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TECHNICAL REPORTS

Waste Management

Sorption Dynamics of Organic and Inorganic Phosphorus Compounds in Soil

Department of Agronomy, 915 W. State Street, Purdue University, West Lafayette, IN 47907

^* Corresponding author (bjoern{at}purdue.edu)

Received for publication November 4, 2005. Phosphorus retention in soils is influenced by the form of P added. The potential impact of one P compound on the sorption of other P compounds in soils has not been widely reported. Sorption isotherms were utilized to quantify P retention by benchmark soils from Indiana, Missouri, and North Carolina when P was added as inorganic P (Pi) or organic P (ß-D-glucose-6-phosphate, G6P; adenosine 5'-triphosphate, ATP; and myoinositol hexaphosphate, IP₆) and to determine whether soil P sorption by these organic P compounds and Pi was competitive. Isotherm supernatants were analyzed for pH and total P using standard protocols, while Pi and organic P compounds were assayed using ion chromatography. Under the controlled conditions of this study, the affinity of all soils for P sources followed the order IP₆ > G6P > ATP > Pi. Each organic P source had a different potential to desorb Pi from soils, and the order of greatest to least Pi desorption was G6P > ATP > IP₆. Glucose-6-phosphate and ATP competed more directly with Pi for sorption sites than IP₆ at greater rates of P addition, but at the lesser rates of P addition, IP₆ actually desorbed more Pi. Inositol hexaphosphate was strongly sorbed by all three soils and was relatively unaffected by the presence of other P sources. Decreased total P sorption due to desorption of Pi can be caused by relatively small additions of organic P, which may help explain vertical P movement in manured soils. Sorption isotherms performed using Pi alone did not accurately predict total P sorption in soils.

Abbreviations: Al_CBD, citrate–bicarbonate–dithionite extractable aluminum • Al_ox, ammonium oxalate extractable aluminum • ATP, adenosine 5'-triphosphate • DSEP, dilute-salt extractable phosphorus • Fe_CBD, citrate–bicarbonate–dithionite extractable iron • Fe_ox, ammonium oxalate extractable iron • G6P, ß-D-glucose-6-phosphate • IP₆, myoinositol hexaphosphate • P_ox, ammonium oxalate extractable phosphorus • WSP, water-soluble phosphorus