Application of Degradable Carbon and Nitrogen Moderates Carbon Sequestration Potential of Biochar in Arable Soils

Biochar can affect CO₂ emission and C sequestration from soils, but little is known about the effects of its re-application and interaction with easily accessible substrates. Since most agricultural soils are continuously reworked, understanding the mechanics of CO₂ evolution as affected by soil amendments and their combinations may have important lessons for the global effort to combat climate change. In this study carried out in a controlled environment, we tested the short-term effects of biochar, and its re-application at different rates, on the production of CO₂ emission and C accumulation in samples of arable soils. We used a loamy Haplic Luvisol as the substrate and added varying amounts of biochar and sources of easily accessible N and C. We observed CO₂ evolution for 20 days at optimal temperature and moisture conditions. We found that in the control treatment with no biochar, the total potential respiration after the addition of (NH₄)₂SO₄ (N) and glucose (G) was increased compared to basal respiration. The addition of biochar reduced CO₂ emission in the control, N- and G-stimulated treatments by 12–22, 13‒24 and 2‒21%, respectively. Conversely, the application of biochar increased CO₂ emission in the combined NG treatment. Application of biochar at a higher rate, as well as its re-application, increased soil organic carbon content and reduced emission of CO₂ into the atmosphere.