Phosphate Mobilization by Addition of Organic Acids in Two Soils of the Nigerian Guinea Savanna

Abstract

The application of organic acids has been suggested as a mechanism that can mobilize Phosphorus (P) especially in soils where phosphate levels are too low. The objective of this study was therefore, to evaluate the effectiveness of adding organic acids for mobilizing P in some selected soils of Southern Guinea Savanna of Nigeria by investigating changes in soil plant available P and inorganic P fractions following treatment with citric, tartaric and oxalic acids. Soil samples were incubated at 25± 1oC and 40% moisture content for three weeks with citric, tartaric or oxalic acids at 1.0 mmol kg-1 of soil. Soil Olsen P and inorganic P fractions were analyzed. The result revealed that Olsen – P and NH4Cl - P was significantly increased with the additions of these organic acids. While Aluminium phosphate (Al – P), Iron phosphate (Fe – P), Occluded phosphate (Occl – P) and Calcium phosphate) Ca– P were also mobilized and released to some degree as well. Their capacity for P mobilization appears to follows the order of citric acid >tartaric acid > oxalic acid. P mobilization by the addition of organic acids was also highly soil type dependent and was controlled by intrinsic P status such as amounts and distribution of P fraction in the soil. These result indicate that root released organic acids can increase the solubility of some of the more stable pools of soil P, which can be important for soil P availability and P losses from soil water bodies.