Hypotheses that have been tested for this study are the effects of some
organic acids on availability and adsorption of phosphorus (P) in clay soil as well as corn growth
and phosphorus uptake. In a pot experiment the used organic acids [citric, tartaric and their
mixture at ratio of 1:1 (w/w)], were added to soil at levels of 0, 0.2, 0.5 and 1% (w/w). This
experiment was arranged in a randomized complete design with three replicates and planted by
corn. The results obtained in this study reveal that organic acids addition significantly reduced P
availability (Olsen-P) from 11.9 mg kg‒1 for control to 8.0 mg kg‒1 at 0.5 % level of citric and
mixture of citric and tartaric acids. The maximal adsorption capacity of phosphorus (b) significantly
increased with additions of organic acids. Applying mixture of citric and tartaric acids increased
significantly sorption intensity constant (n). A significant increase of the sorption capacity constant
(Kf) happened with mixed citric and tartaric acids at all concentrations. But, adding 1% citric acid
and 1% tartaric acid to clay soil caused significant decreases in Kf parameter of phosphorus. The
fresh weight of corn and P uptake were enhanced significantly with the addition of organic acids.