Effect of N Depth and Application Rate on Yield, Protein Content, and Quality of Winter Wheat1

Abstract Providing a supply of N to winter wheat (Triticum aestivum L.) after heading may offer a means for increasing grain protein content without the need to apply fertilizer in excess of requirements for maximum yield for fhis procedure to be practical in the winter rainfall climate of the Pacific Northwest, the N at grain fill must be deep in the profile, where water is being absorbed. An experiment was conducted on Mesic Calciorthidic Hap. loxerolls (Ritzville silt loam) in dryland eastern Washington to determine the effect of N depth and application rate on yield, grain protein content, and flour quality of ‘Nugaines’ and ‘Wanser,’ a soft white and a hard red winter wheat, respectively. Nitrogen was placed shallow (less than 50 cm depth) at 55 or 110 kg/ha or deep (60 t0 120 cm depth or deeper) at 55, 110, and 220 kg/ha. Deep placement was achieved by applying Ca(NO3)2, irrigating with 12 cm of water prior to fall planting, and relying on deeper movement from overwinter precipitation. For the shallow placement, the N was applied in late winter of the crop year. All plots received a broadcast application of 35 kg N/ha as (NH4)2SO4 before planting. Maximum grain yields were approached with 55 kg N/ha, and excess N remained in the profile at the higher application rates for both placements. Depth of N did not affect grain yield or protein content when the shallow soil layers were moist much of the time during spring and early summer from above‐normal precipitation. However, with more typical conditions where the upper 1 m of soil was relatively dry at heading, yield and grain protein content of Nugaines wheat and grain protein content of Wanser wheat was increased significantly from deep N placement. Also, deep placement of 55 kg N/ha caused higher gain protein levels than with 110 kg N/ha placed shallow. For the hard red wheat, only flour of grain from the deep‐placed N exceeded minimum bread‐baking standards. All soft white wheat treatments except the 220 kg N/ha application exceeded minimum pastry quality standards, but the highest quality was with the shallow N placement. Thus, in the low precipitation areas of the Northwest, deep N placement may improve quality of hard winter wheat; but it may adversely affect the quality of soft white wheat.