Equilibrium models of aluminium and iron complexation with different organic acids in soil solution

The percentage of Al and Fe bound to identified low molecular weight (LMW) organic acids and phosphate in soil solution was calculated using a chemical equilibrium model. The highest fractions were obtained for the O1 horizon solutions with median values between 38–49% for Al and 18–29% for Fe. Generally the percentage declined in the deeper horizons Acceptable agreement with experimental values using ultrafiltration (85% of the Al and >95% of the Fe were organically bound. The opposite was seen for Ca and Mg for which >85% was modelled to occur as inorganic ions. The modelling results support the theory that LMW organic acids contribute to the translocation of Al and Fe in the podzolization process.