Optimizing nitrogen application timing in no-till soft red winter wheat

As no-till acreage increases, N management guidelines need reexamination du e to the potential effects of surface residue on N transformations and crop development. Our objectives were to determine: (i) if N applied at Zadok's Growth Stage (GS) 25 improves grain yield of no-till winter wheat (Triticu m aestivum L.), (ii) if any yield increase was the result of increased spri ng tillering, and (iii) if there is a critical tiller density above which N application at GS-25 in no-till wheat was not required. Research was condu cted at three sites in North Carolina with seven site-years between fall 19 96 and spring 1999. A continuum of GS 25 tiller densities was generated (16 1-1774 tillers m(-2)) by planting at different seeding rates and dates in a randomized complete block design. Five N treatments were applied at GS-25, and three were applied at GS-30, Tillering response to early spring N, yie ld, and yield components were measured, increasing early spring N rates res ulted in higher tiller densities at GS-30, and GS-25 tiller density was a s ignificant covariate With GS-25 tiller densities >550 tillers m(-2), yields were higher when all N was applied at GS-30. In years without spring freez es, wheat with <550 tillers m(-2) achieved optimum yields when spring N was applied at GS-25, Manipulating the timing of spring N application can opti mize early spring tillering and yield component formation.