Diagnosis of Nitrogen Concentration of Maize Based on Sentinel-2 Images: A Case Study of the Hetao Irrigation District

The rapid diagnosis of nitrogen concentration in maize growth period in the Hetao Irrigation District were carried out to provide reference for fertilization decision and non-point source pollution research. Based on the UAV multi-spectral data and measured nitrogen concentration values, a variety of spectral indices were used to quantitatively characterize plant nitrogen content, and a diagnostic model of nitrogen concentration during maize growth period was established. According to the validation results of spectral index diagnostic models, the spectral index diagnostic models in different growth periods were evaluated, and the nitrogen concentration diagnosis in growth periods was carried out. The optimal nitrogen diagnostic model was established by GBNDVI, RVI, NRI, and NDVI at jointing, small trumpet, large trumpet, and flowering stage of maize in the Hetao Irrigation District, respectively. The planting area of maize in the Hetao irrigation district in 2020 was 4127800 mu. The nitrogen concentration was lower in small trumpet and flowering stage, and higher in jointing and large trumpet stage. The spatial distribution of nitrogen concentration based on maize plant nitrogen diagnostic model can provide reference for fertilization decision and agricultural non-point source pollution research.