Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/15/2008
Publication Date: 1/22/2008
Citation: Vigil, M.F., Poss, D.J. 2008. Managing N Rates for Reduce-till Dryland Wheat. Meeting Proceedings. Proceedings of the 5th Annual Cover Your Acres Winter Conference. Pages 7-11. Oberlin, KS. January 22-23, 2008. Interpretive Summary:
Technical Abstract: Fertilizer nitrogen (N) costs have increased 35% in the last 5 years in the Central Great Plains region (CGPR). With that increase in fertilizer cost farmers have also experienced a decrease in crop yields due to drought. The question then becomes (with a decline in yield and an increase in fertilizer cost), how does optimum fertilizer N rate change when wheat yields are low and fertilizer prices are high? Also, how does the price of wheat affect the optimum N rate? In this analysis, we evaluate reduce-till dryland winter wheat yield response to applied N over a four-year period at the USDA-ARS Central Great Plains Research Station at Akron, Colorado. Wheat was fertilized at 0, 27, 54 and 80 kg N ha-1 (0, 30, 60 and 90 lbs of N per acre) on a Weld silt loam soil (fine, smectitic, mesic Aridic Paleustolls). Fertilizer was applied in a preplant broadcast application as ammonium nitrate. Soil samples to 60 cm were collected from each plot at planting time before fertilization and after wheat harvest each year. Wheat yield was harvested, relative wheat yield was calculated by normalizing each year’s wheat yield data on the maximum yield measured each year and response functions were fit to the data to determine the economically optimum N rate. Wheat yield response varied from year to year and was correlated to rainfall and temperature during the growing season. However, after calculating relative yield the response to N was observed to be similar irrespective of maximum yield. Maximum yield was calculated to be at 58 kg of applied N ha-1 (65 lbs of N per acre) and/or at 87 kg ha-1 (98 lbs of N per acre) of available N at planting (residual inorganic N plus applied N). However, the economically optimum N rate was found to be less than 18 kg N ha-1(20 lbs of N per acre) at yield potentials of less than 1340 kg ha-1 (25 bushels per acre), but increased to up to 46 kg ha-1 (52 lbs of N per acre) at yields near 3800 kg ha-1 (70 bushel per acre) when wheat prices were high.