Corn Rotation Effect on Greenhouse Gases Emission.

The Midwestern region is the United States’ major agricultural production area. Little information exists regarding the crop rotation practices in the region and their effects on greenhouse gases emission (GHGs) from soil surface. The major GHGs are: carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄). To address this knowledge gap, three corn-based long-term rotations at different locations in Wisconsin were selected to assess potential opportunities in mitigating GHGs emission by comparing temporal and spatial variability of the emissions from continuous corn (CC), a 2-yr corn-soybean (CS), and a 3-yr corn-soybean-wheat (CSW) rotation. Each phase of each rotation was always present in a given year. Sampling was done during three growing seasons (2012-2014) on weekly or biweekly schedules using the static chamber method. GHGs emission was strongly influenced by weather conditions and peaks of N₂O followed nitrogen application. N₂O emissions differed across years, locations, and rotations (p<0.05). Cumulative N₂O emissions were the highest in the wet season of 2013 and the lowest in 2012 which was one of the driest seasons ever recorded. Averaged across years, CC had the highest (p<0.05) N₂O emissions among rotations with a significant location x rotation interaction. CO₂ emissions increased as air temperature increased and crop growth progressed. There was no year effect (p>0.05) on CO₂ emissions but there were significant effects of location, rotation, and year x location interaction. Generally, across locations and rotations, CO₂ and N₂O emissions from corn phases were almost always the highest among crops. There was only a year effect in response to CH₄ emissions (p<0.05). Overall, soils appeared to be a small CH₄ sink. These results suggest that application of corn rotations may potentially contribute to the global GHGs mitigation and provide an important understanding on how different weather conditions might affect GHGs emission