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

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,