Trade-offs of gaseous emissions from soils under vegetable, wheat-maize and apple orchard cropping systems applied with digestate: An incubation study

Abstract

ABSTRACTLand application of digestate from anaerobic digestion causes various gaseous emissions. A soil core incubation experiment was carried out in the laboratory to investigate the trade-offs of NH3, N2O and CH4 emissions from soils collected from vegetable, arable and orchard cropping systems. Digestate derived from liquid cattle manure was applied to the soil cores through the surface (SA) and incorporation application (IA) methods under three soil moisture conditions (40%, 60%, and 80% water-filled pore space, WFPS). Gaseous emissions from vegetable soil were significantly greater (P< .05) than those from soils under the other two cropping systems under similar conditions, particularly under a high moisture condition. The greenhouse gas emissions (GHG, in term of CO2-equivalents) of all soils increased with the increasing soil moisture contents, mainly due to rapidly increasing N2O emissions. Trade-offs in the emissions of these three gases were observed between SA and IA. As expected, SA was characterized by greater NH3 and CH4 but lower N2O emissions compared to IA. The increase in GHG under IA could be offset only somewhat by the reduced NH3 (and this reduced indirect N2O) and CH4 emissions under lower moisture conditions (<60% WFPS), which indicates a requirement for other strategies to control gaseous emissions from wet soils applied with digestate. In conclusion, an environmentally friendly strategy for digestate application should consider the soil moisture, types of soils and application methods, and all the presented suggestions need to be verified in the field in the future.Implications: This study shows that digestate incorporation can decrease NH3 but increase GHG emissions verse the surface application method, where the increased GHG could only be offset by the NH3 reductions at relatively dry soil condition, indicating an urgent requirement to mitigating GHG emissions under moist soil condition.