Tillage and Stover Removal Effects on Soil Nitrous Oxide and Methane Emissions from Irrigated Continuous Corn.

Crop residue removal for bioenergy or livestock uses likely will target intensively managed, high-yielding production systems.  To evaluate the effects of residue removal and tillage management on soil greenhouse gas (GHG) emissions, soil emissions of nitrous oxide (N₂O) and methane (CH₄) were measured for five-years at a long-term, irrigated continuous corn (Zea mays L.) system in eastern Nebraska.  Management treatments began in 2002, and measured treatments included no stover removal (0% of rows harvested) or maximum removal (100% of rows harvested) under no-tillage or disk-tillage with full irrigation (n=4).  Since 2011, soil GHGs have been collected weekly during the growing season and monthly during the non-growing season.  Mean annual N₂O emissions over the 5-yr period ranged from 1.5 to 5.8 kg N₂O-N ha^-1 yr^-1, and were lower under no-tillage than disk tillage and when stover was removed.  Greenhouse gas intensity (GHGI) for soil N₂O emissions ranged from 0.191 to 0.506 kg N₂O-N Mg DM grain^-1, and followed similar responses to management observed for area-based N₂O emissions.  Mean annual CH₄ emissions ranged from -0.18 to 0.70 kg CH₄-C ha^-1 yr^-1, with emissions from no-till soils not different than zero flux.  In contrast, disk-tilled soils were CH₄ sources, with greater emissions occurring when stover was removed.  The mean annual global warming potential of soil N₂O plus CH₄ emissions over the 5-yr period ranged from 2.29 to 3.54 Mg CO₂eq ha^-1 yr^-1, and was lower in no-till systems and when stover was removed.  When compared as carbon-equivalents, mean annual emissions of N₂O and CH₄ in 2011-2015 exceeded the mean annual soil organic carbon (SOC) losses reported previously in the top 60 cm of the soils for 2001-2010 at this site.  Although this irrigated system is a net GHG source regardless of management, the use of conservation practices can decrease GHG source strength.