Characterization and Agricultural Evaluation of Local and Standard Biochar

This study characterized standard biochars produced at 300, 400, and 500 °C alongside a locally made biochar (LBC, drum kiln method with newly devised method of Bababe) to assess fertilizer value and toxicity against IBI thresholds. Pyrolysis temperature strongly influenced properties: electrical conductivity and salt content increased with tempera-ture (BC300 and BC500 highest; LBC lowest). All standard biochars were highly alkaline (pH 10.26–10.57), while LBC was near-neutral (7.84). Maximum carbon content occurred at 300–400 °C (56.8–56.9 %). At 10 kg ha⁻¹, standard biochars supplied 308–331 kg ha⁻¹ K, with BC400 providing the highest Ca and Mg. LBC had the highest volatile micronu-trients (B, Cu, Fe, Mn), which decreased with rising temperature. It can be particularly well suited to fertilizer coating or blending systems, especially for salt-sensitive soils where application rates are kept low (< 10 t ha⁻¹), thereby limiting agronomic risks such as Mo contaminant loading. Nevertheless, molybdenum levels in all biochars were 5–8 times above IBI safe limits (5–75 mg kg⁻¹), posing toxicity risk at 10 t ha⁻¹ application. Cd was undetectable, reduced Pb by 90 % at 400–500 °C, and kept Ni and Pd within limits. SEM revealed BC400 had optimal honeycomb porosity and homogeneous mineral dis-tribution. BC400 is most suitable for agricultural fertilizer value, BC500 for carbon se-questration, BC300 for potassium supply, and LBC as a low-cost, low-salinity material. However, excessive molybdenum across all biochars relates feedstock composition as the paramount safety factor. The weakness and limitation of this studies lies in the resource constraints from use of one feedstock, absence of direct measurement of surface area and phosphorus, and absence of measurement of biochar stability.