Phosphorus release kinetics and solubility capacity of phosphorus fractionation induced by organic acids from a black soil in northeast China

Abstract

Phosphorus (P) fertilizers are added to improve the soil P fertility, but the rate of P release can greatly influence its availability. Organic acids are effective in the release of inorganic P (P i ), but the contribution of each P i fraction is not well understood. This study reported the transformation rate of P and solubility of P i fractions induced by organic acids. Path analysis was utilized to explore the direct and indirect effects of P i fractions on the amount of total P i (TP i ) solubilized. Results showed that the P release was initially rapid, followed by a slower release that lasted up to 2160 h, and the Elovich equation was the best-fitted kinetic equation to estimate the transformation rate of available P. The amount of TP i -solubilized by oxalic and citric acids tended to increase with increasing organic acid concentrations. Oxalic acid exhibited a lower TP i -solubility capability than citric acid when the organic acid concentration was ≤1 mmol L −1 , whereas citric acid was higher at ≥1.5 mmol L −1 . The Al-P-solubilized had the highest content of studied fractions, and path analysis revealed that the Al-P-solubilized exhibited a significant direct effect on TP i -solubilized. Thus, Al-P is a potential P source in black soil.