Grain crop farmers who need to know how much nitrogen fertilizer to apply to the soil could save money — and protect the environment — by using a fertilizer application method recently studied by Agricultural Research Service scientists and cooperators.

Farmers who grow grain usually use what's called the “yield-goal” method to figure out how much nitrogen to use. They determine the amount of fertilizer based on the estimated yield. But ARS and University of Missouri-Columbia scientists have completed a large-scale study on corn showing that farmers who use this method may be losing per-acre profit — and using too much nitrogen.

Soil scientist Newell R. Kitchen and agricultural engineer Kenneth A. Sudduth, of ARS' Cropping Systems and Water Quality Research Unit at Columbia, and university collaborators found that yield was a poor predictor of how much nitrogen was needed.

That's because it's hard to determine the season's yield months before harvest. The yield-goal method does not take into account changes in weather or the soil variability within fields. Using new methods, the researchers found that yield only accounts for about 15 percent of what is known as corn's “economically optimal nitrogen fertilizer rate” (EONR).

They discovered that if farmers were able to grow corn knowing the EONR and how that varies within fields, they could make on average $15 more per acre — excluding costs associated with determining EONR and variable-rate fertilizer application — than if they allocated fertilizer by the yield-goal formula. The increase in profit would come from higher yields and less fertilizer.

These researchers, along with other ARS scientists, are trying to develop better tools to determine the EONR. One method they are developing is to use a canopy reflectance sensor to monitor crop vigor, thereby estimating just how much nitrogen fertilizer the corn needs.