Inhibition of Phosphorus Sorption to Goethite, Gibbsite, and Kaolin by Fresh and Decomposed Organic Matter

Authors: HUNT, JAMES - UNIV OF MAINE; OHNO, TSUTOMU - UNIV OF MAINE; He, Zhongqi; Honeycutt, Charles; DAIL, D BRYAN - UNIV OF MAINE

Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2007
Publication Date: 12/1/2007
Citation: Hunt, J.F., Ohno, T., He, Z., Honeycutt, C.W., Dail, D. 2007. Inhibition of Phosphorus Sorption to Goethite, Gibbsite, and Kaolin by Fresh and Decomposed Organic Matter. Biology and Fertility of Soils. 44:277-288.

Interpretive Summary: The plant availability of P in soils is often below that required for optimum crop production due to either precipitation of P with Ca, Fe, and Al or to specific adsorption of P by soil minerals. Additions of plant biomass and animal manures have been studied as one approach for moderating the problems through increasing the bioavailability of the soil bound P fraction. The direct effects of dissolved organic matter (DOM) from plant biomass and animal manures on the sorption of orthophosphate onto several minerals were examined using an one-point phosphorus sorption index and the linear Tempkin isotherm model. This study demonstrates that addition of plant biomass or manures to soil may reduce the sorption of P onto soil minerals, and thus increase the bioavailabilty of P in the soil. The results also show that the extent of inhibition is closely related to the chemical structure of both the DOM molecule and the sorbing surface. This study highlights the importance of DOM in regulating soluble soil P, a key determinant of P availability to plants.

Technical Abstract: The direct effects of dissolved organic matter (DOM) on the sorption of orthophosphate onto gibbsite, goethite, and kaolin were examined using an one-point phosphorus sorption index and the linear Tempkin isotherm model. Dissolved organic matter extracted from fresh and decomposed agricultural residues, as well as model organic and humic acids were used. Changes in the chemical and sorptive characteristics of the DOM in the absence and presence of added orthophosphate (50 mg L-1) were also determined. Sorption of DOM to goethite and gibbsite was significantly decreased in the presence of added P, as were the correlations between the aforementioned chemical properties and sorption. Thus, addition of P substantially lowered fractionation of DOM following sorption to goethite and gibbsite. In contrast, few significant P sorption induced differences were observed in the kaolin system. According to one-point P sorption results, DOM in the form of Aldrich humic acid, oxalate, and decomposed clover and corn residue significantly inhibited P sorption to goethite at concentrations of 50 and 200 mg CTS L-1. Phosphorus sorption to gibbsite was significantly inhibited by 50 mg CTS L-1 derived from decomposed corn residue, fresh dairy manure residue and oxalate solution. At 200 mg CTS L-1, all DOM solutions were found to inhibit P sorption to gibbsite. This study suggests that DOM inhibition of P sorption depends on the chemical properties of both the sorbent and the DOM itself.