Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2007
Publication Date: 2/15/2007
Citation: Vigil, M.F. 2007. Optimal Nitrogen Fertilization of Dryland Wheat. Meeting Proceedings. Research Update 2007. Presented at the High Plains Ag Lab, Feb. 15, 2007. Sidney, Nebr. Pages 20-23. Interpretive Summary:
Technical Abstract: Fertilizer nitrogen (N) costs have increased nearly 30 % 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 dryland crop yields due to drought. The question that arises from this, decline in yield with increased input cost, is 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 study, we evaluate 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 a response function was fitted to that 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). 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.