Development of a User-Friendly Tool to Determine Economically Optimum Nitrogen Rates for Small Grains.

Nitrogen (N) fertilizer is generally the highest input cost for Montana grain growers; therefore, it has become imperative that a tool be developed to assist crop advisers and farmers in determining economically optimum N rates (EONR). Data from all available MSU-conducted N fertility trials were gathered for spring wheat, winter wheat, and barley. Only the data sets for dryland fields following fallow were deemed large enough to have confidence in any resulting models, and all other data were excluded. Regression models that included soil N, fertilizer N, organic matter (O.M.), and yield potential were developed for grain yield and protein for all three data sets, and plump for the barley data set. Predictability (as measured by r²) was determined to be high enough to have confidence in these models. Economic models were then developed that calculated net marginal return (or net revenue) based on grain revenue minus N fertilizer cost. Validation of the models with more recent data sets is ongoing. The models are available online (http://landresources.montana.edu/soilfertility/fertilizereconomics.htm) allowing users to view changes in predicted yield, protein, plump, and/or net marginal return curves as the user changes input parameters with simple slider bars. The models also allow Extension educators to show the effect of varying one input parameter on EONR. It is expected that these models will help optimize profits of small grain farmers in the region.