Abstract:Fertilizer is the link of green development between industry and agriculture and an important substance that supporting green transformation development. In the new period, the green development of industry and agriculture has faced great challenges with high environmental costs during production and low resource use efficiency, especially in the process of fertilizer production, a large number of nutrient resources can not be efficiently used. In order to better solve the key problems faced by industrial and agricultural development, this paper propose the idea of full use of mineral resources and its industrial approach, focuses on introducing the basic concept and connotation, full use strategy and industrial approaches, in order to provide solutions for the development of green intelligent fertilizer industry with the cross-integration of industry and agriculture, promote scientific and technological innovation to solve key industrial problems, and provide strategic support for the innovation of green intelligent fertilizer and the promotion of green transformation and upgrading of fertilizer industry.

Abstract:The objective of crop production is to harvest the photosynthetic products of crops. The harvest of these products reduces the amount of organic materials returned into the croplands, resulting in a decline in organic matter and available nutrient contents in farmland soil. Such characteristics of farmland production and the plant-soil feedback result in the unsustainable nature of farmland soil productivity. Therefore, it is crucial to implement appropriate countermeasures to sustain soil productivity. The application of chemical fertilizers addresses the issue of nutrient depletion in farmland soil and substantially enhances crop yield. Intensive agriculture, characterized by the high use of chemicals, achieves high crop yield, but also generally stimulates the activity of soil-borne pathogens. Consequently, the frequent occurrence of crop soil-borne diseases has become a bottleneck restricting the sustainable development of intensive agriculture. The existing studies have demonstrated a close association between aboveground biodiversity and soil microbial biodiversity, and plant-derived organic resource serves as the foundation for this relationship. Generally, soil-borne pathogens benefit more from crop root exudates than the antagonistic microbes. Monocropping in intensive agriculture leads to the simplification of available organic resources, resulting in a reduction in the biodiversity of active soil microbes, which further weakens soil suppressive ability against soil-borne pathogens. This paper proposes the addition of organic compounds during crop cultivation that can sustain the biodiversity of active soil microbes or enhance the activity of beneficial microbes, as an effective strategy to maintain soil biological health and suppress soil-borne diseases in intensive agriculture. To achieve this, it is crucial to investigate the organic compounds preferred by soil beneficial microorganisms and determine the optimal methods for organic amendment during crop growth.

Abstract:Soil is a porous medium composed of solid, liquid and gas phases. Soil physical, chemical and biological processes mainly occur in soil pores that are filled with liquid or gas and at the interface of soil pore and solid. With the rapid development of non-destructive detection tools that can reveal the three-dimensional(3D) structure of soil pore system, the in situ methods to measure soil biochemical processes, coupled with computer simulations capacity, it is now possible to study dynamic soil processes intuitively and accurately at pore scale considering soil pore morphology, structure and function. This can provide in-depth understanding of soil microscopic hydro-ecological processes and functions that occur in real soil environment. Based on soil pore related research progresses, we propose that the era of the physics of transparent soils, i.e. Soilporelogy, has sailed. Soilporelgy studies soil physical, chemical and biological properties and processes and their interactions from the viewpoint of soil pore space. In this paper, we firstly introduced the methodological progress to acquire the 3D soil pore structure, and then discussed the experimental and simulation studies based on fluid movement, biochemical processes, root and biological activities, as well as soil microscopic eco-hydrology in soil pores. Finally, we proposed the research methods and theoretical development direction of Soilporelogy. It is quite promising that the study based on soil pores will promote the new development of soil science research.

Abstract:Farmland quality construction is a strategic requirement for ensuring food security in China. There is an urgent need to address issues such as soil acidification, salinization, infertility, and declining biological functions for medium to low-yield farmland, in order to comprehensively enhance farmland productivity in China. Based on long-term observation, research, and demonstration, the Institute of Soil Science, Chinese Academy of Sciences has clarified the evolution rules and degradation control mechanisms of soil quality for major cultivated soil types such as fluvo-aquic soil, red soil, and saline-alkaline soil, and developed the theories and technical systems for farmland quality cultivating in different agricultural areas. For fluvo-aquic soil, the formation mechanisms of the internal stability for soil fertility through the synergetic linkage among organic matter, aggregate, and microbe were clarified, the sensing equipment for monitoring farmland soil and crop information were developed, and the models to integrate the construction of fertile cultivated layer and the balanced enhance of crop yield at large-scale were established. For red soil, the mechanisms for inhibiting soil acidification by improving acid buffering capacity and microbial keystone taxa-driven nutrient transformation were revealed, the technologies for synergistic inhibition and resistance of soil acidification and biological fertility cultivation of soil macro-aggregates were developed, and the ecological modes for farmland quality and productivity enhancement in Jiangxi Province were classified and established. For saline-alkali soil, the nitrogen migration and conversion processes associated with soil water-salt management were clarified, the synergistic mechanism and key technologies of salinization obstacles reduction and nutrient enhancement were developed, the soil accelerating fertility cultivation mode and the soil salinization ecological remediation mode were innovated for the coastal region and Hetao Irrigation District respectively. Future research should focus on farmland quality investigation and construction management, farmland soil obstacle remediation and productivity improvement, and soil health management and ecological protection. We need to break through the technical bottleneck for soil obstacle remediation, develop a series of conditioners and biological fertilizer products, improve the implementation rate of regional management modes, and finally establish a systematic solution for improving farmland quality and sustainably utilizing farmland resources in China.

Abstract:Most soils in China have acidified to some degree in the past decades. This increase in soil acidity has a negative impact on crop yield, agricultural product quality, and biodiversity. Since the 1950s, Chinese scientists have performed lots of work on acid soils and the achievements are significant. However, there are still some issues in the use of acid soils including the inexact distribution of acid soils in China, controversial explanation for soil acidification mechanisms in cropland, lack of acid soil-tolerant crop cultivars, unclear critical pH for optimal plant growth, and poor applicability of products and techniques in acid soils, which limits acid soil use. Considering these issues, a new soil pH map of China based on the recently obtained soil data was drew. The area of acid soils with pH values lower than pH 6.5 is about 3.11 million km², accounting for 32.4% of the total national land area. About 60.3%, 23.3%, and 16.4% of these acid soils are distributed in the south red and yellow soil region, northeast region, and other regions in China, respectively. The mechanisms for soil acidification under natural conditions and by acid deposition are much clearer, but whether nitrogen fertilizer induces cropland soil acidification is controversial. The relationship between soil acidification and nitrogen fertilizer is very complicated, depending on the production and consumption of H⁺ during soil nitrogen transformation. Large amounts of nitrate loss through leaching may be the main mechanism for soil acidification induced by nitrogen fertilizer, so it is suggested that the inhibition of soil nitrification can be used as an effective measure to alleviate soil acidification, especially in south acid soil regions of China with dual effects of high nitrogen use efficiency and low nitrogen loss. Soil acidification has various negative effects, including inhibition of plant growth, reduction of agricultural product quality, and damage to ecological environments. Nitrogen fertilizer induced serious soil acidification and remarkably decreased crop yield in some red soil regions of south China. In addition, increased soil heavy metal bioavailability, pests, and diseases by soil acidification have become important issues in recent years. Plants and microbes have developed external and internal mechanisms to tolerate various stressful factors such as aluminum toxicity, phosphorus deficiency, and manganese toxicity co-existing in acid soils. Nevertheless, how to apply these mechanisms to the improvement of crop productivity in acid soils remains a huge challenge. Four strategies are proposed for the improvement and use of acid soils: (1) the improvement strategies for acid soils should be implemented according to soil requirements in different districts, acidity grades, and soil types; (2) the same importance for improving soil acidity and fertility should be accorded to all acid soils; (3) the combined application of organic and chemical fertilizers should be encouraged; and (4) the development of agriculture with local acid soil characteristics should be the new focus. Furthermore, six research directions to be strengthened in the future are suggested: (1) develop new products for the improvement of acid soils; (2) clarify the critical pH for optimal growth of different crops; (3) research efficient N application techniques for reducing soil acidification; (4) emphasize the role of micro-elements in plants in acid soils; (5) breed acid soil-tolerant crop cultivars; and (6) predict soil acidification trend in the following period. Provided the national soil acidification trend, the Chinese government has begun to stop soil acidification in 20 counties of 15 provinces since 2023. At the same time, several national projects related to acid soils are being performed and/or will be approved. With the implementation of these projects, soil acidification in China will be effectively controlled, and the quality and productivity of acid soils will be greatly improved. This will lay a solid foundation for ensuring food security.

Abstract:Soil geography is the soil science discipline that studies the spatio-temporal changes and formation of soil as well as its resource environment. The basic objectives and tasks of soil geography are to understand the key processes and controlling factors, predict the future co-evolution of the soil environment, and illustrate soil resource distribution and their potential for multiple uses. Thus, this provides scientific support for agricultural development and eco-environmental protection. The long-term development and the most recent scientific achievement especially from the soil series study has provided substantial support to the ongoing national soil survey. The subdisciplines of soil geography, including soil morphology, soil genesis, and soil mapping have achieved substantial progress during the last 20 years especially the most recent 10 years, with a significant shift of research subjects and contents. With the ever-deepening understanding of the pedosphere, the study object of soil geography has shifted from traditional surface soil to the earth's surface system, meanwhile, human activities and their impacts on soil system have gotten more attention and related studies have appeared. Along with the rapid development of remote and proximal sensing and GIS technology, modern soil survey has seen a regime shift thanks to the emergence and evolution of digital soil mapping, large-scale soil map products have been generated and become available, thus, providing strong support to other sectors. In the future, soil geography should focus on the coupling of multiple processes in the atmosphere, hydrosphere, biosphere, pedosphere, and lithosphere in the context of the earth's surface system, rapid and efficient acquisition of soil information, multiple-scale soil-environment modeling, to realize accurate prediction of soil spatio-temporal changes.

Abstract:As the largest agricultural country and emitter of greenhouse gas (GHG) in the world, China aims to peak its emissions before 2030 and achieve carbon neutrality before 2060. This target imposes challenging mitigation demands on agricultural systems, which account for～14% of China's national GHG emissions. Crop production is a major contributor to agricultural non-CO₂ GHG emissions, primarily due to high methane (CH₄) and nitrous oxide (N₂O) emissions from intensive use of irrigation water and fertilizers. After the achievement of carbon peak, the contribution of GHG emissions from crop production and the associated mitigation necessity will become increasingly important. It is unclear whether and how crop production can transition to carbon neutrality. This paper reviewed the source and sink effects as well as the temporal and spatial characteristics of GHG emissions from crop production in China, summarized the effective agricultural management practices in mitigating CH₄ and N₂O emissions and enhancing soil organic carbon sequestration, analyzed the trade-offs between GHG mitigation and carbon sequestration and the associated countermeasures, and put forward prospects and suggestions on future studies regarding this research area in China.

Abstract:Heavy metal(loid)s-contaminated farmlands exist commonly in China, which is an urgent agricultural and environmental problem to be solved. According to heavy metal levels, application of low accumulation crops and soil amendments, as well as the utilization of agricultural managements are the current safe utilization technologies of contaminated farmlands. It was pointed out that the insufficient attention of farmland pollution sources, unclear relationship between soil pollution and crop safety, as well as the potential risk of soil amendments application and restriction of heavy metal(loid)s-low accumulation crops, were the main issues during the process of safe utilization of contaminated farmland. The improvements of evaluation standard, prevention system and safe utilization technologies of contaminated soils are suggested to guarantee the safety of crops production.

Abstract:Soil aggregates are the essential building blocks of soil, which impact the retention and distribution of water, air, heat, and nutrients. Binding materials play a pivotal role in the formation of soil aggregates. However, the specific functions of different types of binding materials as well as the mechanisms of the complex interactions in the formation of these aggregates still lack a systematic summary. This article reviews the key theories related to soil aggregates and sorts out types, forms, transformations, and interaction mechanisms of binding materials in soil aggregates under different geographical contexts and human activities. It also describes the effects of binding materials (e.g., organic matter, minerals, roots, organisms and their derivatives such as Extracellular Polymeric Substances) on the structure and stability of soil aggregates. Furthermore, it introduces models illustrating the self-organization process driven by binding materials within soil aggregates and elucidates the mechanisms of the formation and transformation of soil aggregates. Finally, the future development of soil aggregates is suggested. Specifically, future research could investigate the in-situ analysis of soil aggregates, quantitative description of the formation process of soil aggregates, spatial structure of soil aggregates at the landscape scale in relation to its stability, and development of product/technology in cultivating good soil aggregates for applications. This research holds significant scientific and practical value in promoting the development of healthy soil aggregates, unraveling the processes of soil elemental cycling and evolution, and enhancing overall soil quality and productivity.

Abstract:Non-point source pollution from agriculture is characterized by its dispersed and random occurrence, uncertain discharge, fluctuating concentrations, diverse pollutant types, and widespread, high-volume impact, making its management a global challenge. At present, the prevention and control of non-point source pollution in China remains a challenge due to unclear overall pollution levels, and the estimation of non-point source pollution load varies greatly among different departments or researchers. Based on decades of site-specific experiments and holistic observational data, it was believed that even though both the national pollution census data and estimations from researchers have overestimated the proportion of pollution emissions from plantations in the total amount of non-point source pollution, the total emissions from plantation remain high and must be given adequate attention and control. Drawing on more than 30 years of experience in controlling non-point source pollution in China, scholars from the Institute of Soil Science, Chinese Academy of Sciences have proposed the 3R (Reduce-Retain-Restore) and 4R (Reduce-Retain-Reuse-Restore) strategies for agricultural non-point source pollution control. Accompanied by upgrades in prevention and control technology, optimization of combinations, technological productization, and equipping the 4R strategy has gradually evolved and expanded into 4R⁺, providing theoretical support and practical guidance for the control of non-point source pollution in China. After being implemented in some typical areas, these strategies have resulted in successful experiences and case studies in controlling agricultural non-point source pollution. Nevertheless, the prevention and control of agricultural non-point source pollution still faces many challenges. A deeper understanding of the interaction mechanisms between soil and pollutants is pivotal. Moreover, to achieve efficient resource recycling, it is imperative to enhance the purification and recovery rates of key pollutants such as nitrogen and phosphorus, ensuring that agricultural productivity is increased while simultaneously reducing the environmental pollutant load.

Abstract:Environmental soil science is an emerging interdisciplinary field that integrates soil science and environmental science. Initially focused on serving agricultural productivity, the research in environmental soil science has evolved to encompass soil health. This article primarily reviews the development of environmental soil science in terms of the impacts of exogenous substances on soil and soil quality evolution. The study of soil pollution on soil environmental quality focuses on identifying pollutant speciation, revealing soil reaction processes, assessing pollution effects, and carrying out soil remediation projects, based on soil element background values and the current state of pollution. In the context of soil quality evolution, research on the cycling of carbon, nitrogen, sulfur, and phosphorus elements has expanded from soil fertility and non-point source pollution in agriculture to exploring the adaptation and response of soil in global climate change. The study of soil degradation processes has progressed from investigating soil productivity or functional loss to examining the sustainability of agricultural development and soil ecological functions under the background of global climate change. Environmental soil science is expected to develop in four important directions in the future, including fostering interdisciplinary integration, evaluating the potential impacts of global climate change on soil element cycling, enhancing the establishment of soil environmental evaluation indicators within the framework of soil health assessment, and aligning the development of environmental soil science with the major needs of the country.

Abstract:The biological uptake of iron(Fe)is one of the important processes during Fe biogeochemical cycling in the environment. It not only controls the enrichment of Fe concentration in rice grain but also affects the uptake and transport of zinc and cadmium within rice. Therefore, understanding the fate and mechanism underlying Fe uptake and transport has significant implications for increasing rice yield, overcoming human nutrient deficiency, and ensuring human health. To solve the above scientific issues, the research progress on gene expression of Fe transporter and Fe isotope fractionation together with spectroscopic analysis in soil-rice systems were investigated. This study aimed to provide a more comprehensive understanding of root uptake and transport in soil-rice systems and to reveal the impact of Fe on zinc and cadmium uptake. Intending to provide a theoretical basis for the quality improvement of food crops and safe crop production, this study starts from the perspective of analyzing the mechanism of Fe transport and transporter in the soil-rice system and provides an in-depth discussion of the research progress at three levels: the function of plant transporter proteins in the process of Fe transport, the isotopic fractionation characteristics of Fe in the soil-rice system, and the subcellular localization of Fe. The combination of gene expression quantification, isotope fractionation, and subcellular localization analysis provides new scientific evidence and knowledge on Fe transport in rice. Therefore, to more accurately identify the transport processes of multiple heavy metals in the soil-plant system, the combination of isotope characterization and spectroscopic techniques and tools such as gene expression can provide more scientific information for a deeper understanding of the metal isotope signatures of metal species and fate, biotic and abiotic processes, or for the validation of specific hypotheses. Based on the current study, the following research points remain to be elucidated: (1)Fe uptake strategies have been further corroborated by isotope fractionation methods in Fe-deficient or Fe-rich environments as well as flooded or fall-dry conditions. However, the mechanism of Fe redox-driven response to Fe uptake during the typical dry-wet alternation in rice whole-life processes remains elusive.(2)Fe deficiency promotes the expression of OsZIP5 and OsZIP9, the common transporter proteins for zinc and cadmium, as well as the cadmium transporter proteins OsNRAMP1 and OsNRAMP5. In addition, rice can maintain the internal homeostasis of Fe and zinc during wet and dry alternation. Therefore, it is hypothesized that the expression of OsZIP5 and OsZIP9 can be enhanced by properly regulating the environmental Fe deficiency for stable absorption of zinc, and the expression of OsNRAMP1 and OsNRAMP5 can be reduced by exogenous inhibition to reduce cadmium uptake. This will effectively achieve the triple combination of efficient Fe uptake in rice as well as simultaneous promotion of zinc uptake and reduction of cadmium uptake. Nevertheless, the exact methodology needs to be thoroughly researched over a long period. Thus, this study will provide important theoretical and scientific support for the food crop's quality improvement, safety production, and design of new research directives for understanding the transport of Fe in rice plants and the fate of zinc and cadmium.

Abstract:Soil health plays important roles in maintaining food production, plant, animal and human health, and is the foundation of sustainable agricultural development. Soil microorganisms are extremely complex and diverse, including archaea, bacteria, fungi, protists, and virus. They participate in a variety of ecosystem functions and services, such as primary production, nutrient cycling, decomposition, climate regulation and pathogen control, which are closely linked to global food supply and soil health. Arid regions account for about 41% of the world's land surface and sustain more than 38% of the world's population. As an important grain production reserve area in China, the arid and semi-arid region of Northwest China still lacks research on soil health, due to the complexity, fragility and sensitivity of soil ecosystems in this region. In this review, we summarize the relationship between soil microorganisms and the ecosystem services that related to soil health, including plant growth regulation, continuous cropping barrier reduction, water quality improvement, human health maintenance, climate change mitigation, and soil carbon sequestration, suggesting the important roles of soil microbiome for soil health. In addition, we review the development of soil microorganisms as indicators in soil health assessment in arid region. Meanwhile, we introduce the characteristics of soil microbiome in arid region and their responses to environment stresses, particularly drought. Besides, the research progresses of soil health in arid regions are summarized. Finally, we prospected key research questions of soil microbiome and soil health in arid region, and provide new insights for applying soil microbial resources to maintain and improve soil health in arid regions.

Abstract:The high geological/geochemical background of heavy metals in soil is one of the hot spots in academic research in recent years, involving geology, geochemistry, pedology, environmental science and other disciplines. High concentrations of heavy metal (loid) s in soils including cadmium (Cd), arsenic (As), chromium (Cr), nickel (Ni), etc, pose a threat to environmental quality, food safety, and ecological security. This review uses bibliometric methods to analyze the research progress and recent hotspots in the field of high geological background of soil heavy metal. The distribution characteristics, causes, and types of high geological background of soil heavy metals in the world and China are systematically reviewed. The geological high background area in the world shows diversified distribution characteristics, and the causes of geochemical anomalies are complex. In China, the geological high background is mainly distributed in the southwest (Guangxi, Yunnan, Guizhou, Sichuan, etc.), the east, the Yangtze and the Pearl River basins, and is closely related to long-term weathering and migration and transportation of carbonate rock, basalt, black shale and other rocks. Lithological types, topography and organisms are key factors that affect elemental geochemical processes in the differentiation of heavy metals during soil formation. The total concentrations of heavy metals (especially Cd) in soils of geological high background areas often exceeded the risk screening values of the Chinese Soil Environment Quality Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018). Also, the bioavailability of heavy metals is usually low, especially in carbonate rock areas. The superposition of human activities has intensified the migration, diffusion and enrichment of heavy metals in the soils of geological high background areas, increasing the risk of heavy metal absorption by crops and human health. The screening values for elements such as Cd in the current standards in China are not suitable for ecological risk assessment of geological high background soils, therefore, soil Cd thresholds based on extractability or bioavailability need to be developed. There is still a lack of specialized research on the safe utilization and remediation technology for high geological background areas where the heavy metals concentration in crops exceed the standard. This review aims to provide theoretical and technical references for understanding the mechanism and risk control of high geochemical background soil heavy metal. Future work in high background areas can focus on the investigation of soil heavy metal background values and environmental benchmark values, enrichment and formation mechanisms, potential activation and migration, risk assessment and control technologies.

Abstract:Soil serves as a natural habitat for microorganisms, hosting both beneficial and pathogenic species that can either promote plant growth or pose risks to human and animal health. Pathogenic bacteria, such as Ralstonia solanacearum and Erwinia amylovora, which are soil-borne plant pathogens, can infect economically important crops, resulting in significant agricultural losses. Likewise, common human pathogens like Escherichia coli and Salmonella can persist in soil over extended periods, presenting severe health risks through direct or indirect contact. The presence of pathogenic bacteria in soil contributes to soil biological contamination, leading to reduced crop yields, environmental degradation, and safety hazards, which have garnered considerable attention. Controlling the number of these pathogenic bacteria within a safe range is a requirement of One Heath. Numerous studies have demonstrated the crucial role of beneficial microorganisms in the soil in controlling the invasion of pathogenic bacteria. Among them, bacteriophages, which are viruses that selectively infect bacteria, are widely distributed in the environment. Compared to bacteria and fungi, bacteriophages possess advantages such as specific targeting capabilities, rapid lysis, and minimal disruption to the environment, making them an increasingly prominent focus of research. However, similar to other control strategies, enhancing the stability of bacteriophage application in soil remains a significant challenge. Here we discuss the stabilities of bacteriophages in reducing pathogenic bacteria as well as soil biological pollutions by summarizing the following points: 1)the host spectrum and population of bacteriophages in the soil, 2)the polymorphism of pathogenic bacteria, and 3)the potential impacts of soil factors such as temperature, pH, structure, nutrients, and multiple pollutants on the bacteriophage's antibacterial effects in the soil. For bacteriophages, the host spectrum determines the availability of host bacteria in the soil, which affects the bacteriophages' ability to survive in the soil. The more bacteriophages there are around the target pathogenic bacteria, the higher the chance of infecting them, thus, increasing the frequency of bacteriophage-pathogen interactions and the probability of successful infection. As for pathogenic bacteria, they possess a high degree of ecological and genetic diversity in the field and have abundant anti-bacteriophage systems, which limits the effectiveness of individual bacteriophages in suppressing them. Various environmental factors also influence the colonization and functional performance of bacteriophages in the soil. For instance, high temperatures and inappropriate pH can inactivate bacteriophages, soil particles may adsorb bacteriophages and reduce their migration ability, nutrient levels can alter bacteriophage-bacteria interactions, and soil pollutants like heavy metals and antibiotics may affect bacteriophage activity. To enhance the stability of bacteriophage-mediated control of soil-borne pathogens, strategies such as constructing efficient bacteriophage cocktails, improving bacteriophage product formulations, and optimizing bacteriophage application techniques are proposed. This review provides a theoretical basis and technical support for establishing a comprehensive bacteriophage therapy for soil-borne pathogenic bacteria.

Abstract:The development of phosphate (P) fertilizer industry is closely related to China's food security, P resource utilization, and environmental protection. Nowadays, soil available P rapidly increased due to the large amount chemical P fertilizer application in the past 40 years, especially in the surface soil. It is of great significance to predict and regulate the future demand for P fertilizer in China based on the action of green development of agriculture. The integrated analyses show that in this paper, a large proportion of soil for cereal crops production in China has reached the crop agronomic P threshold (15～25 mg·kg^-1), which means above this threshold there is no yield increase response with P application. In particular, the soil available P had considerably exceeded the threshold value for cash crops such as vegetables and fruit trees. Soil available P should be maintained at the agronomic threshold based on the requirement of crop root/rhizosphere biological capacity, nutritional quality and environmental risks. Consequently, it is critical to implement “crop agronomic threshold” oriented P fertilizer management system. Meanwhile, the agricultural green development needs to maximize the recycling and reuse efficiency of P in agricultural waste, which should focus on the recycling process and agronomic utilization. Accordingly, considering the demand for food and other agricultural products in China, this paper re-predicted the future demand for P fertilizer, following the prediction of China's P fertilizer demand in 2007 based on changes in soil P fertility. The consumption of chemical P fertilizer in China will be 10.84 million tons and 7.42 million tons by 2030 and 2050, respectively. Therefore, based on the continued and multiple optimized measures, the overall demand for P fertilizer in China in the short term by 2030 could reduce about 1.5 million tons, in the long term by 2050 could be adjusted to 7.5 million tons per year, more than 30% reduction from the current consumption.

Abstract:【Objective】The differences in soil detachment and transport mechanisms between interrill and rill erosion lead to the differences in organic carbon loss by interrill and rill erosion. However, few studies have explored the effects and contributions of interrill and rill erosion on organic carbon loss during the erosion process because of the limitation of research methods. Successful use of the radionuclide ⁷Be to document soil erosion provides a means of addressing this need. Thus, the objectives of this study were to first estimate the contribution of interrill and rill erosion to sediment yield and then quantitatively explore the effects and contributions of interrill and rill erosion on organic carbon loss in the loess slope. 【Method】Simulated rainfall experiments with five slope gradients(5°, 10°, 15°, 20°, 25° and 30°) were conducted under different rainfall intensities in the field to investigate soil and organic carbon loss and ⁷Be tracing technology was used to quantify the contribution rate of interrill and rill erosion on sediment yield and organic carbon loss for the loess slope.【Result】Interrill erosion is the main and the relative contribution of interrill erosion on sediment yield was 86% on the 5° plot. However, rill erosion dominated on the plots with a gradient greater than 5°. The relative contribution of rill erosion on sediment yield ranged from 61% to 71% and could even reach 96% during the rainfall. The average enrichment ratio of organic carbon of sediment from the entire plot and the interrill area was 1.16±0.15 and 1.50±0.50, respectively, during the rainfall. Also, the enrichment could increase the organic carbon loss rate from 0.008 to 0.028 g·m^-2·min^-1. In addition, the relative contribution of rill erosion to organic carbon loss was between 55% and 62% on plots with a gradient greater than 5° and was lower than those of rill erosion to sediment production, but still dominant. Sediment yield from the entire plot and the interrill area could respectively explain 97% and 89% of the variations of organic carbon loss from the entire plot and interrill area. 【Conclusion】The organic carbon enrichment ratio had lesser effects on organic carbon loss when rill erosion occurred severely. Sediment yield determined the amount of organic carbon loss and severe rill erosion could enhance the enrichment ratio of organic carbon of sediment from the interrill area.

Abstract:【Objective】 The information of temporal-spatial variation of soil organic carbon content (SOC) with high resolution and high precision is the base for assessing the capability of soil in sequestrating carbon. Though there had been much research on the changes in topsoil SOC, research on SOC of deeper soil layers is still rare. To reduce the gaps in understanding of the ability of deep soil to sequestrate carbon, our research sought to investigate the sensitive area where SOC had changed significantly, the depth where SOC had changed significantly, and the factors that drive SOC change. Thus, research on the temporal-spatial changes of SOC of 0~15 cm, 15~30 cm, 30~60 cm and 60~100 cm of cultivated land in Henan, China from 1982-2010 was conducted and the SOC accumulation rate in this area was compared with that of the COP21 target . 【Method】The legacy soil data that was collected from the second national soil survey carried out in 1982 and the recent topsoil data and soil profile data that were sampled in 2010 were used in this research. Digital soil mapping technology with the aid of a quantile random forest algorithm (QRF) and 26 environmental covariates was used to produce SOC maps. For every soil layer in both 1982 and 2010, 500 SOC distributions with equal probability were produced by QRF, and then the SOC map pools for both 1982 and 2010 were derived. Then, stochastic sampling with replacement was repeated 1 000 times from both SOC map pools, respectively, and each time, a subtraction of the two SOC maps was performed to get a SOC change map. So, 1 000 SOC change maps with equal probability were got and based on that the uncertainties of SOC change were assessed. Only those SOC changes with a probability above 0.66 were received as significant results and were used to calculate SOC storage change in the next step. To better understand the mechanism of SOC change, SOC changes among soil types were compared, and the Pearson correlation coefficient between SOC change and primitive SOC content, some climate variables, crop yields, straw returning amount, soil texture, and soil pH were analyzed. 【Result】It was revealed that the significant increase of SOC in 0~15cm, with a magnitude of 2~4 g·kg^-1, had taken place across the plain and basin regions of Henan province. Nevertheless, the increase of SOC in 15～30 cm soil layers with a magnitude of 0~2 g·kg^-1 mainly took place in the Fluvo-aquic soils that were distributed alongside the Huang river and scattered to the Cinnamon soils and Paddy soils. The changes of SOC in soil layers below the 30 cm depth were low in probability. Overall, the total storage of SOC in 0~1 m depth of soils across the cultivated land of Henan province increased by 7.04% in the past 28 years with a mean annual rate of 2.43‰, which was far from the expected value of COP21 4‰. It was also found that the effects of bio-climate variables were more important than soil variables in SOC change. Except for single-cropping rice areas with a fallow period every year, SOC significantly or extremely significantly correlated with biomass input. The mean annual temperature range (the difference between the mean hottest month temperature and the mean coldest month temperature) was positively correlated with SOC accumulation, while climate warming had a negative effect on it. Probably due to the differences in the environment and soil properties, the relationships between SOC change and soil texture, between SOC change and soil pH in different soil types were high variable. The initial SOC values were negatively correlated with SOC change in 0~15cm in two of five soil categories, so was that in 15~30 cm in all the five soil categories, which may be implied a slowing rate for the SOC accumulation in the future. 【Conclusion】The SOC accumulating rate in Henan province will be difficult to meet the object of COP21 in the future. Thus, it is suggested not to overestimate the effects of agricultural soil on carbon sequestrating and much attention should be paid to reducing net carbon emission.

Abstract:【Objective】Soil color is an important soil property. It is frequently used by soil scientists for the identification and classification of soil. It is also used as an indicator of many soil properties. Soil organic matter(SOM)is the most important pigment, that colors the soil in black color.【Method】In this study, a total of 30 mollisol samples were collected from the typical black soil region of northeast China. The SOM was physically separated into four fractions: light fraction, coarse particle fraction, fine particle fraction, and mineral‐associated fraction. Based on the CIE L*a*b* color analysis system, the darkness of bulk soil and soil physical fractions were analyzed using a spectro-colorimeter. The objective was to quantify the relationships between SOM content and the color of black soil and to reveal the contribution of different physical fractions to soil blackness.【Result】Bulk soil blackness was strongly positively correlated with the SOM content. Similarly, significant relationships were observed between the blackness of physical fractions and the organic carbon content in corresponding fractions. This relationship was gradually strengthened with the increase in the stability of the fractions. As for the color of soil physical fractions, the blackness value of light and coarse particle fractions was greater than that of fine particle and mineral‐associated fractions. Also, correlation analysis showed that there was no significant relationship between the blackness of light or coarse particle fractions and the bulk soil blackness, and the contribution rate of the two fractions to bulk soil blackness was only 2.6%.【Conclusion】The the mineral‐associated fractions, as the main storage location of soil humus, contributed more than 81% to bulk soil blackness and plays a decisive role in coloring the soil black.

Abstract:【Objective】Particulate organic matter is an important component of soil labile organic matter and a sensitive index to evaluate a change of the soil organic matter. The climate in Northeast China is very cold, so, paddy fields therein have a short flooding period and a long non-flooding period since the soil is frozen for most of the time. However, little research has been carried out on the incorporation of exogenous rice straw carbon (C) and nitrogen (N) into particulate organic matter in black soil with different rice planting years.【Methods】A 300-day incubation experiment was conducted, in which dual-isotope- labeled(¹³C/¹⁵N)rice straw was added to a cultivation chronosequence of paddy soils ranging from 0 to 85 years(0 a, 12 a, 35 a, 62 a and 85 a). Flooding incubation experiments were conducted at a temperature of 20 ℃ and a 1 cm water-flooded layer in a laboratory for 150 days while the freezing incubation experiments were also carried out for 150 days under a soil temperature of -15 ℃ and water-saturated.【Result】Throughout the entire incubation period, the contents of particulate organic carbon(POC)and particulate organic nitrogen (PON) in all paddy soils from the samples with and without rice straw were lower than that in the control soil (0 a). The contents of POC and PON in all soils from the samples with rice straw increased after 5 days of flooding incubation, but they did not show a consistently increasing trend in the subsequent incubation period. For paddy soils of different rice planting years, the relative contribution of the added rice straw C (N) to POC (PON) was 0.2%-13.9% (0.4%-3.8%). 0.7%-13.8% (1.4%-9.9%). At the end of freezing incubation, incorporation of the rice straw C into POC in control soil(0 a)and 12-year paddy soil(12 a)decreased significantly compared with that at the end of flooding incubation. Also, the added rice straw N into PON in control soil (0 a) and 85-years paddy soil(85 a) decreased while the added rice straw C(N) into POC(PON) in other rice cultivating years was still increasing. The incorporation of the added rice straw C into POC was significantly negatively correlated with soil organic C, total N and alkaline N, and significantly positively correlated with soil C/N, available phosphorus and microbial biomass C. In addition, the incorporation of straw N into soil PON showed a significant negative correlation with soil organic C content.【Conclusion】The study showed that the longer the years of rice planting in a typical black soil of northeast China, the contents of soil organic C, total N and alkaline N were relatively low, while the soil C/N, available phosphorus and microbial biomass C contents were relatively high. The greater the incorporation of straw C and N into soil particulate organic matter, the more the response of soil particulate organic matter to rice straw addition.

Abstract:【Objective】Straw returning is generally considered to be an effective way to increase soil "carbon sink" and mitigate climate change. China is rich in straw resources, but the rate of straw returning to the field is less than 20%, which is the main reason for a long-term deficit of carbon pool in farmland soils in China. There are many kinds of straw resources in subtropical region, which also account for about 30% of the total output of the country. Therefore, clarifying the quantitative relationship between the amount of straw returning and soil carbon sink in subtropical areas of China is an important basis for formulating carbon sequestration measures and implementing national strategies such as carbon neutralization.【Method】Paddy soil in Fujian Province, a typical subtropical region in China, was selected as our study area. The spatial database was constructed by the digitization of 1:50, 000 soil map paper data from 84 counties (cities and districts) in Fujian Province during the second soil census in 1982. The soil attribute database is composed of 15, 833 surface samples from the arable land fertility survey conducted by the Ministry of Agriculture and Rural Areas in 2016. ArcGIS software and the PKB method (Pedological Knowledge-Based Method) connect the spatial data and attribute data in a 1:50 000 soil database. Using the latest established 1:50000 soil database and DNDC (DeNitrification and DeComposition) model widely used in the agricultural ecosystem, the future dynamic changes of soil organic carbon under different rates of straw returned in Fujian Province were simulated. 【Result】 Results showed that the average annual carbon sequestration rates can reach 173, 302, 478 and 838 kg·hm^-2, and the sequestration of carbon amounts were 11.56, 20.15, 31.90 and 55.95 Tg during the period of 2017-2053 under the treatments of conventional management (15%), straw returning of 30%, 50%, and 90%, respectively. Straw was returned to the field from the perspective of carbon sequestration rate, the average annual carbon sequestration rates of Acid sulfate paddy soils and Salinized paddy soils were the highest, which ranged from 220 to 920 kg·ha^-1 under different straw returning rates. In terms of total carbon sequestration, the total carbon sequestration of Percogenic paddy soils and Hydromorphic paddy soils under different straw returning rates accounted for 81% of the total carbon sequestration over the whole province. Considering the administrative areas, the average annual carbon sequestration rate and total amount in Longyan and Quanzhou were relatively large, ranging from 202~937 kg·hm^-2and 1.55~8.34 Tg under different straw returning rates, respectively.【Conclusion】In general, the increase in straw returning ratio contributed significantly to the "carbon sink" of paddy soil in Fujian Province, which is worth promoting. However, under different straw returning rates, due to the influence of soil properties, climate, fertilization and other factors, the contribution of different soil subtypes and administrative regions in Fujian Province to carbon sequestration varies greatly. In the future, it is necessary to formulate reasonable management measures for carbon sequestration and emission reduction for different soil types and prefecture-level cities.

Abstract:【Objective】The soil acidification rate in current environment is the basis for controlling soil acidification. However, the accurate estimation of soil acidification rate is difficult due to the buffer effect of soils. The soil consumes exogenous H⁺ and releases base cations through mineral weathering (compensating for base cations loss and inhibiting soil acidification) and the cation exchange process (increasing exchangeable H⁺ and inducing soil acidification). Nevertheless, it is difficult to distinguish these processes, which leads to large errors in estimating soil acidification rate. Since silicon (Si) only comes from mineral weathering reaction and has nothing to do with cation exchange, the stoichiometry of base cations (BC: K⁺, Na⁺, Ca²⁺, Mg²⁺) and silicon release (BC: Si) during soil mineral weathering can quantify the H⁺ consumed through mineral weathering, which is helpful to determine accurate soil acidification rate. The purpose of this research is to explore the BC: Si difference and its causes in Udic Cambosols derived from three parent materials of Mica schist, Gneiss and Andesite. 【Method】 First of all, the physical, chemical and mineralogical properties of test soils were measured. To avoid the influence of the base cations adsorbed by soil colloid on stoichiometry of the mineral weathering process, soil exchangeable base cations were washed by elution experiment. Then, the release of base cations and silicon of soils derived from three parent materials were obtained by leaching of simulated acid rain. 【Result】The results showed that content and distribution in the profile of clay, pH, organic matters, exchangeable base cations (K⁺, Na⁺, Ca²⁺, Mg²⁺), cation exchange capacity (CEC) and mineral compositions were significantly different for different parent materials. During simulated acid rain leaching, BC: Si values of base-uneluted soils were three times more than that of base-eluted soils. Only when the exchangeable base cations adsorbed by soil colloid were eluted can obtain accurate BC: Si values. The smallest BC: Si value was in the humus surface horizon (Ah) in the same soil profile with different soil genetic horizons and the largest BC: Si value was in the parent materials horizon (C). BC: Si value of Udic Cambosols derived from different parent materials soils followed: Gneiss > Mica schist > Andesite. The mineral proportions of plagioclase, illite, chlorite, and vermiculite in soils controlled the BC: Si values. 【Conclusion】Therefore, only on the basis of corresponding BC: Si, the response degree of Cambosols with different parent materials to the acidification process can be accurately evaluated. The results can provide data support for soil acidification rate evaluation regionally.

Abstract:【Objective】Biochar application in soil has a positive effect on reducing nitrogen loss and improving nitrogen utilization efficiency. However, information on the interaction between naturally aged biochar and nutrients in the field is limited. Exploring the influence mechanism of aged biochar on soil nitrogen retention is helpful to further understand the environmental and chemical process of biochar in soil.【Method】The method of in-situ embedding of biochar in nylon bags in the field and batch equilibrium adsorption experiment in the laboratory were carried out. The field experiment included four treatments, namely fresh biochar (A0), aged biochar for one year(A1), two years(A2) and three years(A3). The dynamic changes of surface structure characteristics and physicochemical properties of aged biochar and their effects on NH₄⁺-N adsorption were investigated using scanning electron microscopy, BET-specific surface, differential thermal and thermogravimetric analysis techniques.【Result】The results showed that the surface pore structure of biochar after naturally aging for three years in the field collapsed. With the increase of field aging time, the BET-specific surface area, total pore volume, mesoporous pore volume and average pore size of biochar increased, while the micropore surface area decreased. Compared with the A0 treatment, the BET-specific surface area, total pore volume and average pore size of biochar in the A3 treatment increased by 18.93%, 42.31% and 20.71%, respectively, and the micropore surface area decreased by 26.17%. With respect to the chemical structure of aged biochar, the contents of C and N elements increased by 7.92% and 95.61%, respectively, and the aromatization degree and thermal stability of biochar decreased. With the increase of field aging time, the amount of NH₄⁺-N adsorbed by biochar decreased in the order A0 > A1 > A2 > A3, although aged biochar maintained a strong adsorption capacity. Also, batch equilibrium adsorption experiments showed that the adsorption rate of biochar to NH₄⁺-N complied with the pseudo-second-order adsorption kinetics and Langmuir models. 【Conclusion】The present study suggests that the adsorption of NH₄⁺-N to biochar mainly occurred through the single-molecular layer mechanism, followed by physical adsorption. Therefore, studies on the enrichment effect of biochar on carbon and nitrogen and the adsorption mechanism of NH₄⁺-N are significant in exerting carbon sequestration and improving nitrogen utilization efficiency in the soil ecosystem for biochar.

Abstract:【Objective】Maintaining moderate soil phosphorus (P) supply intensity and determining the P application rate based on the P requirement of the crop target yield, and combining with acid, slow-release water-soluble P fertilizers and applied in the early stages of crop growth is a novel P management approach in cotton. Here we test the feasibility and effectiveness of this method and provide a basis for reducing the P fertilizer application amount and increasing its use efficiency. 【Method】A two-year field experiment was employed using cotton (Gossypium hirsutum) in the moderate Olsen-P soil (23.6 mg·kg^-1) in Shihezi, Xinjiang. Based on the P requirement of the target lint yield of 2.7 t·hm^-2, 52.4 kg·hm^-2was selected as the P application rate. Four treatments were set-up with three types P fertilizers: (1) no P fertilizer (CK); (2) monoammonium phosphate (MAP); (3) urea phosphate (UP); and (4) ammonium polyphosphate (APP). It was analyzed that the lint yield, P uptake and above-ground biomass of cotton in different treatments. The partial productivity of P fertilizer (PFP), agronomic efficiency (AE_P), P utilization efficiency (PUE) and P recovery index (the ratio of shoot P uptake to the amount of P fertilizer application, PRI) were calculated. Through stratified sampling, soil Olsen-P and P fractions in different soil layers were tested. Those allowed us to clarify the relationships between the P spatial availability and cotton growth requirements with different P fertilizers. 【Result】The significant results were: (1) The average lint yield of P applied treatments in two years was 2.73 t·hm^-2, which was classified as the high yield level in northern Xinjiang. Compared with the CK treatment, the lint yield of MAP, UP, and APP treatments were increased by 21%, 25%, and 11%, respectively. (2) The P surplus was 2.2-4.8 kg·hm^-2 and the P use efficiency was 24% across P applied treatments. The P recovery index of MAP, UP, and APP treatments was 91.7%, 95.6%, and 94.8%, respectively. (3) P fertilizer applied by drip irrigation in the cotton bud and boll stages can move to the 10-20 cm soil layer, which may maintain the soil P supply intensity during the cotton-growing period. Compared with the CK treatment, the mean Olsen-P in P applied treatments were increased by 94%～302%, 104%～144%, and 42%～67% in the 0～5 cm, 5～10 cm, and 10～20 cm soil layers, respectively. 【Conclusion】In summary, our results indicate that maintaining soil available P near the agronomic thresholds and determining the P application rate according to the P requirement of the target yield, and combining with acid, slow-release P fertilizer and applied in the cotton bud and boll stages can improve lint yield and P use efficacy under balanced P input-output conditions. Furthermore, the P recovery index based on the balanced P input-output can better reflect the real P use efficiency.

Abstract:【Objective】Low phosphorus (P) availability limits the increase in the productive capacity of acidic soils. The bacteria phoC and phoD genes encode acid and alkaline phosphatase (ACP and ALP), respectively, which mineralize organic phosphorus (P) to inorganic P, are affected differently under different fertilization regimes. However, the combined responses of phosphorus-solubilizing microorganisms (PSM) to fertilization strategies and the rhizosphere effect are still unclear.【Method】In this study, we evaluated the response of maize to the interaction of different nitrogen forms (ammonium nitrogen and nitrate nitrogen) and phosphate fertilizer levels. The phoC and phoD genes, separately coding for acid and alkaline phosphatase productions, were used as molecular markers to investigate the effects of fertilization strategies and rhizosphere effect on soil phosphatase activities and associated functional microbial communities in acidic soil. 【Result】The rhizosphere effect significantly increased soil phosphatase activities in the rhizosphere. ALP activities in the rhizosphere under nitrate-nitrogen treatment were lower than in the corresponding ammonium nitrogen treatment. Also, the strength of the rhizosphere effect was greater than that of nitrogen forms and phosphate fertilizer levels. Nitrogen forms, phosphate fertilizer levels and rhizosphere effect all significantly affected the operational taxonomic units (OTU) number and Shannon index of phoD-harboring bacteria, but only nitrogen forms and rhizosphere effect affected the OTU number of phoC-harboring bacteria. Principal coordinate analysis (PCoA) and PERMANOVA analysis showed that the rhizosphere effect exhibited more influence on the phoC- and phoD-harboring bacterial community composition than nitrogen forms and phosphate fertilizer levels, with more effects on the phoD-harboring bacterial community. The stimulation of soil phosphatase activities in the rhizosphere was closely related to the increase in soil organic matter. Additionally, changes in the composition and structure of phoC-harboring bacterial community were mainly related to the changes in rhizosphere nutrients, while the changes of phoD-harboring bacterial community structure may be attributed to combined effects of root exudates and nutrient changes. 【Conclusion】The rhizosphere showed more influence on soil phosphatase activities and associated functional bacterial communities than nitrogen forms and phosphate fertilizer levels in acidic soil. However, the strength of the effect strongly relied on the fertilization strategies.

Abstract:【Objective】The ecology of mining areas in the Loess Plateau is relatively fragile, while the vegetation restoration is closely related to soil microbe-mediated nutrient cycling. This study was designed to clarify the influence and regulatory roles of vegetation restoration on the functional groups related to soil carbon, nitrogen and phosphorus cycles, which are significantly important to rebuilding the ecological resilience and self-sustaining mechanism of mining areas.【Method】In this study, high-throughput qPCR chip technology, random forest model and structural equation model were used to reveal the changes and mutual feeding mechanism of soil characteristics, enzyme activities, carbon, nitrogen and phosphorus functional groups under different vegetation restoration modes of Antaibao open-pit reclamation waste dump on the Loess Plateau. 【Result】 The results showed that Caragana korshinskii (bushwood, BL), Pinus tabuliformis (coniferous forest, CF), Robinia pseudoacacia (broad-leaved forest, BF) and Robinia pseudoacacia + Ulmus pumila (mixed forest, MF) were superior to soil nutrient accumulation compared with Populus simonii forest (CK). Compared to CF, soil organic carbon (SOC) of BL, BF and MF increased by 82.26%, 168% and 56.65%, respectively. The total nitrogen (TN) of BL, BF and MF enhanced by 68.31%, 130% and 46.75% comparing with CF, while the available phosphorus (AP) contents increased by 10.41%, 27.65% and 20.89%, respectively. Nevertheless, these were still significantly lower than that of CK (P<0.05). The soil catalase (CAT) activities of BL, CF, BF and MF increased by 95.6%, 101.0%, 46.4% and 120.0% respectively, and are significantly higher than that of CK (P<0.05). Also, the soil β-glucosidase (BG) and leucine aminopeptidase (LAP) activities decreased significantly (P<0.05). The β-glucosidase activities of BL, CF, BF and MF decreased by 66.5%, 67.0%, 58.9% and 59.8%, while the leucine aminopeptidase activities decreased by 57.8%, 67.7%, 78.0% and 67.7%, respectively. The different modes of vegetation restoration significantly changed the relative abundances of functional groups related to carbon, nitrogen and phosphorus (P<0.05), whereas the variation tendencies always keep a consistent correspondence. The functional groups related to carbon, nitrogen and phosphorus were significantly positively correlated with soil nitrate nitrogen (P<0.001), but they presented negative correlations with ammonium nitrogen (P<0.01). The functional groups involved in the carbon cycle, nitrification process and organic phosphorus mineralization were significantly positively correlated with available phosphorus (P<0.01). In addition, results of the structural equation model showed that vegetation restoration could directly affect CAT and AP, thereby regulating the carbon, nitrogen and phosphorus cycle. Otherwise, the vegetation restoration could affect soil AP indirectly, thereupon then regulating the abundances of carbon, nitrogen and phosphorus functional groups, together with other soil characteristics, such as nitrate nitrogen or ammonium nitrogen. 【Conclusion】 This study might help deepen the knowledge about soil microbiology mechanism of vegetation restoration, which will furtherly help the ecological restoration of damaged mines in the Loess Plateau.

Abstract:【Objective】This study aimed to analyze the response of soil carbon composition to long-term nitrogen addition in the Stipa baicalensis meadow steppe. 【Method】A nitrogen addition experiment was designed in the meadow steppe of Ewenke Banner, Hulunbuir City, Inner Mongolia in 2010, and 8 nitrogen treatments were set as 0 (N0), 15 (N15), 30 (N30), 50 (N50), 100 (N100), 150 (N150), 200 (N200) and 300 (N300) kg·hm^-2·a^-1(calculated as N). Soil samples were collected in August 2019 and soil organic carbon and its fractions were measured to investigate the changes and drivers of soil organic carbon and its fractions after 10 years of nitrogen addition. 【Results】The results showed that: (1) Compared to the control, soil organic carbon (SOC) content and soil recalcitrant carbon (RP-C) did not change significantly under long-term nitrogen addition. The content of soil labile organic carbon (LP-C) increased, among which labile carbon fraction I (LPⅠ-C) and II (LPⅡ-C) increased by 0.48%-15.59% and 1.94%-8.41%, respectively. Soil easily oxidized organic carbon(EOC)did not respond, whereas the contents of dissolved organic carbon (DOC) and microbial biomass carbon (MBC) changed significantly. The overall soil carbon composition was more sensitive to N addition at the level of 30, 50 and 100 kg·hm^-2·a^-1; (2) The responses of sensitivity index (SI) of soil organic carbon to nitrogen addition showed that MBC was more sensitive to long-term nitrogen addition, which could be used as an indicator suggesting the changes in organic carbon component in the region; (3) Structural equation modeling (SEM) indicated that soil carbon fractions were regulated mainly by plant biomass and soil pH under long-term nitrogen conditions. 【Conclusion】Nitrogen addition increases soil labile carbon content in Stipa baicalensis and the changes in soil organic carbon and its fractions are mediated mainly by soil pH and plant biomass.

Abstract:【Objective】Biochar loaded bacteria is a practical application of microbial immobilization. Biochar is considered as the ideal carrier of microorganisms in recent years because of its large specific surface area, pore diameter and good absorbability. Biochar loaded with Bacillus and other exogenous functional microorganisms can increase crop yield, improve root activity, and improve soil enzyme and microbial activity. However, In the process of gradual potassium deficiency, it needs to be further explored that the impact of biochar-loaded potassium-solubilizing bacteria on soil enzyme activity and microbial community structure. Therefore, this paper aims to explore the effect of potassium-solubilizing bacteria-loaded biochar on soil microbial characteristics.【Method】Based on pot experiment with ryegrass and five treatments: control (CK), chemical potassium fertilizer (KCl), inoculation of potassium solubilizing bacteria (KSB), application of biochar (BC) and potassium solubilizing bacteria loaded biochar (BC-KSB), it was analyzed that the change characteristics of soil urease, acid phosphatase, invertase and catalase enzyme activities and microbial community structure, also the effects of biochar-loaded potassium solubilizing bacteria composite materials on soil nutrients, soil pH, microbial biomass carbon, microbial biomass nitrogen and ryegrass yield were discussed.【Results】The soil urease and acid phosphatase activity increased first and then decreased while the soil invertase and catalase activity decreased with an increase in the number of harvests for treatments with microbial agents or biochar. Compared with other fertilization treatments, BC-KSB was more conducive to the increase of soil urease, invertase, acid phosphatase and catalase activities. In terms of soil bacterial community, BC-KSB improved the species diversity and flora uniformity of soil bacteria, increased the abundance of soil beneficial bacteria (Chloroflexi, Actinobacteriota, Bacillus and Bradyrhizobium), and inhibited the reproduction of soil pathogenic bacteria (Proteobacteria and Rhodobacteria). Compared with CK, all fertilization treatments significantly increased the dry weight of ryegrass and BC-KSB treatment showed the largest increase. Also, compared with CK and KCl, BC-KSB treatment can significantly increase the contents of soil microbial biomass carbon, microbial biomass nitrogen, organic matter, total nitrogen and available potassium. However, the content of soil total potassium and total phosphorus in different treatments showed no significant difference. Furthermore, BC significantly increased soil pH compared to other treatments. Redundancy analysis showed that soil organic matter, available potassium, acid phosphatase, urease and microbial biomass nitrogen were the main influencing factors of bacterial community structure, whereas the growth of ryegrass was mainly affected by Burkholderia and Rhodobacteria.【Conclusion】KSB loaded biochar has a positive impact on ryegrass yield, soil nutrients, soil enzyme activity, and bacterial community structure, which provides profound significance for fertilizing soil and improving soil ecological environment.