Grain Protein Content as an Indicator of N Sufficiency for Winter Wheat1

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Abstract
A great majority of the dryland winter wheat (Triticum aestivum L.) producers in the west central Great Plains currently do not use soil tests to determine N fertilizer needs although most producers have grain protein data from their fields. Field experiments with N rate as the variable were conducted throughout eastern Colorado over a 4‐year period with winter wheat grown under summer fallow cropping. The objective was to determine if grain protein content could be used as a post‐harvest indicator of sufficiency of N for maximum grain yield. The soil types were of the Paleustoll, Argiustoll, Paleargid, and Haplargid great groups. The yield and protein response data from the experimental locations were analyzed by an interaction chisquare procedure.Grain protein content was found to be an effective post‐harvest indicator of N nutrition adequacy for grain production. Both a critical level and a transitional zone of grain protein content were defined using interaction chi‐square analysis. The most critical level was determined to be 11.5% protein and the transition zone between the deficient and N sufficient populations of yield observations was between 11.1 to 12.0%. The amount of yield lost to N deficiency was not related to grain protein content. Workers in other geographic areas should be able to take existing N response data and develop similar guidelines appropriate for those areas.