Effects of Irrigation, Cover Crop, and Manure on Soil Greenhouse Gas Emissions after Stover Removal in No-till Continuous Corn.

Corn stover is used widely for livestock co-feed and is targeted as a near-term feedstock for the developing cellulosic ethanol industry. High biomass production in intensely managed systems, such as irrigated continuous corn, may have a greater potential to provide stover for either livestock or bioenergy end-uses.  Amelioration practices for stover removal can improve physical protection of soils and replace some carbon inputs, but it is unclear how residue management and amelioration practices will impact soil greenhouse gas (GHG) emissions and system GHG mitigation potential.  Soil GHG emissions were measured for three years in an irrigated continuous corn system where stover removal was ameliorated with the addition of animal manure or use of winter rye cover crop.  Total annual emissions (Mg CO₂e ha^-1 yr^-1) were highly variable from 2011 to 2013, with CO₂ usually contributing >90% of the total emissions and N₂O comprising the remainder.  Emission factors for N₂O (e.g percent of fertilizer N lost as N₂O) ranged from 1 to 4%, depending on treatment and year.  Soils tended to be CH₄-neutral in all treatments, but varied as a slight source or sink depending on year.  Relative to the conventional business-as-usual scenario of stover removal under optimal fertilization, full irrigation resulted in higher overall GHG emissions compared to deficit irrigation (60% of full).  Under either irrigation scenario, adding manure or using a winter cover crop resulted in decreased N₂O emissions relative to no amelioration treatment.