Spring wheat (Triticum aestivum) yield and grain protein responses to N fertilizer in topographically defined landscape positions

A 3-yr field study was initiated in 1996 to examine the different grain yie ld and grain protein responses of wheat to varied N fertilizer rates in a t ypical glacial till landscape in Saskatchewan, Canada. Our objective was to assess the agronomic and economic feasibility of variable rate fertilizer (VRF) N application for wheat. Results suggest that spring soil water statu s largely determined the yield and the protein content of wheat both within different years of the study and between different landscape positions wit hin a given year. Although grain yield was strongly related to spring soil water and was predictable on that basis, the grain yield response of wheat to fertilizer N additions was highly variable due, in part, to the dual rol e that N played in determining both grain yield and grain protein content. As a consequence of the unpredictable nature of the varied response of whea t to N fertilizer additions, there was little economic rationale for using VRF strategies in the 3 yr of this study. However, in the long-term, we bel ieve that VRF N application strategies can be employed to manage N inputs f rom the perspective of managing and replacing harvested N.