• Volume 56,Issue 2,2019 Table of Contents
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    • >Insights and Perspectives
    • Prevention and Remediation of Soil Contamination to Strengthen the Foundation for Green and High-Quality Agricultural Development in China

      2019, 56(2):251-258. DOI: 10.11766/trxb201901200043

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      Abstract:How to take scientific and effective countermeasures to prevent and remediate soil contamination, so as to ensure the quality and safety of agricultural products, has become a great public concern in China. This paper illustrated the status and functions of soil in the new era; reviewed the progress in research and development on agricultural soil contamination control and remediation. Furthermore, the strategic focus and technical approach for science and technologies on soil contamination prevention, control and remediation, along with their industrial applications, were proposed to promote the green and high-quality agricultural development.

    • >Reviews and Comments
    • Advancement in Research on Bacterial Chemotaxis in Soil

      2019, 56(2):259-275. DOI: 10.11766/trxb201807210385

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      Abstract:In the geoecosystem, soil is an important component, the highest in vitality, because of its unique pore structure, which accommodates numerous micro lives, the highest in abundance and diversity in the biosphere, and plays numerous regulatory and provisional functions essential to life. Soil is a steadily evolving and developing ecosystem. The microorganisms therein are at the core of the soil ecological functions that drive the key biogeochemical cycles of carbon, nitrogen and other elements. Evolving systems of the soil microbes enable them to adapt themselves rapidly to any dynamic changes in local environment. Chemotaxis is an instinct bacteria have acquired through long-term evolution to help them hunt for food or move along nutrient gradients or away from toxicants. Heterogeneous distribution of nutrients, exogenous contaminants, and water is the main factor triggering bacterial chemotaxis everywhere in soil, which in turn always affect configuration of soil microbial community and its spatial and temporal distributions. In recent years, bacterial chemotaxis in soil has become a hot spot of focus of the study on soil microbiology both at home and abroad and this trend is likely to continue in the near future. In this review, attempts were done to summarize frontier issues and advancement of the researches the world over on soil bacterial chemotaxis, to elucidate modes of bacterial chemotactic behaviors, conduction paths of bacterial chemotactic signals, and mathematical models for bacterial chemotaxis, with a particular focus on soil bacterial chemotaxis, to explore phenomena of bacterial chemotaxis existing universally in the soil and to introduce main technical means involved in the research, such as fluorescence in situ hybridization, microfluidics and microscopy. In the end, prospects are presented of the trend and development of the research in a view to providing certain references for researches to and practical application of the study on microbial chemotaxis in future.

    • Progress in Researches on Diphenylarsinic Acid Pollution of Soil-water Environment and Its Remediation

      2019, 56(2):276-287. DOI: 10.11766/trxb201806070306

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      Abstract:Chemical warfare agents containing organoarsenic compounds such as Clark I (diphenylcyanoarsine) and Clark II (diphenylchloroarsine) were widely produced and used during World Wars I and II. After the wars, remains of these agents were simply dumped into the sea or buried underground, thus inevitably polluting the soil-water environments of the sits where they were disposed with the arsenic contained in the chemical weapons. In the environment, these abandoned chemical agents are easily hydrolyzed and oxidized into diphenylarsinic acid (DPAA), rather stable in structure, and other organoarsenic compounds. So far, DPAA has been detected in quite a number of the areas where these chemical weapons were dumped. The detection has aroused extensive concerns because the presence of DPAA may bring about environmental and health risks. Scholars both at home and abroad have already begun doing some researches, trying to find ways to analyze DPAA in the soil and water environments, determine their status and behaviors and remedy the polluted environments. However, few have done any to summarize systematically progresses in the research. In this paper, a review is presented to introduce some high-effect inorganic and organic extractants and GC as well as LC analytical methods for DPAA in the soil, and sources and status of the pollutant in the soil-water environments. Generally speaking, the DPAA contaminated areas are located mainly in Northeast China, and South and Southeast Japan. Especially in the chemical weapons dumping sites, the concentration of total arsenic is far beyond the criteria for safety. At the same time, the paper also discusses how DPAA is adsorbed/desorbed, translocated and transformed in the soil-water environment, what are the factors affecting the processes and what are the mechanisms. Studies in the past reported that the adsorption/desorption of DPAA in soil was controlled by a variety of factors, including pH, inorganic ions, Fe/Al oxides, organic matter, redox potential (Eh), etc. and adsorption of the substance was completed via ligand exchange reactions between hydroxyl groups of Fe/Al oxides and arsenate of DPAA, rather than the hydrophilic effect of organic matter; the effective transformation of DPAA in the soil occurred under flooded anaerobic conditions, and under sulfate-reducing conditions, in particular; and iron reduction and sulfate reduction were the two key factors controlling desorption and transformation of DPAA. In the end, the paper elaborates the physical, chemical and biological technologies available for remediation of DPAA contaminated soil-water environments, and their remediation efficiency, controlling factors and mechanisms as well. In terms of physic-chemical remediation, application of activated carbon, Fenton and Fenton-like oxidation and photochemical degradation has been demonstrated to be able to effectively remove DPAA in soil-water environments. In terms of bioremediation, certain progresses have been made, like screening of highly efficient DPAA degrading bacteria, unfolding microbial remediation and combined microbial-phytoremediation and previewing directions of the future researches. The paper holds that all the relevant research findings will serve as theoretical reference for future in-depth studies on DPAA pollution of soil-water environments, remediation of DPAA polluted environments, and protection of environmental quality and human health from DPAA pollution. For further researches, emphases should be laid on the following aspects: (1) To perfect quality assurance and quality control system for DPAA analytical methods, with focus on development of standard alternatives, purgation of internal standards and markers; (2) To launch investigations on scope and extent of DPAA contamination, while taking into the consideration of geographical locations, soil types and land-use patterns of the chemical weapon burial sites; (3) To explore forms of DPAA bonding with soil colloids, clay minerals and oxides in the soil and molecular binding mechanisms, and elucidate the mechanisms responsible for adsorption/desorption, translocation and transformation of DPAA in multi-media environment and at microscopic interfaces; (4) To explore for develop new remediation materials, intensify researches on physic-chemical-phyto combined remediation and continue to screen out highly efficient DPAA degrading bacteria and probe mechanisms of their effectiveness at molecular as well as genetic levels, while integrating genetic engineering, molecular biology with phytoremediation technologies, so as to eventually establish a bioremediation technical system applicable to DPAA contaminated media different in type and condition.

    • >Research Articles
    • Distribution and Formation Environment of Fe-Mn Nodules in Soils Derived from Quaternary Loess in North China

      2019, 56(2):288-297. DOI: 10.11766/trxb201802250024

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      Abstract:【Objective】Fe-Mn nodules in soils, pedogenic products of the soils, contain a lot of information related to soil-forming processes and variation of soil-forming environment and can be used as important basis for soil classification. So distribution of Fe-Mn noudles plays an important role in understanding of the mechanism of Fe-Mn noudles formation and soil classification. It is generally believed that Fe-Mn noudles are mainly distributed at lowlands with shallow groundwater table. However, Fe-Mn nodules are found in uplands with deep groundwater table in Northeast of China, which causes a lot of problems in soil classification in this region. The objectives of this study were to explore the spatial distribution of soil Fe-Mn nodule and explore the environment and mechanism of their formation in North China. The principles for selecting soil profiles were: (1) choose soil profiles situated in stable uplands with deep groundwater table, to ensure that the soils are not affected by groundwater, and in uplands free of obvious evidence of erosion and deposition in the processes of soil formation; (2) pick soils developed from the Quaternary loess-like materials, to ensure that soils were derived from the same parent materials as much as possible. 【Method】A total of 345 soil profiles, based on the soil series survey in 2010’s and the legacy data of the Second National Soil Survey (SNSS) during 1980’s, were prepared in 10 provinces in the temperate zone of North China. Whether the Fe-Mn nodules were presence or not in each soil horizon was examined. The mean annual precipitation (MAP) and mean annual temperature (MAT) of each soil sample site was retrieved from the China Meteorological Science Data Sharing Service. Relationships between formation of Fe-Mn nodules in soils and climate conditions of soil-forming were analyzed. 【Result】 Results show that Fe-Mn nodules were found in 74 profiles or 21.5% of 345 soil profiles studie in totald. The soil profiles with Fe-Mn nodules are distributed mainly in a region, 120.82°~133.37° E and 41.19°~49.01° N, a part of the humid temperate zone, where MAP is 370.6 mm~ 917.7 mm, and MAT 0.9℃ ~14.9℃. In winter the soils there in remain frozen for a long time, and in spring they undergo a long period of freezing-thawing alternation, with the surface soil getting pulpy, because soil water keeps moving up in the topsoil layer when it gets frozen in winter and when the frozen topsoil begins to thaw, soil water remain in the topsoil layer making it pulpy in early spring because the subsoil layer is still not thawed, preventing the water in the topsoil layer from percolating down. This results in a reducing environment close to the freezing layer for a period of time before the frozen soil thaws thoroughly, which lays a solid foundation for the formation of Fe-Mn nodules. 【Conclusion】 It is, therefore, concluded that the formation of Fe-Mn nodules in stable upland soils is closely related to the alternation of freezing and thawing in spring.

    • Numerical Comparison between Hydragric Anthrosols of Different Parent Materials in Development in Hill Regions of South China

      2019, 56(2):298-309. DOI: 10.11766/trxb201804120177

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      Abstract:【Objective】How to measure development degrees of Hydragric Anthrosols is still an unsolved problem in pedogenesis. Therefore, it is essential to define indices that can be used to quantitatively evaluate developments of Hydragric Anthrosols.【Method】In this study, chronosequences of three types of Hydragric Anthrosols derived from purple sandy shale (PS), Quaternary red clay (RC) and red sandstone (RS), separately, in the hilly regions of South China were studied in an attempt to characterize development degree of Hydragric Anthrosols with attribute distance and soil development indices and to exposit effect of parent materials on development rate of Hydragric Anthrosols. Five morphological characteristics, including rubification, melanization, texture, structure and moist consistence, were cited as horizion indices (HI), while common soil properties, like pH, clay contents, free iron (Fed), soil organic carbon (SOC) and magnetic susceptibility (MS), were for horizon distance (HD) calculations.【Result】Compared with their respective original soil profiles, the paddy soil profiles generally had complicated patterns with pedogenic horizons getting more obvious with depth due to pedogenesis. Similarly, clay, SOC, pH, iron oxides and magnetic properties varied observably with cultivation history. HI is an indicator for layer difference in soil morphology and HD one for layer difference in soil property between paddy and their original soils. They can be used to measure development of individual horizons within a profile from different angles. The variations of SOC, pH, clay and MS in soil development were significantly related to HD, indicating that they played important roles in determining HD and the soils, easier to have these properties changed were often higher in developing rate. It was also quite obvious that rubification was the most closely related to HI, explaining 83.1% of the variation of HI at all depths, and followed by melanization and moist consistence, which indicated that soil color and soil consistence played important roles in determining HI in this study. Moreover, an intrinsic relationship was observed of morphological features with general soil properties in pedogenesis of Hydragric Anthrosols. As RC-derived soils were thick in soil layer, red in color, and high in clay content, in soil moisture and nutrient retention capacity, and in cohersiveness and plasticity, they were liable to have SOC accumulated and develop rapidly. As PS-derived soils were thick in soil layer, high in clay+silt (<0.10mm) content and in moisture and nutrient retention capacity, and fairly high in cohersiveness and plasticity, they were liable to have SOC accumulated too and develop quite rapidly or rank second in soil development rate. And as RS-derived soils were thin in soil layer and low in clay and silt content, in soil moisture and nutrient retention capacity and in cohersiveness and plasticity, it was hard for them to accumulate SOC or to develop fast.【Conclusion】The effects of parent material on development of Hydragric Anthrosols were reflected through their effects on development rate of the soil. All the findings show that Hydragric Anthrosols develops at a much higher average rate than natural soils do, particularly under paddy cultivation towards a set direction. But with the cultivation going on and on, development rate of the soil generally declines. The relationship between soil development rate and soil forming history or age can be fitted with a logarithmic equation. This quantification method may help improve knowledge about the soil forming process of Hydragric Anthrosols and realize quantitative comparison of Hydragric Anthrosols of different regions in development rate, and hence it may enjoy a bright future in application. However, as this method is still at its initial test stage, it needs further validation and improvement through researches.

    • Stoichiometry of Soil Mineral Weathering in Intensely Weathered Soil as Leached by Simulated Acid Rain

      2019, 56(2):310-319. DOI: 10.11766/trxb201806080217

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      Abstract:【Objective】As the problem of soil acidification is becoming increasingly serious, the research of soil acidification rate appears to be of critical importance, especially on stoichiometry of mineral weathering, which plays an important role in quantifying soil acidification rate. The soils undergone intensive weathering in the subtropical region of China are highly acid-sensitive. In recent years, acid deposition has become very serious, making the problem of soil acidification prominent. Therefore, in this research, a leaching experiment with simulated acid rain was conducted to explore stoichiometric relationship between released elements during the weathering process of minerals in intensively weathered soil derived from granite in the subtropical region, in an attempt to provide a certain basis for quantitative estimation of soil acidification rate.【Method】First of all, soil samples were collected. The soil derived from granite in the subtropical region. Some of the samples were treated with EDTA-ammonium acetate solution to elute base cations adsorbed on soil colloids, which can avoid the effect of cation exchange reaction in subsequent processes of the experiment. Then the two groups of soil samples, eluted and uneluted, were leached with simulated acid rain at the same time by modified Batch. The leachates were collected for analysis of K+, Na+, Ca2+, Mg2+ and Si.【Result】(1) During the eluting process, the amount of K+, Na+, Ca2+ and Mg2+ eluted from the samples was related to the contents of exchangeable base in the soil. For highly weathered ferrisol, eight rounds of elution processes were performed to elute all the exchangeable base cations from soil colloids; (2) In the leaching process with simulated acid rain, the amount of released base cations from the eluted samples were low and stable while that from the uneluted samples varied sharply from the initial stage. A quite large amount of base cations were released at the initial stage of the leaching and did at a rapidly reducing rate with the leaching till they got quite close to the eluted samples in base leaching rate. This result indicates that the base cations released at the initial stage of leaching for uneluted-base soil came mainly from cation exchange reaction, while those released at the later stage originated from mineral weathering; and (3) During the leaching process by simulated acid rain, weathering of polyminerals in the soil mainly were feldspar, hydromica and vermiculite with releasing base cations. Based on the released amounts of base cations and Si, the stoichiometric relationships of K+:Na+:Ca2+:Mg2+ and base cation and Si (BC:Si) in horizons A, B1 and B2 of the eluted and uneluted soils were obtained. The BC:Si of the eluted soil was 0.8~1.4:1 and of the uneluted soil was 3.4~4.0:1. The sharply difference between them indicates the importance of eluted soil exchangeable base cations for accurate stoichiometric relationships of mineral weathering.【Conclusion】(1) During the base eluting process, the base cations eluted from the soil come mainly from the exchangeable base cations. Eight rounds of elution can elute this portion of base cations completely for the highly weathered soil; (2) During the process of leaching with simulated acid rain, the eluted and uneluted soils differ sharply in released amount and pattern of base cations because the base cations released come mainly from weathering of minerals for the eluted soil, while they include exchangeable base cations for uneluted soil; and (3) The main weathering polyminerals in the soils are hydrolysis of feldspar, hydromica and vermiculite as triggered by acid rain. The stoichiometric relationship of BC:Si of the eluted soil is 0.8~1.4:1 while that of the uneluted soil is 3.4~4.0:1. The sharply difference means that to achieve accurate stoichiometry of mineral weathering, it is essential to elute exchangeable base cations adsorbed on soil colloids.

    • Estimation and Mapping of Soil Salinity in the Ebinur Lake Wetland Based on Vis-NIR Reflectance and Landsat 8 OLI Data

      2019, 56(2):320-330. DOI: 10.11766/trxb201805070182

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      Abstract:【Objective】Soil salinization, one of the most critical ecological problems in agriculture, is a progressive soil degradation process that reduces soil quality and hence crop yield and agricultural production. Therefore, it is necessary to monitor soil salinity for prevention and mitigation of land degradation in the arid regions. Producers and decision-makers also require updated accurate soil salinity maps of agronomically and environmentally relevant regions. 【Method】A total of 147 soil samples were collected from the Ebinur Lake wetland, Xinjiang Uyghur Autonomous Region of China, during the rainy season (May) and dry season (September) in 2017 for analysis of electrical conductivity (EC) when prepared into suspensions, 1:5 in soil and distilled water ratio, and for acquisition of Vis-NIR (visible-near infrared) reflectance spectra in the laboratory. Spectra were resampled in line with Landsat8 OLI sensor’s resolution, i.e., band 1 (Coastal) 433~453 nm, band 2 (Blue) 450~515 nm, band 3 (Green) 525~600 nm, band 4 (Red) 630~680 nm, band 5 (Red) 845~885 nm, band 6 (SWIR 1) 1 560~1 660 nm, and band 6 (SWIR 7) 2 100~2 300 nm. Furthermore, NDSI (Normalized Difference Vegetation Index), SI (Salinity Index), SI1 (Salinity Index 1), SI2 (Salinity Index 2), SI3 (Salinity Index 3), S1 (Salinity Index, S1)、S2 (Salinity Index), S3 (Salinity Index), S5 (Salinity Index), S6 (Salinity Index), Int1 (Intensity Index 1), Int2 (Intensity index 2) and COSRI (Combined Spectral Response Index) were also calculated in this study. A quantitative estimating model was constructed based on partial least squares regression (PLSR), and evaluated in light of its root mean square error (RMSE), determination coefficient (R2) and ratio of performance to deviation (RPD). 【Result】Results show that the surface soil of the Ebinur lake wetland was strongly salt-affected, with soil salinity during the rainy season (23.90 mS•cm-1) being much higher than that during the dry season (11.62 mS•cm-1). 2) The PLSR model based on resampled spectral data and 13 spectral indexes performed quite ideally in predicting soil EC in the study area, with quite high accuracy (R2 = 0.91, RMSE = 6.48 mS•cm-1, and RPD = 2.45), which indicates that the model constructed in the study could be used to predict quantitatively EC in the Ebinur Lake wetland; and 3), the areas of slightly saline soil and saline soil decreased, while those of moderately and heavily salinized soils increased during the study period (from May to September). 【Conclusion】In the present study, the model, established by combining two types of remote sensing data different in resolution, has obviously improved the traditional optical remote sensing (Landsat8 OLI) model in precison, as well as elevated the Vis-NIR spectral data to the pixel scale, thus providing certain scientific reference for remote sensing extraction of soil salinity information. The performance of Vis-NIR-based prediction of soil salinity might be affected by adsorption capacity of soluble salts in these electromagnetic ranges being lower than that of: water, soil iron, organic matter, certain types of clay minerals, and some other soil components. To further improve the prediction accuracy, further efforts should be done to define the most dominated factor affecting spectral reflectance of soils different in salinity degree.

    • Effects of Pattern and Amount of Earthworm Cast Application on Water Infiltration in Soil

      2019, 56(2):331-339. DOI: 10.11766/trxb201807250261

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      Abstract:【Objective】Earthworms are one of the most common soil animals, and generate cast that forms water stable aggregates rich in organic matter. As is known to all, earthworm cast has already been extensively used as organic manure in farmland, because it can promote solubility of the insoluble minerals and increase nutrient elements in the soil. Then how and how much earthworm cast is applied will no doubt affect spatial distribution of the cast in the soil, and little has been reported on impacts of earthworm cast application on soil water dynamics. Therefore in this study, an indoor experiment using simulated soil columns was carried out to explore effects of pattern and rate of the application of earthworm cast on water infiltration in soil.【Method】The experiment was designed to have treatments for earthworm cast application rate, i.e. 50 g·kg-1, 75 g·kg-1 and 100 g·kg-1 and five treatments for application pattern i.e. A: mix cast with soil in the 0~10cm soil layer of the column; B: mix cast with soil in the 10~20 cm soil layer; C: mix cast with soil in the 5~8 cm soil layer; D: mix cast with soil in the 10~13 cm soil layer; and E: mix cast with soil in the 15~18 cm soil layered. So the experiment had 15 treatments (3x5) plus a control (no cast applied) for comparison, and each treatment had 3 replicates. A given amount of water was added to start water infiltration in all the 48 columns. The process of water infiltration lasted 180 minutes. Wetting front movement was recorded and accumulated infiltration calculated for analysis of differences between the treatments. In addition, samples of the soil were collected from each column by layer at the end of the infiltration for analysis of water content.【Result】Results show that the treatments of 50 g·kg-1 earthworm cast had wetting fronts going deeper than all the others or 4.1 cm deeper to the maximum. Compared with Control group, all the Treatments A, regardless of cast application rate, had wetting front going deeper, and the wetting front was found to be 1, 1 and 0.3 cm deeper in Treatment A50, A75 and A100, respectively, than in Control at the end of the infiltration process. Among the group of Treatment B, Treatment B75 and B100 has wet front going 3% and 11% shallower than Control. When earthworm cast was applied by layer as designed in the experiment, the treatments of cast application rate, regardless of depth of the application, displayed an order of 50 > Control >75 >100 in terms of wetting front depth and the groups of Treatments 75 and 100 inhibited water infiltration, with the effect reducing with increasing application depth. Among the group of Treatments C, Treatments C75 and C100 had wetting front going 6.3% and 19.5% shallower than Control. Among the group of Treatments A, Treatment A75 and Treatment A100 did not differ much from Control in cumulative infiltration, while among the group of Treatment B, Treatment B50, B75 and B100 was 8.2, 7.6 and 11.8 mm respectively, lower than Control, and among the group of Treatments C, Treatment C75 and C100 was 70.7 and 59.7 mm respectively lower than Control (74.2 mm) (P<0.05) at the end of the infiltration. The Kostiakov infiltration model was adopted to fit temporal variation of the measured cumulative infiltration, with determination coefficient R2 ranging from 0.996 to 0.999, which indicates that the fitting is good. In the experiment, water content in the soil-cast mixed layer and the soil layer right underneath increased correspondingly, but with cast application rate being beyond 75 g·kg-1, water content in the deep soil layer (16~20 cm) might decrease.【Conclusion】It can be concluded that the impact of cast application on water infiltration may vary with pattern and rate of the application. The application of 50 g·kg-1 earthworm cast in the 0~10 cm soil layer promotes downward movement of the wetting front while the application of 100 g·kg-1 earthworm cast in the 10~20 cm soil layer significantly inhibits movement of the wetting front depth. The application of cast in layers reduces cumulative infiltration and hence alters soil water redistribution.

    • Macropore Structure Characteristics of Black Soil under Freeze-Thaw Condition

      2019, 56(2):340-349. DOI: 10.11766/trxb201805230516

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      Abstract:【Objective】 Freeze-thaw action will change the microstructure of a soil, and the change in pore characteristics is an important reflection of the change in soil structure. Most of the regions along the mid-latitudes on earth are affected by seasonal freeze-thaw processes, especially the black soil in Northeast China. It is of great significance to study mechanism of the erosion on black soil and rational utilization of the black soil resources. So this study is oriented to analyze three-dimensional structure of the soil under freeze-thaw condition, extract quantitative indices of pore characteristics, and then explore effects of freeze-thaw cycle on soil macropores, in an attempt to provide evidence for further revealing influences of seasonal freezing and thawing on soil structure of the black soil area. 【Method】 In this paper, through indoor simulation experiment of freeze-thaw cycle and with the aid of the CT scanning technique, changes in macropore in the undisturbed black soil samples under different numbers of freeze-thaw cycles and different moisture contents were studied. Undisturbed soil samples, 0~15 cm in depth, were collected with PVC pipe from a typical black soil area for the indoor simulation experiment of freeze-thaw cycle, which was designed to have two moisture contents (30% and 40%), and seven levels of freeze-thaw cycles (0, 1, 3, 5, 7, 10 and 15), each ranging in temperature from -10 to 7°C. With the aid of a medical CT, 1.25 mm in resolution, changes in pores > 1.25 mm in pore size were studied. 【Result】 Results show that with the increasing number of freeze-thaw cycles, soil porosity continuously increased, especially after the 7th freeze-thaw cycles, while the number of pores decreases; regular porosity (RP) and irregular porosity (IRP) continued to decrease, but lengthening porosity (EP) increased; and pore size increased, especially that of those >3 mm in diameter. Besides, freeze-thaw action caused formation of a lot of branches along pores, and the more the numbers of freeze-thaw cycles, the higher the proportion of branches. Among the soil samples subjected to the same temperature variation in freeze-thaw cycles, those high in soil moisture content changed more significantly in pore characteristics than those low in soil moisture content. 【Conclusion】 As affected by freeze-thaw cycle, soil porosity, pore size and pore branching increased, and soil pores changed significantly in shape and distribution. All the findings in this study show that the number of freeze-thaw cycles and soil moisture content are the two major factors affecting pore structure of the soil. Properties of the soils under freeze-thaw cycle is not only a very important research hotspot, but also a major factor concerning sustainable development of the agriculture in Northeast China. In order to reveal mechanism of freeze-thaw erosion of the soil, further study should be done focusing on pore structure characteristics of aggregates and relationships between pore structure characteristics and soil water-holding and infiltration characteristics in the soil under freeze-thaw cycle. The study may provide a theoretical basis for researches on mechanism of freeze-thaw erosion of soil and reasonable evaluation and utilization of farmlands in cold-temperate areas.

    • Groundwater Nitrate Removal through Denitrification under Farmland in Yangtze River Delta

      2019, 56(2):350-362. DOI: 10.11766/trxb201809050445

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      Abstract:【Objective】The Yangtze River Delta is one of the areas, where the input of nitrogen(N) fertilizer is very high, in China, but it is not quite clear whether nitrate (NO3--N) has accumulated in the soil profile in the region as in the North China Plain.【Method】In the present study, two-year field observation combined with indoor incubation experiments were carried out to investigate distribution of NO3--N and denitri?cation capacity in subsoil and groundwater as affected by arable land systems.【Result】The groundwater NO3--N concentration in 1~4 m depth was varied significantly with type of the cultivation system. In the paddy field, groundwater NO3--N was always low (<1 mg·L-1), and did not vary much with depth. While in the vegetable field and vineyard, the average NO3--N concentration reached 5.6 and 17.5 mg·L-1 in 1 m depth, but the NO3--N concentration dropped sharply with the depth and to a very low concentration (<1 mg·L-1) in 4 m depth which was comparable to that in the paddy field. High groundwater NO3--N were only observed in vegetable field and vineyard during the fertilization period and NO3--N was low in non-fertilization period. The findings indicated that no apparent NO3--N accumulation in the farmland soil profile occurs in the Yangtze River Delta. The indoor incubation experiment using undisturbed soil columns shows that denitrification activity was high through the 0~4 m soil profile. The removal efficiency (RE) of NO3--N by denitrification was estimated by direct determination of N2 and N2O, products of denifrifiction, in groundwater. The RE increased with depth and removed 86%, 93% and 89% of the groundwater NO3--N in 4meter depth in paddy field, vegetable field and vineyard, respectively. 【Conclusion】All the findings in this experiment demonstrated that denitrification can effectively remove groundwater NO3--N, which explains why NO3--N does not accumulate in farmland soil profiles in Yangtze River Delta. Highly dissolved N2 produced by denitrification accumulate in groundwater, and flow into nearby water bodies mainly via groundwater. In the case of vegetable field and vineyard, soil N loss in the form of dissolved gaseous N is nearly equal to that of NO3--N and hence an important fate of soil N, which deserves close attention.

    • Effect of Using Purple Parent Rock as Substrate or Cover Material on Removal of Nitrogen and Phosphorus in Landscape Water

      2019, 56(2):363-373. DOI: 10.11766/trxb201806050257

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      Abstract:【Objective】The subject of how to construct landscape water bodies for reshaping living environment is getting increasingly popular among scholars. However, most landscape water bodies are closed or semi-closed catchments and easy to get polluted by external pollutants from agricultural wastewater, ornamental fish excretion, and atmospheric sedimentation and eventually eutrophied. Often in those eutrophied landscape water bodies harmful algal blooms, fish kills, and many other related problems occur. The primary cause of landscape water eutrophication is the excess of N and P in the water body. Thus, reduction of N and P in the water body is the key to control of landscape water eutrophication. 【Method】Samples of three kinds of purple parent rocks (Peng-lai-zhen Formation (J3p), Fei-xian-guan Formation (T1f), and Sui-ning Formation (J3s)), which are widely distributed in Chongqing, were collected and used as substrate or super stratum in a simulation experiment to explore effects of the purple parent rocks on landscape water purification. Isothermal adsorption tests were conducted to determine physical adsorption abilities of the purple parent rocks, separately. Microbial community structure of each treatment system was analyzed with phospholipid fatty acid (PLFA). 【Result】The following findings were obtained. The three kinds of purple parent rocks, when used as substrate, varied in total nitrogen (TN) and total phosphorus (TP) removing efficiency, with J3p in the lead. However, when used as substratum, they effectively inhibited sediments from releasing TN and TP but to a similar extent. The isothermal adsorption tests show that TN adsorptions on the three kinds of purple parent rocks were all in the form of monolayer adsorption and surface adsorption, and TP adsorptions mainly in the monolayer adsorption. Among them, J3p was the highest in physical adsorption capacity and its maximum theoretical adsorption capacity of TN and TP reached 0.259 mg·g-1 and 0.619 mg·g-1, respectively. The use of the purple parent rocks as either substrate or cover material altered the microbial community structures of their respective treatment systems. Compared with CK, T1f and J3s as substrate promoted significantly growth of the bacteria, fungi and protozoa in the landscape water, while J3p did little the growth of water microorganisms. Used as cover material, all the purple parent rocks promoted markedly growth of the bacteria in the water and sediment, but varied in the effect on fungi in the water and sediment. At the same time, number of the bacteria (labeled as PLFA18:0) in the matrix treatment system was significantly and positively related to the content of total nitrogen in the overlying water, while numbers of the bacteria (labeled as PLFA16:0) in the overlay treatment system was significantly and negatively related to the content of total phosphorus in the overlying water. Moreover, the rocks also varied in release of trace elements. J3p released more Ca, K, Cu, Mn and Mo than T1f and J3s did 【Conclusion】All the findings demonstrate that application of Peng-lai-zhen Formation purple parent rock as substrate or barrier material could effectively control both nitrogen and phosphorus pollutions in landscape water, which is attributed to its high physical adsorption capacity. Furthermore, releasing of trace element from purple parent rock during the treatment process could alter microbial community structure of the system, and hence affect removal of TN and TP from the system.

    • Variation of Organic Matter in Soil Aggregates with the Succession of Tidal Flatland from Barren Land-Saltmarsh-Upland in the Yellow River Delta

      2019, 56(2):374-385. DOI: 10.11766/trxb201802020082

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      Abstract:【Objective】Organic matter in soil aggregates (POM, particulate organic matter) is a biologically and chemically active fraction of soil organic matter that plays an important role in terrestrial carbon cycling. The objectives of this study were to characterize the fraction of organic matter and to analyze stability and sources of the soil organic carbon pool in this study area. 【Method】 Soil samples were collected from three tracts of land typical of the studied region in land use, that is, barren land, saltmarsh and upland, for analysis of POM and stable organic carbon isotopes. 【Result】Results show that the content of soil organic carbon presented a curve of first rising from barren land to saltmarsh and then declining from saltmarsh to upland, and was found in a significant positive relationship with the content of soil macroaggregates. The organic matter in soil aggregates could be fractionated into free particulate organic matter (fPOM) on the surface of macro- (micro-) aggregates, intra-macro- (micro-) aggregate particulate organic matter (iPOM, 250~2 000 μm) and mineral-associated soil organic matter. Contents of fPOM, iPOM and mSOM (Mineral-associated Soil Organic Matter) were quite low in the barren land, but soil organic carbon content increased significantly in the three types of SOM in the saltmarsh where some halophytes began to grow, reaching as high as 410.0 g•kg-1, 98.8 g•kg-1 and 18.8 g•kg-1 respectively. When saltmarsh was reclaimed into upland, the rising trend of the three types of POMs leveled off. The POM (including fPOM and iPOM) accounted for only 20% or below of the organic carbon in the barren land, for 41.8%~75.2% in the saltmarsh that had some halophytes growing, and for 54% in the upland. In terms of δ13C, the three types of POM exhibited an order of fPOM < iPOM < mSOM, and the three tracts of lands did an order of saltmarsh < upland < barren land. 【Conclusion】 All the findings in this study demonstrate that although the content of total soil organic carbon is relatively lower in the barren land in the Yellow River Delta, it has a relatively stable carbon pool consisting mainly of mineral-associated organic matter, which is highly affected by marine originated organic carbon. The growth of halophytes in the saltmarsh (wetland) increases the content of total organic matter in the soil and its relative proportion in the active carbon pool, too. Soil organic carbon pool is very sensitive to changes in environment. Cultivation of corn and wheat lowers the relative proportion of active carbon pool, but enhances stability of the so carbon pool.

    • Chemical Composition and Structure of Humus Relative to Sources

      2019, 56(2):386-397. DOI: 10.11766/trxb201805070241

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      Abstract:【Objective】Recently, woody peat is widely used in horticulture, facility agriculture and soil amelioration, however, little is known about chemical composition and molecule structure of the humus it contains as the main component and ability of the substance to increase soil organic matter (SOM) in the soil. Therefore, in this research, samples were collected of woody peat (WP), two types of soils (paddy soil (PS) and black soil (BS)), two kinds of organic manure (Mix fermented organic manure (MFOM) and fermented chicken manure (FCM)), for analysis of content, micromorphological features, chemical composition, molecule structure and functional group structure characteristics of humus to evaluate differences between the substances of different sources in these indices and in ability to increase SOM.【Method】Different fractions (fulvic acid (FA), humic acid (HA) and humin (Hu))of the humus in the samples of WP, PS, BS, MFOM and FCM were extracted for analysis of concentrations of Carbon (C), nitrogen (N), hydrogen (H), sulfur (S) and oxygen (O), micromorphological features with the aid of a scanning electron microscope, and molecule structures by means of fourier transform infrared spectrometry (FTIR).【Result】Results show that the humus content of WP approached 862.7 g·kg-1which was 30.5~41.7 times and 4.1~5.1 times that in the soils and organic manures, respectively. The WP humus was dominated with HA, which accounted for 73.28% of the WP sample in dry weight, while the humus in PS, BS, MFOM and FCM was with Hu which accounted for less than 11.28% only of the samples in dry weight. The finding indicates that the humus in WP is more humified than that in soils or organic manure. The HA in WP was smaller in particle size than the HA and Hu in PS, BS, MFOM and FCM, which suggests that the molecules and particles on the surface of WP humus are denser in arrangement and hence lower in activity. The humus in WP, regardless of fraction was relatively high in C concentration, but lower in all the fractions in N concentration than their respective ones in PS, BS, MFOM and FCM, which led to a high, even over 100, C/N ratio, about 5~11 and 9~14 times that in the soils and organic manures, respectively. Besides, except for the HA fraction in BS, both the FA and HA fractions in WP were the lowest in H/C ratio, which suggests that the humus in WP is more condensed than that in all the others. FTIR analysis shows that the values of 2920/1 620 and 2 920/2 850 of the HA and Hu fractions in WP were much higher than that in PS, BS, MFOM and FCM, which indicates that WP humus contains more aromatic and polymethylene groups. The higher humification and condensation degrees, more compact and inert surface and more aromatic and polymethylene groups suggest that the humus in WP is more complicated in molecule structure than that in all the others, and therefore it is harder for organisms to decompose. However, according to the FTIR spectra, the FA and HA fractions of humus in WP displayed absorption peaks higher their corresponding ones in all the others at 1 720 cm-1 and 1 420 cm-1 featuring carboxyl C=O bonds. In addition, in the humus of WP, the HA fraction was higher in (S+O)/C ratio than that in all the others, although the Hu fraction was the lowest in (S+O)/C ratio, which suggests that the WP humus is still quite high in oxidation degree and that its oxygen functional groups have not yet been completely decomposed.【Conclusion】All the findings in this study demonstrate that WP is quite high in potential ability to raise SOM concentration in the soil. Therefore, when WP is applied into soil, it is essential to regulate the fractions in the humus to a proper ratio to reduce its particle size and polymethylene bonds, and meanwhile, to spike some biological activator and to incorporate straw into the soil, so as to stimulate organism inversion and balance WP decomposition.

    • Spectral Characteristics of Humus in Chernozem in Qinghai-Tibet Plateau under Reclamation and Long-Term Fertilization

      2019, 56(2):398-407. DOI: 10.11766/trxb201804030107

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      Abstract:【Objective】 Since the 1980s, a large area of meadow on the Qinghai-Tibet Plateau has been reclaimed to be cropland along with a long term of fertilization, which may have an import influence on soil humus and thereby soil fertility and environmental chemical process in soil. This study was oriented to explore effects of reclamation and long-term fertilization on humification degree, relative molecular weight, aromaticity and source of the humus in an oilseed cole field of chernozem in Qinghai, with a view of providing certain theoretical support for management of agricultural activities in meadows of the QingHai-Tibet Plateau. 【Method】 In this study, basic physic-chemical properties of chernozem and spectral properties of the humus in a cole field of chernozem under reclamation and long-term fertilization and a tract of virgin meadow of chernozem in Qinghai were characterized by means of UV-vis, Fourier-transform infrared and Parallel factor analysis, three-dimensional fluorescence spectroscopy for comparison.【Result】 Results show that reclamation and long-term fertilization significantly affected basic physico-chemical properties of the chernozem, the spectral properties of the humic acid and fulvic acid in the soil and molecular composition of the soil humic substances. In terms of soil physico-chemical properties, reclamation significantly reduced soil organic matter, while fertilization enhanced soil fertility and nutrient supply. However, long-term fertilization led to soil acidification, while slowing down the decreasing process of soil organic matter, thus causing degradation of soil quality. UV-vis spectra indicate that reclamation and long-term fertilization enhanced humification degree, relative molecular weight, aromaticity and dependence-on-extraneous-sources of humic acids, but affected all the indices of fulvic acids reversely, except for dependence-on-extraneous-sources, while FT-IR spectra indicate that long-term fertilization facilitated formation of carboxylic acids in the soil, increased biomass of the crops, which in turn depleted much carbohydrate and aliphatic organic matter in the soil. Parallel factor analysis and three-dimensional fluorescence spectra identified five components of soil humus including two types of humic acid-like substances, two types of fulvic acid-like substances and a soluble microbial by-product. Reclamation and long-term fertilization also affected composition of the humus, by relatively expanding the fraction of large-molecule humic acids and shrinking the fraction of small ones, but expanded the fractions of both large- and small-molecular fulvic acids, especially the latter. 【Conclusion】All the findings in this study suggest that careful attention should be paid to agricultural reclamation of the meadow resources of the Qinghai-Tibet Plateau and that it is advisable to apply organic manure to retard reduction of organic matter, and to expand the sources of fulvic acids while increasing humidification degree of soil humus. Further study on the response of functional structure of soil humus to the reclamation and long term of fertilization is also suggested to detect the carbon sequestration and to put forward management practice to maintain carbon balance in soil of the Qinghai-Tibet Plateau.

    • Sources and Risk Assessment of Heavy Metal in Agricultural Soils Based on the Environmental Geochemical Baselines

      2019, 56(2):408-419. DOI: 10.11766/trxb201804120050

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      Abstract:【Objective】To study the characteristics and risk of heavy metal contents in the agricultural soils highly disturbed by anthropogenic activities in the suburbs of a City, Zhejiang Province, Southeast China, and to establish Environmental Geochemical Baseline models of heavy metal elements, a total of 534 topsoil samples were collected in the study areas.【Methods】 The contents of heavy metals, As, Cr, Cd, Cu, Hg, Ni, Pb, Zn, and inert elements, Li, Eu, Sc and Sm in the soils were analyzed. As and Hg were measured with the atomic fluorescence spectrometry; Pb and Zn, with the X-ray fluorescent spectroscopy (XRF); Cd, Cu, Ni, Li, Eu, Sc and Sm, with the inductively coupled plasma mass spectrometry (ICP-MS). Using Li, Eu, Sc and Sm as standard factors, the Environment Geochemical Baseline models of the heavy metal elements were established. According to the Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018),the method of Single Factor Pollution Index were applied to assess the degree of heavy metal pollution in the study areas. While the enrichment factor (EF)and the potential ecological risk (PER) by individual metal and combined effect of metals were determined, by using the Environment Geochemical Baseline Values as standard factors.【Results】 The contents of heavy metal elements, As, Cd, Cr, Cu, Hg, Ni, Pb and Zn in the soils were in the ranges of 2.28~106.0 mg·kg-1, 0.04~4.91 mg·kg-1, 16.00~221.0 mg·kg-1, 12.90~216.0 mg·kg-1, 0.03~2.31 mg·kg-1, 6.76~102.0 mg·kg-1, 12.40~245.0 mg·kg-1 and 51.70 ~864.0 mg·kg-1, respectively.Choose the inert elements with the best correlations to heavy metals as the standard factors to obtain the Environment Geochemical baselines of As 11.13mg·kg-1, Cd 0.38mg·kg-1, Cr 57.49 mg·kg-1, Cu 43.86 mg·kg-1, Hg 0.30 mg·kg-1, Ni 21.55 mg·kg-1, Pb 51.91 mg·kg-1 and Zn 132.68 mg·kg-1. A polluted rate of the monitoring points of the different heavy metals was in the decreasing order of Cd 59.55%> Cu 24.34%>Hg 17.42%>Pb 13.11%>Zn 12.36%> As2.81%>Cr 0.37%=Ni 0.37%.The concentration of Cd, Cr, Cu, Hg, Ni, and Pb were higher than the Environment Geochemical Baseline Values in more than 40% of samples; those heavy metal elements were anthropogenically loaded into the agricultural soils of the study areas. Although large area of he study areas experienced moderate to serious level of pollution, most of the heavy metals showed low risk to the environment. Only Cd and Hg showed moderate to high risk to the environment.【Conclusions】Spatial analyses of EF and PER of the heavy metal elements by applying the GIS information system can effectively determine the source and scope of heavy metal pollution,and assess the potential ecological risks of heavy metal pollution for early warning in the study areas. Over 68.91% of the agricultural soils in the study areas were polluted by heavy metals to different extents, and 3.18% were severely polluted due to intensive anthropogenic activities. The polluted areas were mainly distributed nearby metal mines and printing and dyeing companies.

    • Targeted Inactivation of Pathogenic Bacteria in the Farmland Soil by Polyvalent Phage Therapy

      2019, 56(2):420-431. DOI: 10.11766/trxb201801020006

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      Abstract:【Objective】 Given the drastic development of livestock industry in China, animal manure amount increased significantly in the last few decades. Without proper environmental management, the manure as well as relevant wastes have made the agricultural soil near the livestock site a hotspot of pathogens, which has posed potential threat against the public health and environmental safety. Therefore, it is urgent to carry out bioremediation technologies to effectively inactivate the targeted pathogens in the soil. Among various techniques, phage therapy provides a novel way for eliminating pathogenic bacteria in the soil. In this work, polyvalent phages were firstly isolated, and further screened for their capacity of inactivating various host pathogenic bacteria, in an attempt to apply the polyvalent phage therapy for controlling the pathogens contamination in the soil. 【Method】In this work, double-layer agar was employed to isolate phages from the soil applied with cow manure in a dairy farm in Nanjing Eastern China,which was contaminated by Enterobacteriaceae and Pseudomonas pathogenic bacteria. Two host-specific phages (YSZ1 and YSZ5) were isolated from the polluted soil. Then with the accelerated human-directed evolution in the laboratory, two polyvalent (broad host range) phages (YSZ1R and YSZ5k) were obtained each corresponding to YSZ1 and YSZ5. Meanwhile, the biological characteristics including morphology and molecular technology were carried out for the identification of the four phages obtained. Moreover, by studying the optimal multiplicity of infection and growth characteristics, the capacity of inactivating pathogenic bacteria among four phages were also determined. Meanwhile, Biolog ECO plates were used to investigate the impact of phage therapy on the diversity of the soil microbial community. 【Result】The morphological and molecular identification indicated that the four phages described above all belonged to Stylovinidaeacid. Meanwhile, in both aqueous system and contaminated soil, the four phages exhibited significacnt but varying capacity of inactivating Fecal Coliform and Pseudomonas, following the order of YSZ5K>YSZ1R>YSZ5>YSZ1. In addition, compared with the control, host-specific phage inoculation (YSZ5 and YSZ1) slightly decreased the AWCD value, while polyvalent phage inoculation (YSZ5K and YSZ1R) significantly increased the AWCD value after 120 h of incubation. Shannon index showed the same trend of YSZ5K/YSZ1R> CK> YSZ5/YSZ1. Therefore, polyvalent phages therapy applied in this work was able to maintain and increase the diversity and stability of the indigenous microbial community in the soil.【Conclusion】The polyvalent phages isolated from the pathogen contaminated soil were determined as Stylovinidaeacid. Both polyvalent phages (YSZ5K and YSZ1R) could significantly stimulate the dissipation of the pathogenic bacteria in both aqueous and soil systems. Meanwhile, the diversity of the indigenous bacteria community in the soil could be clearly enhanced after polyvalent phage therapy, suggesting that the polyvalent phage therapy developed in this work was an applicable technique to inactivate broad range pathogenic bacteria in the soil.

    • Impacts of Litter Decomposition of Eucalyptus on Soil Microbial Community:A Microcosm Study

      2019, 56(2):432-442. DOI: 10.11766/trxb201804200092

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      Abstract:【Objective】Eucalyptus is one of the main tree species introduced into the country for afforestation because of its fast growth and economic value. By the end of 2015, its plantation had expanded up to 4 500 000 hm2. Afforestation of fast-growing Eucalyptus has received considerable attention with regard to its impacts on forest ecosystem. It is now known to affect physical and chemical properties of the soil, and plant community biodiversity. A number of studies have shown that it causes the soil degrading once it takes the place of native forests, but still little has been reported on its effects on soil microbial communities in South China. Soil microbial communities play a central role in litter decomposition, nutrient mineralization, and nearly all soil ecological processes in forest ecosystems, and may serve as an early indicator of changes in soil because of its rapid response to anthropogenic disturbances relative to soil biogeochemical properties. Litter decomposition provides the main source for soil microbial communities in forest ecosystems, whereas decomposition of Eucalyptus litter can disrupt the ecological associations between soil microbial communities and previous native communities. It is, therefore, very important to understand impacts of decomposition of Eucalyptus litter on structure and functions of the soil microbial community and its mechanisms to elucidating impacts of a single plant species on ecosystem services. 【Method】 A simulation pot experiment was laid out in random block design and designed to determine impacts of Eucalyptus litter on structure and functions of the soil microbial community by means of comparison with mixed litter of natural secondary forest. Three types of natural secondary forest soils different in soil carbon and nitrogen contents were used in the experiment. A portion, 2 g each, of air-dried litter was mixed separately with 200 g (dry weight) soil in each pot, except for control (no litter added). Structure and functions of the soil microbial community in the soil of each pot were determined with the PLFA (phospholipid fatty acids) and BIOLOG (single carbon metabolism) methods, 10, 20 and 30 days after the decomposition started. 【Result】 Results show: (1) Eucalyptus litter was higher in carbon content but lower in nitrogen content than the litter of natural secondary forest, and so significantly higher in carbon-nitrogen ratio; (2) PLFA abundances of bacteria, fungi, actinomyces and total PLFA were significantly higher in the soil treated with Eucalyptus litter than in the soil of the control, but significantly lower than in the soils treated with natural secondary forest litter; Principal component analysis (PCA) of the PLFA data shows that the treatment of Eucalyptus litter differed significantly from the treatments of mixed natural secondary forest litter in soil microbial community structure, and principal component one (PC1) explained 84.02% of the variation; and (3) PCA of the BIOLOG data also shows that significant differences existed between treatments in carbon utilization profiles of the soil microbial community, and PC1 and PC2 explained 36.99% and 16.95% of the variation, respectively; the treatment of Eucalyptus litter significantly lower than the treatments of natural secondary forest litter in carbon metabolic intensity, richness and diversity of soil microbial community, too. 【Conclusion】 All the findings in this study demonstrate that Eucalyptus litter is lower in capability of supplying soil microbial communities with adequate habitat and food than the mixed natural secondary forest litter.

    • Comparative Study on Rhizosphere Effects and Bacterial Communities in the Rhizospheres of Rice and Wheat

      2019, 56(2):443-453. DOI: 10.11766/trxb201806020042

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      Abstract:【Objective】 In China, rice and wheat rotation is an important mode of agricultural production, composed of two subsystems i.e. flooded-cultivation and dry farming, with rice and wheat being the representative respectively. The two subsystems differ significantly in irrigation and fertilization condition and soil microbial community structure. The migration of soil active components and microbial characteristics as affected by rhizosphere effect are crucial to the formation and development of soil fertility. Bacterial communities play an essential role in biogeochemical cycles, plant nutrition and disease biocontrol. Most papers available in the literature focused mainly on rhizosphere effect, root exudates and enzyme activity in the upland soil, with little efforts on comparison between upland and paddy soils in pattern of rhizosphere effect and associated microbial community dynamics. Therefore, it is so far still unclear about rhizosphere effects of rice and wheat and their relative contributions to soil function. 【Method】 A pot experiment cultivating rice and wheat separately was conducted in gleyic-stagnic anthrosols, a typical type of soil in the Changshu Ecological Experiment Station of the Chinese Academy of Sciences. Rhizosphere soil was separated from non-rhizosphere or bulk soil with a rhizobox system. Comparison was made between the two portions of soil in content of soil active components, dehydrogenase activity, microbial biomass carbon and bacterial community composition under the two cropping systems for analysis of differences between rice and wheat in rhizosphere effect. Principal component analysis (PCoA) and canonical correspondence analysis (CCA) was performed of the results of High throughput sequencing of the obtained data for analysis of soil bacterial community composition.【Result】 In both rice and wheat soils, the two portions of soil varied significantly in content of dissolved organic carbon and microbial biomass carbon and in dehydrogenase activity. Obviously they were higher in the rhizosphere than in the bulk soil, whereas dissolved organic nitrogen content and bacterial alpha diversity was significantly lower in the rhizosphere than in the bulk soil. Proteobacteria and Bacteroides were the dominant bacteria in both rice and wheat soils, accounting for more than 40%. However, in terms of dominant genera, differences were obvious between rice and wheat as well as between rhizosphere and non-rhizosphere. On the whole, soil microbial community was more complex in the rhizosphere than in the non-rhizosphere soil, and higher in population in the rice soil than in the wheat soil. Principal component analysis clearly shows that sharp difference existed between the two soil systems cultivated with rice and wheat in bacterial community, and the difference between rhizosphere and non-rhizosphere soils was significantly sharper in the wheat soil than in the rice soil. Rhizosphere effects (DOC: 2.07%; MBC: 8.61%; dehydrogenase activity: 41.11%; DON: 61.07%; and Chao1: 7.62%) in the rice soil were all lower in absolute value than their respective ones in the wheat soil (DOC: 3.37%; MBC: 22.62%; dehydrogenase activity: 44.48%; DON: 71.43%; and Chao1: 16.59%). 【Conclusion】 All the above listed findings suggest that the difference between rhizosphere and non-rhizosphere was narrower in the rice soil than in the wheat soil, that is to say, the rhizosphere effect of rice is lower, facilitating transport of photosynthetic carbon and soil nutrients and favoring growth of soil microbes, especially in rhizosphere. And the findings illustrate from a new angle the rhizosphere effect and mechanism of the effect on sustainable development of the soil under the rice and wheat rotation system, and shed lights on a new perspective for improving soil fertility, especially in the soil under upland cropping systems.

    • Responses of Acid Phosphatase Secreted by Watermelon Roots to Organic Manure Nutrition

      2019, 56(2):454-465. DOI: 10.11766/trxb201807090318

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      Abstract:【Objective】 About 30%~ 65% of the total P in soil is present in the form of organic P, mainly like phospholipids, phytate, and nucleic acids, which are not readily available to plant root. However, organic P would release, through hydrolysis, phosphate ions which are available to plant root. Phosphatase is an important enzyme to hydrolyze organic P to phosphate. Furthermore, nutrients in organic manure are important to higher watermelon quality, but the mechanism of how watermelon root absorbs soil P is not clear. The objectives of this study were to (1) investigate forms and quantity of the phosphorus nutrient supplied by organic manure; (2) validate whether the organic acids secreted from watermelon root influence availability of the P in organic manure; and (3) demonstrate responses of the acid phosphatase secreted by watermelon root to organic manure application. 【Method】 The analogy method was adopted to determine contents of water soluble total P and inorganic P in organic manure, as well as impacts of the organic acids secreted from watermelon root on concentrations of soluble total phosphorus and inorganic phosphorus in organic manure. A sand culture experiment was conducted to explore responses of the acid phosphatase in activity to substitution of chemical fertilizer P with organic manure P. In addition, a field experiment was carried out to investigate effects of the replacement and application rate of organic manure on acid phosphatase activity in rhizosphere soil, content of available P in rhizosphere soil, and phosphorus nutrition, yield and quality of the watermelon. 【Result】 Results show the organic manure used in the experiment contained 6.9 g·kg-1 soluble total phosphorus and 525.1 mg·kg-1 soluble inorganic phosphorus. Of the soluble total phosphorus 7.6% was inorganic P and 92.4% organic P. Organic phosphorus could not be absorbed by root until it is hydrolyzed. Organic acids, either citric acid, malic acid or succinic acid, secreted from watermelon root increased soluble total P content, but did not influence the content of inorganic P in the organic manure. Citric acid, low or high, increased the content of soluble total P significantly or by 78.9% and 223.6%, respectively, while high concentration of malic acid and succinic acid did by 151.5% and 112.8%, respectively, in the organic manure. But high concentrations of citric acid and succinic acid did reversely. Substitution of chemical fertilizer with organic manure lowered the accumulation of dry matter in watermelon. Activity of the acid phosphatase in the rhizosphere of watermelon root was significantly enhanced when chemical fertilizer P was replaced by organic manure P. And root/shoot ratio of the plant was improved by the substitution. The field experiment demonstrates that the application of organic manure (6 t·hm-2) to replace chemical fertilizer did not affect yield of the crop. The application of organic manure at 18 t·hm-2, triple the replacement rate, significantly increased yield of the crop, and the application of organic manure at 6 t·hm-2 or 12 t·hm-2, double of the former, both improved the activity of acid phosphatase in the rhizosphere. However the application at 18 t·hm-2 did not affect much the activity, nevertheless it did increase the content of available P in the rhizosphere soil at the mature stage of the crop. 【Conclusion】 The organic manure does contain a small amount of soluble inorganic P, available directly to root for absorption, but most of the soluble P is organic P, hard to be absorbed by root before is hydrolyzed. The organic acids secreted from watermelon root improve soluble total P in content, but not soluble inorganic P. However, the soluble organic P increased by the organic acids secreted by watermelon root is still not available for absorption before it is hydrolyzed. The substitution of chemical fertilizer P with organic manure P enhances the activity of acid phosphatase secreted watermelon root and the capability of the crop of utilizing organic P. Acid phosphatase is higher in activity in the treatment applied with organic manure than in the treatment applied with chemical fertilizer, equivalent to the former in P application rate. However, excessive application of organic manure does not further enhance its effect on activity of acid phosphatase. Application of organic manure at a higher rate increases the content of available P in rhizosphere soil and hence P absorption and watermelon yield.

    • Soil Erosion Resistance Characteristics of Zanthoxylum Bungeanum and Lonicera Japonica Forest Land in Canyon Areas of Karst Plateau

      2019, 56(2):466-474. DOI: 10.11766/trxb201804040607

      Abstract (1676) HTML (430) PDF 1.33 M (1795) Comment (0) Favorites

      Abstract:Abstract 【Objective】 Rocky desertification in karst areas is a leading problem in Guizhou Province, Southwest China, especially the Huajiang Valley, which is one of the most prominent areas suffering from the problem. In order to address this problem with comprehensive ecological measures, it is of great essence for us to recover forest vegetation so as to promote changes in structure of the eco-environment in karst areas. However, there are still many major issues waiting to be solved in management of the desertification, for example, what kind of ecological as well as economic plants to be selected, how to make reasonable and effective use of natural elements and people's subjective sense of motivation under harmonization between the conditions of local eco-environment and the needs for economical development; how to realize sustainable development of the ecology and economy; how to build a society where people and nature coexist harmoniously; and how to teach people to live coexistently with ecology. Therefore, the paper is aimed to address these issues in an attempt to provide some scientific basis for restoration of water reserving forests and construction of eco-environment. To that end, investigations were made in the Huajiang karst gorge area to explore effects of Zanthoxylum planispinum var dintanensis forest and Lonicera japonica forest controlling soil erosion. Four plots of forests were set up for comparison in effect on soil erosion, i.e. Plot A, a tract of pure Zanthoxylum planispinumvar dintanensis forest; Plot B, a tract of pure, Lonicera japonicaforest; Plot C, a tract of Lonicera japonica-Zanthoxylum planispinum var dintanensis mixed forest; and Plot D, a tract of deserted land. The trees are native in the Huajiang karst valley area.【Method】Three key indices of soil erosion resistance, i.e. soil permeability, soil scour resistance and soil erosion durability, were measured. To measure soil permeability, the cutting ring method was adopted. Based on volume of the water(mm) passing through a cutting ring per unit of time, initial-infiltration rate ( mm•min-1), stable-infiltration rate (mm•min-1), and average-infiltration rate (mm•min-1) of water were worked out, and then soil permeability was. To measure soil scout resistance, the undisturbed soil scouring trough method designed by Jiang, et al. was used. It is mainly expressed by how long it takes for water flow to scour one gram of soil at a flow velocity set in line with mean annual rainfall. And to measure soil erosion durability, soil samples collected from the four plots were sifted trough a stack of sieves (7mm and 10mm) to get soil particles 7~10 mm in size, of which 50 were taken out for erosion test that lasted for 10 min. and how many particles were collapsed was recorded every minute for calculation of percentage of the collapsed particles against the total particles tested, the index value of soil erosion durability.【Result】1) In all the soils, regardless of type, the higher the non-capillary porosity and the total porosity, the higher the soil permeability, while, the higher the bulk density, the lower the soil permeability. 2) In terms of soil scour resistance, the four plots displayed an order of Plot A (2.02 min•g-1) > Plot C (0.82 min•g-1) > Plot B (0.43 min•g-1) > Plot D (0.31 min•g-1) 3. In terms of soil erosion durability, Plot C was in the lead among the four. 【Conclusion】 After overall evaluations of soil permeability, soil scour resistance and soil erosion durability of the four plots, a conclusion comes as that mixed forest is the most conducive to improvement of soil erosion resistance.

    • >Communications and Comments
    • Problems and Improvements of Methods of Regionalization for Soil and Water Conservation at a County-Scale

      2019, 56(2):475-486. DOI: 10.11766/trxb201806150134

      Abstract (1411) HTML (690) PDF 4.01 M (2062) Comment (0) Favorites

      Abstract:Regionalization of soil and water conservation in China is to, based on the inhomogeneous of natural characteristics and socio-economic conditions, and also takes into consideration, where available, already developed maps of spatial variations of soil erosion, divide a certain area into functional regions, with the hope that region-specific management rather than site-specific management could be applied without too much adjustment in each region. China spans nearly 50 degrees in latitude and has almost all existing landform patterns; types and rates and controls of soil erosion vary substantially from one region to another (e.g. the Loess Plateau versus the Tibet Plateau). In light of these particularities, appeals for regionalization of soil and water conservation could be justified. Hence this article examed the nearly 70 year’s development of regionalization of soil and water conservation in China with the purpose to recognize its characteristics and if exist, drawbacks, and thus put forward a new method for regionalization of soil and water conservation at a county-scale with the hope to help with further improvement of the regionalization. To catch sight of the characteristics in the developing process of regionalization of soil and water conservation, a total of more than 400 articles were downloaded from CNKI and reviewed and studied. To detect the drawbacks of existing regionalizations of soil and water conservation, statistical analysis is used here. To design the new method of regionalization at county-scale, scenario simulation is employed and the P-S-R model were adopted. Based on thoroughly retrospection of the nearly 70 year history of development of regionalization of soil and water conservation in China, the authors characterized the methodical advance that from qualitation to quantitation, including the employment of “3S”(RS/GIS/GPS) technology and mathematical models, and the progress of regionalization’s conceptional framework, especially the introduction of knowledge within economics and ecology disciplines. These methods, however, have their limits because of the conflict between old fashions and new prospect which could be concluded to three point: first, indicators used by quantitative methods are miscellaneous, making some of which have strong correlation, while the scale effect have not been reflected by indicator system; second, some of the key qualitative factors (such as enthusiasm for soil conservation practice) are difficult to be included in the process of regionalization because quantitative methods are unable to process indicators identified by descriptions but not data, moreover, mathematical methods only calculate indicators as numbers without concerning their actual meanings of the data in calculate; third, ecosystem functions are integrated in the process of regionalization in a manner that could hardly influence the result of regionalization scheme. In this end, based on the already existing schemes and theories of other discipline, methods of regionalization of soil and water conservation at county-scale are re-designed: risk of soil and water loss, soil erosion condition, capacity of soil and water conservation are used to build a three-dimension indicator framework, and a total of nine indicators are included in the indicator system, which are slope (°), vegetation coverage (%), population density (person•m-3), land use intensity (%), ecosystem functions (Yuan), index of soil erosion (1), capital/technique input (Yuan•a-1), traffic accessibility (m•m-2), and enthusiasm on soil conservation practice (1). For each evaluating unit, combination type of the three dimensions are employed to determine its region in the regionalization of soil and water conservation. Compared with the existing regionalization schemes where cluster analysis is also integrated, this new county-scale-oriented regionalization method eliminates unnecessary indicators into the indicator system while also maintains their practical implications. By combining qualitation and quantitation in determining the region of each evaluating unit belongs to, this new method could to some extent contribute to a more accurate regionalization of soil and water conservation and therefore, contribute to further soil and water conservation practice.

    • >Research Notes
    • Study on Comprehensive Quantitative Relationship of Soil Fertility Quality and Nitrogen Application Rate with Wheat Nitrogen Use Efficiency

      2019, 56(2):487-494. DOI: 10.11766/trxb201805170170

      Abstract (1584) HTML (674) PDF 3.71 M (2355) Comment (0) Favorites

      Abstract:Both soil fertility and fertilizer N application rate (NA) have important influences on yield and fertilizer N use efficiency (NRE) of wheat. However, it is still unclear about quantitative relationship and relative contribution of their comprehensive effects to the latters. A field experiment was conducted in Changshu of the Taihu Basin. It was designed to have plots different in soil fertility and N application rate for wheat growth, and oriented to explore, how NA and integrated quality index of soil fertility (IFI) affect yield and NRE of the crop. Besides, their quantitative relationships were fitted with the multivariate regression method for analysis of relative contribution rate of the comprehensive effect of NA and IFI to yield and NRE of wheat. Results show that higher NA and IFI helps increase wheat yield, but not NRE of the crop, and that IFI was higher than NA in the effect, and their relative contribution rate was 1.09:1 to wheat yield and 1.32:1 to NRE. The findings of the study suggest that to improve comprehensive quality of the soil may achieve the goal of safety for both grain and ecology, while minimizing N application rate. So to build up soil fertility quality of the farmland is more basic and more important in agricultural production.

    • Effect of Biochar-Based Fertilizer on Properties of Tobacco-planting Yellow Soil, and Nutrient Accumulation, Yield and Quality of Flue-Cured Tobacco

      2019, 56(2):495-504. DOI: 10.11766/trxb201806060133

      Abstract (1743) HTML (578) PDF 1.30 M (2279) Comment (0) Favorites

      Abstract:In order to solve the problems with tobacco-planting yellow soil (acidification, loss of water and nutrient, low productivity) and flue-cured tobacco ( low nutrient uptake and yield) in Guizhou, a field fertilization experiment on flue-cured tobacco, Yun 87 in variety was conducted in 2016 in a tract of tobacco-planting yellow soil typical of Guizhou, to explore effect of different fertilization on chemical and biological properties of the soil, and nutrient accumulation, yield, volatile aroma components and chemical components of the flue-cured tobacco. The experiment was designed to have three fertilization treatments, (1) NF, (no fertilization)as CK, (2) CF (conventional fertilization, band placement of organic manure of vinasse + base fertilizer specialized for flue-cured tobacco + pit placement of side-dressing specialized for flue-cured tobacco), and (3) BF (band placement of biochar-based organic manure of vinasse + biochar-based compound fertilizer + pit placement of side-dressing specialized for flue-cured tobacco). Compared to CF, BF significantly increased soil pH, the contents of soil available phosphorus and available potassium, the amounts of soil bacteria, actinomyces and fungi, and also the activities of soil urease and catalase (CAT), among of which, CAT activity was increased significantly by 10.6%. In addition, BF improved the fertilizer agronomic efficiencies , the yield and the accumulation of nitrogen, phosphorus and potassium of the flue-cured tobacco, and the total contents of volatile aroma components and carotenoid in the flue-cured tobacco leaves. All the findings demonstrate that the application of biochar-based fertilizer can help build up quality of the tobacco-planting yellow soil, promote nutrient accumulation of the flue-cured tobacco, regulate aroma components in the flue-cured tobacco. Therefore, the biochar–based fertilizer can be extrapolated in similar flue-cured tobacco planting areas in Guizhou and Southwest China.

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