Evaluation of green, red, and near infrared bands for predicting winter wheat biomass, nitrogen uptake, and final grain yield

Presently normalized difference vegetative indexes (NDVI) based on red (RNDVI) or green (GNDVI) reflectance are commonly used to evaluate plant health, biomass, and nutrient content. This study was conducted to determine which of these two indexes is more correlated with biomass, forage nitrogen (N) uptake, and final grain yield of winter wheat. Three experimental sites were established in Oklahoma in the fall of 2001 at Stillwater. Spectral reflectance measurements were taken at Feekes growth stage 4, 6, and 10.5 followed by winter wheat forage harvest. When evaluated at specific stages of growth, RNDVI was consistently more highly correlated with biomass than GNDVI. Green NDVI and RNDVI were more highly correlated with forage N uptake than with dry biomass at each stage of growth, but neither index appeared to have a comparative advantage over the other. Both indexes were highly correlated with final grain yield and grain N uptake across all locations. Neither index appeared to have a sizeable advantage over the other, suggesting that either will perform equally well when predicting forage N uptake, grain yield, and grain N uptake in winter wheat. Red NDVI does appear to be a better predictor of forage biomass, specifically at earlier stages of growth.