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Nitrogen Requirement to Change Protein Concentration of Spring Wheat in Semiarid Pacific Northwest

Dan S. Long, John D. McCallum, Catherine L. Reardon, Richard E. Engel
Agronomy journal 2017 v.109 no.2 pp. 675-683
Triticum aestivum, cultivars, fertilizer rates, grain protein, hard red spring wheat, harvest date, nitrogen, nitrogen fertilizers, protein content, rain, soft white wheat, spring wheat, water supply, Montana, Oregon
CORE IDEAS: Nitrogen removal maps combined with the fertilizer N equivalent are useful for precision N management. More N is needed to change spring wheat protein in Pacific Northwest than in northern Plains. The fertilizer N equivalent is generalizable among spring wheat cultivars. Growers can use yield and protein maps to implement the N replacement approach On‐combine yield monitors and grain protein analyzers enable mapping of grain N removal at time of harvest. Nitrogen removal maps combined with estimates of the fertilizer nitrogen equivalent (FNE) for each 10 g kg⁻¹ change in grain protein concentration (GPC) are useful for developing site‐specific fertilizer prescriptions for fields. This study was conducted to determine the critical protein concentration where yield is maximized and FNE for spring wheat (Triticum aestivum L.) grown under low annual precipitation (<350 mm) in the inland Pacific Northwest. Five hard red spring (HRS) cultivars and one soft white spring (SWS) cultivar were grown under three water levels over an N application range of 0–235 kg ha⁻¹ in eastern Oregon. The critical protein level required to maximize yield was 140 g kg⁻¹ for HRS wheat and 117 g kg⁻¹ for SWS wheat. When water was limiting, GPC increased with added N while yield response was absent indicating GPC may not be useful as a post‐harvest indicator of N sufficiency when yields are water limited. The FNE for HRS wheat was 59 kg ha⁻¹ which is three times that reported in northern Montana. For SWS wheat, the FNE was 54 kg ha⁻¹ under low water supply. To achieve acceptable GPC for spring wheat, growers in low rainfall areas of inland PNW should expect to add (or subtract) these amounts of N to change protein by 10 g kg⁻¹.