• Volume 60,Issue 1,2023 Table of Contents
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    • >Insights and Perspectives
    • Origination of the Earth Soil and Its Implications for the Establishment of the Earth Inhabitability

      2023, 60(1):1-6. DOI: 10.11766/trxb202209220524

      Abstract (899) HTML (1016) PDF 1.32 M (1668) Comment (0) Favorites

      Abstract:Controlled by soil forming factors, the origination and development of earth soil had been experiencing contrasting environmental changes and corresponding processes. Previous studies have shown that the earliest weathering regolith appeared during the Archean Eon, with evolution of the Earth, biological forcing had been involved in soil formation and soils as defined by the modern concept got appeared during the Cambrian period. Over the geological periods soils formed and developed in episodic changing environments while the formation of soil and the establishment of soil cover (pedosphere) gave feedback to landscape evolution, topography, ecosystem and atmospheric system, therefore substantially changing atmospheric composition and altering global biogeochemical cycling. The formation of pedosphere is a prerequisite of the inhabitable earth.

    • >Reviews and Comments
    • Progress of Functional Genes Related to Soil Nitrogen Cycling Based on Knowledge Mapping

      2023, 60(1):7-22. DOI: 10.11766/trxb202110270580

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      Abstract:Functional genes related to soil nitrogen (N) cycling are widely involved in a series of ecological processes, including N fixation, ammonification, nitrification and denitrification, and are key components of the N biogeochemical cycling, which greatly affects soil productivity, carbon neutralization, and agricultural sustainable development, as well as global environmental changes. In recent decades, the rapid development of molecular and microecology technology has promoted the research about functional genes related to soil N cycle and their microbial functional communities. In order to objectively and analyze the research trends, hotspots, and historical trends in the field of functional genes related to soil N turnover, the pertinent literature retrieved from the Web of Science database from 2001 to 2020 was analyzed from four aspects of publications amount, highly cited papers, high-frequency keywords and historical direct citations based on knowledge mapping. The results showed that: 1) The application of molecular biology techniques to excavate the functional genes and community structure related to soil N turnover so as to explore the microbiological mechanism is the current hotspot and entry point in the research field. 2) The research about soil N turnover functional genes mainly focused on three aspects: (1) Using metagenomics and other technologies to screen, identify and annotate the functional genes related to soil N turnover, so as to discover new microbial functional gene sequences and updates primer database, etc.; (2) Effects of environmental factors and agricultural management practices on soil N turnover related microbial indicators; (3) Using functional gene abundance to characterize the soil N cycling processes-related functional microorganisms, as well as analyze the relationship between functional genes, soil properties, and microbial community structure, in order to reveal the molecular mechanism of soil nitrogen turnover. 3) The historical development context of soil N turnover functional genes was from the screening, identification, identification, corresponding primer design and analysis method determination of N-cycling functional genes, to the influencing factors (or environmental conditions) of soil N turnover functional genes, combined with the current data of the activity, abundance of functional genes related to soil N turnover, and functional microbial populations, community structure and even soil properties, to comprehensively explore the microbial mechanism of soil N cycling.

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

      2023, 60(1):23-38. DOI: 10.11766/trxb202105060240

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      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 Pospeciation. Then we reviewed the evolution trends and controls of different Pospeciation 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.

    • Environmental Behavior and Control of Antibiotic Resistance Genes in Soil — A Review

      2023, 60(1):39-49. DOI: 10.11766/trxb202111100608

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      Abstract:Over the past several decades, the long-term misuse and abuse of antibiotics in human health and livestock production have significantly contributed to the widespread dissemination of antibiotic resistance. Antibiotic resistance has been regarded as the top of the six emerging environmental issues and global challenges humans face in this century. Antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in natural and agricultural environments such as soil may have a substantial impact on the spread of resistance determinants to the human microbiome. Research on the distribution, source, diffusion and elimination techniques of ARGs in soil has become a hot topic.

      ARGs have been widely identified in diverse environments affected or unaffected by human activities, including soil, water sources, and atmosphere. Soil undoubtedly contains a complex natural resistome and also acts as a key reservoir for ARB and ARGs in the environment. The ARGs in soil primarily originate from internal resistance and external input. The internal resistance in microorganisms mainly indicates the presence of ARGs in the genomes of microbes. However, the antibiotic resistance in microbial can also be ascribed to the random mutation of genes under special conditions. In addition, with the widespread use of antibiotics in clinical care, livestock and agricultural production, more ARB and ARGs are introduced into the soil, resulting in an increased enrichment of ARGs.

      The transfer of ARGs often occurs via environmental media. However, recent studies have shown that they may also be transmitted between parents and offspring or among different species of bacteria by vertical and horizontal gene transfer (HGT), respectively. ARGs in the soil can be transferred to surface/groundwater, atmosphere and the phytosphere. Both natural factors and human activities play vital roles in ARGs transmission in soils. For example, soil physicochemical properties (pH, organic matter, water content, etc.), agronomic regulations (cropping patterns, reclaimed water irrigation, organic fertilization, etc.), and environmental contaminants (heavy metals, nanoparticles, microplastics, etc.) can significantly affect the structural diversity and function of soil microbial communities. They have been identified as important environmental pressures that induce the evolution and spread of antibiotic resistance.

      ARGs are also identified in human clinical pathogens conveyed by soil microbes. When comparing the multidrug-resistant resistome of soil bacteria with those in clinical human pathogens, the functional metagenomic analysis indicated a high nucleotide identity (>99%). This inferred possible HGT among bacteria from various environments. To reduce the threat posed by ARGs, treatment measures (aerobic composting, anaerobic digestion, and wastewater treatment technologies) have been examined to alleviate the selective pressure and reduce the import of ARGs into the soil. Generally, the reduction of ARGs in the environment is mainly related to extracellular DNA and cell transport, death of the host, and attenuation of extracellular ARGs.

      Although the threat of ARB and ARGs to humans is generally recognized, it is difficult to determine threshold values for the maximum admissible levels of ARB and ARGs in diverse environments highly related to human activities. Furthermore, there is insufficient information to quantitatively evaluate the associated human health risks. Considering the urgency of the problem, it is necessary to establish a global systematic and publicly available monitoring network, for consecutively measuring antibiotic usage and the diversity of antibiotic resistance from clinical and agricultural practices. Continuous surveillance of antibiotic resistance can contribute to disease therapy, effective antimicrobial management and policy formulating. Thus, the “One Health” theory was proposed to manage the development and spread of ARGs in an interdisciplinary manner, and holistically reduce human risk to the lowest level. More attention should be paid to ARGs pollution with investment in both fundamental and applied research, to provide a strong scientific basis for formulating effective alleviation actions and a standardized assessment system. This will serve as a baseline for preventing, reducing, and removing these environmental contaminants.

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

      2023, 60(1):50-62. DOI: 10.11766/trxb202107240275

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      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.

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

      2023, 60(1):63-76. DOI: 10.11766/trxb202103120140

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      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.

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

      2023, 60(1):77-88. DOI: 10.11766/trxb202103020119

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      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.

    • Effects of Land Use Change on Evapotranspiration in the Loess Tableland

      2023, 60(1):89-98. DOI: 10.11766/trxb202103150143

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      Abstract:【Objective】 Studying the response of evapotranspiration to land use change in Chinese Loess Plateau (CLP) is of great significance to clarify the effects of the Grain for Green Project on regional climate. Many studies have focused on the temporal trend or spatial distribution of reference evapotranspiration based on meteorological or satellite data at the watershed or regional scales. However, these studies cannot reflect the actual situation of the impact of land use change on surface evapotranspiration. Thus, the quantitative evaluation of actual evapotranspiration at the stand scale is lacking. Therefore, the objective of this study is to evaluate the effects of conversion from cultivated farmland into apple orchard on the actual evapotranspiration. 【Method】 A paired experimental study was conducted at the Changwu Tableland, south of the CLP. Both the cultivated farmlands and 20-year-old apple orchards were sampled with a soil auger (0.06 m in diameter) at 0.2 m intervals at each of the five selected sites, with a total of 10 deep soil cores (10 m). The volumetric soil water content was calculated by mass water content and soil bulk density, and the chloride concentrations of soil water were measured by extraction method. Since the local apple orchards were all converted from cultivated farmlands and the soil texture is uniform, the space-for-time method was applied. As precipitation is the only source of water for local crops, the chlorine mass balance method can be used to estimate groundwater recharge. Therefore, the surface evapotranspiration can be estimated by combining soil water mass balance with chloride mass balance. 【Result】 The results show that the averaged soil water content of 4~10 m soil layer in 20-year-old apple orchard was 0.20 m3 m–3. This was significantly lower than that in farmland (0.28 m3·m–3) and implies that soil water content were obviously affected by deep root after cultivated farmland converted into apple orchard 20 years ago. The long-term averaged groundwater recharge rate was 57±13.5 mm·a–1 in cultivated farmlands, which resulted in the actual evapotranspiration of 527±13.5 mm·a–1 and accounting for 90%±2.3% of the annual precipitation. After cultivated farmland converted into 20-year-old apple orchard, the actual evapotranspiration significantly increased, with an average of 625 mm·a–1, accounting for 107% of the annual precipitation. Compared to cultivated farmlands, the actual evapotranspiration, in total, increased 1960 mm in 20-year-old apple orchard from 20 years ago, with an annual average of 98 mm. Within the 20-year-old apple orchards, soil water in 4~10 m, and 10~18 m soil layers contribute 24 mm·a–1(4%), and 41 mm·a–1(3%) to the annual evapotranspiration, respectively. 【Conclusion】 The small contributions of 4~10 m and 10~18 m soil layers indicated that the deep soil water (below 4 m) has an important role in evapotranspiration of the deep rooted apple tree. However, the main water sources for evapotranspiration still depend on the shallow soil water (0~4 m) that is easily recharged by the latest precipitation. This is the first study that quantitatively evaluated the impacts of cultivated farmland being converted into apple orchard on the evapotranspiration and the contribution of deep soil water to evapotranspiration. This study provides a scientific basis for evaluating the effects of land use change on the regional evapotranspiration and climate on the CLP and other regions with a significant land use/cover change.

    • Effect of Different Rice Planting Years on Pore and Infiltration Properties of Soda Saline-alkali Soil

      2023, 60(1):99-105. DOI: 10.11766/trxb202105180262

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      Abstract:【Objective】The existing scientific literature and production practice have proved that rice planting can effectively improve soda saline-alkali soil. However, there is still a lack of research on how rice planting affects soil structure and infiltration performance to improve saline-alkali land. 【Method】In this paper, the pressurized mercury method was used to study the micro-pore changes of soil in different years of rice planting and the difference of soil infiltration performance was studied by soil column experiment, to clarify the influence of rice planting on the change of saline-alkali soil structure and infiltration performance. 【Result】The result show that the average pore size of soil increased with an increase in the planting years. Specifically, the average pore size of soil in the 7th year increased by 0.808μm compared with that in the 1st year. Also, the specific surface area of soil decreased with an increase in planting years, and the specific surface area of soil after 7 years was decreased by 0.087m2·g–1 compared with that after one year. Soil porosity increased with the planting years, and the soil porosity after 7 years was increased by 8.35% compared with that in the 1styear. With the increase of planting years, the number of small pores decreased while that of large and medium pores increased. The pore size of the soil planted for 7 years was 28.25% (ranging from 30~75μm) and 12.45% (ranging from 75~200μm). Also, the infiltration performance of the soil was also significantly improved. The steady infiltration rate of soil planted for 7 years was 107 times higher than that of waste land. 【Conclusion】 Planting rice in saline alkali land is conducive to the formation of soil pores and the transformation from small pores to large and medium pores. The increase of soil pore size and porosity can effectively improve soil structure and improve soil infiltration performance. Under the experimental conditions, the leaching rate of salt in saline-alkali soil was increased, thereby enhancing the desalination efficiency of the soil tillage layer.

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

      2023, 60(1):106-116. DOI: 10.11766/trxb202104140195

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      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 nitrogen 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 nitrogen and other soil properties in the soil were determined. 【Result】The results show that soil ammonium nitrogencontent 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 nitrogen 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 nitrogen 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 nitrogen 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 nitrogen 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 nitrogen 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 ammonium nitrogen pollution.

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

      2023, 60(1):117-126. DOI: 10.11766/trxb202105210265

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      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.

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

      2023, 60(1):127-137. DOI: 10.11766/trxb202104010174

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      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】 Soil samples were collected 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-/NO4+ 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 NO4+ into a part of those slurries made with water to adjust their external NO3-or NO4+ 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 NO4+ 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 NO4+ 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 NO4+ 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 NO4+ 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.

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

      2023, 60(1):138-150. DOI: 10.11766/trxb202103200154

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      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.

    • Effects of Shrub-encroached Grassland on the Stability of Soil Aggregates and Cementing Materials in Alpine Grassland of Qinghai-Tibet Plateau

      2023, 60(1):151-163. DOI: 10.11766/trxb202107290253

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      Abstract:【Objective】Soil aggregate is an important storage unit of soil organic carbon, and its stability directly affects the sequestration of organic carbon. This study explored the effects of shrub encroachment on the stability of soil aggregates and their cementing materials in grassland.【Method】The content of soil aggregates and their cementing materials (soil aggregate organic carbon, Fe-Al oxides, Ca bond organic carbon, and Fe-Al bond organic carbon) and the stability of aggregates (the content of aggregates >0.25 mm, mean weight diameter/MWD and fractal dimension)were determined at four typical shrub-encroached grasslands(Spiraea alpina, Sibiraea angustata, Caragana microphylla, Potentilla fruticosa) in the eastern margin of the Qinghai-Tibet Plateau. 【Result】 The results show that shrub encroachment significantly decreased the aggregate content of 2~0.25 mm and <0.002 mm and aggregate stability in the Caragana microphylla plot. However, there was no significant effect on the other three shrub grasslands. Shrub encroachment mainly changed the content of cementing substances in the aggregates of the Caragana microphylla and Sibiraea angustata plot. The results of boosted regression tree analysis between cementing materials and MWD show that the main contributing factors to the stability of aggregates in Spiraea alpina polt were complexed iron (Fep) and amorphous iron and aluminum (Feo, Alo). Also, the major contributors to grassland and other shrub plots were soil aggregate organic carbon (SAOC) and free iron oxides(Fed). 【Conclusion】 Although shrub encroachment increases the content of main cementing material—SAOC in <0.053 mm in Caragana microphylla plot, it reduced the content of large aggregates and clay, as well as the content of Fed in the Caragana microphylla plot. Thus, the stability of aggregates is reduced, which may be detrimental to the retention of organic carbon. This study provides theoretical knowledge for the stability theory of aggregates and the dynamic change of the organic carbon pool in this region.

    • Effects of Humic Acid on Biodegradation of Pyrene by Mycobacterium sp. NJS-1

      2023, 60(1):164-174. DOI: 10.11766/trxb202110010341

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      Abstract:【Objective】Pollution by Polycyclic Aromatic Hydrocarbons(PAHs)in the soil environment has become a serious problem. In recent years, microbial degradation of PAHs to achieve soil remediation has become an important method. However, microbial degradation is not a very efficient and ideal process for the remediation of PAHs-polluted environments. In this study, humic acid(HA)was added during the degradation process to explore its effect on the microbial degradation of PAHs. 【Method】Using pyrene as a typical PAH and HA as representative dissolved organic matter, Mycobacterium sp. NJS-1 with high pyrene degradation efficiency was selected to degrade pyrene with or without HA. Fourier transform cyclotron resonance mass spectrometry(FT-ICR-MS), laser confocal microscopy(CLSM), and techniques such as infrared and Raman spectroscopies were used to analyze the residual characteristics of pyrene, intermediates and colony changes during degradation.【Result】Results show: 1)The presence of HA significantly accelerated pyrene biodegradation. Approximately 88.33%±3.40% of pyrene was biodegraded within 7 days of incubation with the addition of HA, but only 35.33%±3.27% was biodegraded without HA; 2)The FT-ICR-MS results indicated that addition of HA induced two biodegradation pathways - attacking of 1, 2-positions and 4, 5-positions of pyrene by dioxygenase, whereas in the absence of HA only the 4, 5-position was attacked; 3)The CLSM results showed that HA enhanced the growth of Mycobacterium sp. NJS-1 with no death of bacteria cells. Simultaneously, tyrosine proteins and fulvic acid-like compounds under visible light were detected and showed that HA enhanced bacterial activity by biofilm formation; 4)The results of the spectral analysis showed that a series of bands, mainly including protein amide, tyrosine, tryptophan and phenylalanine, red-shifted, implying that the interacted forces from the functional groups of bacterial surfaces changed in the presence of HA.【Conclusion】HA can improve the degradation efficiency by increasing the degradation pathway of pyrene and inducing the interaction of functional groups on the cell surface to form a microbial membrane. Meanwhile, the addition of exogenous HA could also promote the interactions among colonies and accelerate the degradation.

    • A Novel Alkaline Fertilizer and Its Function as well as Mechanism to Remediation Soil Acid and Cd Pollution

      2023, 60(1):175-188. DOI: 10.11766/trxb202102100092

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      Abstract:【Objective】 This study aimed to provide a theoretical basis for reducing soil Cd pollution through the application of alkaline fertilizer.【Method】Field and constant temperature incubation experiments were carried out to study the effect of alkaline fertilizer on soil acidification, Cd pollution, and the effect of soil pH on the thermodynamic properties of soil Cd adsorption and desorption.【Result】Application of alkaline fertilizer significantly (P < 0.05) increased the soil pH and reduced the content of available Cd. This shows that soil treatment with alkaline fertilizer is an effective and reliable measure to reduce soil available or extractable Cd. When the ambient Cd concentration was ≤60 mg·L–1, pH values from 5.0 to 9.0 had almost no effect on the adsorption strength of Cd (between 15.77 mg·kg–1/mg·L–1 and 16.67 mg·kg–1/mg·L–1) while Cd concentrations > 60 mg·L–1 showed increased adsorption strength as the pH was increased. Nevertheless, the adsorption rate decreased with the increase in the initial concentration of Cd. Under the same Cd concentration conditions, the higher the pH value, the higher the adsorption capacity and adsorption rate of Cd. The Freundlich, Langmuir, and Temkin equations fitted the Cd isothermal adsorption data well. Of all three equations, the Freundlich equation had the best fit and was the most suitable to quantitatively describe the characteristics of Cd adsorption. The adsorption of Cd was a spontaneous process and characterized by a negative adsorption free energy (△G). Importantly, △Gincreased with an increase in Cd concentration at constant pH whereas △Gdecreased with an increase in soil pH. Under alkaline conditions, △G was lower than under acidic conditions. However, Cd adsorption was more intense under alkaline conditions than in acidic conditions. This shows that increasing the soil pH with alkaline fertilizer was beneficial in improving the Cd adsorption capacity of the soil. At relatively low Cd concentration, Cd adsorption occurred through the specific adsorption mechanism. When the degree of Cd contamination was high and at high pH, the variable charge of the soil and its non-obligate adsorption played a positive role. Furthermore, the Cd desorption capacity and the rate decreased significantly (P < 0.05) after the application of alkaline fertilizer. 【Conclusion】 At constant pH and increasing Cd concentration, the adsorption capacity of Cd and the free energy increased while the adsorption rate decreased. Also, at higher soil pH, the adsorption capacity, adsorption rate, and reaction free energy were significantly increased while the desorption rate was decreased. There was a negative correlation between soil pH and the availability of soil Cd. Increasing the soil pH can enhance the ability of soils to fix and passivate Cd, thus, reducing the bioavailability of Cd. It is suggested that alkaline fertilizers should be applied in agricultural practices to manage soil acidification, improve soil pH, increase heavy metal cations adsorption and reduce their bioavailability in soils. This will help to control soil acidity and reduce heavy metals pollution in agro-production.

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

      2023, 60(1):189-200. DOI: 10.11766/trxb202106230326

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      Abstract:【Objective】The purpose of this study was to determine the amount of fertilizer that could be replaced by straw returning under the condition that crop yield and soil nutrients were not lost, and to reveal the microbial mechanism that promoted the efficient utilization of straw nutrients, so as to provide a basis for promoting the reduction of fertilizer application.【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.

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

      2023, 60(1):201-211. DOI: 10.11766/trxb202102070085

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      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.

    • Soil Nitrogen Supply and Retention Capacity Determine the Effect and Utilization Rate of Nitrogen Fertilizer in Paddy Field

      2023, 60(1):212-223. DOI: 10.11766/trxb202104070181

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      Abstract:【Objective】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. 【Method】There were three N treatments as follows: no N treatment (CK), low N rate and high N rate (N 150 and 300 kg·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. 【Result】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–1for WS. This observation was consistent with the results that the 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. 【Conclusion】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.

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

      2023, 60(1):224-234. DOI: 10.11766/trxb202102050078

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      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

      2023, 60(1):235-246. DOI: 10.11766/trxb202104210207

      Abstract (439) HTML (1169) PDF 628.71 K (1092) Comment (0) Favorites

      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.

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

      2023, 60(1):247-257. DOI: 10.11766/trxb202108050327

      Abstract (499) HTML (715) PDF 660.96 K (912) Comment (0) Favorites

      Abstract:【Objective】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. 【Method】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. 【Result】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–1with 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. 【Conclusion】 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.

    • Effects of Long-term Application of Phosphorus and Organic Fertilizer on Transformation of Zn Forms in Yellow Paddy Soil

      2023, 60(1):258-268. DOI: 10.11766/trxb202107290283

      Abstract (347) HTML (493) PDF 532.10 K (803) Comment (0) Favorites

      Abstract:【Objective】To investigate the variation of zinc (Zn) speciation in yellow paddy soil under different long-term fertilization and its effect on available Zn, a field experiment was designed in 1995. 【Method】There were six treatments: the control (no fertilizer, CK), P deficiency (NK), balanced application of chemical N, P and K fertilizer (NPK), single manure (M), lower organic and inorganic fertilizer combination treatments (0.5 MNP), and higher organic and inorganic fertilizer combination treatments (MNPK). The change process of soil available Zn and the temporal variation of different forms of Zn were studied. Also, the relationship between different forms of Zn and available Zn was analyzed with correlation and path analyses. 【Result】The results showed that the available Zn and Zn activation coefficient of soil with NK treatment decreased with the increase of experimental years. During this time, the linear fitting formula of the Zn activation coefficient reached a significant level, and the annual growth rate was -0.052 percentage points. Compared with NK treatment, the available Zn and Zn activation coefficient of soil with NPK treatment increased by 44.1% and 1.49 percentage points, respectively in 2019. Also, the contents of weak acid soluble Zn and reducible Zn increased by 15.9% and 5.3%, respectively. For treatments with organic fertilizer, the available Zn and Zn activation coefficient of soil increased linearly with the increase of experimental years, and the annual growth rate was 0.074-0.1244 mg·kg–1and 0.032-0.063 percentage points, respectively. Compared with NPK treatment in 2019, the available Zn and Zn activation coefficient of soil in the manure treatments increased significantly by 6.3%-22.6% and 0.68-1.47 percentage points, respectively. For these treatments, the contents of weak acid-soluble, reducible, and oxidizable Zn increased significantly by 33.6%-84.0%, 32.5%-47.4%, and 25.5%-36.3%, respectively. In addition, the proportions of weak acid-soluble, reducible, and oxidizable Zn increased significantly by 0.6-1.3, 1.7-3.4, and 1.2-7.3 percentage points, respectively. On the contrary, the proportion of residual Zn was observed to decrease by 3.6-12.0 percentage points. Correlation analysis showed that soil available Zn was significantly positively correlated with weak acid-soluble, reducible, and oxidizable Zn, but significantly negatively correlated with residual Zn. Path analysis results showed that the direct path coefficient of weak acid-soluble Zn was the largest and had a significant direct positive effect on available Zn, residual Zn showed a significant direct negative effect on available Zn, while reducible and oxidizable Zn indirectly affected weak acid soluble Zn and had a strong indirect positive effect on available Zn. 【Conclusion】The weak acid-soluble Zn was the main source of available Zn in yellow paddy soil, while reducible and oxidizable Zn were the important cache database of available Zn. In agricultural production, the soil Zn efficiency could be improved by applying organic fertilizer reasonably to promote the transformation of Zn to weak acid-soluble, reducible, and oxidizable Zn, and avoid the accumulation of Zn in the residual state.

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

      2023, 60(1):269-279. DOI: 10.11766/trxb202103280167

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      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.

    • Impacts of Artificial Revegetation on Soil Fungal Community in Desertified Alpine Grassland

      2023, 60(1):280-291. DOI: 10.11766/trxb202107050329

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      Abstract:【Objective】This study aimed to illustrate the impacts of different revegetation approaches on the resilience of soil fungal communities in desertified alpine grasslands, and to explore the main environmental factors in driving the succession of soil fungal community.【Methods】We sampled surface soils within 0-10 cm from four different types of alpine grasslands, i.e., natural grassland (NG), desertified grassland (DG), herb-based artificial grassland (AG) and shrub-based artificial grassland (AS). Fungal community biomass, α-diversity and structure were studied using qPCR and Illumina Mesiq high-throughput sequencing technologies.【Result】1) grassland desertification significantly decreased soil fungal biomass and α-diversity, which showed no significant difference among AG, AS and NG after 22-year revegetation. 2) Both desertification and artificial revegetation significantly changed the fungal community structure. The relative abundance of Basidiomycota significantly (P<0.05) decreased after desertification. Some rare fungi phyla with less than 1% relative abundance tended to disappear, while the relative abundance of unclassified fungal phyla significantly (P<0.01) increased. After 22 years of revegetation, there was no significant difference in the relative abundance of most fungal phyla among AG, AS and NG. AG and NG showed more similar fungal structure than that of AS and NG. 3) The correlations of soil fungal α-diversity with vegetation and soil properties were diversity-index-dependent, while fungal structure significantly (P<0.01) positively correlated with most of vegetation and soil properties. Importantly, vegetation and soil properties jointly explained 21.4%-50.0% of variations in soil fungal community structure.【Conclusion】These findings indicate that fungal diversity and biomass in desertified grassland almost paralleled to the undegraded level after 22 years of revegetation. Despite fungal community structure in revegetation sites was still not similar to that of natural grassland, it is more beneficial to use grassland plants than shrub species for the restoration of soil fungal community structure in the degraded alpine grassland.

    • Effects of Different Fertility Improvement Measures on Microbial Community Structures in Biological Red Soil Crusts of Woodland

      2023, 60(1):292-303. DOI: 10.11766/trxb202108130311

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      Abstract:【Objective】Microorganisms play an important role in the formation of biological soil crusts while biological soil crusts are important for controlling soil erosion. However, there is limited research on microbial community in the biological soil crusts of southern red soil. Therefore, the changes of microbial community structure under forest fertility improvement measures in this area are unclear.【Method】The present study was conducted in the Pinus elliotti forest of tropical Quaternary laterite in the middle subtropical zone. Organic fertilizer, biochar, and lime + microbial fertilizer were added to soil, and bare land was set as the control (CK). High throughput sequencing technology (Illumina MiSeq) was used to study the effects of the three fertility improvement measures on bacterial and fungal community structures. 【Result】Results showed that 21 bacteriophyta and 7 mycobionta were detected in biological soil crusts. The dominant bacteriophyta were Acidobacteria (27.39%), Proteobacteria (25.90%), Actinobacteria (16.68%), Chloroflexi (12.26%), while the dominant mycobionta were Basidiomycota (61.19%) and Ascomycota (29.48%). The three fertility improvement measures had no significant effects on the diversities of bacteria and fungi, but significantly changed their community structures in order of organic fertilizer > biochar > lime + microbial fertilizer, and these effects were higher in bacteria, compared to fungi. Also, the effects of the three fertility improvement measures on specific bacteriophyta and mycobionta were different. The three fertility improvement measures increased the relative abundance of Proteobacteria, and decreased the relative abundance of Chloroflexi. Organic fertilizer and lime + microbial fertilizer increased the relative abundance of Ascomycota, but decreased the relative abundance of Basidiomycota, while biochar had opposite effects on mycobionta. Among the soil environmental factors, pH, organic carbon, and total nitrogen had a great influence on microbial community structure.【Conclusion】These results provided significant scientific guidance for the regulation of soil microbial community structures in biological soil crusts, which is beneficial for the formation of biological soil crusts and the control of water and soil erosion in southern red soil.

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