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 N topdressing later in the season. Where a premium is paid for protein, growers are more likely to adjust N management practices to affect protein. Colorado wheat production has traditionally 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: 1) develop N management strategies for optimum yield and protein content for dryland wheat, 2) compare yield and grain protein responses of red and white wheat varieties across N rates and application timing, 3) compare and evaluate flag leaf N content, chlorophyll readings and GreenSeeker^(R) measurements, and 4) develop comprehensive dryland winter wheat best N management guidelines.

The experiment was conducted at two farmer field locations in eastern Colorado, one each in Lamar and Brandon Counties. A third site was located at the USDA-ARS Central Great Plains Research Station in Akron, Colorado. Wheat varieties utilized were Byrd (HRWW) and Antero (HWWW). The ARS site treatments included a combination of six N rates (0, 25, 50, 75, 100, and 125 lb N/A), and two application timings (all in the fall, or all in spring). Nitrogen treatments in the farmer fields included a combination of four N rates (0, 30, 60, and 120 lb N/A) and two application timings (all applied in fall, and split). The split application consisted of 1/3 applied in the fall, and remainder in the spring at Feekes 10, or boot stage.

The Lamar site was abandoned due to lack of soil moisture, and precipitation at the Brandon site was significantly lower than average. Yield at the Brandon site was increased by N fertilizer application, with the single fall application having the overall greatest impact. The performance of the split application treatment may have been compromised by the lateness of spring topdress. Protein level was greater overall in the HRWW variety, but the HWWW variety showed greater protein response to N application. Nitrogen fertilization had no significant effect on yield at the ARS site. This was likely due to elevated levels of residual soil N due to drought and crop failure in previous years. Interestingly though, grain protein did respond to N fertilization at the ARS site, with spring application of 50 lb N/A or greater resulting in significant protein increases. This project is scheduled to continue another year.