(A) Research progress of land resources evaluation methods
1. Foreign land evaluation methods
The purpose of land evaluation is to provide scientific basis for rational use of land and economic development. According to the different evaluation process and indicators, land evaluation methods can be divided into three categories. The first category is qualitative method, the second category is quantitative method, and the third category is semi-quantitative land valuation method between the first two. Typical qualitative land evaluation methods in the world include land potential evaluation represented by the United States and land suitability evaluation by FAO. Quantitative land evaluation methods mainly include model method and system dynamics method; Semi-quantitative land evaluation includes parameter method and ecological area (area) method.
1) land potential evaluation method. 196 1 year, the United States evaluated and classified the land potential. The land potential classification system first classifies land into four categories according to its use, namely, wild, forestry, animal husbandry and agriculture, and then divides land into eight levels according to the limitations and obstacles of the influencing factors of land potential (Table 2- 1 and Figure 2- 1).
2) Land suitability evaluation method. In 1976, FAO issued a land suitability evaluation framework. The land suitability evaluation and classification system of FAO classifies land into two categories: suitable and unsuitable, and further divides it into four levels according to suitability and limiting factors (Table 2-2). As can be seen from Table 2-2, FAO land suitability evaluation grading system is only an evaluation framework, and the detailed degree of evaluation results can be determined according to different regional conditions and evaluation requirements.
Table 2- 1 American land potential classification system Table 2- 1 American land potential classification system
Figure 2- 1 Schematic diagram of land potential classification in the United States
In the figure, I-VIII represents the classification of land.
Figure 2- 1 Schematic diagram of land potential classification in the United States
Table 2-2 Classification System of Land Suitability Evaluation of FAO Table 2-2 Classification System of Land Suitability Evaluation of FAO
3) Agro-ecological zone method (AEZ). 65438-0978 The Agricultural Ecological Zone Law (AEZ) issued by the United Nations is a method to divide a land area into small land units with the same properties, and evaluate the land suitability, land potential and environmental impact. Agro-ecological region is a land resource unit defined by climate, topography, soil and land cover, and each region has specific land use potential and limited scope; Agricultural ecological unit is the smallest unit composed of topography, soil and climate characteristics, and it is the basic unit of agricultural ecological zoning method. Its basic working procedures are as follows: first, determine the land use mode and its ecological requirements, that is, determine the land use mode and its ecological requirements; The second step is to investigate land resources from the aspects of soil and topography, climate, land use or land cover, administrative divisions and so on. Combined with agricultural ecological zones, agricultural ecological units are divided according to land characteristics and quality; The third step is to classify the land according to the natural output.
4) Evaluation of sustainable land use management. In 1993, FAO issued an international framework for assessing sustainable land management. The evaluation method follows five evaluation criteria (pillars), such as productivity, safety, protection, economic feasibility and social acceptability. FESLM indicators can be divided into four categories: natural indicators, biological indicators, economic indicators and social indicators. Various indicators are detailed and complicated. For example, the natural indicators in the Guide to Evaluation of Agricultural Land without Irrigation include solar radiation, temperature, effective water supply, effective oxygen supply (drainage) in the root layer, effective food intake, nutrient retention capacity, rooting conditions, conditions affecting germination and seedling formation, air humidity affecting growth, mature conditions, flood risk, climate risk, salinization, toxic substances, pests and diseases, soil availability, mechanization potential and so on. Storage and processing conditions, conditions affecting production progress, accessibility in production units, size and location of potential management units, erosion risk, soil degradation risk, etc.
5) Model method. 1990, according to the requirements of the G-7 Summit in 1989, the Organization for Economic Cooperation and Development (OECD) launched a research project on eco-environmental indicators and established the conceptual framework of the "pressure-state-response" (PSR) model. See Table 2-3 and Table 2-4 for relevant indicators.
Table 2-3 Some Indicators of Pressure-Condition-Reaction Model
Table 2-4 Environmental Trait Related Indicators (EPI) Table 2-4 Relative Environmental Trait Index
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2. Domestic land evaluation methods
In ancient China, land classification and grading started earlier. For example, in Gong Yu period, land was divided into 9 grades, in Warring States period, land was divided into 3 grades, with 90 kinds of18 * *, and in Song, Ming and Qing dynasties, land was divided into 5 grades, 13 grades and 4 grades respectively. The classification and grading of modern land in China mainly involves three departments or units, namely, the Ministry of Agriculture, the Ministry of Land and Resources and the Nanjing Institute of Soil Research, Chinese Academy of Sciences.
(1) investigation and quality evaluation of cultivated land fertility
The purpose of the national survey and quality evaluation of cultivated land fertility carried out by the Ministry of Agriculture is to find out the nutrient status and soil pollution status of cultivated land in China. The work is based on the county, and the map scale is1:50,000; The elements of basic fertility of cultivated land include site conditions, soil conditions and farmland infrastructure conditions. Site conditions include landform type, topographic slope and slope direction, soil-forming parent material (residual slope deposit, slope deposit, flood deposit, alluvial deposit, lacustrine deposit, marine deposit, loess parent material, etc. ); Soil conditions include soil profile and soil configuration, soil conditions (thickness of plough layer, effective soil layer, soil thickness, depth and thickness of barrier layer, etc. ), physical and chemical properties of topsoil (texture, bulk density, pH value, exchange capacity, organic matter, mineral nutrients, salt content, salt composition, groundwater salt content, alkalinity, lime content, etc. ), background value of direct pollution source and soil erosion degree; Farmland infrastructure conditions include farmland water conservancy projects, soil and water conservation projects, ecological construction of pastoral areas and vegetation, soil fertility and level, etc. The evaluation factors of cultivated land basic fertility in different types of areas should reflect regional characteristics (Table 2-5).
Based on the investigation and quality evaluation of cultivated land fertility in China, the cultivated land types in China are systematically divided into northeast black soil type (paddy soil), northern plain moist soil-Jiang Sha black soil type, northern hilly brown soil-cinnamon soil type (including yellow brown soil and yellow cinnamon soil), loess type of loess plateau, inland irrigated desert (silt) soil type, southern paddy field type and southern hilly red yellow soil (yellow soil). 1996 The industry standard of the Ministry of Agriculture, National Farming Types and Cultivated Land Fertility Classification, was promulgated. In 2002, the National Agricultural Technology Extension Service Center and relevant units formulated the Technical Specification for National Cultivated Land Fertility Survey and Quality Evaluation (for Trial Implementation). As can be seen from the above, the evaluation system focuses on classification, and land classification is still based on grain output, which does not reflect natural conditions and human input.
Table 2-5 Evaluation Factors of Cultivated Land Basic Fertility in South China Table 2-5 Evaluation Factors of Cultivated Land Soil Fertility in South China
(2) Classification and evaluation of agricultural land
The grading and evaluation of agricultural land carried out by the Ministry of Land and Resources is an important part of the "new round of land and resources survey-land and resources monitoring survey project". It is a large-scale agricultural land quality and price survey to find out the quantity and ownership of agricultural land after detailed land investigation, aiming at finding out the quality grade and price of agricultural land in China and establishing the grading and pricing system of agricultural land. The agricultural land classification rules, agricultural land classification rules and agricultural land valuation rules were officially promulgated and implemented on August 1 2003.
The technical idea of agricultural land classification is that land classification reveals production capacity and its distribution, including light and temperature production potential (land quality difference benchmark), natural quality (land natural condition difference), development and utilization (average utilization level difference of producers) and comprehensive factors (average input-output level difference) and so on. Agricultural land valuation system has the following characteristics: ① it is connected with the results of detailed land investigation and soil investigation; ② Comprehensive application of theories and methods of land natural evaluation, land economic evaluation and land use evaluation; (3) Comparability across the country is achieved through a national parameter system including light and temperature production potential index, standard farming system, yield ratio coefficient, maximum yield of designated crops, and maximum "yield-cost" index. ④ Comprehensive evaluation of the present situation, potential and suitability of agricultural land utilization, combining grading with grading. Its shortcoming is that soil samples are not sampled and analyzed, and some data are out of date.
(3) Study on the evolution law and sustainable utilization of soil quality.
The general objectives of the National Key Basic Research Program (973 Project) "Evolution Law and Sustainable Utilization of Soil Quality" funded by Nanjing Institute of Soil Research, Chinese Academy of Sciences are: to establish an index system and an evaluation system for soil quality, and to put forward suggestions on national standards for soil quality; Evaluate the soil quality of main cultivated land types in China and reveal its evolution law; Reveal the law of material exchange at soil interface and its influence mechanism on soil quality; Establish the theory of soil quality maintenance and directional cultivation of main cultivated land, and establish the database and consulting system of soil quality of typical cultivated land. The main scientific issues involved include: ① the evolution mechanism, differentiation law and the theory of conservation and directional cultivation of soil quality, focusing on the main processes, mechanisms and regulation theories that affect the change of soil quality in China, so as to put forward the theoretical basis for balancing soil nutrients and improving soil fertility, regulating saline-alkali and acidification obstacles, repairing polluted soil, reducing soil erosion and effectively improving soil quality, and lay the foundation for developing the theory of sustainable utilization of soil resources; (2) The influence mechanism of material exchange on soil quality and animal and plant health, focusing on the main material exchange process, rate, flux and key factors at the interface between PEDOSPHERE and water, gas, biology and lithosphere, revealing the law of material exchange at the interface in PEDOSPHERE and its relationship with soil quality formation and environmental evolution, and putting forward the interface regulation theory and approach for soil quality cultivation; (3) Characterization theory and method of soil quality indicators, using advanced quantitative expression theory and method, the selected indicators representing soil quality are assigned and standardized, and the soil quality status is evaluated according to the soil quality index system and evaluation system established by systematic research.
Through key research, the soil fertility quality evaluation index and soil health quality benchmark of main soil types in China have been preliminarily formulated.
(2) Research progress of soil quality.
1. Evaluation of soil quality abroad
Soil quality is a comprehensive measure of soil's ability to provide nutrients necessary for life and produce biomass, its ability to contain, degrade and purify pollutants and maintain ecological balance, and its influence and promotion on the safety and health of plants, animals and human beings in a certain ecosystem.
Soil quality includes three connotations and functions: first, soil productivity, that is, the ability of soil to improve plant and biological productivity; The second is environmental quality, that is, the ability of soil to reduce the harm of environmental pollutants and bacteria; Third, animal health, that is, the ability of soil quality to affect the health of animals, plants and humans. These three functions are also called soil fertility quality, soil environmental quality and soil health quality. See Table 2-6, Table 2-7 and Table 2-8 for relevant indicators.
Table 2-6 Description Index of Field Soil Quality Table 2-6 Description Index of Field Soil Quality
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Table 2-7 Common Analysis Indicators of Soil Quality Table 2-7
Table 2-8 Parameters of soil quality and health status and their relationship with soil quality Table 2-8 Parameters of soil quality and health status and their relationship with soil quality
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2. Domestic soil quality assessment
Domestic research on soil quality mainly focuses on three aspects: soil background value, soil environmental capacity and soil environmental quality standard.
Investigation on (1) soil background value
The background value of soil environment refers to the inherent chemical composition and content of soil itself in the process of its development and formation, which is not or rarely affected by human activities, especially in the case of being unpolluted or destroyed. It basically reflects the original material composition, properties and structural characteristics of soil environment. During the "Seventh Five-Year Plan" period, the national key scientific and technological project "Study on the background value of soil environment" sponsored by the State Environmental Protection Bureau and co-sponsored by the State Education Commission and the China Academy of Sciences is the most systematic research result of the background value of soil heavy metals so far. Compared with the world soil, the contents of arsenic, zinc and copper in China soil are higher than the world average. Mercury, manganese and cobalt are worldwide values; Cadmium, chromium and nickel are lower than the world average; The change of lead exceeds the world average. The second national soil survey, which lasted 16 years, systematically tested and analyzed nine nutrient elements in soil, such as nitrogen, phosphorus, potassium, iron, manganese, copper, zinc, boron and molybdenum, and established soil fertility grading standards.
(2) Study on soil environmental capacity.
The concept of environmental capacity was introduced into the field of environmental science in 1970s. At present, the concept of soil environmental capacity is still being explored. One view is that there is a certain amount of pollutants in the soil, which will not pollute crops. Generally speaking, the maximum allowable amount of pollutants in soil is called soil environmental capacity. Another view is that soil environmental capacity is the maximum amount of pollutants in soil without destroying the structure and function of soil ecosystem. The latter emphasizes the need to clarify the impact of pollutants on the structure and function of soil ecosystem, as well as the requirements of system structure and function. Many countries, such as the former Federal Republic of Germany, Japan, the former Soviet Union, Australia and other countries, have determined the soil environmental pollution standards of some pollutants. There have been some reports on the study of soil environmental capacity in China.
The critical capacity of soil can be used to characterize the capacity of soil to accommodate various pollutants. After obtaining various eco-environmental effects of soil on pollutants and the critical content of various single systems, the critical content of the whole soil ecosystem can be obtained by using the comprehensive critical index of various effects, which can be used as the basis for the state to formulate environmental standards and determine soil environmental capacity. Table 2-9 shows the critical content of each single system in China meadow cinnamon soil area.
Table 2-9 Critical content of each single system in China meadow brown soil area Table 2-9 Critical content of each system in China meadow brown soil area
Note: * Surface runoff and underground leakage do not exceed the standard; * * When it is 3.5 mg/kg, the surface runoff and underground leakage do not exceed the standard. (According to Xia Zenglu 1986)
The method of quantitative expression of soil environmental capacity by mathematical model is still being explored. At present, the commonly used methods to determine soil environmental capacity are soil static capacity and soil dynamic capacity. Static soil capacity is a simple method to calculate the capacity according to the difference between the environmental background value of soil and the environmental standard, which can be expressed by CS = M (Ci-CBi) (where: M is the soil weight per mu (kg), Ci is the soil critical content of element I (mg/kg), and CBi is the soil background value of element I (mg/kg)). At this time, the existing capacity CSP = m (CI-CBI-CP), and CP is the increase of human pollution in the soil. In addition, the soil environmental capacity can also be roughly estimated by Q=(CK-B)× 150 (where q is the basic soil environmental capacity (g/ mu), CK is the standard value of soil environment (mg/kg), and b is the regional soil background value (mg/kg)).
Soil is an open material system, and pollutants can enter the soil or be exported. Soil dynamic capacity is to calculate the environmental capacity of soil according to the residual amount of pollutants. Suppose the annual input is Q, the annual output is Q', and if Q is greater than Q', the remainder is Q-Q'. As time goes on, more and more residues are left, resulting in accumulation. Cumulative rate (k) is the ratio of residual quantity (Q-Q') to input quantity Q, so the cumulative total amount of soil pollutants in N years is AT=Q+QK+QK2+…+QKn, while the cumulative total amount of pollutants in N years is RT = qk+qk2+…+qkn. When the current number n is long enough, QKn tends to zero and AT reaches the maximum limit. Therefore, the annual cumulative amount of pollutants in soil is at ′ = k (b+q) (where: ATˊ is the annual cumulative amount of pollutants in soil (mg/kg), k is the annual residual rate of soil pollutants (%), b is the regional soil background value of pollutants (mg/kg), and q is the annual input amount of soil pollutants (mg/kg). Assuming that the annual residue rate (K) is the same and the annual input is the same, the cumulative total amount of soil in N years is AT=BKn+QK. As can be seen from the formula, the value of annual surplus rate K has a great influence on the calculation results. K values of soil and pollutants in different areas are also different, which need to be obtained through experiments. By using this calculation method, the number of years required for pollutants to reach the regional environmental standards can be predicted.
(3) Study on soil environmental quality standards.
In order to implement the Environmental Protection Law of People's Republic of China (PRC), prevent soil pollution, protect the ecological environment, ensure agricultural and forestry production and human health, China formulated and promulgated the Soil Environmental Quality Standard (GB15618-1995 (Table 2-65438+). According to the application function, protection goal and main properties of soil, the standard stipulates the maximum allowable concentration index value of pollutants in soil, which is used in farmland, vegetable fields, tea gardens, orchards, pastures, woodlands, nature reserves and other soils. According to the application function and protection goal of soil, the standard divides soil into three categories: category I is mainly suitable for soils in nature reserves (except those with high heavy metal content in the original background), centralized drinking water sources, tea gardens, pastures and other protected areas stipulated by the state, and the soil quality basically maintains the natural background level; Class II is mainly suitable for general farmland, vegetable fields, tea gardens, orchards, pastures and other soils, and the soil quality basically does not cause harm and pollution to plants and the environment; Class III is mainly suitable for woodland soil and high background soil with large pollutant capacity and farmland soil near minerals (except vegetable fields), and the soil quality basically does not cause harm and pollution to plants and the environment.
Table 2- 10 Standard Value of Soil Environmental Quality
Note: ① Heavy metals (chromium is mainly trivalent) and arsenic are calculated by elements, which are suitable for soils with cation exchange capacity > 5cmol (+)/kg. If ≤5cmol(+)/kg, the standard value is half of the value in the table; (2) Soil environmental quality standards for arsenic in paddy field and chromium in dry land.
The standard stipulates that the first-class standard is the limit value of soil environmental quality to protect the natural ecology of the region and maintain the natural background; The second standard is the soil limit to ensure agricultural production and maintain human health; The third grade standard is the critical value of soil to ensure agricultural and forestry production and normal plant growth. The standard grades of all kinds of soil environmental quality are as follows: Class I soil environmental quality is subject to Class I standard; The second-class soil environmental quality shall be subject to the second-class standard; Class III soil environmental quality shall be subject to Class III standards.