Co-application of biochar and inorganic fertilizer improves soil chemical properties without increasing carbon dioxide efflux in Alfisols of Morogoro, Tanzania

Combining biochar with inorganic fertilizers has gained global significance as a strategy for improving soil fertility; however, the agronomic and biogeochemical responses of soil remain inconsistent across environments and are further underexplored in Sub-Saharan Africa. This study evaluated the interactive effects of biochar and inorganic fertilizer on soil chemical properties and soil CO₂ efflux in Alfisols of Morogoro, Tanzania. A 3 × 3 factorial field experiment was conducted using three biochar rates (0, 5, and 10 t ha⁻¹) and three NPK fertilizer rates (0, 50, and 100 kg ha⁻¹). The efflux was measured using an EGM-5 infrared gas analyzer at 101, 108, 115, 122, and 129 days after biochar application. Selected soil properties: Electrical Conductivity, organic carbon, total nitrogen, available phosphorus, exchangeable potassium, and calcium were measured before and after treatment application. Results showed treatments had no statistically significant effects on soil CO₂ efflux (p > 0.05). Biochar at 10 t ha⁻¹ combined with 50 kg ha⁻¹ fertilizer significantly increased available phosphorus, exchangeable calcium, and electrical conductivity. The combination of 5 t ha⁻¹ biochar with 50 kg ha⁻¹ fertilizer significantly improved total nitrogen, while 5 t ha⁻¹ biochar with 100 kg ha⁻¹ fertilizer significantly improved exchangeable potassium. Principal component analysis revealed treatment-related patterns in soil chemical properties and CO₂ efflux, with B2F1 and B1F2 generally associated with higher organic carbon, total nitrogen, and Cation Exchange Capacity along PC1. Overall, combined biochar and fertilizer treatments tended to separate from low-input treatments in the multivariate space, suggesting distinct soil response patterns.