Nitrogen Rate and Timing Effects on Winter Wheat Grain Yield, Grain Protein, and Economics

Typically, N fertilizer is fall‐applied to dryland winter wheat (Triticum aestivum L.) in the Great Plains, because cheaper N sources (anhydrous ammonia) can be applied in the fall and application can be combined with seedbed preparation tillage. Spring‐ or split‐applied N provides increased N management flexibility and potentially less N loss due to leaching or denitrifi‐cation over the winter. This study was conducted to compare winter wheat grain yields, protein, and economic returns associated with fall‐, spring‐, and split‐applied N at rates of 0, 20, 40, and 60 lb N/acre at 19 sites over 3 yr (1985–1987) in eastern Colorado. Grain yield response to N fertilizer was dependent on precipitation or residual soil NO3 levels, while grain protein response was not. Spring‐applied N increased grain yields and protein more than fall‐ and split‐applied N. Fall‐applied N required 20 and 18% (mean) more spring‐applied N to achieve the same grain yield and protein content, respectively. Spring‐applied N was more profitable than fall‐ or split‐applied N. Without application cost (“free ride”), N applied to solely increase grain protein was profitable. In semiarid climates, spring‐applied N is more available to winter wheat and more profitable than fall or split‐applied N.