Effects of Biochar and Compost on Soil Nutrient Dynamics and pH in Alfisols across Two Cropping Cycles at Ibadan, Nigeria

This study evaluated the residual effects of biochar and compost on soil nutrient dynamics and pH in an Alfisol over two tomato cropping cycles under screen house conditions at the University of Ibadan, Nigeria. Biochar and compost were produced from maize stover, cow dung and moringa leaves and applied at 0, 15, 30, 45 and 60 kg/ha in a completely randomized design with three replications. Soil samples collected after each cropping cycle were analyzed for pH, total nitrogen (N), available phosphorus (P) and exchangeable potassium (K). Biochar contained higher K (3.20 mg/kg) but slightly lower N and P than compost, which was richer in P (1.44 mg/kg), indicating contrasting short against long term nutrient availability. Across two cropping cycles, biochar-amended soils retained more N than the control, although N declined by 36–84.9% depending on rate, reflecting high N mobility. In contrast, biochar significantly increased soil P and K storage, with average increments of 112.98% and 405.9%, respectively, over one cropping cycle. Compost significantly enhanced N at 15 and 30 kg/ha (up to 12% increase) and sequestered P and K by 173.4% and 123.68% on average over two cycles. Both amendments increased soil pH from slightly acidic (~5.2) to near neutral–alkaline levels (7.6–7.8), demonstrating strong liming effects. Overall, biochar and compost proved complementary organic amendments for sustaining N, P and K availability and ameliorating soil acidity in Alfisols, supporting their use as climate-smart, low-input options for smallholder tomato production.