Exploring the Mechanisms of Biochar’s Effect on GHG Emissions across Agricultural Soils

Modern agricultural systems have allowed us to feed a rapidly growing population but with environmental costs depleting soil organic carbon (C), releasing reactive nitrogen (N) into water supplies and contributing to climate change through GHG production. Biochar soil amendments show potential to increase C sequestration, retain reactive N, and decrease N2O emissions. Biochar’s properties, including its typically high pH, cation exchange capacity and porosity, have been hypothesized to impact C and N cycling in soils but few studies have explored the mechanisms driving biochar’s impact on soil biogeochemistry across different soil types. While many biochar incubations have focused on different biochar feedstocks and production processes, this study explores biochar’s impact on GHG emissions (CO2, N2O and CH4), N transformation and microbial biomass across a gradient of soil textures, pH, and C and N content. This study found biochar reduces overall GHG emissions and increases C sequestration over a 60 day incubation across four agricultural soils. Biochar’s ability to reduce N2O production is largely mediated by soil aeration with some of the great reductions around 80% water filled pore space (WFPS). Under aerobic conditions (60% WFPS) biochar reduced N2O production in all fertilized soils but to varying degrees. The biochar treatments had no significant impacts net N transformation indicating that N2O reduction is not caused by preferential mineral N retention on biochar surfaces. These results contribute to a mechanistic understanding of how biochar reduces N2O production and combined with similar studies can help in developing biogeochemical models to predict such impacts.