The investigation of sample plot is divided into two parts: one is vegetation investigation, including plant species, density, coverage, DBH, height and spacing. The second is the investigation of geological structure, including soil lithology, texture, temperature, water content, various nutrient contents and root distribution characteristics. The acquisition of related properties and indicators is completed through a series of links such as digging sample pits, stratified sampling, field testing and indoor testing.

(1) vegetation survey

Vegetation survey adopts the sample plot survey method introduced in Plant Ecology. This study focuses on the plant species and growth status of different life forms, highlighting the corresponding relationship between ground layers and life forms, as well as the relationship between water and fertilizer conditions of each layer and the growth of plants (mainly crops).

During the investigation, the dry land in the loess hilly area of Dayugou is in the growing season of cotton, sesame, sorghum, corn, sweet potato, beans and other crops. Common tree plants in the wild are paulownia, Broussonetia papyrifera, jujube, persimmon, wild mulberry and so on. Common shrubs are Vitex negundo, Uncaria rhynchophylla and Lespedeza. Herbs are mainly weeds in the field, such as amaranth, pig excrement beans, Setaria viridis and Compositae. Most of the crops in the farmland are drilled and grow well. Trees, shrubs and wild herbs are mixed. The spacing between trees is uncertain, most of them are single trees, and the artificial forest belt is rare. On the narrow edge of farmland and the slope of terraced fields, shrubs and herbs flourish, showing a certain canopy level. The artificially cultivated land under the coal gangue mountain is mainly artificial forest, mostly poplar, and occasionally paulownia. The undergrowth is overgrown with weeds, and the dominant species are hops and humulus. There are some artificially planted melons and beans in the gaps, which grow generally. See tables 5.2 ~ 5.5 for details.

Table 5.2 1 Soil Survey and Sample Vegetation Questionnaire in Sample Pit

Note: quadrat area, 20m×12m; Longitude, e11305' 26.7 "; Latitude, n34 43'13.8 "; Artificial reclamation of land in industrial square.

(2) Survey of geographical structure

The investigation of geological structure is mainly realized by the excavation of sample pits. The sample pit is located in the center of the sample plot. According to the above boundary definition standard, the excavation depth is generally kept at1.1~1.2m.. The size of the sample pit is 1m× 1.8m, which is rectangular (Figure 5. 1), and the vertical side of the pit wall should be smooth, which is sampling. The distance between the surface and the base of trees or shrubs should be about 1m to avoid excessive damage and death to root groups. After the sample pit is excavated and shaped, the following tasks are completed in turn on the main survey profile: ① identification and stratification of soil lithology; (2) Soil temperature measurement: the topsoil should be removed during temperature measurement. In order to avoid the interference of temperature, the soil temperature value should be read at intervals of 65438+/-00 cm from top to bottom; (3) At the same time of temperature measurement, the water content of core soil is determined; (4) Trim the profile again, and use nylon wire as a net, each grid 10cm× 10cm, for root system investigation and statistics; ⑤ After the root system investigation and statistics are completed, soil samples of1000 cm are taken from top to bottom in the main investigation area, and indoor physical and chemical indexes such as fertilizer content and soil enzymes are determined.

Table 5.3 Soil Investigation and Vegetation Questionnaire of Sample Pit No.2

Note: quadrat area, 20m×15m; Longitude, e113 05' 20.2 "; Latitude, 34 43' 35.8 "N; Farmland on the top of loess hill.

Table 5.4 Soil Investigation and Vegetation Questionnaire of Sample Pit No.3

Note: Square area, 20m×20m；; Longitude, e11305'17.9 "; Latitude, 34 43' 39.5 "N; Beside the loess hilly slope.

Table 5.5 Soil Investigation and Vegetation Questionnaire of Sample Pit No.4

Note: quadrat area,10m×10m; Longitude, e11305'15.6 "; Latitude, 34 43' 4.7 "N; Farmland at the foot of loess hillside.

Fig. 5. Schematic diagram of1sample pit section

The investigation of plant root system is a tedious work, which needs to be careful. In order to ensure the rationality of statistical results, the investigation of a sample pit should be completed by one person from beginning to end, so as to maintain the systematic error of unified vision. The investigation of roots should be observed and counted from left to right and from top to bottom according to the grid on the profile. When counting, you can press the thick root (diameter >; 1cm), middle root (diameter 1 ~ 0.2 cm) and fine root (diameter ≤0.2cm) are divided into three levels, and the number of each grid is recorded separately, and dead roots are not counted. Statistical work should be carried out on the spot. Calculate the total number of roots and the total number of fine roots line by line according to the grid, and get the frequency of different lines, that is, the frequency of different depth intervals. Next, the frequency chart and cumulative percentage chart of the whole section shall be drawn according to the statistical results (Figure 5.2 ~ Figure 5.5).

Figure 5.2 1 Survey and Statistics of Root Groups in Sample Pit

Fig. 5.3 Investigation and Statistics of Root Groups in No.2 Sample Pit