Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: April 20, 2010
Publication Date: October 31, 2010
Citation: Vigil, M.F., Poss, D.J., Nielsen, D.C., Benjamin, J.G. 2010. Rainfall probability and EONR for dryland corn in Colorado. [Agronomy Abstract]Presented at the annual ASA/CSSA/SSSA meetings. Oct. 31 thru Nov. 5, 2010. Long Beach, CA. Technical Abstract: Nitrogen fertilizer costs have increased 70% in the last 6 yrs in the Central Great Plains Region (CGPR). This cost increase coincides with a decrease in dryland grain yields due to drought. How does the economic optimum N rate (EONR) change with grain price and fertilizer cost? Here we evaluated 11 years of dryland corn response and 4 years of winter wheat response to applied N. For winter wheat, simply using relative yields produced a predictive relationship that was reasonably acceptable for estimating optimal N rates for both wet and dry years. For corn a more elaborate analysis was needed that indicated some data years are more important than others in that they reflect a greater percentage of the actual weather expected based on a 100-year weather record. We used the probability of rainfall based on our long term weather record to evaluate the validity of 11 site years of N response and then used that information to determine EONR for no-till dryland corn in Colorado. Our analysis also included using math associated with the “delta yield concept”. That math summarized the 11 site years nicely into a single relationship. However, the rainfall probability distribution combined with individual regression equations is more useful in determining reasonable N rates than the math associated with the delta yield concept.