Operational Process for Biochar Preparation from Castor Bean Stalk and its Characterization for Soil Application

Thermo-chemical decomposition of unusable crop residues to biochar appears to be a novel and sustainable strategy to address concerns with regard to crop residue management, long term C sequestration and soil fertility. Castor bean (Ricinus communis L) stalk was charred at different loads (kg/kiln) and residence periods (min). Grey and blue gas color for different combination of load and residence period was correlated with internal kiln temperature (350–400°C and 450–500°C). Operational (process) parameters viz., loading rate, residence period, internal kiln temperature range and conversion efficiency were standardized. Volatile matter content decreased, whereas fixed carbon and ash content increased with increase in temperature in each load. Biochar yield decreased with increasing temperature in each load types. The yield of biochar made from castor bean stalk ranged from 17.1 to 24.4% and total carbon content ranged from 494.8 to 613.1 g/kg which corresponded to 443.7 g/kg of carbon in the biomass. The value of pH and EC varied with increase in production temperature. Total P, K, Ca, Mg, Fe, Cu, Mn and Zn contents were higher in biochar compared to castor bean stalk. The CEC of the biochar samples ranged from 16.4 to 40.8 cmol/kg. Water retention properties of biochar increased with increase in temperature. Maximum water holding capacity (3.4 g/g of dry biochar) and available water capacity (2.4 g/g of dry biochar) of biochar was highest at 450–500°C and it may help balance fluctuations in water availability to plants during prolonged dry spells. Results suggest that biochar generated in the study at 450–500°C temperature was enriched with nutrients and carbon, and could be optimally used as a soil amendment for improving biogenic carbon storage and soil fertility in dryland agriculture.