agricultural output. Exploring the effect of different improvement measures on soil fertility is integral for realizing sustainable use of middle and low yield fields.【Method】In this study, dryland red soils derived from Quaternary red earth were collected from a field experiment in Yueyang, Hunan Province and used to measure the changes in soil pH and nutrient contents across different soil layers and years of different treatments. These treatments included fallow (F), no fertilizer control (CK), a single application of inorganic fertilizer of nitrogen, phosphate, and kalium (NPK), inorganic fertilizer combined with straw-return (NPKS), inorganic fertilizer combined with lime (NPKL), inorganic fertilizer combined with amendments of organic crushed-bones (NPKA), and inorganic fertilizer combined with commercial bio-organic fertilizer (NPKC). We also compared the activity of enzymes related to carbon, nitrogen, and phosphorus cycles in this soil using the microplate fluorescence method.【Result】Some treatments significantly affected soil nutrients and enzyme activities. Soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), and available phosphorus (AP) in the 0-20 cm soil layer treated with NPKC in 2020 increased by 73%, 29%, 61%, and 1 847%, respectively, relative to the control. This treatment also significantly increased the enzyme activities of the enzymes that participate in the carbon cycle, including α-1,4-glucosidase (αG), β-1,4-glucosidase (βG), β-1,4-xylosidase (βX), and cellobiohydrolase (CBH). Also, the activity of β-1,4-N-acetylglucosamine (NAG), which is involved in the nitrogen cycle, was increased. Correlation analysis showed that SOM was significantly positively correlated with enzyme activities of αG, βG, βX, CBH, and NAG (P < 0.01). Additionally, the pH value was significantly negatively correlated with acid phosphatase (ACP) activity (P < 0.01). The effect of improvement measures on the enzyme activity of 0-20 cm soil layer was greater than on deeper layers. In 2019, compared with the control, NPKA treatment increased CBH enzyme activity in the 0-20 cm soil layer by 352%, but only by 2% in the 20-40 cm soil layer. Besides, ACP enzyme activity in the soil also showed a trend of increasing with years of treatment.【Conclusion】The combination of inorganic fertilizer and organic materials can significantly improve the nutrient status and soil enzyme activity in red soils. This can be used to efficiently improve the fertility of barren red soil.

      • The Spatial Distribution Characteristics of Soil Nutrients Underlying Biological Crusts at Regional Scale: A Case Study of Mu Us Sandy Land

        GUO Qi, LI Yiping, BU Chongfeng, JU Mengchen, LI Yahong, WEI Yingxin

        DOI: 10.11766/trxb202007230412

        Abstract:

        【Objective】As an active ground cover widely distributed in arid areas, biological crusts have an important impact on the nutrient cycle of desert ecosystems. At present, research on the nutrient effects of biological crusts is mostly concentrated on the plot scale. This study explores the spatial characteristics of biological crust nutrients at the regional scale. We aim to provide a reference for research methods on the nutrient characteristics of biological crusts at the regional scale and also provide a scientific evaluation for the ecological value of biological crust in a desert ecosystem. 【Method】The ecological restoration project carried out since 1959 has enabled the vegetation coverage in Mu Us to reach 40-50%, and biological crusts are widely distributed in this area as a sign of sandy land fixation. This study selected 146 sample points that cover the entire Mu Us Sandy land, and used geostatistics combined with multivariate statistical analysis to explore the spatial heterogeneity, distribution pattern and influencing factors of the soil organic carbon (SOC), total nitrogen (TN ), and total phosphorus (TP). 【Result】Biological crusts increased the nutrient content of the desert soil. The autocorrelation range of SOC and TP was relatively large, with variable ranges of 171.83km and 147.78km respectively, while the autocorrelation range of TN was relatively small. The nugget coefficients of SOC, TN, and TP were 53.3%, 49.86%, and 20.2%, respectively. SOC and TN exhibited moderately strong spatial autocorrelation, while TP exhibited strong spatial autocorrelation. The content of TP decreased from east to west, whereas the content of SOC and TN presented a high-low-high-low band distribution from east to west. Importantly, the main control variation factors of the three soil nutrients were different. The stepwise regression model of SOC introduced three variables, soil moisture (sm), surface downward shortwave radiation (srad), and normalized vegetation index (NDVI), while the stepwise regression model of TN introduced two variables, average temperature (Tas) and normalized vegetation index (NDVI). Additionally, wind speed (ws) and soil moisture (sm) were introduced into the stepwise regression model of TP as the first and second factors, respectively. 【Conclusion】Biological crusts in the Mu Us sandy land increased the nutrient content of desert soils. Three kinds of nutrient elements(TN, TP and SOC) showed spatial correlation and were directly or indirectly affected by vegetation conditions, surface water and heat balance, and other factors. On a regional scale, the nutrient content of soils under this biological crust was higher in the eastern part of the study area and lower in the southwest.

      • Taxonomy and Formation Causes of Soils Derived from Two Types of Calcium-enriched Rocks under Rice-planting Conditions

        LIAN Maoshan, ZENG Manman

        DOI: 10.11766/trxb202007220408

        Abstract:

        【Objective】In Chongqing, changes in soil morphological characteristics of paddy soil derived from calcareous mudstone are not obvious from top to bottom of the soil profile in most cases, but the phenomenon are not always so in paddy soil derived from limestone. The reason is not clear, which needs further study to reveal. In this paper, two types of paddy soils derived on different slope positions of calcium-enriched rocks (including calcareous mudstone and limestone) were selected as the research objects. Taxonomy and formation cause of the soils developed from calcium-enriched rocks under rice-planting condition are discussed, which provided scientific basis for understanding the development and evolution mechanism of paddy soils in different calcium-enriched rock regions comprehensively. 【Method】Field soil surveys were conducted to specify six paddy soil profiles of different slope position (mesoslope, baseslope and footslope) on limestone and calcareous mudstones respectively, and obtained soil-forming conditions and soil morphological characteristics of the profiles. Soil samples were collected from the profiles by horizon for analysis of physical and chemical properties. The soil genesis of tested soils was discussed based on the characteristics of organic carbon mineralization. According to the “Keys to Chinese Soil Taxonomy (3rd ed.)”, diagnostic horizons and diagnostic characteristics for the tested soils were determined, and the soils were attributed and named in Chinese Soil Taxonomy level by level. 【Result】 From the mesoslope to the footslope, there were only very few of rust mottles on the structural plane of paddy soil derived by calcareous mudstone (CS), and the vertical differentiation of free iron was not obvious. However, there were very few to many amounts of rust mottles on the structural plane of paddy soil derived by limestone (LS), and the distribution was different in different slope positions. Especially in the acid soil on the baseslope, the lower layer of free iron accumulates significantly. This showed that there are obvious differences in iron migration characteristics between the paddy soils derived from two types of parent rock. The accumulation of organic carbon mineralization (C15) of CS was lower than that of LS at the same slope position (P < 0.05) significantly. The lower amount of easily mineralized organic carbon made it difficult to reduce the high valent iron in CS, and the iron migration in profiles was not obvious, resulted in the typical soils of CS at different slope positions were classified as Typic Hapli-Stagnic Anthrosols. From the mesoslope to the footslope, the C15 of LS increased gradually, and the C15 of footslope was higher than that of other slope positions (P < 0.05) significantly. Combined with the influence of slope position on water condition, the typical soils from mesoslope to footslope were classified into Typic Hapli-Stagnic Anthrosols, Typic Fe-accumuli-Stagnic Anthrosols and Typic Gleyi-Stagnic Anthrosols. 【Conclusion】The concentration of easily mineralized organic carbon is a key factor to determine whether the slope position can cause the different type of paddy soil derived from calcium rich mother rock. In addition, some of the paddy soils derived from limestone have anthro-recalcification, but they can not be classified into the sub category of "Recalcaric" according to the current standards. Therefore, it is suggested to relax the retrieval requirements for the adjective "Recalcaric" of the sub category of paddy soil.

      • Research Progress on the Acid-base Properties of Variable Charge Soils Using Potentiometric Titration

        WEN Xiaocui, LI Jiuyu

        DOI: 10.11766/trxb202010090558

        Abstract:

        Compared with the constant charge soils that distribute in temperate regions, the variable charge soils in tropical and subtropical zones are unique soils, with highly variable particle surface charges. Investigations on the surface chemical characteristics of variable charge soils have received considerable attentions. The potentiometric acid-base titration method is the most straightforward approach to qualitatively and quantitatively identify the surface chemical characteristics of variable charge soils. In this paper, the characteristics of variable charge soils are briefly described and the concept and difference of point of zero charge (PZC) is described and classified according to (i) the conditions for surface charge measurement, (ii) the modes of expression for PZC, and (iii) measurement methods for surface charge of soil colloidal particles. On this basis, the influence of the acid-base potentiometric titration setup conditions on the observed PZC, including co-existing ions, ionic strength of the solution, pre-equilibrium time, titration ranges, reaction atmosphere and titration method, is summarized and discussed. Furthermore, the research progresses on the application of potentiometric titration combined with surface complexation model (SCM, including diffuse layer model, basic stern model, triple layer model and distribution multi-site complexity and so on) to analyze the acid-base buffering capacity of variable charge soils were further summarized. Moreover, how related factors such as clay mineral composition, metal oxides, organic matter and other factors, affect the acid-base buffering capacity of variable charge soils are discussed. We believe that future studies on the variable charge soils could be carried out with the hope to: (1) establish a typical acid-base potentiometric titration method for all types of soils; and (2) verify if the combination of various surface complexation models could accurately quantify the acid-base buffer capacity of variable charge soils. It is hoped that this review can help soil science beginners to understand the basic concepts of variable charge soils, invite more researchers to pay more attentions to variable charge soils, and further encourage sustainable utilization of soil resources.

      • Leaching is the Main Pathway of Nitrogen and Phosphorus Losses for Citrus Orchards with Sandy Soil in Three Gorges Reservoir Area

        LI Hongying, WANG Sichu, GAO Mengning, XIA Lizhong, HAN Qingzhong, WANG Qinglong, WU Yonghong

        DOI: 10.11766/trxb202010200584

        Abstract:

        【Objective】Citrus production is one of the main income of farmers in the Three Gorges Reservoir area. The loss of nitrogen and phosphorus caused by excessive fertilizer in the Three Gorges Reservoir area present negative impacts on the aquatic environment. 【Methods】In this study, sandy soil citrus orchard with natural grass mulching was chosen. The amount of nitrogen and phosphorus loss from surface runoff and leaching was observed for two consecutive years by plot experiment at six levels of fertilization. The pathways of nitrogen and phosphorus losses in the citrus orchard and the effects of different fertilization levels on nitrogen and phosphorus losses were investigated. Seven treatments were set in the experimental plot, with an average row and plant spacing of 4.7 m × 3.4 m; with no fertilizer application (T1) as the control, the application rates of nitrogen, phosphorus and potassium fertilizer for the T3, T4, T5, T6 and T7 treatments were 1.67, 2.33, 3.00, 3.67 and 4.33 times those of T2, respectively. During the growth season of navel orange in 2016—2017, rainfall and atmospheric deposition of nitrogen and phosphorus were monitored. Surface runoff water, sediment, and infiltration water were sampled for total nitrogen (TN) and total phosphorus (TP) content. 【Results】 Under the ecological protection mode of grass mulching, the surface runoff and soil erosion were effectively controlled. The main pathway of water loss in the rain-fed citrus orchard was leaching with a low coefficient of surface runoff and weak soil erosion. During the study period, the rainfall loss by seepage accounted for 48.9% of the rainfall, and the surface runoff only accounted for 1.73% of the rainfall. The amount of fertilization applied in deep furrow had no effect on the amount of nitrogen and phosphorus loss from the surface runoff. Leaching was the main pathway of nitrogen and phosphorus loss. The average leaching loss of total nitrogen and total phosphorus accounted for 99.0% and 76.9% of the total loss of nitrogen and total phosphorus respectively. Also, the amount of nitrogen loss (y) by seepage increased with the increase of application rates (x), and there was a significant linear correlation between them (y = 0.35x-5.77, P<0.01). However, no significant correlation existed between the amount of phosphorus loss and application rates (P = 0.05). Also, only a small amount of phosphorus can be leached to the bottom of the soil after the roots uptake and soil particles adsorption in up layers. Moreover, the residual phosphorus in the deep soil; after deep plough before citrus planting, had an impact on the leakage of phosphorus. 【Conclusion】The problem of nutrient loss; leaching nitrogen loss in citrus orchards, in particular, should be given more attention. To reduce nutrient loss and achieve efficient utilization, nutrient management should be further optimized.

      • Identifying the Status of Heavy Metal Pollution of Cultivated Land for Tradeoff Spatial Fallow in China

        ZENG Siyan, YU Haochen, MA Jing, LIU Junna, CHEN Fu

        DOI: 10.11766/trxb202009270541

        Abstract:

        【Objective】 Farmland pollution affects national food safety and public health. From the perspective of soil pollution, clarifying the scale and spatial layout of fallow land at the national scale is of great importance. To restore heavy metal-contaminated farmland soils and ensure green development of agriculture, an urgent scientific solution is needed for soil pollution. In recent years, fallow has been pioneered as a means of recuperation and management of polluted farmland. However, some important management issues such as how much farmland should be fallowed, location of the fallow area, and how to fallow are yet to be defined at the national scale.【Method】 In this study, we constructed a database of heavy metal pollution in Chinese farmland soils which comprised of 6 490 sample data from 2 343 farmland locations. These data were extracted from 569 published papers on the topic of farmland heavy metal pollution (Including combined pollution and single heavy metal pollution, such as Ni, Hg, As, etc.), published from 2000 to 2018 on Web of Science and China National Knowledge Infrastructure (CNKI). We assessed heavy metal pollution, the influence index of soil comprehensive quality, and the potential ecological risk to identify the spatial distribution of fallow priority grades, including urgent-fallow zone (I), regular-fallow zone (II), controlled-rotation zone (III), and general-rotation zone (IV). 【Result】 The results showed that the excessive concentration rates of heavy metals was Cd (18.03%)>As (2.95%)>Ni (2.26%)>Hg (1.55%)>Zn (1.42%)>Pb (1.34%)>Cu (0.49%)>Cr (0.10%). The proportions of soil environmental quality index such as severely, moderately and slightly exceeded were 1.71%, 3.89% and 23.84%, respectively. Also, the ratio of extremely strong and very strong potential ecological risk accounted for 0.29% and 2.89%. The ratio of the fallow area in China due to soil heavy metal pollution is 15.58%, of which the proportions of level I, II and III are 0.77%, 1.53% and 3.26%, respectively. Level I fallow areas are mainly distributed in 8 provinces of China including Henan, Hunan, Yunnan, Anhui etc. Additionally, fallow areas are mainly distributed in Henan and Hunan province, followed by Liaoning and Shandong province.【Conclusion】 To promote the remediation of heavy metal pollution in Chinese surface soils, the implementation of differentiated fallow strategies for farmland areas with different pollution levels is recommended. This study shows the status of heavy metal pollution in farmland soils and spatially identified the urgency of fallowing areas in China. It also provides theoretical support for controlling farmland soil pollution and fallow space-time allocation in China.

      • Estimation of Soil Total Nitrogen Density and Storage in Fujian Province by Using 1:50 000 Soil Database

        ZHANG Liming, CHEN Zhongxing, ZHANG Nan, HUANG Kai, QIU Longxia, CHEN Hanyue, XING Shihe, SHEN Jinquan

        DOI: 10.11766/trxb202008100447

        Abstract:

        【Objective】Soil total nitrogen (STN) plays an important role in terrestrial ecosystems, and hence is of great significance to mitigating the greenhouse effect and water eutrophication. Any slight changes in the STN pool will pose an important impact on global climate. It is, therefore, essential to make a precise estimation of STN density and storage in the effort to optimize nitrogen fertilizer management. However, so far most of the studies on estimation of STN have been done based on medium or small scale soil maps, and few have been reported to be based on provincial level detail soil databases. Consequently this study on STN estimation based on a provincial level soil database may help implement agricultural sustainable development with data support, and design agricultural management strategies.【Method】In this study, based on the most detailed soil database of Fujian Province, consisting of 3 082 sampling profiles and a 1:50 000 soil map, analyses were carried out of spatial distributions of STN storage and density in the surface soil layer (0 ~ 20 cm) and soil profile (0 ~ 100 cm), in the bulk soil of the main types of soils of the Province as well as in the soils of different administrative divisions of the Province. The pedological knowledge based method, i.e, PKB, was used to correlate soil attributes with soil spatial data. So the 1:50 000 scale soil map consisted of 247 969 soil patches and 3 082 soil profiles. 【Result】Results show that Fujian province has a total of 12.08 x 106 hm2 of soils. The STN density in the surface soil layer and soil profile of the province was averaged to be 0.35 kg?m-2 and 0.97 kg?m-2, respectively, while the STN storage was 42.06 Tg and 116.83 Tg, respectively. Analysis of the soils by prefecture shows that Nanping City was the highest, being 0.40 kg?m-2 and Longyan followed, being 0.39 kg?m-2 in STN density in surface soil, whereas Nanping City was the highest, being 1.19 kg?m-2 in and Sanming City followed, being 1.11 kg?m-2 in STN density in profile soil. Zhangzhou City was the lowest, being 0.24 kg?m-2 and Xiamen City the next, being 0.27 kg?m-2 in STN density in surface soil, whereas Zhangzhou City was the lowest, being 0.67 kg?m-2 and Putian City the next, being 0.71 kg?m-2 in STN density in profile soil. In terms of soil type, Mountain meadow soil was the highest, being 0.85 kg?m-2 and Skeletal soil followed, being 0.57 kg?m-2 in STN density in surface soil, whereas Mountain meadow soil was the highest, being 2.09 kg?m-2 and Yellow soil followed, being 1.27 kg?m-2 in STN in profile soil. Aeolian soil was the lowest, being by 0.11 kg?m-2 and Latosolic red earth the next, being 0.17 kg?m-2 in STN density in surface soil, whereas Aeolian soil was the lowest, being 0.27 kg?m-2 and Latosolic red earth the next, being 0.53 kg?m-2 in STN in profile soil. 【Conclusion】Consequently, the STN density in the surface and profile soil of Fujian demonstrates a declining trend from north to south, and from inland to coastal area, too. To sum up, the STN in Fujian Province varies significantly in spatial distribution. The findings in this study may be helpful in designing agricultural management strategies and controlling non-point source N pollution in the province.

      • Effects of Biochar-based Fertilizer on Physiology and Nitrogen Uptake of Flue-cured Tobacco and Nitrogen Balance in Yellow Soil

        CHEN Yi, LIN Yingchao, YANG Zhixiao, CHENG Jianzhong, WANG Zhihong, KONG Dejun, WU Chun, LIN Yechun

        DOI: 10.11766/trxb202009290375

        Abstract:

        This study was conducted to explore effects of biochar-based fertilizer on physiology and nitrogen uptake of flue-cured tobacco and nitrogen balance in the yellow soil-flue-cured tobacco system, which will provide certain scientific guidance for optimizing nitrogen management in the yellow soil of the tobacco-planting areas in Guizhou and reducing pollution in the ecological environment of the farmland of tobacco-planting areas in Guizhou. A field experiment, carried out with flue-cured (Yunyan 87) in yellow soil for the study, was designed to have three treatments, i.e. no nitrogen (CN), conventional fertilizer (CF), biochar-based fertilizer (BF). Results show that Treatment BF significantly increased soil urease activity, root length and surface area, glutamine synthase and glutamate synthetase activities in leaves, and nitrogen uptake of flue-cured tobacco. Treatment BF was significantly 35.06%and 14.24% higher than Treatments CN and CF in nitrogen uptake of flue-cured tobacco, respectively. Treatment BF was the highest in activity, volume and dry biomass of root and yield of flue-cured tobacco, and significantly higher than Treatment CN. Nitrogen surplus was obviously detected in the yellow soil-flue-cured tobacco system in all the treatments, the nitrogen input was mainly the initial soil inorganic nitrogen, while the nitrogen output consisted mainly of soil inorganic nitrogen residue and nitrogen uptake of flue-cured tobacco. Treatment BF increased inorganic nitrogen residue in the 0-20 cm soil layer. Moreover, Treatment BF decreased nitrogen apparent loss significantly by 44.42 kg?hm-2, and decreased nitrogen surplus by 37.70 kg?hm-2, and significantly increased nitrogen apparent recovery efficiency by 16.15%. Therefore, the reasonable application of biochar-based fertilizer is an effective way to optimize management of nitrogen in the yellow soil and protect ecological environment of tobacco-planting areas in Guizhou.

      • Co-precipitation-Triggered Molecular Fractionation of Dissolved Organic Matter at the Ferrihydrite/Water Interface

        Han Lanfang, Yang Yan, Sun Ke

        DOI: 10.11766/trxb202009030393

        Abstract:

        【Objective】As the most dynamic and bioavailable fraction of the soil carbon pool, dissolved organic matter (DOM) plays important roles in a wide range of biogeochemical processes in the environment. The interaction of soil minerals with DOM would induce structural fractionation of the DOM at the mineral/water interface, thereby influencing long-term preservation and biogeochemical processes of the DOM in the soil. Ferrihydrite, a poorly crystalline iron oxide, is known to be highly reactive to DOM in the soil owing to its high specific surface area and abundant reactive binding sites. Widespread in the environment, it can associate with DOM through either adsorption or co-precipitation. However, so far, few studies have been reported on structural fractionation of DOM at the ferrihydrite/water interface induced by co-precipitation at the molecular level. 【Method】To explore molecular fractionation of DOM at the ferrihydrite/water interface during its co-precipitation process, this study prepared ferrihydrite-DOM complex separately in solutions different in C/Fe ratio via co-precipitation and adopted the technology of combining ultraviolet (UV) spectrum with electrospray ionization Fourier transform ion cyclotron resonant mass spectrometry (ESI-FT-ICR-MS) to probe changes in DOM composition after co-precipitation ended. Species of carbon and Fe in the complex were determined with the aid of X-ray photoelectron spectroscopy (XPS) and Fe K edge XAS.【Result】Results show that Fe in the complex existed mainly in the form of ferrihydrite, of which the proportion gradually decreased from 95.9% to 68.0% with the increase in initial C/Fe ratio of the solution. UV and ESI-FT-ICR-MS analysis collectively revealed that during the co-precipitation process, ferrihydrite fixed in priority aromatic components high in molecular weight and rich in oxygen (mainly combustion-derived condensed polycyclic aromatic- and vascular plant-derived polyphenols-like substances) in the DOM, leaving aliphatic components in the solution. The lower the solution in C/Fe ratio, the higher the molecular fractionation in degree. This feature is basically consistent with what has been reported about the fractionation induced by adsorption, which indicates that no matter whether in the process of adsorption or co-precipitation, ferrihydrite tends to fix DOM components high in molecular weight and aromaticity, thus leading to changes in chemical composition of the DOM as well as surface properties of the ferrihydrite, which will in turn affect sorption, transportation and transformation processes of the contaminants therein. In addition, this study was the first to find that ferrihydrite varied dynamically with the reaction in time in selectivity to structure of the DOM, that is, combustion-derived condensed polycyclic aromatics were preferentially fixed in the ferrihydrite-DOM complex, and with the reaction going on, vascular plant-derived polyphenols-like substances followed.【Conclusion】The findings in this study are expected to be able to help understand in depth the mechanism of molecular fractionation that affects geochemical behavior of DOM in the environment via co-precipitation during the process of ferrihydrite formation.

      • Characteristics of Soil Electrochemical Properties and Soil Environmental Impact Factors in Karst Ecosystem in South West China

        ZHAO Chu, SHENG Maoyin, LI Yuxuan, BAI Yixin, LIU Shuxi

        DOI: 10.11766/trxb202007200407

        Abstract:

        【Objective】 Soil surface is the main place for various chemical and biochemical processes in soil and most of the negative charges are concentrated here. The five electrochemical characteristics; surface potential, surface charge density, surface electric field strength, specific surface area, and surface charge, deeply affect a series of physical and chemical processes in soils. Therefore, an accurate understanding of the electrochemical properties of soil surface has extensive and profound significance for the prevention and control of soil erosion, soil management and regulation, vegetation restoration and reconstruction in karst areas. However, it is still unclear how soil surface charge properties evolve with environmental factors change in different succession stages of rocky desertification.【Method】 For this study the method of combined analysis of surface properties was applied to measure surface potential, surface charge density, surface electric field strength, specific surface area, and surface charge of the soils varying in different rocky desertification grades in Anshun area. Correlation and redundancy analyses were used to explore the effects of soil environmental factors on its surface electrochemical properties. 【Result】 Soil surface charge density, surface electric field strength, specific surface area, and surface charge decreased with the increase in rocky desertification intensity, and the variation range was 0.34 C·m-2~0.42 C·m-2, 4.85×108 V·m-1~5.86×108 V·m-1, 47.11 m2·g-1~53.16 m2·g-1, 16.86 cmol·kg-1~22.82 cmol·kg-1, respectively. Also, the soil surface potential increased with the increase in rocky desertification intensity and the variation range was -113.74 mV~-115.10 mV. Soil clay, sand, amorphous alumina, and humic acid were the main factors affecting soil surface electrochemical properties change, and the interpretation rates were 48.3%, 38.1%, 13.0% and 12.0%, respectively. The effects of soil particle size composition, organic matter composition, and metal oxides on soil surface electrochemical characteristics were as follows: soil clay > sand > silt, humic acid > organic carbon > fulvic acid, and amorphous alumina > free iron oxide > amorphous iron oxide. 【Conclusion】 Our study revealed that during the succession of karst rocky desertification, soil physical properties, chemical properties, and oxide content changed significantly, and this led to changes in soil surface electrochemical properties.

      • Effect of Long-term Elevated CO2 Concentration on CH4 Emissions from Rice Paddy Fields

        XU Hua, YU Haiyang, WANG Tianyu, HUANG Qiong, ZHANG Guangbin, MA Jing, ZHU Chunwu

        DOI: 10.11766/trxb202009110515

        Abstract:

        【Objective】Increases in atmospheric CO2 concentration have certain direct or indirect impacts on CH4 emission from rice paddy fields. So it is of great significance to have an in-depth study on impacts of long-term elevated atmospheric CO2 concentration on CH4 emission and related microorganisms for assessing and managing CH4 emissions from rice paddy fields in the context of future climate.【Method】To investigate effects of long-term elevated atmospheric CO2 concentration on CH4 emission and its mechanism, CH4 emission fluxes and abundance of the methanogens and methanotrophs under ambient CO2 (ACO2) and elevated CO2 conditions (ECO2) in rice paddy fields were monitored during the 2016-2017 season, with the aid of the Chinese rice FACE platform that has been operating for more than 10 years. Moreover, meta-analysis was conducted to determine quantitatively effects of elevated CO2 relative to duration on CH4 emission from and the abundances of methanogens and methanotrophs in rice paddy fields.【Result】Results show that compared with ACO2, long-term ECO2 significantly reduced CH4 emission and the abundance of methanogens by 28% and 39%, respectively (P<0.05), but increased the abundance of methanotrophs by 21% (P>0.05). Meta-analysis shows that with the increase in duration of CO2 elevation, the effect of elevated atmospheric CO2 concentration promoting CH4 emission and the abundance of methanogens gradually decreased, while the effect on the abundance of methanotrophs gradually increased.【Conclusion】Therefore, it could be concluded that under future climate conditions, long-term elevated CO2 will reduce CH4 emission from rice fields, which is of great significance for mitigating the greenhouse effect brought about by rice cultivation.

      • Migration and Risk of Loss of Soluble Organic Nitrogen in Paddy Soil After Incorporation of Chinese Milk Vetch

        XING Shihe, YANG Jing, GUO Wenqi, YANG Wenhao, ZHOU Biqing, ZHANG Liming,

        DOI: 10.11766/trxb202009100469

        Abstract:

        【Objective】Soluble organic nitrogen (SON) is one of the most active components of the soil nitrogen pool in farmland and plays an important role in nitrogen transformation and ecological environment security. As SON is highly mobile, it is prone to get lost with runoff or leaching, and thus, and hence affect water quality. 【Method】To provide a theoretical basis for rational fertilization in paddy fields, prevention and control of non-point source nitrogen pollution from paddy fields and improvement of the theory of nitrogen cycling, a field experiment, designed to have the following treatments, all equivalent in nutrient content, i.e. CK (application of chemical fertilizer only), CMV1 (application of chemical fertilizer plus incorporation of milk vetch at 15 000 kg?hm-2); CMV2 (application of chemical fertilizer plus incorporation of milk vetch at 30 000 kg?hm-2 ); and CMV3 (application of chemical fertilizer plus incorporation of milk vetch at 45 000 kg?hm-2), was carried out to explore dynamics, migration and loss of SON and dissolved organic nitrogen (DON) in grey-mud field soils. Soil samples from the treatments were analyzed for SON, respectively, using the hot water extraction method. SON concentrations were calculated by deducting TSN from the sum of SIN in the extracts. 【Result】During the growing period of rice, SON content in the 0-60 cm soil layer varied in the range from 2.09 to 22.32 mg?kg-1, showing a trend of "increasing - decreasing - increasing - decreasing to stable". In the treatments the SON concentration was 140.95% and 364.44%, higher in the 0-20 cm soil layer, respectively, than in the 20-40 cm soil layer and the 40-60 cm soil layer, and 92.75% higher in the 20-40 cm soil layer than in the 40-60 cm soil layer. It is quite obvious that incorporation of Chinese milk vetch during the growth period of rice is beneficial to accumulation of SON in the soil (0-60 cm). In SON concentration in the 0-60 cm soil layer during the rice growth period, Treatment CMV1, CMV2 and CMV3 was 5.57%, 10.11% and 21.39%, respectively, higher than CK. Total loss of DON from the grey-mud fields under different fertilization treatments ranged from 18.33-58.55 kg?hm-2, accounting for 46.52%-50.16% of the TSN. Of the total loss, 3.77-37.85 kg?hm-2 was attributed to runoff, while 14.5-18.02 kg?hm-2 to leaching. Moreover, leaching of DON between soil layers was delayed to some extent. Compared with CK, Treatment CMV1, CMV2 and CMV3 was 16.90, 31.09 and 37.52 kg?hm-2, respectively, lower in DON loss.【Conclusion】Incorporation of milk vetch can increase the accumulation of SON in the 0-60 cm soil layer of the grey-mud field and promote the migration of SON. However, the effects decline with soil depth. DON is one of the important forms of nitrogen loss in paddy fields. Incorporation of milk vetch can reduce DON loss and then mitigate non-point source N pollutant from the paddy fields. The environmental impact of the loss of DON from paddy fields is worthy of attention. If only the loss of inorganic nitrogen with leaching of paddy soil solution is considered, the total nitrogen loss from paddy fields will be underestimated.

      • Effects of Fertigation on Nitrogen Use Efficiency and Ammonia Volatilization in Greenhouse Tomato Cultivation in Lower Reaches of the Yangtze River

        WANG Yuan, XU Jiyuan, PAN Yunfeng, ZHAO Dongqing, YANG Dongping, JU Shengrong, MIN Ju, SHI Weiming

        DOI: 10.11766/trxb202007260420

        Abstract:

        【Objective】Greenhouse vegetable production in China has played an important role in ensuring market vegetable supply and increasing the income of farmers. As in the greenhouse vegetable production, a high rate of fertilizer was applied, the production brings about a series of environmental problems, such as soil degradation and increased risk of greenhouse gas emission, which undermines the sustainability of the greenhouse vegetable production. In the lower reaches of the Yangtze River, the problem of non-point source pollution and labor shortage the greenhouse vegetable production faces are prominent. It has become an urgent need to have some labor-saving, efficiency-enhancing, and environment-friendly fertilization techniques. Fertigation is a technology that can save both water and fertilizer, improve fertilizer utilization efficiency, and reduce greenhouse gas emission. Fertigation is mainly applied in greenhouses in the water-deficient areas in North China, and no so common in the lower reaches of the Yangtze River. So little is available in the literature about the effects of fertigation on emission reduction and efficiency improvement in this area. 【Method】 In this study, a field experiment, designed to have three treatments, i.e. CK (no N fertilizer applied), SF (chemical fertilizer broadcast) and DF (fertigation), was conducted in Yixing, Jiangsu. Tomato (Solanum lycopersicum) was grown in a row of plastic greenhouses. In Treatment SF, chemical fertilizer was broadcast three times, one base application and two topdressings, making up a total of 225 kg·hm-2 nitrogen (N), and in Treatment DF, 225 kg·hm-2 fertilizer was divided into five portions applied with irrigation separately as topdressing. Then, yield, N use efficiency, ammonia volatilization rate, and soil soluble N were measured for each treatment and systematically analyzed. 【Result】 Results show that fertigation significantly improved N use efficiency, and reduced soil ammonia volatilization rate and cumulative ammonia emissions, as compared with the treatment with fertilizer broadcast at the same N application rate. Treatment DF increased N use efficiency from 23.92% to 40.89% and was 71.10% higher than Treatment SF, and reduced cumulative ammonia emission from 37.25 kg·hm-2 to 3.07 kg·hm-2, and the ammonia loss rate from 16.56% to 1.36% during the entire tomato growth period. In Treatment CK, SF and DF, the mean NO3--N residue in soil was 32.18, 45.70, and 67.06 mg·kg-1, and the mean NH4+-N residue in the 0~50 cm soil layer was 3.07, 8.27, and 19.27 mg·kg-1, respectively. Fertigation significantly reduced the soil NO3--N residues by 31.85% as compared to the treatment of fertilizer broadcast. However, it increases the risk of N leaching to some extent. 【Conclusion】 Fertigation is an efficient method combining irrigation and fertilization, which can significantly improve N use efficiency and reduce ammonia volatilization loss and soluble N residues, when applied to greenhouse vegetable fields in the lower reaches of the Yangtze River. All the findings of the research may serve as a scientific basis for extrapolation of the technique of fertigation in the Lower Yangtze River Region.

      • Effects of Hexachlorocyclohexane on Bacterial Community in Red and Purple Soils in Terms of Variaty and Structure

        Tang Kai Di, Gao Nai Zheng, Liu Juan, Ling Wan Ting

        DOI: 10.11766/trxb202008200416

        Abstract:

        【Objective】 Although hexachlorocyclohexane (HCH) has been banned as pesticide in agriculture for decades, its residue, still high in concentration, has been frequently observed in soil due to its property of persistentcet, So it remains to be an important task to well elucidate how HCH affects soil microbial communities in diversity and structure, and a topic of great significance to ecological health of the agro-environment systems.【Method】In this work, a greenhouse experiment was conducted, in red and purple soils grown with wheat, spiked with HCH at a rate of 0, 600, or 1500 g/ha. Soil bacterial community structure and diversity in the soils were determined using the high throughput sequencing technique. Total DNA in the soil samples were extracted using the Power Soil DNA Isolation Kit, a product of from MOBIO and tested with 1% agarose gel electrophoresis for quality. Compositions of the soil microbial communities were characterized with the sequencing technique.【Result】Alpha index analysis revealed that HCH significantly increased diversity of the bacterial community in the red soil, while no significant effect was observed in the purple soil at the beginning of the wheat cultivation. However, after 42 days of cultivation, no significant differences were found between the soils spiked with HCH and CK in soil bacterial community diversity in the soils. Analysis of bacterial community compositions showed that Proteobacteria and Actinobacteria were the dominant phyla at the phyluma level, and HCH increased the diversity of Actinobacteria and Acidobacteria in the red soil, while Proteobacteria and Acidobacteria were the dominant ones in the purple soil. Relative abundance of Bradyrhizbium in red the soil increased with the spiking rate of HCH, and its abundance did about 150% and 180% in the soils spiked with 600 and 1 500 g?hm-2 HCH, as compared ing with that in the control treatment. However, in the purple soil, relative abundance of the nitrogen-fixing bacteria decreased with the addition of HCH.【Conclusion】The residue of HCH obviously induced the changes in diversity and structure of the of soil bacterial community in the soils, and the impact was more obvious in the red soil than in the purple soil. The findings provide a basis for understanding of the micro-ecological effects and safety assessment of HCH in the soil environments.

      • Magnetic Characteristics of Yellow-Red Soil and Transformation of Its Magnetic Minerals, in Zhouning, Fujian Province

        LIU Xin, LÜ Bin, ZHENG Xingfen, CHEN Zixuan, DU Jiahao

        DOI: 10.11766/trxb202008240424

        Abstract:

        【Objective】In order to explore magnetic characteristics of the yellow-red soil in the subtropical region and transformation of the magnetic minerals in the soil under relatively humid and cold climate conditions, the author selected a profile of yellow-red soil (Profile ZN) derived from granite weathering crust in Zhouning County, northeast of Fujian Province. Under a mid-subtropical monsoon mountain climate, this area had an average annual temperature of 15 ℃, an average annual rainfall of 2 049.3 mm, and an elevation of 906.4 m counted from the bottom of the profile. The profile was about 1.9 m thick. With the floating soil on the surface removed, a total of 20 samples were collected at 10 cm intervals from the soil and weathering crust layers of the profile.【Method】In this study, room temperature magnetic parameters of the samples were measured, and thermomagnetic analysis conducted of representative samples, in combination of chroma, major geochemical elements and diffuse reflectance spectrum analyses.【Result】Results show: The profile was low in magnetic susceptibility, and relatively low in content of magnetic minerals, the upper part of the profile contained relatively more superparamagnetic particles, while the lower part did relatively more multi-domain particles. a*, b* and Ca*b* varied in the same trend, being the highest in Horizon B and the lowest in Horizon C, while b*/a* was high in the profile surface. The content of Fe2O3 increased with the degree of pedogenesis, indicating that during the soil forming process, other elements were leached while iron accumulated relatively. Iron content was not a major factor limiting magnitude of magnetic susceptibility. The profile was lower than those in the humid and hot low altitude tropical and subtropical regions in CIA (chemical index of alteration).【Conclusion】By comparing this profile with the three (NPN, PC-GL, PC-SY) in the adjacent area, the following conclusions were drawn: (1) Profile ZN contains relatively less magnetic minerals, which are composed of mainly ferrimagnetic mineral and small portions of maghemite, antiferromagnetic minerals hematite and goethite as well as paramagnetic minerals. Moreover, its content of goethite is higher than that of hematite. The magnetic particles in the lower part of the profile are coarser, and mainly multi-domain particles. And the particles get finer, and the portions of single-domain and superparamagnetic particles increase with decreasing soil depth. (2) Parent material and climatic conditions are two important factors contributing to the difference in magnetic characteristics between different profiles, and the climate conditions are the main ones controlling the content of secondary magnetic minerals (especially hematite and goethite). Chroma index b*/a* can be used to measure the content of goethite/hematite. (3) Under a relatively humid and cold climate the transformation of magnetic minerals in the soil is dominated by the transformation of strong magnetic minerals (magnetite and maghemite) into weak magnetic minerals (hematite and goethite). (4) Temperature, instead of precipitation, is the dominant factor influencing the content and relative proportion of goethite and hematite in the soil derived from granite weathering crust in humid subtropical regions.

About

Supervisor: Chinese Academy of Sciences

Sponsor:Soil Science Society of China

Editor-in-Chief:Xu Renkou

Address:71 East Beijing Road, Nanjing 210008, P. R. China

Zip Code:210008

Phone:+86-25-86881237

Email:actapedo@issas.ac.cn

ISSN:0564-3929

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