Net Returns from Terrain-Based Variable-Rate Nitrogen Management on Dryland Spring Wheat in Northern Montana

Abstract

Agricultural producers can use variable‐rate application technology to vary N fertilizer within fields. This study was conducted to estimate changes in net returns from implementation of variable‐rate N management (VNM) on hard red spring wheat (Triticum aestivum L.) in a summer‐fallow region in northern Montana. Net return from uniform N management (UNM) traditionally used by producers was compared with that from VNM in eight dryland fields between 1994 and 2004. Field experiments consisted of a replicated series of four to six N rates applied within strips oriented with the length of each field. Management zones (MZs) were created by dividing the fields into upper slopes, south‐facing middle slopes, north‐facing middle slopes, and lower slopes. Nitrogen recommendations for MZs were based on soil N testing and expected yields. Grain yield data were obtained using a production‐size combine equipped with a yield monitor. Mean grain protein and yield were similar between VNM and UNM. Yield differences were <223 kg ha−1 and averaged only 18 kg ha−1. Grain yield did not differ significantly among N rates within MZs. In seven of the eight sites, net returns from VNM were up to US$27.97 ha−1 less than from UNM and were not profitable if Environmental Quality Incentive Program payments of US$6.36 ha−1 were considered as part of net income. Little evidence existed that VNM based on constructed MZs and predetermined N recommendations improves grain yields and profits or reduces N use in water‐limited, summer‐fallow systems of northern Montana.