Relationship between chlorophyll content in leaves of sorghum and pigeonpea determined by extraction method and by chlorophyll meter (SPAD-502)

The estimation of chlorophyll content in leaves by the chlorophyll meter (SPAD 502) is more convenient than by the extraction method for studies on photosynthesis or senescence where the total chlorophyll is estimated on the same leaf over time. This study was to test hypothesis that specific leaf weight (SLW) appears to be one of the factors determining SPAD index under different conditions. The influence of SLW on SPAD index and an improved simple method to determine chlorophyll content of sorghum and pigeonpea by a chlorophyll meter was studied. The results indicated that regression lines were significantly different between sorghum and pigeonpea, and at the vegetative and physiological maturity stages in each crop. Residuals of simple regressions calculated from all data of each crop were correlated with SLW. Multiple-regression with SPAD index as the dependent variable, and chlorophyll content and SLW as the independent variables gave the best estimation of chlorophyll content in leaves of sorghum and pigeonpea. These results suggest that SLW is an important factor affecting SPAD index and the influence of SLW on SPAD index can vary with crop species. Devices for estimating SLW could be incorporated into the chlorophyll meter to provide SPAD values adjusted for SLW. Further investigation is required on the influence of SLW on SPAD index for other crops.