Phosphate Mobilization by Citric, Tartaric, and Oxalic Acids in a Clay Loam Ultisol

Abstract

Phosphate mobilization by organic acids has been shown to be soil type dependent and controlled by the soil's intrinsic P status. The objective of this study was to evaluate the capacity and mechanisms of three organic acids in the mobilization of phosphate from an upland clay loam Ultisol that had received different long‐term fertilizer treatments. Soil samples were incubated at 25 ± 1°C and 40% moisture content for 3 wk with citric, tartaric, or oxalic acid at 1.0 mmol kg −1 of soil. Soil pH, inorganic P fractions, and plant‐available P (Olsen P) were analyzed after incubation. The results indicated that Olsen P and the loosely bound P extracted with 1.0 mol L −1 NH 4 Cl (NH 4 Cl‐P) were significantly increased by the treatment of the three organic acids, and Fe phosphate (Fe‐P), occluded phosphate (Oc‐P), and Ca phosphate (Ca‐P) were mobilized and released to various degrees as well. The order of increased mobilization of P by the organic acids was citric acid > tartaric acid > oxalic acid. These three organic acids have the potential to increase the availability of P in soil but need to be evaluated at the field scale.