Modifying Nitrogen Rate and Timing Applications in Response to Winter Wheat Planting Date.

Winter wheat (Triticum aestivum L.) yield potential can be dependent upon planting date, and nitrogen (N) rate and timing strategies may offer the opportunity to improve both the production and efficiency of this cropping system. A two-year field experiment was initiated in Lansing, MI to determine the effects of planting date, N application timing, and N application rate on winter wheat growth and yield. Three planting dates, three N rates (84, 118, and 151 kg N ha^-1), and three N application timings (green-up, 50% green-up and 50% Feekes 5, and Feekes 5) were arranged in a split-split plot design with four replications for a total of 27 treatments. Data collection included chlorophyll measurements, autumn and spring tiller counts, tissue sampling and analysis at Feekes 5 and 9, plant lodging, disease incidence, grain head counts, test weight, and yield. In the 2013-14 growing season, autumn and spring tiller counts were significantly (P < 0.10) impacted by planting date. Excessive tillering on the early planting date (2013-14) treatments resulted in significant lodging and a 1.5 megagram/hectare yield reduction from the intermediate planting date. In the 2013-2014 growing season a significant (P < 0.10) planting date by N rate interaction showed the 84 kg N ha^-1 rate maximized yield for the early planting date with no N rate yield differences within the intermediate planting date. Wheat yield for the late planting with the 118 kg N ha^-1 rate was significantly greater than the 84 but similar to the 151 kg N ha^-1 rates, respectively. Additional field measurements and yield data will be discussed following the summer 2015 harvest season.