Leaf and spike reflectance spectra of rice with contrasting nitrogen supplemental levels

Reflectance (350-1060 nm) of leaves and spikes were measured from rice plants with three contrasting nitrogen supplemental levels at the grain-filling stage. The rice spikes have the typical reflectance spectra characteristic of plants, but they reflected more radiation and had longer wavelengths of maximum/minimum reflectance in the visible region in comparison with the rice leaves. The spike differed from the leaf by its negative PRI (Photochemical Reflectance Index), evidently showing lower ratios of near-infrared (NIR) reflectance to red reflectance and much greater NPCI (Normalized total Pigment to Chlorophyll ratio Index). The NPCI decreased with increased nitrogen level, PRI increased with nitrogen level for both the spikes and the leaves, and leaf ratios of NIR reflectance to red reflectance increased with increased nitrogen level. The ratio values of spikes were near constant under the different nitrogen supplemental levels. The results suggested that the spectra of rice spikes might be of potential value in predicting rice yield and quality by assessing the spike nitrogen status.