Greenhouse Gases Emission from Wisconsin Soils in Long-Term Corn-Based Crop Rotations (2012-2013).

The Midwestern region of the United States is based on intensive corn production and has been recognized for having a high potential in mitigating anthropogenic greenhouse gas emissions (GHGs) of carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄). Unlike nitrogen fertilizer and tillage management practices, crop rotation effects are often overlooked by farmers in relation to gas emissions. Our objective was to compare GHGs emission during 2012-2013 growing seasons of six phases of crop rotation treatments involving continuous corn, corn-soybean and corn-soybean-wheat at the Arlington, Lancaster and Marshfield research stations. Gas fluxes were measured using in situ closed-cover flux chambers permanently installed in the rows and between the rows. Sufficient time has passed to allow these crop rotation experiments to equilibrate differences between rotation treatments. The whole 2012 growing season was one of the driest seasons ever recorded in Wisconsin. Whereas 2013, especially in the beginning, was one of the wettest seasons. Averaged across locations, 2013 had similar CO₂ and significantly higher N₂O emissions in all treatments compared to 2012. Nitrous oxide emissions appeared at the beginning of the season, but were mediated by soil moisture. However, they differed temporarily between years and locations.  For example, up to mid-season at Arlington in 2013, under wet and cold conditions N₂O emissions were 255% higher compare to 2012. In 2012, averaged across all locations and treatments, soils were a minor CH₄ sink; however, in 2013 at Marshfield significant CH₄ emissions were recorded due to prolonged soil saturation conditions. Our results provide an important understanding on how different weather conditions affect temporal and spatial variability of GHGs emission from agricultural soils during crop production.