Biochar had effects on phosphorus sorption and desorption in three soils with differing acidity

Changes in soil phosphorus (P) availability after biochar application have been reported in a number of glasshouse and field trials. However, the mechanisms underlying these changes remain poorly understood. This study evaluated the effects of four biochar application rates (0, 1%, 5%, and 10%, w/w) on P sorption and desorption in three soil types with different levels of acidity. Results showed that the effects of biochar application on P sorption were highly influenced by soil acidity. As the rate of biochar application increased, P sorption increased in the acidic soil but slightly decreased in the alkaline soil. Desorbed P significantly increased at all levels of biochar application in the studied soils. Inorganic P fractionation revealed that biochar addition sharply increased the Ca-bounded P and slightly enhanced the Al-retained P. However, biochar addition decreased the Fe-bounded P. These changes suggest that the increase in P sorption with biochar addition is attributed to Ca-induced P sorption or precipitation and is less affected by Fe and Al oxides. Biochar application is found to have altered P availability by changing the P sorption and desorption capacities of the soils, and these biochar effects were dependent on soil acidity, which have important implications for improving soil productivity on large scale. (C) 2013 Elsevier B. V. All rights reserved.