Soil Acidity Ameliorative Potentials of Biochar from Sawdust and Tithonia diversifolia Feedstock

Background and Objective: Aluminum toxicity and phosphorus deficiency are adverse conditions in tropical acid soils which conventional liming materials (CLM) alone cannot ameliorate sustainably. Biochar from sawdust (SD) and Tithonia diversifolia (TD) biomass with or without poultry manure (PM) were evaluated for their liming and fertilizer potentials. Materials and Methods: Four biochars: SD+PM, SD-PM, TD+PM and TD-PM prepared at 350 and 450^°C pyrolysis temperatures were applied at 0.38 g/150 g soil. Soil treated with CLM (CaCO₃) at 0.08 g/150 g soil and absolute control (AC) were compared. Amended soils were moistened to field capacity and incubated for four weeks, sown to cowpea and nurtured for two weeks. Results: The biochars had comparatively high liming efficiencies (75-106%) as the CaCO₃ (100%) but outperformed CaCO₃ in macronutrient enrichment, carbon sequestration and cowpea root enhancement. The CaCO₃ however was higher (4.88 cmol kg‾¹) in calcium enrichment compared to the biochars (3.67-4.62 cmol kg‾¹). This did not confer higher exchangeable acidity (1.42 cmol kg‾¹) detoxification potential on CaCO₃ from the initial 2.20 cmol kg‾¹ compared to the biochars (1.20-1.48 cmol kg‾¹). Conclusion: Increasing exchangeable Ca, K and available P, therefore, are major immediate pathways for acidity amelioration in biochar-amended acid soils as indicated by their negative correlations with exchangeable acidity.