Non-destructive Estimation of Water Status of Sugarcane Leaf Using Spectral Reflectance Measurement

Abstract

Non-destructive estimation of relative water content (RWC) of sugarcane leaf was useful in understanding precise irrigation for saving limited water resources. Visible and near-infrared reflectance spectra were measured using a spectroradiometer to clarify the response of reflectance properties, as a basic study on the application of remote sensing. Reflectance spectrum and RWC were measured continuously with a constant interval under natural dryness conditions from 95% to 5%. Reflectance spectra increased with the reduction of RWC. Changes in reflectance were small until 25% of RWC, and then became large within the range from 25% to 15%. Reduction of chlorophyll content in the samples with the decrease of RWC seemed to be a cause of rapid increase of reflectance. Red edge position (REP) was shifted to the short wavelength side with the reduction of RWC. Some reflectance indices near 700 nm showed high correlation with RWC in each sample. A well-fitted regression model for all samples from different plants was not found out using 700 nm reflectance. Difference of the reflectance at short wavelength and the long one showed comparatively good correlation to all samples. At a plant level, RWC can be predicted non-destructively with a sufficient accuracy using the developed model.