The Potential of Different Cover Crop Systems in Mitigating Agricultural Greenhouse Gas Emissions

Abstract:

Cultivated lands that support high productivity have the potential to produce a large amount of greenhouse gas (GHG) emissions. Extensive research shows that different land management practices have various effects on three major GHGs: CO₂, CH₄, and N₂O. For example, CO₂ could be released through soil disturbance events and N₂O emissions could be stimulated under excessive nitrogen fertilizer inputs. Cover crop establishment is considered one of the sustainable land management strategies under warm and humid environmental conditions. To investigate which cover crop performs best in minimizing GHG emissions, in this study, we compared trace gas fluxes (CO₂, N₂O and CH₄) from a corn field with three cover crop systems: crimson clover (CC); cereal rye (CR); white clover (WC) and no cover crop system (traditional, Tr) in 2018. Observational data were collected during growing season once a week from Watkinsville, GA, USA. In 2018, mean CO₂ flux from CC, CR, WC and Tr was 4.01, 3.91, 5.77, 2.42 μmol m^-2 sec^-1, respectively. Mean N₂O flux from CC, CR, WC and Tr was 0.596, 0.139, 0.706, 0.588 μmolN m^-2 hr^-1, respectively. Highest fluxes of both CO₂ and N₂O were from the WC plots, especially at the late growing season, due most likely to the decomposition of added white clover residue. The soils served as a sink for CH₄, with a mean flux from CC, CR, WC and Tr being -1.10, -0.875, -1.05 and -0.627 μmol m^-2 hr^-1, respectively. Tr system was the smallest CH₄ sink compared to the other three cover crop systems. Among the three cover crop systems, CC was the largest CH₄ sink, although the three cover crop systems did not differ significantly. Comparing four systems with a net CO₂e, mitigation effects from CH4 sink, soil carbon sequestration, reduced fertilizer and herbicide application are still not capable of counteracting higher CO₂ and N₂O emissions generated in the field. The net CO₂e from CC, CR, WC and Tr was 2184.80, 2129.10, 3161.30 and 1307.75 kg CO₂e ha^-1, respectively.