Evaluation method of comprehensive index of soil moisture in returning farmland
The unsealed drought conditions in northwest China are very serious, especially in heavily arid and semi-arid loess hilly and gully regions. Soil moisture is not only the main influencing factor for plant growth and vegetation recovery during soil erosion, but also an important agricultural water resource.
In arid and semi-arid loess regions, deep loess layers (typically 50 to 200m in thickness) accumulate large amounts of water to form soil reservoirs, and the initial conditions in the “banks†are also the main limiting factors for vegetation recovery. The condition, plant species invasion, and growth status are different, and the specific succession direction and rate of the community are significantly different.A long-term use of a soil moisture temperature meter measures the soil in Northwest China and concludes that improved soil moisture conditions can improve plants. Root conditions of the germination and initiate the succession process of the ecosystem.The validity of soil moisture is the main indicator to evaluate the effect of vegetation on the availability of soil moisture and the effect of water stress on vegetation growth, and the amount of soil water storage is the vegetation restoration and reconstruction. The important soil environmental factors of this area were developed earlier in foreign countries, and the research content has involved the water absorption rate of the roots of plants and the effectivity dynamics of soil moisture and the effect of vegetation on soil water storage performance. The resource evaluation index system is not only the basic work of water resources evaluation, but also It is the direction and driving force for the forward development of water resources research.We discuss the concept of soil water more comprehensively, discuss the characteristics of soil water and its effectiveness on plants, and put forward the evaluation coefficient of soil water resources. It mainly elaborates the definition of soil water resources and the significance of studying soil water resources, analyzes the structure of soil water resources, focuses on renewable soil water resources and available and exploitable soil water resources, and proposes a method for evaluating soil water resources. In the restoration and reconstruction of vegetation, soil moisture characteristics of the cultivated land should be taken into account to ensure the selection of ideal and practical vegetation restoration targets.
The soil moisture characteristics of existing plant communities with different years of retreating farmland have very important reference values ​​for effective intervention and regulation of vegetation restoration. Therefore, it is of great practical significance to evaluate the status of soil moisture in the reclaimed land on the Loess Plateau. However, the existing soil moisture evaluation methods have difficulties such as unclear things identification, human factors interference, and non-intuitive evaluation results. Therefore, in this paper, based on the analysis of measured data of soil moisture evaluation indicators in different soil layers, an integrated model based on the entropy weight attribute recognition model was used to comprehensively evaluate the soil moisture of different years of returning cultivated land in the Loess Plateau. in accordance with.
Research Area Overview The research area is located in the Yanhe River Basin and is located in the hinterland of the Loess Plateau. The total length of the river basin is 286.9 km and the total area is 7,687 km. The study area is a semi-arid climate zone with an annual rainfall of 500mm and an annual average temperature of 9°C. The main soil is silty loess soil. Loose soil, poor impact resistance, serious soil erosion, is a very strong erosion area. Vegetation type is forest steppe vegetation---temperate steppe vegetation. According to the mainstream view of Loess Plateau Vegetation Division, the area is a forest steppe zone, and the representative vegetation is B. chinensis (Swallowgrass, Artemisia sacrorum, Gardenia jasminoides, and Dalbergia zhizhizi, etc.) The main type of land-use water is the first in the region. The formation of sexual productivity has played an important role, which has become one of the leading factors in the evaluation of land resource quality. Soil water has a restrictive effect on vegetation restoration. It not only affects the occurrence, development and succession of plant communities, but also determines the plant community performance. The alternative direction, because the soil moisture is basically the slope vegetation, terraces, orchards, arbor woodlands, shrub lands, natural grasslands, and barren slope lands, etc. The landforms, soil types, parent material, and land use in the Yanhe River Basin The method is well represented in the Loess Plateau.
We are now collecting and measuring soil moisture samples mainly through the method of spatial generation time to determine the change of soil moisture in different years. In order to reduce the resulting error, multiple points of repeated surveys were performed for each time series to increase the number of samples. First, the time for returning farmland was determined through interviews and historical data verification. The soil moisture was measured with an earth-drilled sample, dried (105°C), with a depth of 5m and a sample depth of 20cm. The sampling time is July-August 2005. When analyzing the acquired data, the outliers formed due to the influence of special sites were excluded. The number of samples used for analysis and evaluation was 66. Evaluation indicators and evaluation criteria According to the characteristics of the soil conditions and soil water availability in the study area, and the characteristics of soil water holding capacity and moisture constant (mainly the wilting coefficient and the field water holding capacity), the effective soil moisture interval was divided. In general, the effective use of water by plants is difficult to distinguish, and the closer the water to the wilting coefficient, the more difficult it is for plants to absorb it. In the Loess Plateau, 60% of the field water capacity is generally used as a vegetation growth retardation point. Accordingly, referring to the research results of relevant personnel on soil moisture, the soil moisture content in the study area is divided into 5 levels (Table 1).
Through this sampling survey, in determining most of the evaluation issues, the determination of weight is affected by subjective factors. The evaluation results are not uniform and there is no comparability. Attribute recognition model is based on attribute set theory and attribute measurement as the basic concept. Based on ordered segmentation and attribute recognition criteria, it can effectively identify and compare things. The model reduces the influence of subjective factors to a certain extent and has been successfully applied in environmental quality assessment, water quality and water resources assessment. The basic idea of ​​comprehensive evaluation of soil moisture based on the attribute recognition model based on entropy weight is to calculate the attribute measure of each sample index and its weight coefficient, use the multiplication principle to find the attribute measure of the sample, and finally according to the confidence criterion and score. Guidelines classify, compare, and rank samples.
In this study, the entropy method was used to determine the weight coefficient of each evaluation index, and the soil water temperature recorder was used to comprehensively evaluate the soil moisture of the abandoned farmland in Yanhe River Basin. Statistical software was used to statistically analyze the actual soil moisture data. The weight of the soil moisture evaluation index weight value refers to the degree or contribution rate of soil moisture in different soil layers to the overall soil moisture, indicating that the role and status of soil moisture in different soil layers in the comprehensive evaluation of soil moisture. In information theory, the entropy value reflects the degree of disorder of information and can be used to measure the size of information. The more information an indicator carries, the greater the effect of the indicator on the decision. The smaller the entropy value is, the smaller the degree of disorder of the system is. Therefore, information entropy can be used to evaluate the degree of order of the obtained system information and its utility. This paper uses the entropy method to determine the weight, which is the entropy weight, which is the utility value of the index information calculated by the evaluation matrix consisting of the evaluation index values ​​under objective conditions.
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