PHOSPHATE, ALUMINUM AND IRON IN THE SOIL SOLUTION OF 3 DIFFERENT SOILS IN RELATION TO VARYING CONCENTRATIONS OF CITRIC-ACID

Several plant species excrete di- and tricarboxylic acids as a reaction to P and Fe deficiency. Therefore, the effect of citric acid on P, Al, and Fe soil solution concentrations of three soils was investigated in an incubation experiment Citric acid additions of 10 - 50 mumole/g soil increased P, Al, and Fe solubility. The effect was strongly pronounced in the pod-zol with humic-P complexes as the main P fraction. The maximum increase was about 80 mumole P/L in the luvisol, 500 mumole P/L oxisol, and 3000 mumole P/L in the podzol. The Fe and Al solubility increased parallel to that of P with a ratio of Fe+Al(solubized)/P(solubized) of 10 or more. The solubization effect by citric acid was strong even after 90 days. Possible solubization reactions are discussed.