effect of organic acids on sorption and immobilization of fe in acidic and calcareous soils

organic acids exuded by plant roots increase solubility of soil micronutrient complexes. this study was carried out to evaluate adsorption isotherms of 4 acidic and 4 calcareous soils at presence of organic acids (citric, malic and oxalic acids). iron sorption and desorption isotherms are defined in to two systems including; system 1; soil-water-metal, system 2; soil-water-organic acid-metal). data fitted to different adsorption/desorption isotherms model including langmuir (cs= kbce/ 1+kce) and frundlich (cs=kce1/n) and appropriate model developed for quantitative behavior of iron adsorption/desorption. the results showed that in acidic soils, fe adsorption data fitted well with frundlich (r2>0.98, p0.94, poxalic acid>malic acid>control, respectively. it can be concluded that complexing organic acids with fe decrease its adsorption and promote availability for plant.