Yield and nutrient composition of biochar produced from different feedstocks at varying pyrolytic temperature

Variation in pyrolytic temperatures and feedstocks affects the yield and nutrient composition of biochar. Selection of suitable feedstock and optimum pyrolytic temperature is crucial before using it for agricultural purposes. We compared biochars produced from two feedstocks (wheat straw and rice) at three temperatures (300, 400 and 500 degree C). Biochar yield decreased significantly (p less than 0.05) with increasing pyrolysis temperature, while ash contents were increased. The cation exchange capacity was significantly higher (119 cmolc per kg) at temperature 400 degree C. The pH, electrical conductivity (EC) and carbon content of biochars increased significantly with increasing temperature and maximum pH (10.4) and EC (3.35 dS m-1) were observed in rice straw biochar (WSB) at 500 degree C and carbon content (662 g per kg) in wheat straw biochar (RSB) at 500 degree C. Concentration of phosphorus (P) and potassium (K) increased significantly with increasing temperature, while of nitrogen (N) decreased. Overall, the maximum N (13.8 g per kg at 300 degree C) and P (3.4 g per kg at 500 degree C) concentrations were observed in WSB while, maximum K (48 g per kg at 500 degree C) in RSB. High pyrolysis temperature reduced AB-DTPA extractable nutrients (expect Mn). The highest AB-DTPA extractable nutrients such as P (113 mg per kg) and Ca (1.07 g per kg) were observed in WSB at 300 degree C while, K (18 g per kg) and magnesium (Mg) (1.55 g per kg) in RSB at 300 degree C. Selected feedstock and use of low pyrolysis temperature may produce nutrient-rich biochar, with high CEC and low pH and these could have positive effects on calcareous soils.