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

Relationships between N recovery efficiency (NRE) and nitrous oxide (N₂O) emissions in traditional or high-yield corn production systems in the US Corn Belt are poorly understood. Our objectives were to assess the relationships between N₂O emission and corn N uptake and NRE as affected by: 1) production practices aimed at both high yield and environmental gains versus traditional production practices, 2) long-term tillage systems (no-till; strip-till; chisel plow; and moldboard plow) and N application with/without nitrification inhibitor (Instinct®), and 3) N timing treatments including intentional late-split application of the last 25% of the total annual N fertilizer at the V12-14 growth stage.

To address Objective 1, we expanded research on a Global Maize trial established in 2012 with IPNI financial support in West Lafayette, IN. In this experiment, we had compared ecological intensification, EI (high plant density and three N rates applied with Instinct®) relative to farmers’ practice, FP (moderate plant density and three N rates without inhibitor), but had not had resources to measure greenhouse gas emissions until now. Objective 2 research took advantage of a 41-year old experiment on prairie soil near West Lafayette for the evaluation of tillage and N source interactions on N₂O emissions. Objective 3 research utilized an ongoing late-split N experiment established at Wanatah, IN. Following UAN fertilizer applications in all three experiments, intensive gas sampling occurred twice-weekly for 6 to 8 weeks and weekly thereafter until corn maturity to permit calculations of daily and cumulative N₂O emissions. At maturity, corn biomass was harvested for N concentration, N uptake, and N efficiency determinations.

In project 1, corn yields (>200 bu/A) and corn whole-plant N uptake (~200 kg N/ha) at maturity in 2015 were highest in EI treatment with the highest N rate (240 kg N/ha). Cumulative N₂O was high (> 2.5 kg N/ha) even for zero-N control plots under either FP or EI (presumably because of excessive May and June rainfall), but there was little increase in N₂O loss with N fertilizer treatments. Simple regression showed a negative linear relationship between cumulative N₂O and NRE, which demonstrated that N₂O decreased as NRE increased, especially under EI management. Cumulative N₂O, soil and plant N analysis samples from projects 2 and 3 are still being processed. The resulting data will be used to estimate cumulative seasonal N₂O, N uptake and NRE as affected by long-term tillage, UAN timing and nitrification inhibitors.