Abstract:Soil temperature(especially surface temperature)is a key physical quantity in the interaction between land and atmosphere, and plays a very important role in the earth system. Soil temperature prediction technology has always been the core scientific problem in land surface model, numerical weather prediction and climate prediction. This paper systematically reviews the research progress of soil temperature prediction equation, from the classical heat conduction equation to the heat conduction convection equation that takes into account the physical process of vertical movement of soil moisture, from the single sine wave approximation to the Fourier series approximation of the daily change of surface temperature, from the assumption that the diurnal change of convection parameters is constant to the consideration of its diurnal change, and emphatically summarizes the creation, improvement and solution of the soil heat conduction convection equation. Finally, this paper reviews the application of heat conduction convection equation in the study of surface energy balance, vertical movement of soil moisture, water flux, earthquake and frozen soil heat transfer. At the same time, it is pointed out that the influences of soil water phases and plant roots on the heat conduction-convection equation is warranted for the future research of soil temperature prediction equation.

Abstract:Soil compaction by agricultural machinery has become one of the most serious soil degradation problems in the world. This paper reviewed the research progress of soil compaction from four aspects: detection, impact, alleviation and prevention of soil compaction. It shows that new detecting methods are urgently needed for field soil compaction detection. The impact of soil compaction is mostly focused on the top cultivated soil layer, but the effects of subsoil compaction and its potential ecological services in addressing climate change have been overlooked. Reasonable agricultural management strategies such as crop and tillage rotation methods could be applied to alleviate soil compaction. Overall, subsoil compaction is difficult to alleviate in a short period and prevention should be the top priority although there is still a lack of practical prevention methods. Agricultural mechanization in China is still in the early development stage, and effective preventive measures should be taken to avoid soil compaction like that in developed countries.

Abstract:As the basic unit of soil structure, soil aggregates play an important role in the soil and are vital for maintaining soil ecological functions(such as carbon sequestration and nutrient retention, etc.). The formation and stability of aggregates are based on the complex interactions between minerals, organic matter and organisms in the soil, but the mechanisms of these interactions still lack a systematic summary. This article reviews the research history of soil aggregates over the past century and sorts out the historical nodes for the proposition of key theories, including important theoretical viewpoints, main theoretical models(Monnier’s aggregate stability model, Tisdall and Oades’ aggregate hierarchy model, Six’s aggregate turnover model and Christensen’s tertiary structure model), indexes for evaluating the structure and stability of soil aggregates, comparison of two main sieving methods(dry and wet sieving), and classification basis and classification type for soil aggregates. Furthermore, it expounds on the action mechanism of aggregate basic structural units(minerals, organic matter, organisms and their derivatives)and the formation and stabilization mechanism of microaggregates and macroaggregates, detailing the aggregate formation by organo-mineral interactions(Wershaw’s bilayer model and Kleber’s zonal model)and biological control of aggregate turnover(Miller’s sticky string sag theory). Through this review, it is found that there are more in-depth discussions on the factors affecting the formation and stability of soil aggregates, but few studies have addressed the effects of pH and redox processes on the aggregates in the paddy and waterfront soil systems. Finally, the future development of soil aggregate research is highlighted, in expectation of providing theoretical reference for the sustainable use of soil resources.

Abstract:Forest is the main body of the terrestrial ecosystem, and plays a central role in regulating terrestrial ecological balance. At present, the total amount of forest resources are insufficient, and there are increasing demands for wood, which require the development of plantations globally. Soil is the basic resource supporting the growth of plantations and the main site for nutrient transformation and biodiversity protection. To date, the decline of soil fertility has become a serious problem in plantation management in China, severely restricting the sustainable management of forestry production and leading to an increased vulnerability of ecological security barriers. Therefore, it is important to increase our understanding of the formation and impact factors of biological barriers derived from soil fertility decline in plantations and to explore key technology for modulating plantation health and primary productivity. The present study systemically discussed the mechanism of maintaining soil fertility in plantations from soil physical and chemical properties, soil biological community characteristics and functions, and probed the underground ecological processes affecting soil fertility of plantations, including forest age structure, stand density, tree species type and tending management mode. In the future, more attention should be paid to the mechanism of coupling soil's physical, chemical, and biological properties in plantations when the environment changes. Besides, it is necessary to further quantify the interaction model among tree health, soil biology and environment, and to form a comprehensive directional system of regulating plantation health through afforestation, process management, symptom diagnosis and soil fertility modulation, so as to ensure the sustainable and multi-objective management of plantations.

Abstract:Paddy soil is suffering from serious heavy metal pollution due to rapid industrial and agricultural development. As the main food crop in South Asia and Southeast Asia, rice safety issues are particularly prominent due to increasing heavy metal pollution. The remediation of cadmium and arsenic-contaminated paddy soil has always been a complex issue because of the differences in their biogeochemical cycle. Our study reviews the research progress on in-situ passivation technology for paddy soil contaminated by cadmium and arsenic. We group the passivation technology into four types: redox type, microbial transformation and accumulation type, material immobilization type, and coupled passivation technology. Redox type passivation technology focuses on the migration and transformation mechanisms of Cd and As driven by Eh, pH changes, biogeochemical cycles of different elements, and organic matter under the influence of water regulation in paddy fields; microbial transformation and accumulation type passivation technology focuses on clarifying the mechanism of functional microorganisms on the absorption, transformation, compartmentalization and bacterial surface adsorption of arsenic and cadmium; material immobilization type passivation technology focuses on the classification of existing passivation materials and their immobilization mechanisms with cadmium and arsenic; coupled passivation technology focuses on summarizing the application analysis of synergistic passivation of cadmium and arsenic under the comprehensive system of the above three technologies. Also, we propose the forecast on the in-situ passivation restoration of paddy soils contaminated by cadmium and arsenic. Besides, the research direction of new mechanisms involved in the biogeochemical cycle of cadmium and arsenic in paddy soil, the innovation and extension trend of remediation technology are further discussed. We hope that a soil passivation improvement technology model will be created in future, which integrates modern agricultural production models with a guarantee of food production and security.

Abstract:【Objective】 Upland soil, as an important type of arable land in China, plays an extremely important role in national food security and stability. Since the reform and opening of China, there were many great changes in farmers' fertilization patterns and planting habits because of soil testing formula fertilization, straw returning and fertilizer reduction to increase efficiency. However, there is still a lack of systematic research on the effects of these changes on the input of potassium (K) fertilizer and soil K in the main dry-farming grain of China. Therefore, the objective of this study was to evaluate the evolution characteristics of K input and fertility in major wheat and/or maize production regions of the whole country, which will clarify the present situation of K fertility and provide certain theoretical guidance for rational application of K fertilizer in different regions. 【Method】 This study was based on the National Cultivated Land Quality Monitoring database, which was from the Center of Cultivated Land Quality Monitoring and Protection, Ministry of Agricultural and Rural Affairs. Then, the K fertilizer input, soil available K (AK) and slowly available K (SAK) contents were analyzed in five regions of China, which included Northeast of China(NEC), North of China (NC), East of China (EC), Northwest of China (NWC), Southwest of China (SWC) during 1988—2007 and 2008—2018. Meanwhile, the effects of soil AK on SAK were also discussed. 【Result】 There was a relatively stable chemical K, straw K, and total K fertilizers (K₂O) input in the whole country during 1988—2018, with 125 kg·hm^-2·a^-1, 148 kg·hm^-2·a^-1, and 273 kg·hm^-2·a^-1, respectively. There was no significant change for K input during 1988—2007 and 2008—2018. In different regions, it was observed that K input in NC and NEC regions was significantly higher than that in other regions. Compared with those of 1988—2007, the total K input in NEC, NC, EC, and SWC regions was increased during 2008—2018 by 4.22%-23.8%, while it was decreased slightly in the NWC region. The AK and SAK of the whole country were 139 mg·kg^-1 and 665 mg·kg^-1, respectively. Compared with 1988—2007, the AK and SAK during 2008—2018 increased by 15.1% and 6.72%, respectively. The order of soil AK in the different regions was higher in NWC and NEC regions (more than 150 mg·kg^-1), lower for NC and EC regions (136-149 mg·kg^-1), and lowest for SWC region (116 mg·kg^-1). During 2008-2018, soil AK in NC, EC, NWC and SWC regions was increased more than during 1988-2007 by 15.7%, 17.7%, 4.16% and 34.5%, respectively. Also, the soil SAK was increased by 8.95%, 2.15%, 5.71% and 4.19%, respectively. In the main dry-farming food soils of the whole country, the relationship between soil AK and SAK could be fitted by a linear equation. With the increase in soil AK, the growth rate of soil SAK in 2008—2018 (14.2 mg· kg^-1) was significantly higher than 1988—2007 (7.23 mg·kg^-1). Meanwhile, the fitting equations among different regions in 1988—2018 also showed that the growth rate of soil SAK in NEC, EC and NWC regions was significantly higher than that in the NC region. 【Conclusion】 On the long-term monitoring platform of farmlands in China, compared with 1988—2007, the AK and SAK of main dry-farming grain soil were increased significantly during 2008-2018, and there was an increasing trend in most regions. Also, there was a significant linear relationship between soil AK and SAK. These results should provide a technical reference for the rapid estimation of SAK content even though there were differences in the fitting equations during different experimental periods and regions. Thus, it is recommended that different areas should accurately classify soil K supply capacity through AK and SAK by local conditions since it would establish the foundation for realizing the goal of storing K in the soil.

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

Abstract:【Objective】The massive application of nitrogen fertilizer to agricultural soils plays an important role in ensuring the world’s food supply. However, it also leads to a large amount of reactive nitrogen(N) entering the environment, which strongly interferes with the biogeochemical cycle of N and causes a series of ecological and environmental problems. As the last step of N cycling, denitrification is the predominant pathway, converting reactive N into inert N(i.e., N₂). However, measuring soil N₂ production from denitrification is a major challenge in terrestrial ecosystems because of the high atmospheric background N₂ concentration. Recently, direct methods for measuring N₂emission rates have been developed. Among them, robotized incubation and analyzing system(Robot system) which is based on N₂ free headspace(i.e., helium environment) have been widely used for measuring N₂ emission in pure denitrifying culture or soil, due to its advantage on platform construction and high throughput for N₂ determination. Nevertheless, frequent sampling with the small-diameter steel needle is required during the operation and determination of the Robot system, which inevitably causes leakage of N₂. This seriously interferes with the determination of low N₂ emission rates(i.e., background N₂ flux in upland soil). Therefore, to enable the Robot system to measure background N₂ emission rate in upland soil without exogenous substrate, the leakage rate of the system must be further reduced.【Method】In this study, helium-washed rubber septa, solutions prepared by helium-washed distilled water and destructive sampling treatments were explored to optimize the Robot system aiming at reducing the N₂ leakage therein. Additionally, results of soil N₂ emission determined by the optimized Robot system were compared with those of acetylene inhibition technique(AIT) and Robotized continuous flow incubation system(RoFlow system).【Result】Our results showed that the N₂ leakage rate of the Robot system could be remarkably reduced by optimizing with helium-washed septa, solutions prepared by helium-washed distilled water and destructive sampling treatments. The N₂ leakage rate was reduced to 0~0.78 μL·L^-1·h^-1 by the aforementioned treatments. Under similar treatments, the N₂ emission rate measured by the acetylene inhibition method was highest, followed by the RoFlow system, and the Robot system had the lowest results. Furthermore, the optimized Robot system was capable of determining upland soil N₂ emissions in response to carbon and N addition, which also had the smallest standard error(0.003~0.045 mg·kg^-1·d^-1) compared with the AIT method(0.34~3.29 mg·kg^-1·d^-1) and RoFlow system(0.41~1.02 mg·kg^-1·d^-1).【Conclusion】Overall, the optimized Robot system is characterized by low N₂ leakage, effective response to substrate addition and good consistency in determining soil N₂ emission. In the future, it will have a favorable application in investigating background N₂ emissions and the associated mechanism of upland soil.

Abstract:【Objective】Atmospheric ammonia (NH₃) is an important precursor for the formation of PM_2.5. Hence, identification and quantification of the sources of atmospheric NH₃ are important for NH₃ emission abatement and air pollution control. Farmland NH₃ volatilization is one of the important sources of atmospheric NH₃. The technology of natural abundance of nitrogen isotopes (δ¹⁵N) has been used to trace NH₃ sources in recent years. Despite these advances, studies on the dynamic change of δ¹⁵N values from the whole process of NH₃ volatilization from farmland soils are lacking. Moreover, NH₃ volatilization from farmland soils is affected by different factors such as soil properties, pH, which can directly or indirectly influence the δ¹⁵N values of volatilized NH₃ and may lead to uncertainties in sources traceability. Upland soil NH₃ volatilization dominates total farmland NH₃ volatilization in China. We selected four types of upland soil from different regions in China to study the δ¹⁵N values of NH₃ volatilization from the whole volatilization process to clarify the changes of δ¹⁵N-NH₃ values and their impacting factors.【Method】Urea was applied to four types of soils from Liaoning, Hebei, Henan and Tibet, and NH₃ volatilization was studied in a 15-day indoor culture experiment by the sponge absorption method under controllable conditions. The δ¹⁵N value during the whole process of NH₃ volatilization was measured by the chemical transformation method.【Result】Results showed that the values of δ¹⁵N during NH₃ volatilization from Beipiao soil from Liaoning Province ranged from -26.14‰ to -5.57‰, with an average of -21.74‰±1.89‰. The variation range of δ¹⁵N values of Xinxiang soil (from Henan province) was from -31.92‰ to -26.31‰, with an average value of -29.31‰±1.72‰ while that of Tangshan soil (from Hebei province) and Linzhi soil (from Tibet) ranged from -24.41‰ to -3.11‰ with an average of -19.82‰±2.04‰, and from -29.17‰ to -2.20‰ with an average of -23.25‰±2.16‰, respectively. Overall, the δ¹⁵N values of the NH₃ volatilization process in upland soils from different regions are different. During the whole process of soil NH₃ volatilization, the δ¹⁵N-NH₃ values of Xinxiang continued to increase, and the δ¹⁵N-NH₃ values of Beipiao, Tangshan and Linzhi first decreased and then increased. Soil properties and NH₃ volatilization rate are the main factors affecting the δ¹⁵N value.【Conclusion】Our results showed that soil pH, NH₃ volatilization rate and cumulative NH₃ loss were significantly negatively correlated with the δ¹⁵N-NH₃ values. In addition, isotope fractionation also impacts the δ¹⁵N-NH₃ values. The results of this study can provide better support for the quantitative traceability of atmospheric NH₃.

Abstract:【Objective】Biochar is an important soil amendment material, as it plays an increasingly prominent role in carbon sequestration and greenhouse gases mitigations, especially in nitrous oxide (N₂O) mitigation. To investigate the effects and the mechanisms of the biochar aging process on soil N₂O emissions under a rice-wheat rotation system, an in situ field experiment was conducted.【Method】Five treatments were established as follows: CK (without urea and biochar), N (urea), NB_0y(urea with fresh biochar), NB_2y(urea with 2-year aged biochar) and NB_5y(urea with 5-year aged biochar). Soil N₂O emission dynamics were monitored during rice and wheat annual rotation. Also, soil physicochemical characteristics and the abundance of relevant microbial functional genes during the N₂O production process were determined after rice and wheat harvest.【Result】Biochar treatment significantly reduced the cumulative N₂O emissions by 32.4%-54.0%, with the reduction capacity following NB_0y> NB_2y> NB_5y. Compared with the N treatment, NB_0y, NB_2y and NB_5y treatment significantly increased soil pH by 0.6-1.2 units, soil NO₃^--N content by 1.7%-31.3%, and soil organic carbon content by 21.4%-58.6%. Nevertheless, the ability of biochar to improve soil pH was decreased with aging. Also, NB_0y, NB_2y and NB_5y treatments significantly increased the abundance of nosZ gene by 54.9%-249.4%, and the soil (nirS +nirK)/nosZ ratio increased with the biochar age. Meanwhile, the cumulative N₂O emissions showed a significant negative correlation with soil pH, and a positive correlation with NO₃^--N content and amoA -AOB gene abundance.【Conclusion】In summary, both fresh and aged biochar can significantly improve soil physical and chemical properties and decrease soil N₂O emissions, but the effect of fresh biochar was better than that of aged biochar. The mitigation capacity of aged biochar decreased mainly due to the increase of soil NO₃^--N content and (nirS +nirK)/nosZ ratio.

Abstract:【Objective】Studies relating soil N availability to N₂O emissions commonly focus on NO₃^- and in some cases NO₂^-. Thus, less effort has been devoted to measuring soil despite its role as a central substrate in N₂O production. 【Method】In this study, two typical greenhouse vegetable soils (alkaline vs. acid soil) were selected to explore the influencing mechanism of NO₂^- on N₂O emission. Also, its association with the inorganic nitrogen transformation processes, gaseous emission (N₂O, N₂, CO₂), and the abundances and transcription copies of functional genes (amoA, nirK, nirS and nosZ) under anaerobic (0% O₂) and aerobic (21% O₂) conditions through in-lab incubation and real-time quantitative polymerase chain reaction (qPCR).【Result】The natural accumulation and tolerance of NO₂^- were higher in alkaline soil than in acidic soil. With respect to pH, the relative concentration of NO₂^- in soil did not correlate with N₂O emissions. However, the addition of NO₂^- significantly increased the N₂O emission and N₂O/(N₂O+N₂) index (I_N2O) of the two soils (P <0.05), and decreased the N₂ emission in both soils under anaerobic conditions (50.9% and 94.2% in alkaline and acidic soils, respectively). In the alkaline soil, exogenous NO₂^- at 60 mg·kg^-1 had no significant inhibition effect on soil CO₂ emission, and the transcription copies of nirK gene at 16 h under anaerobic incubation, amoA gene at 16 h and nirS gene at 84 h under aerobic incubation were significantly higher than that of control check (N0), but nosZ gene had no such phenomenon. In acid soil, the overall gene and transcription activity of amoA was low, and the transcription copies of the nirS gene increased with the increase of incubation time in aerobic N0 treatment (P <0.05). Exogenous NO₂^- at 60 mg·kg^-1 significantly reduced the CO₂emission, and the abundance and transcription copies of related genes in the acid soil. Oxygen significantly reduced the transcription copies of denitrification functional genes in both soils, and nirK was more sensitive. Compared with the N0 treatment under anaerobic incubation, the transcription copies of nirK, nirS and nosZ in alkaline soil were reduced by 97.3%, 74.5% and 89.0%, respectively, at 16 h under aerobic incubation. The variation trend of the denitrification genes transcription copies in both soils under aerobic conditions was different. In the alkaline soil, the transcription copies of denitrification functional genes were significantly decreased with the increase in incubation time (P <0.05). In the acidic soil, only nirK transcription copies decreased significantly with the increase of incubation time (P<0.05) in N0 treatment under aerobic conditions, while nirS and nosZ transcription copies increased, or decreased first and then increased, respectively. 【Conclusion】The accumulation of NO₂^- in soils will increase soil I_N2Oand affect the N₂O emission pathway by inducing nir gene transcription to compete for electrons with N₂O reductase and inhibiting N₂O reductase activity. These results provide a scientific basis for exploring the efficient utilization of soil nitrogen and N₂O reduction in greenhouse vegetable soils.

Abstract:【Objective】This study aimed to reveal the effects of biogas slurry instead of chemical nitrogen fertilizer on soil Denitrification (Den) and Dissimilatory nitrate reduction to ammonium (DNRA).【Method】A field plot experiment was carried out in a typical coastal paddy field in Dongtai, Jiangsu Province. Five treatments were set up: a single application of chemical fertilizer (C), a single application of biogas slurry (B), combined application of biogas slurry and straw (BS), combined application of chemical fertilizer and straw (CS) and control (CK). The variation characteristics of soil Den and DNRA potential at different growth stages of rice plants were studied by the ¹⁵N isotope tracer technique.【Result】The results showed that: (1) In the whole rice growth period, Biogas slurry instead of chemical fertilizer effectively reduced the Den intensity (1.48 μg·kg^-1·h^-1) and the total amount of N₂O by 27% in paddy soil. Compared with the combined application of chemical fertilizer and straw, the combined application of biogas slurry and straw resulted in a significant increase in total N₂O (70%).(2) Looking at different growth stages, the regulation of N₂O in the mature stage of the plant is particularly necessary. The N₂O production in biogas slurry (B, BS) and chemical fertilizer (C and CS) treatments peaked at maturity, accounting for 70%～71% and 75%～92% of the total production on average, respectively. Also, the soil DNRA potential was the highest at tillering stage, and the DNRA potential of B and BS treatments were significantly higher than that of C and CS treatments. (3) The Den potential of biogas slurry or chemical fertilizer treatment was positively correlated with pH and negatively correlated with C: N. Also, the increase in C: N resulted in a decrease in Den intensity of biogas slurry instead of chemical fertilizer (i.e. treatment B). When combined with straw, the factors leading to changes in Den potential are transformed into NO₃^--N and NH₄⁺-N, and the decrease of C: N leads to an increase in Den intensity.【Conclusion】Biogas slurry instead of chemical fertilizer can play a positive role in the preservation of nitrogen in soils. This study provides a theoretical basis for clarifying the impact of biogas slurry replacing chemical fertilizer and straw returning on the process of Den and DNRA in paddy soils. Also, it highlights the environmental impact as well as the exploration of biogas slurry application mode in coastal farmland.

Abstract:【Objective】Collapsing gully is an erosion phenomenon of hillside soil under the effect of gravity damage collapse and hydraulic scouring. It is also the most serious and harmful typical soil erosion mode in the granite red soil area in South China. Collapsing gully is mainly distributed in granite hilly areas in seven provinces of Guangdong, Jiangxi, Guangxi, Fujian, Hunan, Hubei and Anhui, and their erosion modulus is large and widely distributed. This causes serious concerns for the local ecological environment and economic development. Limiting water content is an important parameter of soil hydraulic properties, which can characterize the ability of the soil state to change with a change in water content. Given that this is closely related to the stability of collapsing gullies soil, it is of great significance to predict the relationship between rainfall and collapsing gullies erosion.【Method】We selected three types of granite collapsing gullies in southeastern Guangxi, active, semi-stable and stable, as the object of study to analyze the spatial variation of soil limiting water content in each collapsing gullies and to reveal the influencing factors by usingpath analysis.【Result】The main results were as follows: (1) Soil limiting water content of each part of collapsing gully varies spatially, the liquid plastic limit of active and semi-stable collapsing gullies soils had maximum value at top of collapsing wall(the liquid limit was 54.45% and 57.08%, the plastic limit was 32.84% and 34.04%, respectively) and minimum value at the top of the pluvial cone(the liquid limit was 35.39% and 30.72%, the plastic limit was 21.92% and 20.23% respectively). Also, the liquid plastic limit of stable collapsing gully had the lowest value at the bottom of the colluvial deposit (the liquid limit was 33.78% and the plastic limit was 22.47%). After gradually stabilizing the development of collapsing gullies, the limiting water content of the soil in each part showed an overall increasing trend.(2) Correlation analysis showed that clay content, organic matter, total porosity and capillary porosity were positively correlated with soil liquid plastic limit and plasticity index, with total porosity having the most significant effect on soil liquid plastic limit. Nevertheless, soil bulk, gravel content and sand content were negatively correlated with soil liquid plastic limit and plasticity index.(3) Path analysis showed that total porosity, clay content, organic matter and capillary porosity played a dominant role in the variation of the limiting water content. Furthermore, total porosity, clay content and capillary porosity were the main factors influencing the liquid plastic limit, plasticity index and liquidity index of soil, respectively. The higher the clay content, total porosity and organic matter, the higher the liquid plastic limit and plasticity index of soil. Also, the stronger the cohesion of the soil, the better the water retention performance of the soil, and the more difficult it is for the soil to crumble and be lost. Capillary porosity negatively affects the liquidity index, that is, the larger the capillary porosity, the lower the liquidity index and the more stable the soil is.【Conclusion】The limiting water content is closely related to the start-up and stability of collapsing gullies. When the limiting water content is low and is washed by rain, the soil state is easy to change, and surface runoff is produced, which causes soil collapse and fertility loss. Therefore, the results of this study can help to clarify the soil erosion process, further clarify the erosion hazards of collapsing gullies and identify high erosion risk areas. It can also provide theoretical support for the prevention and management of collapsing gullies hazard and have important significance for the prediction of regional soil and water conservation.

Abstract:【Objective】The angles formed by exposed rocks and slope surface in a Karst trough area significantly change the hydrodynamic characteristics of the concentrated flow caused by surface runoff convergence. This process of rill erosion is closely related to hydrodynamic characteristics. Thus, it is essential to explore the hydrodynamic characteristics of concentrated flow erosion on a slope at different angles between the rocks and slopes in a Karst Trough Valley area. 【Method】An indoor scouring experiment was designed having six angles between rock and slope, three slope gradients and three inflow rates to study variations of soil erosion rate and hydrodynamic parameters.【Result】The results showed that with scour duration going on, the soil erosion rate first decreased and then tended to be stable. Also, the stream power and shear stress fluctuated but the trend was not obvious. It was also observed that the unit stream power gradually decreased while the unit energy gradually increased. When the angle was 150°, the average soil erosion rate was largest at 0.078 kg·m^-2·s^-1. With the increase in angle, the shear stress, stream power and unit energy decreased at first and then increased while the unit stream power decreased as a whole. Under the experimental conditions, the soil erosion rate, flow shear force, stream power and unit stream power increased with change of slope gradients and inflow rates. Importantly, the unit energy of the flow cross-section increased with an increase in inflow rates, but this change was not obvious with the slope gradients. The differences of hydrodynamic indexes among the angles were significant (P <0.05). The relationship between soil erosion rate and shear stress (R²=0.603), stream power (R²=0.600) and unit stream power (R²=0.583) was better described by the power function equation, while the relationship between soil erosion rate and unit energy of flow section was better described by linear equation (R²=0.294). Nevertheless, it was better to use shear stress to describe the soil erosion rate on the slope with different angles between rocks and slope in Karst Tough Valley area. 【Conclusion】This study may provide a theoretical basis for revealing the hydrodynamic mechanism of concentrated flow erosion under different angles between rocks and slopes in a Karst Valley area.

Abstract:【Objective】The wilt coefficient is a key factor in determining the effective soil water range, reserves and availability to plants. However, the existing wilting coefficient based on plant morphological changes has the disadvantages of unclear physiological significance and is difficult to determine in the field. 【Method】To this end, in this study a pot experiment under dry-down drought was used to determine the wilting coefficients of 4 plant seedlings (Glycine max L., Helianthus annuus L., Medicago sativa L., and Leymus chinensis (Trin.) Tzvel) grown under two soil textures (loessial soil in the Loess Plateau and red soil in the southern hilly area). We evaluated the dynamic response of leaf gas exchange parameters to changes in soil moisture content, the relationship between the lower threshold of soil moisture determined based on plant gas exchange parameters, and the wilting coefficient. 【Result】The results showed that: (1) Soil texture and plant drought resistance significantly affected the wilting coefficient of plants and the corresponding soil water potential at permanent wilting. The wilting coefficients of all four plants were greater on the red soil than on loessial soil. Importantly, the stronger the drought resistance of a plant, the lower its wilting coefficient. The wilting coefficients of the four plants under loessial soil were 0.083 cm³·cm^-3(Helianthus annuus L.)> 0.081 cm³·cm^-3(Glycine max L.)> 0.072 cm³·cm^-3(Leymus chinensis (Trin.) Tzvel) > 0.060 cm³·cm^-3(Medicago sativa L.). Also, the wilting coefficients under red soil were 0.188 cm³·cm^-3(Helianthus annuus L.)> 0.180 cm³·cm ^-3(Glycine max L.)> 0.174 cm³·cm^-3(Leymus chinensis (Trin.) Tzvel) > 0.172 cm³·cm^-3(Medicago sativa L.). (2) The soil moisture lower threshold determined by using a cubic function to simulate the change of stomatal conductance was highly consistent with the measured wilting coefficient.【Conclusion】Thus, the wilting coefficient could be estimated indirectly based on plant gas exchange parameters.

Abstract:【Objective】The loess area is arid with little rain and the soil is loose and porous. The water vapor in this area may play an important role in profiling water migration. Thus, it is important to study and understand the cyclic migration law of soil water vapor flux in unsaturated zone for realizing the sustainable development of water resources in arid regions. 【Method】To explore the flux transfer rule of liquid water and steam water in loess profile, based on the high-frequency in-situ monitoring test of dryland apple orchard profile (0-200 cm) in Loess area, the simulation of water-vapour-heat-air coupling STEMMUS (Simultaneous Transfer of Energy, Mass and Momentum in Unsaturated Soil) model was adopted in this study. 【Result】Results show: (1) STEMMUS model reliably reproduced the dynamic changes of soil moisture (d was between 0.81 and 0.98, NRMSE was between 5.5% and 15%) and soil temperature (d was between 0.98 and 0.99, NRMSE was 1.4% and 4.6%) in the profile of dryland apple orchard. This showed good agreement with the simulation of apple tree evapotranspiration (d was between 0.92 and 0.96). (2) Rainfall had significant effects on matrix potential gradient, temperature gradient, liquid water and water vapor flux. The transport of liquid water and vapor water was mainly driven by the matrix potential gradient and temperature gradient, respectively. During the study period, the maximum recharge depths of the soil moisture was 100 cm and 160 cm, respectively, which indicates that soil water could migrate to deeper soil through downward vapor water. 【Conclusion】STEMMUS model considering soil spatial heterogeneity significantly improves the simulation accuracy and reveals the migration law of water vapor flux in loess profile. The research results can deepen the understanding of water migration in the loess profile.

Abstract:【Objective】Rapid increase in the concentrations of greenhouse gases leads to an increase in global warming. The coastal wetland ecosystem has been identified as an important place to fix atmospheric carbon dioxide because of its powerful carbon sink function. Thus, this study aimed to quantitatively assess the temporal and spatial changes of carbon storage in coastal wetlands in China, explore its influencing factors, and augment current global warming management practices. 【Method】Remote sensing data preprocessing, vegetation index calculation and land cover type extraction were carried out based on the data of Landsat atmospheric correction surface reflectance from 1987 to 2020 provided by Google Earth Engine, and then the carbon density data of coastal wetlands in more than 30 literature were collected. Combining remote sensing quantitative inversion with the life zone method, the soil carbon reserves and biomass carbon reserves of coastal wetlands in China were calculated to research the temporal and spatial dynamics of carbon reserves in coastal wetlands in China over 30 years. 【Result】The results showed that: (1) Saltmarsh wetlands were mainly distributed in the northern coastal area, tidal flats in the eastern coastal area, and mangrove wetlands in the southern coastal area; (2) The spatial distribution of carbon density of coastal wetlands in China was quite different. Also, the maximum biomass carbon density, soil carbon density and total carbon density all existed in the region of Shankou mangrove national nature reserve. The values of maximum biomass carbon density, soil carbon density and total carbon density were 220.21 t·hm^-2, 130.46 t·hm^-2, and 350.46 t·hm^-2, respectively. Comparatively, the carbon density of coastal wetlands in southern coastal wetlands was significantly higher than that in northern and eastern coastal wetlands; (3) It was observed that the total carbon storage of coastal wetlands in China showed a decreasing trend as a whole, and its change trend was consistent with the soil carbon reserves. The biomass carbon storage had an increasing trend, with the maximum value of 5.02 Tg, and the soil carbon storage decreased first and then increased, with a maximum value of 35.54 Tg. Also, the total carbon reserves in the northern coastal region and eastern coastal region were greater than that in the southern coastal area. In addition, biomass carbon storage in the northern coastal region showed a decreasing trend, while biomass carbon storage in the eastern and southern coastal areas showed an increasing trend. The soil carbon storage in the northern coastal area, the eastern and southern coastal areas all had a decreasing trend. 【Conclusion】The results estimated in this study are comparable with those published in previous literature. Climate, vegetation and land-use change lead to a decrease in carbon storage in a coastal wetland. Human activities dominated by reclamation are the main factors affecting the dynamics of carbon storage in coastal wetlands. This paper provides a theoretical basis for effectively evaluating the carbon sequestration capacity of coastal wetlands, Also, it outlines suggestions for emission reduction, guidelines for increasing carbon sequestration measures, guides for coping with climate change, and decision support for coastal wetland ecosystem management and ecological restoration of degraded wetlands in China.

Abstract:【Objective】Climate change and the continuous impact of high-intensity human activities are intensifying soil acidification and has caused serious harm to the ecological environment and agricultural production. In recent years, studies on acid soils have focused on the effects and related mechanisms of soil conditioners on physicochemical properties and crop production, but the combined application of electrochemistry theory and other interdisciplinary principles have been given less attention. Electrochemical impedance spectroscopy(EIS)is an electrochemical measurement method using small-amplitude sinusoidal potential(or current)as a disturbance signal. Its application in the soil field has attracted much attention. In this study, EIS was combined with soil physical and chemical properties to analyze the electrochemical mechanism of biochar in improving acid soils. 【Method】A field study was conducted to amend acid soil by applying biochars produced from five biomass materials (rice straw, maize straw, wheat straw, rice husk, and bamboo). The EIS was used to study the influence of different biochars on the electrochemical characteristics of acid soil. 【Result】Results showed that the equivalent circuit topology structure was the same in different biochar-amended treatments, but the circuit component parameters were different. The equivalent circuit model was the charge transfer resistor R₃ and diffusion resistor R_w at the electrode-solution interface in series, and in parallel with CPE. This part was connected in series with the soil porous layer resistor R₂, and then in parallel with the soil porous layer capacitor C₁. Finally, it was connected in series with pore solution resistor R₁. The addition of biochar had regular effects on Nyquist and Bode diagrams. The Nyquist diagram was in the form of arcs in the high-frequency region and oblique lines in the low-frequency region. The intercepts of each curve and x-coordinate corresponded to the resistance R₂ of the soil porous layer in an equivalent circuit, and a radius of each to a charge transfer resistance R₃. In the Bode diagram, the impedance modulus of the modified soil amended with different biochars tended to decrease as the frequency increased. By fitting the equivalent circuit with Z-view software, it was found that the influence of different biochars on the parameter values of each element was related to changes in soil physicochemical properties. The addition of biochar increased soil contents of total soluble salts and CEC, and the concentration of free-moving ions increased, thus the electrochemical characteristics showed that the pore solution resistance R₁ decreased. Since biochar was almost non-conductive, the conductive capacity of improved soil decreased, and the electrochemical characteristics showed that resistance R₂ of the soil porous layer increased while capacitor C₁ decreased. The cations of acid soil neutralized by biochar slowed down the process of charge transfer, increased the reaction resistance, and weaken the ability to store charge. Thus, this reduced the reaction speed and made the system more stable. The electrochemical characteristics were shown as the increase of transfer resistance R₃ and diffusion impedance coefficient W, as well as the decrease of CPE_-T value. 【Conclusion】The decrease of R₁ indicated the increase of soil water-soluble salt content and CEC. The increase of R₂ and the decrease of C ₁ indicated that the conductivity of the soil medium system decreased. The changes of R₃, W and CPE_-T indicated the charge transfer ability and overall stability of the soil system. The fitting parameters revealed the influence of modified acidification on soil pH and soluble base ions content to a certain extent, which enriched the scope of electrochemical impedance spectroscopy (EIS).

Abstract:【Objective】Root exudates are the main sources of dissolved organic matter, which can affect the stability and transport behaviors of colloids in porous media to some extent. With the wide application of biochar in soils, it is very important to understand the effects of root exudates on the stability and mobility of biochar colloids in the subsurface environment. 【Method】Galactose (Gal), lysine (Lys) and acetic acid (AcOH) are the typical components of root exudates. This study investigated the effects of Gal, Lys and AcOH on the stability and transport behaviors of wheat biochar (WB) and pine sawdust biochar (PB) colloids by aggregation and transport experiments. 【Result】The results showed that the concentration of root exudates had a certain influence on the ζ potential of biochar particles. At low Gal and Lys concentrations, their effects on the aggregation and transport of biochar colloids were small, thus, there were no significant effects on the environmental behavior of biochar colloids. In contrast, AcOH reduced the stability of biochar colloids in NaCl solution and inhibited the transport of biochar colloids in porous media. This may be related to the fact that the organic acid anions in acetic acid were easy to form hydrogen bonds with the oxygen-containing functional groups on the surface of biochar. Thus, the adsorption of AcOH by biochar was increased and the stability of biochar colloids was decreased. 【Conclusion】The concentration of root exudates such as Gal and Lys plays an important role in their ability to influence the aggregation and transport of biochar colloids. However, the adsorption of AcOH, even at low concentrations, significantly affects the aggregation and transport of biochar colloids.

Abstract:【Objective】This study was designed to investigate the growth and migration of bacteria and phages under different water and nutrient conditions, as well as the process and mechanism of the interactions between bacteria and phages.【Method】Using the agar plate, the interaction of Pseudomonas aeruginosa PAO1 and Pseudomonas aeruginosa phage PA-27-1 were performed.【Result】The coexistence of bacteria and phages is mainly affected by phase-induced lysis of bacteria, motility of bacteria and the diffusion of phages. Moisture regulated the relative water film thickness and connectivity on the porous surface of plates. It also affected the movement and proliferation of bacteria, the formation process of biofilms, and morphological characteristics of colonies on the porous interface. Additionally, it regulated the interaction mechanism between bacteria and phages by affecting the spread of phages. Different motility patterns and individual sizes between bacteria and phages also led to differences in their proliferation (diffusion) characteristics in micro-pores. Lower water film thickness and patchy distribution promoted the spatial isolation between bacteria and phages and reduced the probability of phage-reduced lysis, which was important for the proliferation of bacteria.【Conclusion】This study reveals the migration of phages and bacteria in micro-habitats like biofilm and provides a theoretical basis and data support for the temporal and spatial distribution of soil phages, as well as the interaction pattern between soil phages and soil bacteria.

Abstract:【Objective】The negative impact of soil-borne diseases on peanut is enhanced for continuous planting. Thus, green prevention and control practices on soil-borne diseases are always an important part when establishing a resource-saving and environment-friendly sustainable control technology system. As a natural stimulant, humic acid has been shown to suppress the activity of soil-borne pathogenic fungi, and the inhibitory effect has a wide range and diverse manifestations. However, valid information is still lacking about the effects of humic acid on the microbial community. The objective of this work was to investigate the response of soil fungal communities under continuous peanut planting to humic acid from different origins, and to provide a theoretical basis for researching and developing a green-effective prevention and control method on soil-borne diseases in the continuous planting soil.【Method】 Different concentrations of humic acids from mossy peat and weathered coal were respectively added to two peanut planting soils (including 1 year and 6 years continuous planting), and soils were cultured with indoor thermostatic incubation. The soil fungi community was sequenced by Illumina MiSeq PE300. PerMANOVA, correlation analysis, and other methods were used to explain the effect of humic acid on the soil fungi community. 【Result】The results showed that the addition of humic acid had a significant effect on the fungal community structure of six years planting soil, while it had no significant effect on one-year planting soil. The concentration of humic acid both had a significant effect on the fungi community structure of the two planting soils. Effects of humic acid on soil fungi community structure at each culture time were as follows: humic acids significantly changed the fungi community structures of one-year planting soil at 94 d and 193 d, and of six years planting soil at 193 d. Also, the concentration of humic acids had significant effects on the fungi community structure of the two planting soils during the whole culture process. Humic acid also significantly changed the relative abundance of some fungi at the genus level. The effect of humic acid on soil fungal function can be mainly attributed to its significant alteration of the compositions of fungal functional trophic types in the two planting soils. It was also observed that the relative abundance of plant pathogens in soil decreased significantly with an increase in the concentration of humic acid. Spearman correlation analysis further detected that the relative abundances of Fusarium spp. and Rhizoctonia spp. were significantly negatively correlated with the concentration of humic acid, while the relative abundance of Penicillium spp. was significantly positively correlated. The correlation coefficients were -0.270, -0.138, and 0.172, respectively. 【Conclusion】The appropriate concentration of specific humic acid could significantly change the soil fungi community structure and functional trophic composition in peanut soils, especially in reducing the relative abundance of plant pathogens. Results of this study could provide a direct theoretical basis for expanding the application of the ecological function of humic acid, and provide a new perspective for researching and developing efficient green prevention and control technology of soil-borne diseases.

Abstract:【Objective】Soil nitrogen (N) is an important resource for N uptake by crops. The availability of soil N is dependent on soil fertility to a high extent, which in turn affects the absorption and utilization of N by crops. Understanding the various N forms in red soils with different fertility and their contribution to crop N uptake can provide a theoretical basis for clarifying the N cycle mechanism and cultivating high-yield and high-N efficiency soils.【Method】In May 2019, low-fertility, medium-fertility and high-fertility red soils were selected for the field micro-area experiments, and two treatments, no nitrogen fertilizer (N0) and conventional fertilization (N1) were set up. We determined the contents of soil mineral nitrogen (MN), fixed ammonium (FN), microbial biomass nitrogen (MBN) and soluble organic nitrogen (SON) before planting and after harvest of 2020 maize (the third crop of the experiment). The relationship model between each form of N and the quantity of N uptake was established through structural equation modeling (SEM). 【Result】The grain yield of high fertility soil under N0 treatment was about 4.6 times that of medium fertility soil. Under N1 treatment, the maize yield and biomass of high fertility soil had no significant difference with that of medium fertility soil. Meanwhile the N uptake of high fertility soil was significantly higher than that of medium fertility soil. Compared with before planting, the FN content in the medium-fertility soil after harvest was significantly increased by 63%under N0 treatment. The FN oflow and high fertility soil increased by 47% and 11%, respectively, while the contents of MN, MBN and SON in the soil were reduced. The MN content of the soils was decreased by between 0.4-4.0 mg·kg^-1. MBN was decreased by 18%-44% and there was no significant difference in soil fertility. Also, the SON was decreased by 55%-84%. Under N1 treatment, the content of MN was decreased by 22-38 mg·kg^-1and the content of MBN was reduced by 32%-72%. The SON was reduced by 99 mg·kg^-1 in high-fertility soil, which was 2.0 times higher than medium-fertility soil and 9.3 times higher than low-fertility soil. The correlation analysis results revealed a significant positive correlation between the amount of N uptake by the aboveground biomass and the decrement of MBN, SON and NH₄⁺-N. The structural equation model results further showed that the content of SON and NH₄⁺-N directly affected the amount of N uptake, while MBN indirectly affected the N uptake by maize by changing SON and MN.【Conclusion】SON and NH₄⁺-N can directly regulate the maize N uptake. The MBN and FNindirectly affect maize N uptake through the MN and SON. In the future, it is crucial to strengthen the research on the mechanism of soil N form transformation to promote red soil fertility and high-efficiency utilization of N.

Abstract:【Objective】The application of Chinese milk vetch to paddy soil is an effective practice to improve soil fertility and maintain high and stable yields in South China. The soil aggregates distributions and their carbon and nitrogen content may be influenced by the continuous multi-year application of Chinese milk vetch.【Method】We investigated the effects of 12 years of Chinese milk vetch returned to soil on soil aggregate size distribution and aggregate-associated carbon and nitrogen by setting with six treatments including CK (no fertilizers and no Chinese milk vetch applied), GM0 (fertilizer only) and four gradients of Chinese milk vetch applied (GM1-4). The aggregate size distribution and the content and storage of organic carbon and nitrogen in the soil aggregate were analyzed. Also the types and relative intensity of organic functional groups in different size classes were determined using Fourier Transform Infrared spectrometer (FTIR).【Result】The results showed that the >2 mm soil aggregate was dominant (61.12%～68.53%)and followed by the 2～0.25 mm fraction. The application of Chinese milk vetch increased the percentage of the soil aggregate size (>2 mm) by 5.93%～9.91%. Also, the contents of organic carbon and total nitrogen in the >0.053 mm aggregates increased with the application rate of the treatment. There was a significant positive correlation between the contents of organic carbon and total nitrogen and the application rates of Chinese milk vetch. Interestingly, the application of Chinese milk vetch increased the total storage of organic carbon and nitrogen by 19.42%～37.09% and 22.31%～40.13%, respectively. Moreover, the distribution of organic carbon and nitrogen in >2 mm soil aggregate was also increased after the treatment. FTIR spectroscopic analysis revealed that the relative contents of aliphatic and aromatic organic carbons in soil aggregates were increased after treatment, and there was a significant positive correlation between the N-H functional groups and the application rate of Chinese milk vetch. In addition, the relative intensities of 1 630/2 850+2 940 and 1 720/2 850+2 940 in different soil aggregates were increased. There was a significant positive correlation between the values of the relative intensity of 1 630/2 850+2 940 in both aggregate sizes of >2 mm and 2～0.25mm and the application of Chinese milk vetch.【Conclusion】The application of Chinese milk vetch to paddy soil improved the distribution of soil aggregates, increased the activity and stability of organic carbon, and enhanced the organic carbon and nitrogen storage in soil aggregates. These positive impacts of Chinese milk vetch played an important role in enhancing paddy soil fertility.

Abstract:【Objective】Afforestation is the main measure for desertification combating and plays a key role in improving soil quality and reestablishing degraded ecosystem functions. However, the spatial distribution in soil chemical properties and bacterial communities after the forest reconstruction in sandy land has not been well evaluated. The objective of this study was to investigate responses of the soil chemical properties and bacterial communities in soil profiles to afforestation and to provide a scientific basis for the healthy management and fertility cultivation of barren sandy soils in Northern China. 【Method】In this study, we selected Pinus sylvestris var. mongolica plantations which included 0, 5, 8, and 15 by using the space-time substitution method in Mu Us Sandy Land located in Yulin, Shannxi, China. Soil samples were collected from 0-10 cm, 10-20 cm, 20-30 cm, 30-60 cm, and 60-100 cm. The high-throughput amplicon sequencing of the 16S rRNA and Functional Annotation of Prokaryotic Taxa (FAPROTAX) tool was used to quantify the composition, diversity, and putative ecological functions of soil bacterial community, and then to determine the relationship between bacterial community and soil properties. 【Result】Results showed that: (1) The conversion from sandy land to plantations increased soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents, but decreased available nitrogen (AN), available phosphorus (AP) contents, and pH. TN content decreased with soil layers, while AP and pH were increased. TP had no significant change in soil profiles. (2) Afforestation significantly changed the relative abundance of the Proteobacteria, Acidobacteria and Chloroflexi, and increased soil bacterial ACE(abundance-based coverage estimator) index. Importantly, the vertical spatial variation in bacterial communities decreased. (3) FAPROTAX showed that after 15 years of afforestation, cellulolysis and aromatic compound degradation decreased by 54.65% and 72.18%, respectively. However, nitrogen fixation and denitrification were enhanced by 99.26% and 100.5%, respectively. (4) Redundancy analysis and Pearson correlation analysis indicated that SOC and pH were the key factors varying the bacterial community and putative ecological functions. 【Conclusion】Overall, the conversion from sandy land to Pinus sylvestris var. mongolica plantations can negatively affect soil available nutrients such as AN and AP, and also alter the diversity and putative functions of the soil bacterial community. Consequently, artificial control measures (such as regulation of litter degradation and nutrient return) are crucial for improving the bioavailability of nutrient elements and microbial functional diversity in arid and barren sandy soil. In the future, on-the-spot preservation and decomposition of litter in the ecological restoration work of artificial forests in sandy areas should be prioritized.

Abstract:【Objective】Pig is one of the most farmed breeds in China. In 2020, there were 406.50 million pigs in China and 41.13 million tons of pork were produced. Meanwhile, hundreds of thousands of tons of pig slurry and manure were produced during pig breeding in China. Many nutrient elements needed for crop growth are available in pig slurry, such as nitrogen, phosphorus, amino acids, trace elements, etc. Returning pig slurry to the field is one of the best ways for its utilization. To solve the problem of pig slurry application on farmland, studies are required to determine the optimal amount of pig slurry needed for the application and reduce the possible environmental risks which are associated with pig slurry application. 【Method】The experiments were carried out in a self-made soil column with a volume of 42.41 L and were designed with 7 treatments, including no fertilization (CK), 50% (50%W), 100% (100%W), 200% (200%W)and 300% (300%W) replacement of chemical nitrogen fertilizer by pig slurry, 50% replacement of chemical nitrogen fertilizer by pig slurry + 50% chemical nitrogen fertilizer (50%W+50%C), and 100% chemical nitrogen fertilizer (100%C). The average number of spikes, chlorophyll content, spike and straw yield, nitrogen and phosphorus content in spikes and straw, and the changes in physico-chemical properties of soil leachate and the contents of nitrogen, phosphorus and heavy metals were analyzed. 【Result】The results showed that both 50% and 100% replacement of chemical nitrogen fertilizer by pig slurry could promote the growth of rice and wheat to varying degrees and increase the yield. However, the difference between treatments was not significant. The excessive application of pig slurry caused rotten roots and dead seedlings in rice, wild growth in wheat, and increased nitrogen and phosphorus concentration in soil leachate, which increased the risk of contaminating groundwater, and some indexes even exceeded the standard of Class IV water in the National Groundwater Quality Standard (GB/T 14848-2017). Also, the massive application of pig slurry caused the accumulation of Cu, Cd and Pb in the soil whereas Zn content did not increase significantly. The above results indicate that, the replacement of chemical fertilizer by pig slurry is feasible under appropriate conditions as shown in this experiment. 【Conclusion】It is suggested that the application amount of pig slurry should not be more than 200% replacement of chemical nitrogen fertilizer which have a better effect in promoting the growth of rice and wheat, fertilizing the soil and controlling environmental pollution risk of farmland.

Abstract:【Objective】Soil arthropod is an important part of the soil ecosystem. They play an important role in decomposing organic matter, improving soil physical and chemical properties, improving soil fertility and promoting plant nutrient absorption. The arthropod community is sensitive to fertilization management and is, therefore an important indicator reflecting the health and stability of the farmland ecosystem.【Method】Soil samples were collected from experimental plots of reclaimed paddy fields in Jiangsu Tidal Flat, which has been running for 6 years. The plots were treated with biogas slurry instead of chemical fertilizer(0%, 33%, 66% and 100%). The collected samples were, analyzed for the effects of each treatment on species, quantity, community density and diversity of soil arthropods, and their relationship with the changes of soil properties.【Result】In the treatment of biogas slurry instead of chemical fertilizer, 1 024 soil animals were collected, belonging to 9 classes and 18 groups. The results showed that the dominant groups of soil arthropods in the paddy field under each fertilization treatment were Prostigmata, Collembola and Oribatida, accounting for 45.44%, 20% and 13.38% of the total density, respectively. Biogas slurry instead of chemical fertilizer(i.e. combined application of biogas slurry and chemical fertilizer)is beneficial for improving the density, diversity index and richness index of soil arthropods. When the ratio of biogas slurry to chemical fertilizer was 66%(the total amount of N applied was 225 kg·hm^-2), the density, diversity index and richness index of soil arthropods were significantly higher than those of pure chemical fertilizer(the ratio of biogas slurry to chemical fertilizer was 0%)(P <0.05). Compared with pure chemical fertilizer, it increased by 129.25%, 8.67% and 34.78%, respectively. Correlation analysis showed that soil organic carbon and total nitrogen were the main factors affecting soil arthropod density in paddy fields.【Conclusion】The combined application of biogas slurry and chemical fertilizer has a significant effect on the soil arthropod community in paddy fields. From the effect of different proportions of biogas slurry replacing chemical fertilizer on soil arthropod density and community structure, the combined application of biogas slurry and chemical fertilizer is recommended instead of replacing chemical fertilizer.