What are the specific contents of the progress and trends of soil degradation research? Zhongda Consulting will answer the questions below.

In view of the increasingly serious negative impact of soil and land degradation on global food security, environmental quality, and human and animal health, it is necessary to study from the perspective of the interaction between the soil sphere, geosphere-biosphere system and other spheres. Soil degradation, especially the occurrence mechanism and evolution dynamics, spatiotemporal distribution patterns, future change predictions and restoration and reconstruction strategies of soil degradation induced by human factors, has become the most important part of the study of global change and will continue to become the most important part of the international soil research in the 21st century. It is a hot issue of common concern in the fields of science, agriculture and environmental science. However, so far, many theoretical issues and process mechanisms related to soil degradation are still unclear, and there are no recognized or unified soil degradation indicators and quantitative evaluation methods [1]. Therefore, it is necessary to keep abreast of the latest trends in international soil degradation research, And creatively carrying out research work in this field based on my country's actual situation has important academic value and practical production significance.

1. The concept of soil degradation

Soil degradation refers to the agricultural production capacity or land degradation that occurs under the influence of various natural, especially human factors. Utilization and environmental regulation potential, i.e. the process by which soil quality and its sustainability are reduced (both temporarily and permanently) or even completely lost in its physical, chemical and biological characteristics, past, present and future The degradation process is the core part of land degradation. Soil quality refers to the productivity status or health status of the soil, especially the ability to maintain the productivity of the ecosystem, sustainable land use and environmental management, and promote the health of animals and plants [2]. The core of soil quality is Soil productivity is based on soil fertility. Soil fertility is the natural ability of soil to maintain plant growth. On the one hand, it is the result of the long-term interaction of five natural soil-forming factors, namely soil parent material, climate, biology, topography and time factors. It has an obvious response to the dominant soil-forming factors. Physical, chemical and biological properties; on the other hand, human activities also profoundly affect the natural soil formation process, changing the direction of changes in soil fertility and soil quality. Therefore, the decline of soil quality or soil degradation is often a dynamic process caused by the combined effects of natural and human factors. According to the manifestation of soil degradation, soil degradation can be divided into two types: explicit degradation and implicit degradation. The former means that degradation processes (some are even short-lived) can lead to obvious degradation results, while the latter means that although some degradation processes have already started or have been carried out for a long time, they have not yet led to obvious degradation results.

2. Overview of global soil degradation

Currently, soil and land degradation problems caused by various irrational human activities have seriously threatened the sustainability of world agricultural development. . According to statistics, the global soil degradation area reaches 19.65 million km2. In terms of regional distribution, soil degradation is particularly prominent in Asia and Africa, which are located in tropical and subtropical regions. Of the approximately 3 million km2 of severely degraded soil, 1.2 million km2 is distributed in Africa, 110 Thousands of km2 are distributed in Asia. In terms of soil degradation types, soil erosion accounts for 84% of the total degraded area and is one of the main causes of soil degradation. In terms of degradation levels, soil degradation is classified into moderate, severe and extreme. Mainly severe degradation, mild degradation only accounts for 38% of the total degraded area[3～6].

Global Assessment of Soil Degradation research results[3～6] show that soil Erosion is the most important form of soil degradation. Water erosion accounts for 56% of global degraded soil, and wind erosion accounts for 28%. As for the causes of water erosion, 43% is due to forest destruction, 29% is due to overgrazing, and 24% is due to unreasonable Agricultural management, and the causes of wind erosion are 60% due to overgrazing, 16% due to unreasonable agricultural management, 16% due to over-exploitation of natural vegetation, and 8% due to forest destruction; global soil chemical degradation (including Soil nutrient attenuation, salinization, acidification, pollution, etc.) affects a total area of ??2.4 million km2, which is mainly due to irrational agricultural utilization (56%) and forest destruction (28%); the total global physical degradation of soil It covers an area of ??about 830,000 km2, mainly concentrated in temperate areas, and may be mostly related to the compaction of agricultural machinery.

3. Soil degradation in my country

First of all, the situation of soil erosion in my country is quite serious, and there is a trend of further aggravation in some areas. According to statistical data [7], the area of ??soil erosion in my country reached 1.83 million km2 in 1996, accounting for 19% of the total land area. The soil erosion area in the red and yellow soil areas in the south alone reached 61.53 million km2, accounting for 1/1 of the total land area in the region. 4[8]. At the same time, the survey results of soil erosion areas in 13 key erosion counties in the Yangtze River Basin show that in the past 30 years, their soil erosion areas have increased at an average rate of 1.2% to 2.5% per year[9]. The situation is not optimistic.

Secondly, from the perspective of soil fertility, the organic matter content of cultivated land in my country is generally low, with paddy soil mostly ranging from 1% to 3%, while the organic matter content of dryland soil is lower than that of paddy fields, with <1% accounting for 31.2%; the total nitrogen content of most cultivated soil in my country is below 0.2%. Among them, 5 provinces (regions) including Shandong, Hebei, Henan, Shanxi, and Xinjiang have serious nitrogen deficiency areas accounting for more than half of their total cultivated land area; the phosphorus-deficient soil area is 673,000 km2, of which more than half of the cultivated land in more than 20 provinces (regions) is seriously deficient in phosphorus; the proportion of potassium-deficient soil area is relatively small, about 185,000 km2, but potassium deficiency is more common in the south, including Hainan, Guangdong, Guangxi, More than 75% of the cultivated land in Jiangxi and other provinces (regions) is potassium deficient. In recent years, the nutrient balance of farmland across the country has been deficient in potassium. Therefore, the available potassium content of farmland soil has generally declined in both the south and the north. trend; 63.3% of cultivated land lacks medium elements [10]. The evaluation of the comprehensive soil fertility status of the country has not been reported. As far as the eastern red soil hilly area is concerned, soil organic matter, total nitrogen, total phosphorus, available phosphorus, and total potassium are selected. The results of a comprehensive evaluation of soil fertility using 11 soil fertility indicators such as , available potassium, pH value, CEC, physical clay content, powder/viscosity ratio, and surface soil thickness show that most of its soils are affected by fertility degradation to varying degrees. , at medium and low levels, the area of ??soil with high, medium and low fertility levels accounts for 25.9%, 40.8% and 33.3% of the total area of ??the region respectively, in the hilly and mountainous areas of Guangdong, Baise area of ??Guangxi, Jitai Basin of Jiangxi and Fujian Fertility degradation in southern and other regions has been very serious [11].

In addition, other forms of soil degradation are also serious problems. Taking the southern red soil area as an example, about 200,000 km2 of soil has been affected by acidification problems that have affected its production potential. The amount of chemical fertilizers and pesticides applied has increased year by year, and groundwater pollution has continued to intensify. In some coastal areas, the nitrate nitrogen content of groundwater has reached far beyond the It is higher than the maximum allowable concentration of 10mg/l recommended by WHO; at the same time, soil heavy metal pollution near some mining areas, reclamation lands and coastal areas is also quite serious [8].

4. Progress in soil degradation research

Since FAO raised the issue of soil degradation in 1971 and published the monograph "Soil Degradation", the issue of soil degradation has attracted increasing attention. The first global conference on land degradation, the United Nations Conference on Desertification, was held in Nairobi, Kenya, in 1977. The United Nations Environment Program (UNEP) funded Oldeman and others' project plans in 1990 and 1992 to carry out the Global Assessment of Soil Degradation (GLASOD), prepare a global soil degradation map and assess land degradation (ie, desertification) in dry lands. In 1993, FAO and others held an International Conference on Soil Degradation and decided to carry out national-level soil degradation and SOTER (Soil and Terrain Digital Database) pilot studies in tropical and subtropical regions.

At the 15th International Congress of Soil Science in Mexico in 1994, the problem of soil degradation, especially in the tropical and subtropical tropics, received much attention from the participants. Many scientists pointed out that in the next 20 years, there will be soil degradation in the tropics and subtropics. 1/3 of cultivated land has been reduced to wasteland, and grain production in 117 countries will be significantly reduced. It calls for strengthening research on soil degradation and land degradation restoration and reconstruction, and in the concept of soil degradation, degradation dynamic database, degradation indicators and evaluation models and geographical information systems, degradation There have been new developments in remote sensing and positioning dynamic monitoring and simulation modeling and prediction, soil regression performance research, and expert decision-making systems for restoration and reconstruction of degraded systems. The International Society for Soil and Water Conservation also organized an international symposium on the global challenges of watershed-based ecosystem management in Toronto, Canada, in 1997 to discuss soil erosion and other soil degradation issues from the perspectives of ecosystems and watersheds. Moreover, the International Soil Federation held the first and second International Conference on Land Degradation in Turkey and Thailand in 1996 and 1999 respectively, which directly focused on land degradation, and decided to establish the Soil Degradation Conference at the first conference. The research working group specializes in soil degradation. At the second meeting, it paid more attention to the issue of soil degradation. Some scholars proposed to raise soil degradation research to the level of degradation science and decided to hold the third meeting in Brazil in 2001. The International Conference on Soil Degradation[12].

At the same time, in Asia, the "Asian Soil Conservation Network in the Humid Tropics (ASOCON)" and the "Asian Problem Soil Network" supported by UNDP and FAO are also working on land degradation in the Asia-Pacific. A lot of fruitful research work has been carried out in evaluation and control.

In general, international soil degradation research has made important progress in the following aspects:

① Study soil degradation from a comprehensive perspective of the internal causes of soil degradation and external influencing factors (including natural and socioeconomic factors) Degradation evaluation indicators, classification standards and evaluation method systems;

②Start from the physical, chemical and biological processes of soil and their interactions, and study the process, nature and mechanism of soil degradation;

③ From a historical perspective, combined with positioning dynamic monitoring, study the evolution process, development trends and rates of various types of soil degradation, and simulate and predict them;

④ Focus on human activities (especially It is the study of the impact of land use methods and soil management measures) on soil degradation and soil quality, and combines theoretical research on soil degradation with the management and development of degraded soil to conduct experimental demonstrations and demonstrations of land regeneration technology and soil ecological function protection. Promotion;

⑤ Focus on traditional technologies (field surveys, field experiments, pot experiments, laboratory analysis tests, positioning observation tests, etc.) and high-tech technologies (remote sensing, geographic information systems, ground positioning systems, simulation, Expert system, etc.);

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⑥Study on the impact of soil degradation on soil quality and its impact on productivity.

In the past few decades, soil science research in my country has mainly focused on soil occurrence, classification and mapping (especially soil resource inventory); basic physical, chemical and biological properties of soil (especially soil fertility properties) ; Development, utilization and improvement of soil resources (especially soil fertilization, improvement of saline soil and red soil, etc.). Although these works are closely related to soil degradation science in a broad sense, the research work directly on the theme of soil degradation has been mainly concentrated in the past 10 years. Among them, the research work on tropical and subtropical soil degradation has been relatively systematic and in-depth. In the 1980s, I participated in The compilation of the tropical and subtropical soil degradation map completed the preparation of the 1:1 million SOTER map of Hainan Island.

Since the 1990s, the Nanjing Soil Research Institute of the Chinese Academy of Sciences has jointly undertaken the national "Eighth Five-Year Plan" scientific and technological research project "Research on the Degradation Mechanism and Prevention Measures of Red Soils in the South" and the National Natural Science Foundation of China's key project "Soils in the Red Soil Region of Eastern my country" "Research on the spatiotemporal changes, mechanisms and control strategies of degradation" task, combine macroscopic surveys with field positioning dynamic observations and laboratory simulation tests, combine remote sensing, geographical information systems and other high and new technologies with traditional technologies, and integrate nature and social economy. Combining factors, combining time evolution with spatial distribution research, and combining degradation mechanism with control strategy research, we have made useful explorations into the basic process, mechanism of action and control strategies of soil degradation in the red soil hilly areas of southern China, and in the following aspects Important progress has been made [8, 13]:

① Preliminarily defined the concept of soil degradation and clarified the basic process, mechanism and characteristics of red soil degradation.

② In terms of soil erosion, remote sensing data and geographic information system technology were used to compile 1:4 million soil erosion maps and superimposed type maps of the eastern red soil area in the 1990s and superimposed soils in the 1970s, 1980s and 1990s in typical areas. Erosion map, and based on soil erosion map, land use map, soil parent material map, etc., a 1:4 million soil erosion degradation zoning overview map was compiled;

K values ??of erodibility of main types of soil in the South Field measurements were conducted, and the second national soil census data and the corrected Wischmeier equation were used to calculate the erodibility K of the main types of soil in southern my country, and relevant maps were compiled.

③In terms of the mechanism of fertility degradation, a soil fertility database was established in the southern red soil area, a preliminary fertility degradation evaluation index system was proposed, attempts were made to evaluate soil fertility degradation, and relevant maps for red soil degradation evaluation were drawn ; Combining the study of nutrient balance and soil nutrient degradation, this paper summarizes the 10-year change pattern of farmland nutrient balance in southern my country and its relationship with soil fertility degradation. It is believed that the nutrient deficit cycle and nutrient imbalance caused by soil erosion, acidification, nutrient leaching, etc. It is the fundamental cause of soil nutrient degradation; using remote sensing methods and historical data, we compiled soil organic carbon density maps of 0-20cm and 0-100cm soil layers, and discussed the growth and transformation of red soil organic carbon pools and the changing rules of humus composition and properties. ; It is proposed that phosphorus fixation is the main cause of phosphorus degradation in red soil. The essence of phosphorus effectiveness decay is the dinucleation and diffusion of phosphorus into the solid phase, which solves the essential problem of phosphorus degradation in red soil.

④ In terms of soil acidification, the acidification characteristics of red soil were studied. Based on the acid buffering performance of the soil, soil acid sensitivity classification standards were established, the acid sensitivity classification and zoning of red soil were carried out, and the relevant Overview of regional soil acid sensitivity zoning;

The MAGIC model is used and calibrated to predict the acidification of red soil in my country, revealing the spatial and temporal changes in red soil acidity; and important progress has been made in the rapid assessment of crop aluminum tolerance .

⑤ In terms of soil pollution, multi-parameters were used to conduct a comprehensive assessment of heavy metal soil pollution, a calculation method for the Comprehensive Pollution Index (CPI) value was established, and the pollution status in different regions was assessed and drawn. An overview of heavy metal pollution was obtained; the adsorption coefficient (Kd), half-life (t1/2) and matrix migration model of pesticides in soil were used to clarify the mechanism of soil pesticide pollution; the research results on the impact of heavy metal pollution on soil fertility showed that , Heavy metal pollution can reduce the soil's ability to retain potassium and promote potassium leaching; for nitrogen and phosphorus, it mainly reduces the activity of enzymes related to their catalytic degradation and recycling. ⑥ In terms of prevention and control of red soil degradation, regional governance and regulation strategies were proposed, including three-dimensional planting and breeding models such as "top forest-cashew nut-grain farmer-pond fish", etc., and some development models were demonstrated and evaluated.

However, our country has a vast territory, complex natural and socioeconomic conditions, and obvious differences between regions. Various types of areas face various resource and environmental degradation problems to varying degrees in the process of agricultural and rural development. Some problems are unique to the entire area, while others are unique to specific types of areas. Past work only focused on the red soil hilly areas in the south of the Yangtze River, while other areas were less touched. Moreover, research work often focuses on the study of single indicators and single processes. Research on the comprehensive evaluation index system of soil degradation is basically in the blank, and there is insufficient research on the interaction of the degradation process. At the same time, there are still many issues to be further studied in terms of rational selection of alkaline substance amendment types, improvement of economic benefits, and the impact of long-term application of amendments on soil physical, chemical, and especially biological properties. For acid (aluminum) resistant crop varieties, The selection research also needs to be strengthened urgently. In addition, no systematic research has been carried out on other soil degradation issues, such as soil and water pollution caused by intensive agriculture, township enterprises and mineral development, and the decline of soil biodiversity.

5. Research directions on soil degradation

Soil degradation is a very comprehensive and complex process with temporal dynamics, spatial heterogeneity, and highly nonlinear characteristics. . Soil degradation science involves many research fields, not only involving soil science, agronomy, ecology and environmental science, but also closely related to social sciences, economics and related policies. However, to date, most research work at home and abroad focuses on the evaluation of spatial changes or degradation of certain soil properties in specific areas or specific soil types, but rarely involves the time series changes of different degradation types. Moreover, most of the research work on soil degradation assessment methodology and evaluation index system quantification, dynamics, comprehensiveness and practicality, and scale conversion are in the exploratory stage.

Although my country's soil degradation research has made certain and distinctive progress in some aspects, it is still in its infancy as a whole. To this end, the author believes that future research on soil degradation in my country should systematically and comprehensively carry out comprehensive evaluation of soil degradation and research on the reconstruction and restoration of major degraded agricultural ecosystems at a broader and deeper level, and gradually move towards land degradation or environmental protection. Expansion in the direction of degradation. Specifically, research work in the following areas should be strengthened:

(1) Research on soil and land degradation indicator evaluation systems. It mainly includes single and comprehensive evaluation indicators, classification standards, thresholds and elasticities, quantitative and comprehensive evaluation methods and evaluation models used to evaluate different soil and land degradation types;

(2) Soil degradation Research on monitoring and early warning systems. It mainly includes establishing a soil degradation monitoring and research network to monitor and evaluate the type, scope and degree of soil and land degradation at different scales in key regions and countries, and carry out classification and zoning to provide a basis for the remediation of degraded land;

(3) Research on soil and land degradation processes, mechanisms and influencing factors.

Focus on studying the occurrence conditions, processes, influencing factors (including natural and socio-economic) and their interaction mechanisms of several major forms of degradation (such as soil erosion, soil fertility attenuation, soil acidification, soil pollution and soil salinization, etc.) ;

(4) Research on soil and land degradation dynamic monitoring and dynamic database and its management information system. It mainly includes the selection and construction of soil degradation monitoring sites or benchmark sites, the application and development of modern technologies and means such as 3S (GIS, GPS, RS) technology and information networks and scale conversion, soil degradation attribute databases and GIS maps. And its work on dynamic updating, simulation prediction and early warning of soil degradation trends;

(5) Research on the relationship between soil degradation and global change. Mainly including soil degradation and water eutrophication, groundwater pollution, greenhouse gas release, etc.;

(6) Research on the restoration and reconstruction of degraded soil ecosystems. It mainly includes the use of ecological economics principles and expert systems and other technologies to research and develop comprehensive soil and environment remediation decision support systems and optimization models suitable for different soil degradation types and targeting sustainable agriculture. The soil quality of major degraded ecosystem types Work on experimental demonstration research on key technologies for restoration and reconstruction and their integrated application to provide decision-making consultation and demonstration models for soil degradation prevention and control;

(7) Strengthen the impact of soil degradation on productivity and its economic analysis Research and assist the government in formulating policies that are conducive to sustainable land use and prevention of soil degradation.

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