Pyrolysis temperature affects phosphorus availability of rice straw and canola stalk biochars and biochar-amended soils

Purpose Biochars exhibited considerable differences in chemical properties with different feedstocks and pyrolysis conditions. This study was to understand the effects of pyrolysis temperature on the availability of phosphorus in biochars and biochar-amended soils. Materials and methods Biochars from rice straw and canola stalk were produced at temperatures of 250, 350, 450, 550, and 650 degrees C, respectively, and then applied to two acidic soils (Ultisol and Alfisol). The availability of phosphorus in biochars and biochar-amended soils was evaluated. Results The contents of total P and Olsen-P of biochar increased with pyrolysis temperature, reaching the maximum at 650 degrees C. The canola stalk biochar had a higher amount of total P than rice straw biochar. The addition of biochar increased the contents of total P, Olsen-P, and inorganic P (except Ca-P in Ultisol) in soils, varied with pyrolysis temperature, feedstock, and soil type. The highest phosphorous availability appeared in soils amended by biochars produced at 450 degrees C. The inorganic P in soils increased in the order of Ca-P >Fe-P > Al-P. Biochars significantly increased the contents of Al-P and Fe-P in two soils and Ca-P of Alfisol. Correlation analysis showed that there was a positive correlation between biochar pH and Olsen-P in soils, soil pH, and inorganic P. Conclusions Biochar could largely affect the availability of phosphorus in soils. The amount and form of available P were dependent on pyrolysis temperature and feedstock. It was important to consider the most suitable pyrolysis temperature to improve the soil P availability better, which was essential to develop soil productivity on a large scale.