Characteristics and nutrient values of biochars produced from giant reed at different temperatures

► Available N and P in biochar decreased with increasing temperature but K increased. ► Less-soluble crystalline P minerals were formed in high-temperature biochar. ► More NH4+, PO43- and K+ were released from the biochars at low pH (⩽5). ► Biochars released NH4+ slowly but released PO43- and K+ fast. ► Low-temperature biochars could be a good amendment for improving soil fertility.