Nitrogen Management Strategies for Winter Wheat Yield and Grain Protein Improvement in Southeastern Colorado

Nitrogen fertilizer management affects both wheat grain yield and protein content. Grain protein can often be improved by topdressing N later in the season. Where a premium is paid for protein, growers are more likely to adjust N management practices to affect grain protein. Colorado wheat production has mostly been hard red winter wheat (HRWW), but in recent years some growers have been given incentive to plant more hard white winter (HWWW), where a premium is paid for grain protein. This has caused interest in the N fertilizer-grain protein connection. The objectives of this project are to i) develop N management strategies for optimum yield and protein content for dryland wheat, ii) compare yield and grain protein responses of wheat varieties across N rates and application timing, and iii) compare and evaluate flag leaf N content, chlorophyll readings, and GreenSeeker® measurements.

This research was conducted at two farmer field locations in eastern Colorado, one each near Brandon and Bristol. A third site was located at the USDA-ARS research station in Akron. Two wheat varieties were used—Byrd (HRWW) and Antero (HWWW). The ARS site treatments included six N rates (0, 25, 50, 75, 100, and 125 lb/A), and two application timings (all in the fall or all in spring). Nitrogen treatments in the farmer fields included four N rates (0, 30, 60, and 120 lb/A) and two application timings (all applied in fall, and split). The split application consisted of 1/3 fall applied, and 2/3 in the spring at Feekes 10, or boot stage.

Rainfall was above average at all locations in the 2014-15 season, which resulted in favorable yield potential, but also favored incidence of stripe rust. At the Akron site, grain yield of both varieties responded positively to both fall and spring application of N. Byrd yielded significantly less than Antero because of Byrd’s greater susceptibility to stripe rust. The yields averaged across all treatments were 78 bu/A for Antero and 55 for Byrd. Spring N application produced greater yield than fall application for both varieties. The average yield increase from N applied fall vs. spring for Antero was 21 vs. 27 bu/A, and for Byrd it was 8 vs. 21bu/A. Antero produced slightly over 100 bu/A with spring-applied N (125 lb N/A). Yield data for the two farmer field sites is not yet available, nor is grain protein data for any of the sites.