Invasive Species Compendium

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Abstract

Effects of disease, nitrogen source, and risk on optimal nitrogen fertilization timing in winter wheat production.

Abstract

Nitrogen source and timing can interact with glume blotch (Stagonospora nodorum [Phaeosphaeria nodorum]) and take-all root rot (Gaeumannomyces graminis var. tritici) to affect risk in wheat (Triticum aestivum) 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 from 1998 to 2000 in Tennessee, USA. A Just-Pope model was used to estimate separate mean yield and yield variance (risk) effects in evaluating the N timing decision. Main plots were treated on 15 February, 1 March, 15 March, 1 April and 15 April. The N sources and fertilizer 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, fertilizer application 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 treat 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.