Effects of disease, nitrogen source, and risk on optimal nitrogen fertilization timing in winter wheat production
2004
Roberts, R.K. | Walters, J.T. | Larson, J.A. | English, B.C. | Howard, D.D.
Nitrogen source and timing can interact with glume blotch (Stagonospora nodorum) and take-all root rot (Gaeumannomyces graminis var. trittici) to affect risk in wheat (Triticum aestivum L.) production. The objectives of this research were to evaluate the effects of N source, N timing, and disease severity on expected yield and risk and to evaluate the risk-return trade-offs between N sources for farmers with different risk preferences. A Just-Pope model was used to estimate separate mean yield and yield variance (risk) effects in evaluating the N timing decision. Wheat yields for 1998 through 2000 were obtained from an experiment on Collins silt loam (coarse-silty, mixed, active, acid, thermic Aquic Udifluvents). The experimental design was a split plot with five replications. Main plots were fertilized on 15 February, 1 March, 15 March, 1 April, and 15 April. The N sources and fertilization rate were ammonium nitrate (AN) and urea ammonium nitrate (UAN), both applied at 101 kg N ha(-1). Glume blotch occurred in 1998, and take-all occurred in 2000. Nitrogen timing, glume blotch severity, and take-all severity significantly increased risk for AN but not for UAN. Nevertheless, at average disease ratings, fertilization with AN on 8 March was the utility-maximizing N source and date regardless of risk preferences. The finding that AN was the optimal N source is worth $40.74 ha(-1) to net-return-maximizing wheat farmers who fertilize with AN instead of UAN. With take-all severity at its higher 2000 level, risk increased for AN relative to UAN, but the net-return advantage of AN was still positive at $26.41 ha(-1).
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