Biochar Production Technology for Conversion of Cotton Stalk Bioresidue into Biochar and its Characterization for Soil Amendment Qualities

Production and application of biochar from small-scale units on farm level may solve several environmental problems. The aim of the study was to develop a low cost portable kiln and to investigate the relationship between the production parameters with biochar characteristics. On-farm usable portable kiln unit (approx. cost per kiln was 1200) was developed on a single barrel design of vertical structure with perforated base and design function with direct up-draft principle. Cotton stalk bioresidues were subjected to thermo-chemical conversion at different loading rates and holding time. Holding time for each loading rate was correlated with internal kiln temperature. Grey gas colour was correlated with to 350–400°C and blue gas colour to 450–500°C kiln temperature range. 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. Total C and N content of the biochars ranged between 592.4 to 719.3 g/kg and between 10.3 to 17.4 g/kg, respectively. The amount of total C and N recovered in the biochar ranged from 26 to 38% and 16 to 34%, respectively. Total P, K, Ca, Mg, Fe, Cu, Mn and Zn contents were higher in biochar compared to raw cotton stalk. The CEC of the biochar samples ranged from 11.7 to 51.3 cmol/kg. Highest maximum water holding capacity (3.9 g/g of dry biochar) and available water capacity (0.89 g/g of dry biochar) was exhibited at highest at 450–500°C. Therefore, cotton stalk biochar produced at 450–500°C showed the greatest potential for use as soil amendment to improve the fertility of rainfed soils as well as to sequester carbon.