Short-Term Biochar Effects on Soil Fluxes of Methane, Carbon Dioxide, and Water Vapour in a Tea Agroforestry System

Tea (Camellia sinensis) cultivation is a major global industry that faces sustainability challenges due to soil degradation and greenhouse gas (GHG) emissions from intensive management. Biochar—charcoal designed and used as a soil amendment—has emerged as a potential tool to improve soil health, enhance carbon sequestration, and mitigate GHG fluxes in agroecosystems. However, field-scale evidence of its effects on GHG dynamics in woody crops like tea remains limited, particularly regarding methane (CH₄). Here, we present the first field assessment of biochar impacts on CO₂, CH₄, and H₂O vapour fluxes in a subtropical tea agroforestry system in northeastern Bangladesh. Using a closed dynamic chamber and real-time gas analysis, we found that biochar application (at 7.5 t ha⁻¹) significantly enhanced soil methane (CH₄) uptake by 84%, while soil respiration (CO₂ efflux) rose modestly (+18%) and water-vapour fluxes showed a marginal increase (+12%). Canopy conditions modulated these effects: biochar effects on CH₄ oxidation were more pronounced in open conditions, whereas biochar effects on water-vapour flux were detectable only in open conditions. Structural equation modeling suggests that CH₄ flux was chiefly governed by biochar-induced changes in soil pH, moisture, nutrient status and temperature, while CO₂ and H₂O fluxes were shaped by organic matter availability, temperature and phosphorus dynamics. These findings demonstrate that biochar can promote CH₄ oxidation and alter soil carbon-water interactions in tea plantation systems, and specifically support biochar use in combination with shade-tree agroforestry.