GHG Emissions From Corn-Soybean Rotations and Perennial Grasses On a Mollisol.

Changes in management can convert agriculture from a net source to a net sink of greenhouse gases.  A field study was established in 2003 in Indiana on a Typic Haplaquoll to determine the impact of nitrogen management on trace gas emissions.  In the second phase of the experiment (2008-11), there were five treatments for a corn-soybean rotation implemented: 1) Spring chisel/Fall disk tillage (9 yr); 2) No-till (9 yr); 3) No-till with N fertilizer added at 80% of the recommended level (4 yr); 4) No-till with winter rye as a cover crop (9 yr); and 5) Rotational tillage (9 yr) as well as Sorghum-Sudan grass (mowed and removed or not mowed) and native grasses (9 yr).  There were four replicates of each treatment, with both the corn and soybean phases planted each year.  Gas emissions (CO₂, NO₂, CH₄) were measured throughout the growing season. The CO₂ emissions in corn peaked in late June.  Emissions from the chisel-disk and no-till single application systems were similar, with the split fertilizer application, cover crop, and nu-till treatments being slightly lower. For soybeans, CO₂ emissions peaked in late July and were significantly higher than for corn. The chisel-disk treatment had slightly higher emissions. For corn, N₂O emissions peaked 4-6 weeks after fertilizer application.  Emissions were similar for all treatments. Soybean, with no fertilizer applications, had lower emissions than corn.  The cover crop treatment had the highest rates because of the decaying rye residue.  In both corn and soybeans, the treatments served as both source and sink for methane emissions, with the uptake levels being slightly greater over time than emitted levels.  Soil organic carbon (SOC) was significantly higher in the cover crop treatments than in the other no-till treatments, while the tilled treatments were slightly lower than the no-till.  The grass treatments showed a gain in SOC.  Measured biological activity was correlated with the SOC contents.