Effect of Organic Acids on Phosphorus Adsorption Characteristic in Red Soil
Effect of organic acids on phosphorus adsorption characteristic in red soil was studied in the present study. Soil samples were collected from the long-term experiment that had been applied with different levels of P fertilizer for 19 years. Soil phosphorus adsorption curves, soil pH and Olsen-P were measured for the samples that had been incubated by the water content of 20% under room temperature for three weeks. Citric acid, tartaric acid or oxalic acid was added by the concentration of 0.1 mM g-1 soil for each treatment. Present results showed that phosphate adsorption curves of tested soils could be fitted by Langmuir equation and the correlation coefficients were between 0.949 -0.999. Organic acids could change the type of phosphate adsorption curve. Citric acid could change the types of phosphate adsorption curve from type Ⅱ to type Ⅲ, but tartaric acid could change the types of phosphate adsorption curve only in Treatment CK and Treatment NPK. No significant changes were observed in oxalic treatment. Moreover, citric acid reduced Xm by 30% - 75.3%, and the biggest declining degree were observed in the Treatment PM. In contrast, tartaric acid and oxalic acid increased Xm by 0.8-2.3 times and 0.1-0.3 times, respectively. Organic acid could reduce the K value and increase the degree of P saturation. Effects of the three organic acids on P adsorption characteristic value followed the order of citric acid > tartaric acid > oxalic acid.
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