Relationships of Nitrous Oxide Emissions to Fertilizer Nitrogen Recovery Efficiencies in Rain-fed Corn Systems: Research Foundation Building

Little is known about relationships between nitrous oxide loss and crop nitrogen (N) use efficiency metrics despite years of past research. It is commonly assumed that higher fertilizer N recovery will lead to lower nitrous oxide emissions. However, few studies have assessed the hypothesis that greater plant uptake of N or higher recovery efficiency will actually reduce nitrous oxide emissions during crop production.

A two-year study suggested that a functional, negative linear relationship existed between nitrous oxide emission and recovery efficiency for Indiana high-yielding corn production under a wide range of N management and tillage systems. Nitrogen fertilizer management contrasts involved altering rates, timing, and presence of nitrification inhibitors, while corn management contrasts involved multiple tillage systems and two plant densities. The majority of the data supported the hypothesis that nitrous oxide emissions decrease with increased N recovery efficiency following optimized N fertilizer applications to corn. Models showed that cumulative nitrous oxide losses during the growing season were reduced by up to 35 g N/ha for every one percent increase of recovery efficiency by corn in that season. However, both the slope and strength of the relationships varied significantly due to: (1) year-to-year variability of nitrous oxide emission and N recovery efficiency; (2) insufficient data points employed in the models; and (3) perhaps because the relative timings of peak emissions and peak corn plant N uptake did not coincide sufficiently (even with sidedress N timing). This research has made a strong contribution to the understanding of nitrous oxide relationships with N fertilizer efficiencies in a rain-fed production environment.

A companion study was published in 2017, which synthesized these relationships across North America's maize production systems. This synthesis indicated that the appropriate N rate applied at the right time can increase recovery efficiency and reduce nitrous oxide losses, particularly in management systems that increased grain N or plant N uptake relative to the amount of total fertilizer applied to maize.