By: Jim Bamberato, Bob Nielsen
Although nitrogen (N) fertilizer can be costly, it is needed to optimize profit in Indiana cornfields. Applying too little N reduces profit by reducing grain yield. Too much N does not return value and can also damage the environment.
Results from 167 field-scale N response trials conducted over more than 10 years underpin current region-based N recommendations. These data-driven N recommendations replaced the old yield-goal based system1, which was proven ineffective. Current recommendations represent the N rate for maximum profit over the long-term, but differences in soil type, management, and weather can result in lower or higher N requirements in any given situation. Rainfall after N application will primarily determine the efficiency of applied N2, with excessive rainfall causing higher N loss and greater need for fertilizer N. Although N applied prior to planting this season has not been subject to conditions promoting N loss in most areas of Indiana, N loss can occur season-long, particularly prior to the V8 growth stage when corn N uptake and water use are relatively low.
Economic optimum N rates vary by as much as 40 pounds of N per acre across regions so adjusting the N rate by region is important. Recommended rates can also be adjusted by the price of N fertilizer and the expected value of grain using tabular data in the publication “Nitrogen Management Guidelines for Corn in Indiana”3. With N at $0.40 per pound and corn at $3.25 per bushel, the average N rate needed on fine-textured soils to maximize profit is about 30 pounds per acre less than that needed to maximize yield. On sandy non-irrigated soils, the difference is only about 10 pounds per acre. Using the economic optimum N rate, rather than the N rate needed for maximum yield, would reduce yield 1 to 3 bushels per acre across soil textures and regions. The loss in profit when fertilizing to maximize yield would be approximately $7 per acre for fine-textured soils, but only $2 per acre on sandy non-irrigated soils.
Nitrogen rates recommended are for efficient applications of N, such as anhydrous ammonia (AA) within a couple of weeks prior to planting or sidedressed AA or liquid N. Earlier applications of liquid N2 or surface applications of urea on no-till ground4 can reduce profit under certain conditions.