The impact of long-term organic farming on soil-derived greenhouse gas emissions

Agricultural practices contribute considerably to emissions of greenhouse gases. So far, knowledge on the impact of organic compared to non-organic farming on soil-derived nitrous oxide (N₂O) and methane (CH₄) emissions is limited. We investigated N₂O and CH₄ fluxes with manual chambers during 571 days in a grass-clover- silage maize - green manure cropping sequence in the long-term field trial "DOK" in Switzerland. We compared two organic farming systems - biodynamic (BIODYN) and bioorganic (BIOORG) - with two non-organic systems - solely mineral fertilisation (CONMIN) and mixed farming including farmyard manure (CONFYM) - all reflecting Swiss farming practices-together with an unfertilised control (NOFERT). We observed a 40.2% reduction of N₂O emissions per hectare for organic compared to non-organic systems. In contrast to current knowledge, yield-scaled cumulated N₂O emissions under silage maize were similar between organic and non-organic systems. Cumulated on area scale we recorded under silage maize a modest CH₄ uptake for BIODYN and CONMIN and high CH₄ emissions for CONFYM. We found that, in addition to N input, quality properties such as pH, soil organic carbon and microbial biomass significantly affected N₂O emissions. This study showed that organic farming systems can be a viable measure contributing to greenhouse gas mitigation in the agricultural sector.