Investigation of Intrafield Heterogeneities in the Development of Soybean Crops Based on Remote Sensing Data and the Properties of the Plow Horizon (Case Study from the South of the Far East of Russia)

The assessment of the heterogeneities in the development of agricultural crops is one of the key conditions for predicting yield and enhancing the economic efficiency of agriculture. The purpose of the study was to develop methods for assessing intrafield heterogeneities of soybean crops based on remote sensing (RS) data and to determine the relationship between soybean productivity indices and soil characteristics. The study was carried out on a meadow-brown heavy loamy soil. Samples were collected in May and August 2023 from ten plots of a soybean field located in Khabarovsk krai. The total area of selected plots was 36.9 hectares. The study was based on the processed RS data provided by the Sentinel-2 satellite and a DJI Mavic3M drone, assessment of the soybean productivity indices, agrochemical and physicochemical soil characteristics, and its micro- and macroelement composition. The spatial distribution of NDVI, modeled on the basis of Sentinel-2 data (early August), corresponded to the NDVI distribution obtained using the DJI Mavic3M data. A reliable correlation between the NDVI index values in August 2023 and the soybean height (R = 0.64) and the number of pods (R = 0.64) has been revealed. Soil moisture had a positive correlation with NDVI (R = 0.87) and soybean height (R = 0.68) for the whole growing season. NDVI positively correlated with H_g (R = 0.79) and negatively correlated with pH (R = –0.79). The content of NNO₃ ranged from 2.51 to 6.84 mg/kg (V = 35.12%), the content of mobile forms of Р₂О₅ ranged from 2.47 to 6.07 mg/100 g (V = 33.13%), and the content of K₂О varied from 4.98 to 9.37 mg/100 g (V = 20.07%). The variability of the content of NNO₃ and Р₂О₅ decreased by August to 11.61 and 21.99%, respectively. No significant changes in the general soil composition were observed between the first and second sampling. The variation of the content of rare earth elements (Sc, Y, and lanthanides) in the selected plots did not exceed 5%. By the second sampling date, a significant decrease by 4–10.5% (p < 0.05) in the content of rare earth elements in soil was observed.