Characterization of Biochar Produced from Locally Available Agricultural Waste Resources for Soil Enhancement in Western Kenya

Abstract

Valorization of agricultural waste offers a circular pathway to mitigate the intertwined crises of climate change, pollution, and biodiversity loss. Slow pyrolysis provides an effective route for transforming biomass into biochar, a porous carbonaceous material that can condition degraded soils. We quantified the physicochemical attributes of biochar produced from three contrasting residues that dominate western Kenya’s agroecosystems: coffee husk (CH), sugarcane bagasse (SB), and wood sawdust (WS). Each feedstock was air-dried for 72 h, pyrolyzed in a sealed metal kiln at 350 °C for 60 min, and cooled under an inert atmosphere. Yields averaged 37 % for CH, 32 % for SB, and 28 % for WS. Resultant biochars displayed high pH (8.4–9.2), surface area (145–275 m² g⁻¹), and cation-exchange capacity up to 92 cmol c kg⁻¹, indicating liming and nutrient-retention potential. Elemental analysis revealed increasing aromaticity (H/C < 0.35) and carbon stability with decreasing O/C ratios. Bulk density followed the order WS > SB > CH, whereas porosity exhibited the opposite pattern, reflecting structural differences in the biomasses. The correlation of ash alkalinity with calcium and magnesium contents suggested that feedstock mineralogy largely governs biochar buffering capacity. On the basis of these metrics, CH biochar emerged as the most suitable amendment for acidic Ferralsols, whereas WS biochar may serve better in sandy Arenosols requiring structural improvement. The findings supply evidence that can guide county-level policies seeking to couple waste reduction with soil fertility restoration through biochar adoption within smallholder systems.