Influence of Biochar Feedstock and Application Rate on Physical Properties of Sandy Aridisol Soil

Abstract

Biochar is becoming known as an amendment to enhance soil physical properties; however, its efficacy depends on both the type of feedstock and the application rate. The objective of this study was to assess the impacts of the biochar feedstocks (barley residues, sheep manure, woody materials, and chicken manure) and their application rates (1, 3, 5, and 10% w/w) on soil bulk density, porosity, soil water holding capacity, and soil saturated hydraulic conductivity. The results showed that biochar significantly enhanced all measured properties, with statistical analysis confirming highly significant effects of feedstock type, application rate, and their interaction on the studied soil physical parameters (p < 0.001). Across feedstocks, soil bulk density decreased approximately from 1.10–1.11 g cm⁻³ in the control to 0.80–0.82 g cm⁻³ with barley residue and sheep manure biochar, representing reductions of about 25–28%, while woody and chicken manure biochars led to smaller reductions (11–19%). Soil porosity increased from 58% in the control to 68–69% with sheep manure and barley residue biochar, corresponding to increases of 17– 9%. Water holding capacity increased to 35–39% with most feedstocks, representing increases of 6–18% relative to the control, but reached 47% with barley residue biochar, corresponding to a 42% increase compared with the control. Biochar application rate strongly influenced soil physical properties. Bulk density decreased from 1.12 g cm⁻³ at 0% biochar to 0.83 g cm⁻³ at 5% and 0.78 g cm⁻³ at 10%. Porosity increased from 58% in the control to 66% and 68% at 5% and 10% biochar, respectively. Saturated hydraulic conductivity showed a nonlinear response relative to the control, decreasing by 20–24% at 1– % biochar rates, but increasing markedly at 5% (52–69%) and remaining elevated at 10% (33– 38%). Overall, these results indicate that optimal soil improvement depends on both feedstock selection and biochar application rate, with the greatest benefits achieved with manure and residue derived biochars at 5–10% (w/w).