Wheat Crop Chlorophyll Content Estimation From Ground-Based Reflectance Using Chlorophyll Indices

Abstract

The objective of this study is to investigate the relationship between a wide range of spectral chlorophyll indices and chlorophyll content of wheat crop using laboratory measurements. The measurements included the GER-3700 spectroradiometric data, leaf chlorophyll content using the SPAD-502 meter, and leaf chlorophyll content estimated from chemical laboratory analysis. The SPAD-502 readings were correlated with laboratory extracted leaf chlorophyll content to establish calibration equations for the computation of chlorophyll-ab (Chl-ab) and chlorophyll-a (Chl-a) contents. This resulted in coefficients of determination (R2) of 0.72 for the Chl-ab contents and 0.69 for the Chl-a contents and a root mean square error (RMSE) of 3.53 and 1.94 mug /cm2, respectively. These estimates based on these equations were used to establish relationships against spectral chlorophyll indices calculated from the GER-3700 data. The spectral chlorophyll indices, NDPI, SIPI, PRI and SRPI show a relative weak relationship with leaf chlorophyll content with R2s of 0.56, 0.62, 0.54 and 0.57 and RMSEs of 11.06, 10.27, 11.32 and 10.96, respectively. The NPCI shows the best results with R2 of 0.84 and RMSE of 11.0.