Achieving High Yield and Meeting Protein Requirement in Spring Wheat.

This study determines the nitrogen (N) demand of spring wheat market classes that vary for grain protein content (GPC) requirements. In particular, soft white spring wheat (SWSW) requires lower GPC compared to hard red spring wheat (HRSW). The objectives were to: 1) determine optimal N requirement for both market classes, and 2) identify spring wheat traits responsive at a given N input in irrigated and rainfed environment. The experiment was conducted at Creston, MT during 2016 and 2017 as a split-plot design with four replications over two environments. Five N treatments (118 [check], 155, 200, 244, and 289 kg ha^-1 total N) were the main plots and eight cultivars (four HRSW and four SWSW) were the subplots. The effect of N treatment on yield was not significant indicating that residual N levels in check treatment produced optimal yield for both market classes. The main effect of cultivar was significant for both yield and GPC. However, cultivar x environment was only significant for GPC. The irrigated environment showed higher GPC which can be attributed to the efficiency of reallocating plant tissue N to the grain for protein via increased biomass with irrigation. Results from 2016 indicate that optimal yield and GPC for SWSW can be achieved at 118 kg N ha^-1. The same N rate was optimum for yield in HRSW, however, increased N up to 200 kg N ha^-1 increased GPC for this market class. Alturas and UI-Stone, SWSW cultivars, showed the highest yield responses across environments. Regarding HRSW, Vida was the highest yielding cultivar although with the lowest GPC. Egan, a high protein wheat cultivar, showed the highest GPC among HRSW. This study validated that SWSW has lower N requirement to achieve yield and required protein compared to HRSW.