YIELD AND NUTRIENT COMPOSITION OF BIOCHAR PRODUCED FROM DIFFERENT FEEDSTOCKS AT VARYING PYROLYTIC TEMPERATURES

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°C). Biochar yield decreased significantly (p 0.05) with increasing pyrolysis temperature, while ash contents were increased. The cation exchange capacity was significantly higher (119 cmolc kg^-1) at temperature 400°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°C and carbon content (662 g kg^-1) in wheat straw biochar (RSB) at 500°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 kg^-1 at 300°C) and P (3.4 g kg^-1 at 500°C) concentrations were observed in WSB while, maximum K (48 g kg^-1 at 500°C) in RSB. High pyrolysis temperature reduced AB-DTPA extractable nutrients (expect Mn). The highest AB-DTPA extractable nutrients such as P (113 mg kg^-1) and Ca (1.07 g kg^-1) were observed in WSB at 300°C while, K (18 g kg^-1) and magnesium (Mg) (1.55 g kg^-1) in RSB at 300°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.