Red edge parameters of winter wheat canopy under different nitrogen levels

The red edge characteristics of winter wheat canopy at different nitrogen levels and growth periods, and their relationships with agronomic components were studied by the measurement of canopy spectra using Field Spec FR2500. The results show that significant differences of canopy spectra are found at 550 nm, 680 nm, 980 nm and 1100 nm, 350~680 nm, 750~1100 nm, which can be used as the wave bands for nutrition diagnostic of the crop. The red edge position (REP), Location of minimum chlorophyll absorption (Lo) and max of first derivative of reflectance (FD_Max) increase with more nitrogen application during jointing, booting and filling stages, while, the red edge width (Lwidth) decreases. On the whole, little differences are found between the different nitrogen application treatments, but the differences between the fertilizer application and no nitrogen application are quite different. With the growth of winter wheat, REP and Lo move toward longer wavelength, presenting the red shift, while they move to short wavelength from the booting stage, presenting the blue shift. The correlations between REP and agronomic components are better than those between the other red edge parameters and agronomic components. Except aboveground fresh biomass, there are significant correlations between the REP and leaf area index (LAI), leaf water content (LWC), chlorophyll (CHl), leaf soluble protein (LP), leaf fresh biomass (LB) and leaf nitrogen content (LN). There are significantly positive correlations between Lo and LAI, LWC, CH1, LB, SPAD readings and soluble protein, and the correlations between Lwidth and LAI, LWC, LN, CH1, LB, and soluble protein are significantly positive. There are significantly positive correlations between FD_Max and LAI, LWC and LB as well, while the correlation between FD_Max and LN is significantly negative. The mathematical relationships of red edge parameters and agronomic components can be helpful for the estimation of the agronomic parameters.