Nitrogen management and variety selection for dryland production of hard red winter wheat in northeastern Oregon

Abstract

Proper nitrogen (N) management and variety selection are important for profitable hard red winter (HRW) wheat production in the dryland growing regions of northeastern Oregon. In these dryland systems, N management for grain yield and grain protein concentration (GPC) is challenging due to climatic and year-to-year variation in production environments. However, current fertilizer guides make little distinction between locations and incorporate relatively little data from HRW production. Identifying adequate N management practices and scenarios suitable for HRW production will help producers reduce risk and enhance profits. This study investigates the effects of fertilizer N rate, N application timing, variety and location over six site-years in northeastern Oregon from 2007-2009. Whole plant tissue nitrogen (TN) concentration at Zadoks growth stage (GS) 30 and flag leaf nitrogen (FLN) were also evaluated as decision making tools for N management in this region. Three sites representing low and intermediate precipitation zones were chosen for this study. A site at Pendleton, Oregon represented an intermediate precipitation zone (420 mm), while sites at Lexington and Arlington, Oregon were in a low precipitation (250-300 mm) zone. Study sites were minimally responsive to N treatments in terms of yield. Spring N was less detrimental to yield than fall application when N was excessive at Lexington and Arlington. Grain protein concentration response to fertilizer N was significant and varied by site-year. Some site-years proved favorable for efficient production of high GPC HRW wheat, whereas acceptable GPC was very difficult to achieve in others, underscoring the difficulty of consistently producing high GPC HRW wheat in these regions. Fertilizer N use efficiency was 18-39% at Pendleton, but generally less than 20% at Lexington and Arlington, dropping to zero in some circumstances. At all sites the soil N pool was used more efficiently than fertilizer N, indicating that HRW production is best suited where only minimal fertilizer N is required to complement crop N requirements. Spring N application improved GPC one year at Pendleton following above average late spring rainfall, and may therefore be a useful N management strategy in that environment. In contrast, spring N had a neutral or negative impact on GPC at Lexington and Arlington. Overall, current recommendations did not adequately describe N requirements observed in this study. However, requirements for achieving target GPC were generally lower and more stable at Pendleton, indicating that this and similar environments may be more suitable for HRW production than low yield, high stress environments such as Lexington and Arlington. Varieties showed similar response to N treatments regardless of site. Grain yield of HRW varieties were generally competitive with the soft white winter (SWW) variety ‘Stephens’. Among tested HRW varieties, ‘Norwest 553’ expressed the best combination of yield and GPC performance. The relationship of tissue N (TN) concentration at Zadoks growth stage 30 to GPC was stable across site-years. A critical TN level of 41 g kg-1 corresponded to 126 g kg-1 GPC. This level could be used to indicate when additional N is required to achieve desired GPC, but it remains uncertain how useful this test would be at high stress, low rainfall sites considering the poor response to spring N at Lexington and Arlington. Flag leaf N also showed promise for predicting GPC, but additional research is necessary to clarify this relationship.