Winter Wheat Growth Monitoring Using Hyperspectral Remote Sensing Under Different Nutrition Levels

As an important food crop, Winter wheat supplication and demand have significant effects on national security and stability. Therefore, research on winter wheat growth monitoring and yield estimation is of important significance. Hyperspectral remote sensing as a non-destructive, rapid, real-time monitoring means, has great advantages in the winter wheat growing monitoring.The paper analyzed winter wheat canopy spectral features, SPAD values, leaf area index(LAI), plant water content and biomass dry weight in different growth stages and under different nutrient levels in the same stage. To inverse the winter wheat SPAD values, LAI, plant water content and biomass dry weight using hyperspectral data, providing scientific reference basis for farmland environment monitoring real time dynamically, the best spectral parameters were tried to determine.Results showed that(1) under the same level of nitrogen and phosphate applied, the spectral reflectance curves appeared to be with the same characteristics roughly before the flowering stage, in addition to the differences in the canopy spectral reflectance values. The spectral reflectance curve in grain-filling stage was different from the five stages before slightly, while the spectral reflectance curve in maturity stage was completely different from other stages. The reflectance values in grain-filling stage and maturity stage were higher than other stages in visible, and in about 700-1200 nm bands, the maturity stage showed the lowest reflectance with the grain-filling stage had the lower. The canopy spectral reflectance of the maturity stage showed the highest values at the wavelength over 1200 nm.(2)Without the application of nitrogen fertilizer and phosphate, the spectral reflectance curves had higher values than other fertilizer levels in visible and the wavelength over 1300 nm, and lower values in the strong reflection bands of green vegetation. Under different nitrogen and phosphate levels in the same growth stage, winter wheat canopy spectral reflectance curves has some similar characteristics, and in the third level of nitrogen fertilizer and phosphate, the curves had the highest values in about 760-1100 nm.(3)Under the same level of nitrogen fertilizer and phosphate, winter wheat SPAD values, LAI, plant water content and biomass dry weight were reduced after increased through the whole growth stages. Under different levels of nitrogen fertilizer and phosphate, the winter wheat SPAD values, LAI, plant water content and biomass dry weight were increased with the increased of nitrogen fertilizer and phosphate application in the same stage.(4)The spectral parameters of normalized difference vegetation index(NDVI) with higher correlation coefficient with the SPAD values was chosen to inverse the SPAD values. The modeling and inspection decision coefficients were 0.4976 and 0.443 of NDVI. The spectral parameters of D781 and RVI with higher correlation coefficient with LAI were chosen to inverse the LAI. The modeling and inspection decision coefficients were 0.8067 and 0.8208 of D781, showing the better inversion effect. The spectral parameters of NDWI with higher correlation coefficient with plant moisture content was chosen to inverse the plant moisture content. The modeling and inspection decision coefficients were 0.5080 and 0.6424 of NDWI. The spectral parameters of D1065 with higher correlation coefficient with DW was chosen to inverse the DW. The modeling and inspection decision coefficients were 0.9387 and 0.8009 of D1065.