Relationship between greenhouse gas emissions and changes in soil gas diffusivity in a field experiment with biochar and lime

Reducing greenhouse gas emissions from arable soil while maintaining productivity is a major challenge for agriculture. Biochar is known to reduce N 2 O emissions from soil, but the underlying mechanisms are unclear. This study examined the impact of green waste biochar (20 Mg ha −1 ) and lime (CaCO 3 ; 2 Mg ha −1 ) application on soil gas transport properties and related changes in these to soil N 2 O and CO 2 emissions measured using automated chambers in a field experiment cropped with maize. In situ soil water content monitoring was combined with laboratory measurements of relative soil gas diffusion coefficient ( D p / D 0 ) at different matric potentials, to determine changes in D p / D 0 over time. Cumulative N 2 O emissions were similar in the control and lime treatment, but much lower in the biochar treatment. Cumulative CO 2 emissions decreased in the order: lime treatment > biochar treatment > control soil. When N 2 O emissions were not driven by excess N supply shortly after fertilisation, they were associated with D p / D 0 changes, whereby decreases in D p / D 0 corresponded to N 2 O emissions peaks. No distinct pattern was observed between CO 2 emissions and D p / D 0 . Cumulative N 2 O emissions were positively related to number of days with D p / D 0 < 0.02, a critical limit for soil aeration. These results indicate that improved soil gas diffusivity, and hence improved soil aeration, may explain the effect of biochar in reducing N 2 O emissions. They also suggest that knowledge of D p / D 0 changes may be key to explaining N 2 O emissions.