Maize root mucilage decreases adsorption of phosphate on goethite

This work was carried out to determine the influence of root exudates on phosphorus solubility in the presence of a strong phosphate sorbant. Root mucilage was collected from maize grown under field conditions. Polygalacturonic acid (PGA) was also used as a model of exudates. Adsorption of phosphate by synthetic goethite was measured in the absence of either (1) root mucilage collected from maize in the field, or (2) PGA. The ranking order of the adsorption on goethite was phosphate at low concentration >PGA >mucilage >phosphate at high concentration. Then, competitive adsorption between phosphate ions and PGA or mucilage was studied. Increasing the concentration of PGA or mucilage added to the goethite suspension decreased the amount of phosphate adsorbed on goethite. It is likely that PGA, mucilage and phosphate compete for the same adsorption sites on goethite: the effect of the coating of the mineral by the mucilage is another possible explanation.