Managing crop residue to reduce optimum nitrogen fertilizer inputs and increase yield

Issue

There is growing evidence that the amount of both corn and soybean residue affect the optimum nitrogen fertilizer rate to the following corn crop. Higher levels of residue lead to higher optimum nitrogen fertilizer rates. However, recommended nitrogen fertilizer rates do not consider the amount of residue from the previous crop.

Objective

This project will determine the ability for farmers to adjust optimum nitrogen fertilizer rates based on the amount of corn and soybean residue production in the previous year’s crop. A well-established relationship between residue production and optimum nitrogen fertilizer rate would allow farmers to: i) better manage nitrogen fertilizer inputs as they vary from field-to-field and year-to-year as a function of residue production, and ii) manage residue for lower optimum nitrogen rates.

Approach

Researchers will conduct nitrogen fertilizer rate trials in continuous corn and corn following soybean for two years at four locations in central and eastern Iowa. They will adjust aboveground residue inputs in replicated plots according to the following five levels, 300, 250, 200, 150, and 100 bushels per acre, for corn residue preceding corn (i.e., continuous corn) and 80, 70, 60, 50, 40 bushels per acre for soybean residue preceding corn (i.e., corn-soybean rotation). Researchers will then use the APSIM model to determine the relative effects of interannual weather variation and crop residue amount on the maximum return to nitrogen (MRTN).