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

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.