Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2008
Publication Date: October 1, 2008
Citation: Vigil, M.F., Nielsen, D.C., Poss, D.J. 2008. Economic Optimum N Rates for Fertilizing Winter Wheat and Corn. Agronomy Abstract. Presented at the International American Society of Agronomy meetings, Crop Science Society of America and Soil Science Society of America (ASA/CSSA/SSSA) annual meetings. Oct. 5-9, 2008. Houston, TX. Technical Abstract: Fertilizer nitrogen (N) costs have increased 100% in the last 4 yrs in the Central Great Plains region (CGPR) of the USA. With that increase in fertilizer cost the region has experienced reduced dryland crop yields due to drought. The question that arises: “is how does optimum fertilizer N rate change when yields are low and fertilizer prices are high? Also, how does the price of the commodity affect the economically optimum N rate (EONR)? In this analysis, we evaluate dryland corn, and winter wheat yield response to applied N over a several years at the USDA-ARS Central Great Plains Research Station at Akron, Colorado. Crops were 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. Crop yield was harvested, relative crop yield was calculated by normalizing each year’s crop yield data on the maximum yield measured in a given year and a response function was fitted to that data to determine the economically optimum N rate (EONR). Crop 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) for wheat and at 80 kg ha-1 for corn. 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 and corn prices were high.