## 2 Materials and Methods
### Sample Collection and Analysis  
Based on the way of land use, the sampling units are divided into administrative village-level units and cultivated land area, and the sampling principle of random distribution of the system is combined with the latest GF satellite image data to adjust the point error. Finally, the sampling point is determined by an on-site field survey. A total of 306 sampling points were set in the study area (Figure 2), and the elevation of the study area is shown in Figure 3. These sampling points were located in the rice-wheat rotation field, and GPS was carried out to record the location of the sampling points, and multi-point mixed sampling was carried out according to the diagonal method (The specific distribution of cropland land in the study area can be referred to Figure 4). The sampling time was April 2023, and the five-point sampling method was used to set up \(1\times 1\) m standard plots with each sampling point as the center, with a total of 306 plots. Five sampling points (diameter of 0.15 m) were set along the double diagonal direction in the plot, and the profile analysis (0-100 cm) was carried out at the center of the plot. The ring knife method was used to sample (0-15 cm, 15-30 cm, 30-100 cm), and each layer was repeated three times as a physical property test sample. In addition, the topsoil (0-20 cm) of the five sampling points in the plot was mixed, and the excess samples were discarded by the quartering method. The final sampling amount was 1-2 kg. We removed the foreign bodies such as stone particles and plant roots contained in the soil, put them in plastic bags, attached labels, recorded the number, coordinates, profile depth and other information, and brought them back to the laboratory for analysis. In May 2024, a \(1\times 1\) m plot was set up for 306 sampling points recorded by GPS, and all mature wheat on the plot was harvested and brought back to the laboratory for analysis.  
The collected soil samples were subjected to air drying. These dried samples were then ground and sieved through a 2 mm mesh. The sieved soil samples were mixed thoroughly and used for the determination of soil nutrient indicators. Soil physicochemical property indicators were determined following standard methods of China [18]. The pH of the soil was measured using a pH meter with a soil-to-water ratio of 2.5:1. The organic matter in the soil was determined using the potassium dichromate external heating method. Total nitrogen in the soil was determined by the semi-micro Kjeldahl method. Available phosphorus in the soil was determined by the sodium bicarbonate extraction-antimony molybdenum spectrophotometry method. Available K in the soil was determined using  
Figure 1: Textural distribution of typical sampling sites in the study area.  
atomic absorption spectrophotometry, while slow-release potassium was determined using the hot nitric acid extraction-flame photometry method.  
The aboveground part of wheat was divided into three parts: stem and leaf, grain and glume + rachis (referred to as glume) and dried naturally. After weighing, it was placed in an oven at 65 \({}^{\circ}\)C to constant weight. The weight was weighed and the water content of the air-dried sample was calculated, and then the dry matter accumulation of all wheat in the unit plot was calculated.