Biochar Application to Agricultural Soils Can Reduce Labile Carbon Losses and Decrease Apparent Temperature Sensitivity.

Biochar, organic matter that has undergone pyrolysis to become a recalcitrant and C-rich material, can decrease greenhouse gas (GHG) emissions and facilitate carbon (C) sequestration in agricultural. The use of biochar as a soil amendment not only adds a stable source of C into the soil, but it may also decrease soil C respiration further contributing to the decrease in net GHG balance. To test this, sweet corn was grown in a six-week greenhouse experiment under four different soil treatments: Oxisol soil alone, woodchip-based biochar (B), organic fertilizer (OF), and B+OF. Two samples were collected from each pot; one prior to planting and one after harvesting. These soil samples were incubated and headspace sampled for carbon dioxide (CO₂) efflux for 49 days at 16°C, 21°C, and 26°C to assess for labile C (cumulative CO₂ efflux in the pre minus post-corn growth samples after 49 days) and apparently temperature sensitivity (the increases in CO₂ efflux per °C). At 21°C, the application of biochar to soil decreased labile C emission, after accounting for the biochar-C itself using mass balance, by 24% while the addition of biochar to the soil with OF decreased emissions by 36%. Further, biochar amendment significantly reduced the apparent temperature sensitivity of the labile C pool. Despite this decrease in GHG emissions, the application of biochar did not impact corn yields. The mechanisms behind biochar’s ability to mitigate greenhouse gas fluxes by this pathway are not well understood.  It is hypothesized that the biochar facilitates increased complexation of the labile organic matter with soil minerals or itself in addition to decreasing the activity of C-mineralizing enzymes in soils.