A Model for Making Field-Based Nitrogen Recommendations For Winter Wheat in Western Oregon

Abstract

A model based on early spring soil and tissue analysis was developed and evaluated for predicting the need for additional nitrogen (N) fertilizer on winter wheat. To develop the model, On-farm trials were established over three years 1994-95 in grower’s fields at three different locations across the Willamette Valley of western Oregon. Two field-scale validation trials were run in 1996-97. Rotations were soft white winter wheat following grass seed, sweet corn or a legume. Four treatments, including a check receiving no nitrogen, were used at each site. At the site where wheat followed corn, the predicted optimum N rate was 168 kg N ha⁻¹; however, the 112 kg N ha⁻¹ rate was the optimum rate predicted by the developed model. The 84 kg N ha⁻¹ and 140 kg N ha⁻¹ rates were selected to bracket the recommended rate (± 28 kg N ha⁻¹).Wheat following grass seed had high soil supplied N which depressed the yield even at moderate fertilizer N rates. The model overall accurately assess field-specific optimum fertilizer N status.