Corn Residue Removal Effects on Carbon Sequestration and Greenhouse Gas Emissions.

Corn residue is an important component of soil carbon budget and development of soil quality indices. However, corn residue in recent years has been considered as another potential feedstock source for ethanol production in addition to or alternative to corn grain. The current emphasis on using corn residue as a feedstock for future ethanol production presents a soil and environmental challenge that needs to be addressed. Additionally, there have been few studies that examine all three major GHG (CO₂, N₂O, and CH₄) emissions from agriculture soils under different residue removal rates, various N rates, and tillage practices and their interactions effects on soil C dynamics and GHG emissions. The objective of this study was to examine potential changes in soil C sequestration and GHG emissions under no-tillage (NT) and conventional tillage (CT) (fall chisel-field cultivation prior to planting) and nitrogen fertilization rates of 0, 165, and 275 kg N ha^-1 with variable rates of residue removal (0, 50, and 100%). Field studies were established in fall of 2008 on two sites, a poorly-drained soil at the Iowa State University Agronomy Research Farm (North central, IA) and a well-drained soil at the Armstrong Research and Demonstration Farm (Southwest, IA) in continuous corn. Soil C, N, and bulk density was measured every year until 2011. After every harvest, crop measurements included corn grain yield, above-ground biomass, and root-biomass. Weekly measurements of soil surface CO₂, N₂O, and CH₄ emissions coupled with soil moisture and temperatures were collected. Additionally, C budgets were done to estimate net ecosystem productivity. These measurements provide insights on whether these management practices resulted in net gains or losses of soil C sequestration and atmospheric CO₂. Preliminary findings from the North central site suggest that residue removal of 50% or greater increases the potential for net GHG emissions and reduces potential for soil C sequestration regardless of establishment of mitigation practices such as no-tillage and different N fertilization rates.