Effects of biogas slurry irrigation DOC/N ratios on the fate of soil nitrogen and GHG emissions: A laboratory study

Following biogas slurry irrigation, high rates of nitrogen (N) leaching have been measured, and testing increased slurry ratios of dissolved organic carbon (DOC) to N as a potential technique to reduce leaching, have been evaluated in previous research. Here, we explored the effects of slurry DOC/N ratios on the fate of soil N and greenhouse gas (GHG) emissions in a laboratory study. Slurries with DOC/N ratios of 0.9, 7.3, and 17.3 were applied to soil columns. Overall, the application of biogas slurry with a DOC/N ratio of 0.9 and increasing the ratio, enhanced soil mineralization, N immobilization and denitrification, and resulted in net mineralization. Additionally, most of the applied N left the soil through gaseous N emissions rather than by N leaching. Increasing the slurry DOC/N ratio from 0.9 to 7.3 or to 17.3 reduced nitrous oxide (N2O) emissions by 13% and 25%, respectively, and reduced methane (CH4) emissions by 1168% and 483%, respectively. In comparison, the respective carbon dioxide (CO2) emissions were 58% and 113% higher. In summary, an increased slurry DOC/N ratio contributes to soil CO2 emissions, but reduces both soil N2O and CH4 emissions. However, the reductions in N2O and CH4 emissions warrant further study.