Estimating the Economic Optimal Rate of Nitrogen Fertilizer: A Battle of Functional Form

Producers make fertilizer management decisions based on recommended fertilizer rates and soil testing. Crop response models are commonly used to determine fertilizer recommendations; however, there are several different models that can be used to estimate crop yield response to fertilizer.  The models are used to not only predict maximum yields but also the economic optimal rate of fertilizer. Past research has shown that there can be substantial differences between the models when predicting the economic optimum. The objective of this research is to evaluate different crop response models for cotton and compare the resulting economic optimal rates of nitrogen fertilizer. The data are from an experiment conducted at the Wiregrass Research and Extension Center in Headland, Alabama during crop years 2006 – 2008. It is a traditional cotton response trial with five nitrogen rates (0, 30, 60, 90, and 120 lb N ac^-1) applied at sidedress.