Effect of Nitrogen Topdressing at Anthesis and the Association of Flag-Leaf Nitrogen with Grain Protein Concentration in Irrigated Spring Wheat

ABSTRACT

Grain protein is an important component affecting the market value of hard red spring wheat (Triticum aestivum). In high-yielding irrigated environments, consistently attaining desired protein levels is a chronic problem. Nitrogen (N) management has a strong effect on protein concentration. The objective of this experiment was to evaluate the robustness of using flag-leaf N concentration as a tool for guiding in-season N application in order to obtain high-protein wheat. Three on-farm trials were conducted (each location using a cultivar of the farmer's choice) where N rates were varied. Nitrogen rates evaluated were 0, 79, 157, 236, and 314 kg ha⁻¹. To evaluate the benefit of topdressing, all N was applied basally, or 45 kg ha⁻¹ N was reserved from the basal dose for application at heading. Yield and protein response to applied N were variable across the three sites. This study postulated that this response was a function of initial soil-N availability. Where there was a yield response to N, it appeared that reserving a portion of N for topdressing increased protein but tended to decrease yield. At levels of N where yield was not limited, reserving a portion of N for topdressing did not appear to affect yield or protein. Although a linear relationship between grain protein and flag-leaf N was obtained by pooling data across sites, there was enough variation in this relationship to limit its utility as a tool for guiding in-season N application.

Keywords:

• wheat
• nitrogen
• grain protein
• yield
• flag leaf

ACKNOWLEDGMENTS

We thank Mr. Brian Barney, Mr. Rich Lewis, and Macy Farms for their cooperation in this study. We also thank Dr. Don Horneck, Oregon State University, and Dr. Brad Brown, University of Idaho, for their helpful reviews of the manuscript.