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AVAIL copolymer solubilizes phosphate from metal hydroxides


Four million metric tons of phosphate fertilizer are applied annually to U.S. agricultural soils, but less than 40% is taken up by most crops. AVAIL copolymer is a fertilizer additive developed to enhance plant availability of applied phosphate, but its mode of action is still unclear and its effectiveness in the field is variable.

In a recently published article in the Soil Science Society of America Journal, researchers report on experiments evaluating the mechanisms of AVAIL in solubilizing phosphate reacted with poorly crystalline iron and aluminum hydroxides, important phosphate sorbents in soils.

They found that dissolved phosphate increased by up to 34% of added phosphate with increasing levels of co-added AVAIL and phosphate. The mechanism implied by their data was competition between the anionic polymer and orthophosphate anions for adsorption sites on the hydroxides.

The observation that AVAIL enhances dissolved phosphate better at higher phosphate inputs suggests that AVAIL would be more effective when used in banded fertilizer applications that concentrate phosphate in a smaller soil volume. The study also indicated that the effect of AVAIL would be improved when application rates depend on a soil’s phosphate sorption capacity and degree of phosphate saturation.


Figure showing dissolved P concentrations













Read the full article in SSSAJ. Free preview Feb 27- March 6