Spectral response of gram varieties under variable soil conditions
The spectral response of gram (Cicer arietinum) varieties was studied in a crop sequence experiment conducted on three soils in Gondkhairi watershed, Nagpur district of Maharashtra state. A poor relationship between leaf area and Normalized Difference Vegetation Index (NDVI) (r =0.17) and IR/R (r =0.11) was observed in ICCV-88202 and ICCC-37 varieties 66 days after sowing (DAS). The hypothesis that short-duration varieties should show a significant positive correlation (due to these crops attaining high biomass at an early growth stage) did not hold good. Contrary to this, in ICCV-10 (a medium maturing variety) the leaf area showed a poor relation with NDVI (r =0.39) and IR/R (r =0.45) at 84 DAS. As varieties ICCV-88202 (V2) and ICCC-37 (V3) in soil types S1 and S2 are high in biomass at 66 DAS (as is evident from the high values of leaf area) the possible reason for such a poor relationship is masking the effect due to profuse violet and pink flowers at the top of the plant canopy. Analysis of variance (ANOVA) results indicate that the influences due to soils and varieties yield a significant difference in IR/R ratio but a non-significant difference in NDVI both at 66 and 84 DAS. In gram with indeterminate growth habit, the biophysical parameters showed a more consistent relationship with IR/R ratio than with NDVI. The yield prediction is expected to be more valid for ICCV-10 at 66 DAS (R 2=0.90**), whereas ICCV-88202 and ICCC-37 are similar for such a prediction both at 66 DAS (V2, R2=0.66*; V3, R2=0.81**) and 84 DAS (V2, R2=0.66*; V3, R2=0.78**). Regression models encompassing varietal and soil influences at different growth stages were simulated to predict yields.