Synthetic Chelating Agents to Decrease Fertilizer Phosphorus Binding In Soils.

As the world’s supply of available phosphorus (P) declines, there is increasing need to utilize P fertilizers more efficiently.  Most acid soils have a high capacity to bind P strongly as iron and aluminum compounds which can result in low P fertilizer use efficiency.  Organic chelating agents form multiple bonds with metals in soil and may reduce P binding with Fe and Al.  Ethylenediaminetetraacetic acid disodium salt (EDTA), and hydroxyethyl ethylenediamine triacetic acid (HEEDTA), from the aminopolycarboxylates and, gluconic acid and citric acid from the hydroxycarboxylates were tested to determine their influence on  maintaining water soluble P (WSP) concentrations in two acid soils fertilized with P  and incubated for 70 days. Soil P sorption capacity (PSC) was estimated from an oxalate extraction of iron and aluminum, and chelates were applied at rates of 0, 50, 100, 150, 200, and 250% of the PSC to produce a rate response curve for WSP.  Mehlich-1 and Mehlich-3 extractable P levels, before and after incubation, were also measured to evaluate the effects of the chelating agents on routine soil analysis results.  Initial results indicate that EDTA and HEEDTA reduced P sorption and increased Mehlich-1 and Mehlich-3 P available during the 70 day incubation study.