Interaction of Phosphates With Ferric Organic Complexes

Humic acid extracts of soil organic matter had the capacity to complex ferric ions. Methylation studies indicated that non-carboxylic hydroxyl groups present in humic acid are involved in holding iron above pH 4.7.The (humic acid-iron) complex was able to hold phosphate ions against an anion resin. The amount of phosphate held depended on the pH and on the type of resin. It was also found that although the phosphate associated with the (humic acid-iron) complex was nearly all exchangeable with radioactive P32, only a portion of this phosphate was available for plant use.