In-season prediction of potential grain yield in winter wheat using canopyreflectance

Nitrogen fertilization rates in cereal production systems are generally det ermined by subtracting soil test N from a specified N requirement based on the grain yield goal, which represents the best achievable grain yield in t he last 4 to 5 yr. If grain yield could be predicted in season, topdress N rates could be adjusted based on projected N removal. Our study was conduct ed to determine if the potential grain yield of winter wheat (Triticum aest ivum L.) could be predicted using in-season spectral measurements collected between January and March. The normalized difference vegetation index (NDV I) was determined from reflectance measurements under daytime lighting in t he red and near-infrared (NIR) regions of the spectra. In-season estimated yield (EY) was computed using the sum of two postdormancy NDVI measurements (Jan. and Mar.) divided by the cumulative growing degree days (GDD) from t he first to second reading. A significant relationship between grain yield and EY was observed (R-2 = 0.50, P > 0.0001) when combining all nine locati ons across a 2-yr period. Our estimates of potential grain yield (made in e arly Mar.) differed from measured grain yield (mid-July) at three sites whe re yield-altering factors (e.g., late summer rains delayed harvest and incr eased grain yield loss due to lodging and shattering) were encountered afte r the final sensing. Evaluating data from six of the nine locations across a 2-yr period, EY values explained 83% of the variability in measured grain yield. Use of EY may assist in refining in-season application of fertilize r N based on predicted potential grain yield.