Path analysis of phosphorus activation capacity as induced by low-molecular-weight organic acids in a black soil of Northeast China

Abstract

The present study was designed to assess the potential effects of low-molecular-weight organic acids on the activation of inorganic phosphorus, obtain exact information on the acidity effect of proton and complex effect of organic anion in P availability, and determine the components among phosphorus fractions that contributed the most to inorganic phosphorus activation in black soil. Both oxalic and citric acids treated with different concentrations and pH values were carefully selected. The activating amounts of total inorganic phosphorus and individual phosphorus fractions were estimated. Path analysis was used to analyze the direct and indirect effects on inorganic phosphorus activation. The amount of total activating-Pi increased as the concentrations of oxalic and citric acids increased. When the concentrations were ≤ 1.0 mmol L−1, oxalic acid exhibited a lower capability than citric acid in total activating-Pi, but when the concentrations were ≥ 1.5 mmol L−1, oxalic acid exhibited a higher capability. The amount of total activating-Pi decreased as pH of LMWOAs increased. LMWOAs-induced Pi activation might be attributed to combine acidity and complex effects. Correlation analysis showed that the activation of total Pi was significantly correlated with the activation of H2O-Pi, NaHCO3-Pi, NaOH-Pi, and HCl-Pi (p < 0.05). Path analysis revealed that soil activating-H2O-Pi mainly affected Pi activation through an indirect path. The contribution of activating-NaHCO3-Pi alone was maximal on the total activating-Pi by both the direct and indirect effects, followed by activating-NaOH-Pi and activating-HCl-Pi.