In--Field Management of Corn Cob and Residue Mix Effect on Greenhouse Gas Emission.

In-field management practices of loose corn cob and residue mix as feedstock source for ethanol production can have potential effects on greenhouse gas emission. The objective of this study was to investigate the effects of corn cob and residue mix (CRM) storage in-field and subsequent removal on soil CO₂ and N₂O emissions. The study was conducted in 2010-2012 at the Iowa State University Agronomy Research Farm located near Ames, Iowa. The soil type at the site is Canisteo silty clay loam (Fine-loamy, mixed, superactive, calcareous, mesic Typic Endoaquolls). The treatments of corn cob and residue mix consisted of control (no CRM applied and no residue removed after harvest), complete removal of CRM after application (CR) (7.5 cm deep of CRM applied in the fall and completely removed early spring), 2.5, and 7.5 cm deep of CRM  over two tillage systems of no-till (NT) and conventional tillage (CT) and three N rates (0, 180, and 270 kg N ha^-1) of 32% liquid UAN (NH₄NO₃) in a randomized complete block design with split-split arrangements. The findings of the study suggest that soil CO₂ and N₂O emissions increased as the amounts of CRM left on the soil surface are increased.  It was also observed that CRM treatments affected soil moisture content and soil mineral N concentration. However, CO₂ emission was less affected by N rate as it was with N₂O emissions, where high N rate and soil mineral N concentration caused greater soil N₂O emissions regardless of the CRM amount left on the soil surface. Also it was observed that NT produced higher CO₂ emission in 2012 than CT with higher amount of CRM left on the soil surface. Additionally, no differences in N₂O emissions were observed due to tillage system. In general, dry soil condition as in 2012 caused a reduction in both CO₂ and N₂O emissions across all tillage, CRM treatments, and N rates. Proper CRM mix cleanup after corn cob pile removal along with adequate tillage and N management may minimize CO₂ and N₂O emissions.