Characterization of biochar and phosphorus adsorption in charnockite-originated soils

Phosphorus, P deficiency by adsorption and fixation of applied P is a critical problem in the tropical soils coupled with wastage of agricultural land and potential nutrients from crop residues’ decomposition necessitates conservancy and sustainable management. Maize stover biochar (mB) and sawmill waste biochar (sB) pyrolysed for 60-minute at 460 °C using Top-Lit Up Draft (TLUD) carbonizer were characterized by morphological, elemental and proximate properties analysed by Scanning Electron Microscope (SEM), CHNS Elemental Analyser and appropriate methods, respectively. Phosphorus (P) adsorption potential of the biochars in charnockite-originated soils were evaluated using adsorption isotherms after adding biochars at 0, 5, 10 and 20% (w/w) with concentrations of 0, 15, 30, 60, 90, 120, 150 mg P/L. SEM showed macropores (>50 nm) embedded biochars, with higher elemental C and H in sB while mB contained higher N, S, O, available P and pH. P-adsorption decreased inconsistently with increasing biochar rates resulting in P-desorption. Low Langmuir adsorption maximum (Qm) were recorded (−0.0350 to 0.1250 mg kg⁻¹) mostly with negative separation factors (R_L) and the adsorption process were favourable for mB amended soils having Freundlich heterogeneity factor (n_F) of 4.476–9.634 but not for sB amended soils (n_F = 0.638–2.812). Biochar production conserved nutrient loss and potentially reduced soil P fixation.