Research on Relationship Between Canopy Spectral Characteristics and Nitrogen Nutrient of Rice Cultivars Based on UAV Multispectral Remote Sensing

Objective The relationship between canopy spectral characteristics and nitrogen nutrient of main cultivated indica rice cultivars in South China was determined, which provided theoretical basis for expert decision-making system and precise fertilization.

Method A conventional indica rice Meixiangzhan 2(MXZ2H)and a hybrid indica rice Jifengyou 1002(JFY1002)were selected as test materials, with three nitrogen levels including 0 kg/hm²(N0), 150 kg/hm²(N150)and 210 kg/hm²(N210)using farmers'practice(FP). The "Three Control" fertilization technique with nitrogen rate of 180 kg/hm²(N180+)was added in the field experiment with JFY1002 rice cultivar, and the relationship between rice leaf spectral characteristics and nitrogen nutrient was explored.

Result Compared with N0 treatment, the leaf nitrogen concentration of MXZ2H and JFY1002 were increased by 16.05% and 13.76% under N150 treatment, and by 24.29% and 25.00% under N210 treatment, respectively. Leaf nitrogen concentration of JFY1002 was increased by 18.03% under N180+ treatment compared with that under N210 treatment. With the increase of leaf nitrogen concentration, the spectral reflectance of leaves from blue band to red band(450-650 nm)were decreased gradually, but that from red edge band to near infrared band(730-840 nm)were increased gradually. Significant difference was found in the spectral reflectance of MXZ2H and JFY1002 at 650 nm red band and 840 nm near infrared band. The results of correlation analysis showed that the leaf nitrogen concentration of MXZ2H was positively correlated with NDVI, GNDVI, RVI, DVI, and EVI, and that of JFY1002 was positively correlated with RVI, EVI, MNLI, DVI and NDVI. The inversion models of leaf nitrogen concentration of MXZ2H and JFY1002 were established with R² of 0.817 and 0.973, and with RE of 8.35% and 3.48%, respectively.

Conclusion The study established an inversion model of leaf nitrogen concentration for indica rice cultivars in South China, which provided theoretical basis and technical guidance for precise fertilization operation of rice.