Mitigating greenhouse gas emissions from a tropical sandy loam using oil palm empty fruit bunch biochar and compost amendments

Abstract The role of biochar in mitigating greenhouse gas (GHG) emissions from tropical soils, especially when combined with compost, is still not adequately researched. This study evaluated the effects of oil palm empty fruit bunch (EFB) biochar applied at 10 and 20 t ha −1 (B10 and B20), compost at 20 t ha −1 (CP20) and in combination (B10CP20 and B20CP20), an unamended control (B0), and a mineral fertilizer at 100 kg N ha −1 , 60 kg P 2 O 5 ha −1 , and 60 kg K 2 O ha −1 (NPK) on soil physical properties and GHG emissions from a tropical sandy loam soil. Soil physical, chemical, and microbial properties were assessed 12 months post‐application. GHG emissions were measured from intact soil cores at −10 hPa soil water potential following the addition of KNO 3 and glucose as nitrogen and carbon sources, respectively. The CP20 and B20CP20 treatments increased volumetric soil water content by 17%, and the combined treatments improved gas diffusivity and air permeability by 32%–89% and 28%–30%, respectively, indicating enhanced soil pore organization. Compost and combined treatments reduced nitrous oxide (N 2 O) and carbon dioxide (CO 2 ) emissions by approximately 74% and 46%, respectively, but increased methane (CH 4 ) emissions by 136%–765%. The reductions in N 2 O and CO 2 were associated with improved soil pH, air permeability, and arbuscular mycorrhizal fungal biomass. While the treatments show potential for enhancing soil health and reducing N 2 O and CO 2 emissions, increased CH 4 emissions warrant further investigations.