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

Nitrogen (N) fertilizer management affects both wheat grain yield and protein content. Grain protein can often be improved by N fertilizer topdressed later in the season. In regions 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 wheat (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 red and white winter wheat varieties across N rates and application timing, and iii) determine if flag leaf N content, chlorophyll readings and GreenSeeker® sensor measurements are reliable predictors of yield and protein content in response to N rates and application timing.

The experiment was conducted at two farmer field locations in eastern Colorado, near Brandon and Bristol. Two wheat varieties, Byrd (HRWW) and Antero (HWWW), were grown on the sites. Nitrogen treatments included four N rates (0, 30, 60, and 120 lb/A) and at two application times (all fall applied, and split fall-spring). The split application consisted of 1/3 fall applied, and 2/3 in the spring at Feekes 5 growth stage. Other nutrients were applied based on soil test results.

Both moisture and temperature conditions at the sites were favorable over most of the 2015 to 2016 season; however, a hail event in June destroyed the crop at the Bristol site. An analysis of yield results from the Brandon site showed significant differences between N rates and application strategies, but no difference between wheat varieties. Yields as high as 98 bu/A were observed with both varieties at the split 120 lb N rate. The Greenseeker-estimated N response was highly correlated to the N response measured from the harvested yield (grain protein data is not yet available). This project will not be continued.