Biochar-Compost Additions Have Strong Short-Term Effects on Carbon and Nitrogen Emissions from an Agricultural Soil

Biochar (BC) application to agricultural soils has become a promising strategy for mitigation of soil-borne greenhouse gas (GHG) emissions, i.e., carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), but little is known about the effects on nitric oxide (NO) and dinitrogen (N2) fluxes. We conducted a short-term field experiment to evaluate the effects of BC with compost and additional fertilizer on different soil GHG fluxes. Application of 1% BC-compost showed no significant effect on CH4 and CO2 fluxes but lowered NO and N2O fluxes compared to the control without BC-compost. The addition of N to BC-compost (0.5% BC-compost + 175 kg N) showed a small mitigation potential for CH4 whereas N2O and NO fluxes significantly increased for one week after the application. The N2:N2O ratio shifted towards N2O production after the application of N-enriched BC-compost. During storage of pure N-enriched BC-compost, high gaseous losses in the form of NO (71.2 ± 2 µg N g−1 h−1), N2O (1319 ± 101 µg N g−1 h−1), and N2 (337.8 ± 93 µg N g−1 h−1) were measured. Approximately 31% of applied N was lost in gaseous form even in the presence of BC. To avoid this, an optimized strategy to balance easily available N from compost and fertilizer with the amount of BC should be developed