Effects of biochar on soil phosphorus content and cotton nutrient uptake

Influence of biochar on soil phosphorus (P), cotton growth and nutrient uptake under different phosphorus fertilizer application rates was evaluated with a pot experiment in years of 2011 and 2012. Biochar was produced from dried cotton stalks via pyrolysis in oxygen-limited conditions. Three types of biochar produced at 450℃, 600℃ and 750℃ (BC450, BC600 and BC750) were used as the soil organic amendment, and an untreated soil was set as control (CK) in this study. Each soil treatment was applied with three levels of P fertilizer (P2O5) as 0, 0.25 and 0.5 g/kg of soil weight (P0, P1 and P2). The experiment was that of 43 factorial design with four biochar treatments (BC450, BC600, BC750 and CK) and three P application rates (P0, P1 and P2). Cotton was planted for two consecutive growth seasons in 2011 and 2012. The results show that the soil P content and availability are significantly improved with biochar added. With the increase of pyrolysis temperature of biochar, the contents of water-soluble P, available P and total P in soil are increased significantly, and the order of influence of biochar on soil P content is water-soluble P total P available P. The dry matter amounts of cotton are significantly higher under the biochar treatments than those under the control (CK) in both 2011 and 2012, but there are differences among three biochar treatments between 2011 and 2012. The P uptake of cotton is also promoted with biochar added. The order of cotton nutrients uptake under three biochar treatments is BC750 BC600 BC450 These results suggest that biochar can increase soil P content, and enhance cotton growth and nutrients uptake. Thus, pyrolysis temperature is a vital factor for biochar, and the high temperature (750℃) biochar treatment demonstrates higher soil P, cotton dry matter weight and P uptake compared to the low temperature (450℃) biochar.