Gram yield estimation through SVI under variable soil and management conditions
Soil crop management interaction influence on spectral vegetation indices (SVIs) and dry matter (DM) in different growth stages of gram crop were studied through an experiment. Significant differences in the values of IR/R and NDVI in the branching stage (St1: 20.17***, 14.06***) and the pod development stage (St2: 12.73***, 8.48**) and non-significant differences in pod maturity stage (St3: 0.193, 0.023) indicate that plant, soil and management interactions have yielded significant difference up to St2. The values of coefficient of variation (Cv) show the significant differences in DM production between the soils (St1: 43.5***, St2: 228.5***, St3: 36.3***) and treatment (St1: 10.8***, St2: 6.6**, St3: 2.9). These variation are well in agreement with the changes which have taken place in the values of SVIs, as it can be clearly seen that the increase in SVIs corresponds with the consistent increase in DM up to stage 2. The significant differences between SVIs values between soils and treatments and the positive correlation with DM at St2, justifies their consideration in estimating the yield of gram crop under variable soil and management conditions. The regression relation of DM with NDVI in three soils and four management factors has yielded 12 regression models in order to predict DM/grain production using SVI's values in St2. Based on goodness of fit and considering the highest R2 value, the best yield prediction models for S1, S2 and S3 soils are (i) y 0.91 0.03 NDVI (R2 0.42) S1 soils (ii) y 1.89 0.06 NDVI (R2 0.96) S2 soils (iii) y 3.85 0.46 NDVI (R2 0.32) S3 soils.