The effect of parameter uncertainty on whole-field nitrogen recommendations from nitrogen-rich strips and ramped strips in winter wheat

This paper estimates the relative profitability of using optical reflectance-based measures to predict crop needs for topdress nitrogen application to hard red winter wheat (Triticum aestivum). The data are from nitrogen yield response experiments where midseason optical reflectance data were recorded. Both nitrogen-rich strips and ramped strips are considered. Unlike past research, optimal nitrogen recommendations are calculated with and without accounting for parameter uncertainty. The expected profit-maximizing strategy is to follow the historical extension advice of applying 90 kg ha-1 preplant nitrogen using anhydrous ammonia. This strategy is more profitable than the best optical reflectance-based prediction system by $18.74 ha-1. When anhydrous ammonia is unavailable and preplant nitrogen must be applied as dry urea, the extension recommendation and the optical reflectance-based predictors are not significantly different. Ramped strips are no better than nitrogen-rich strips. Accounting for estimation uncertainty in the parameters increases expected profit by about $10 ha-1.