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REVIEW

Competitive sorption reactions between phosphorus and organic matter in soil: a review

C. N. Guppy A D , N. W. Menzies B , P. W. Moody C and F. P. C. Blamey B
+ Author Affiliations
- Author Affiliations

A School of Rural Science and Agriculture, The University of New England, Armidale, NSW 2351, Australia.

B School of Land and Food Sciences, The University of Queensland, Brisbane, Qld 4072, Australia.

C Queensland Department of Natural Resources, Mines and Energy, Brisbane, Qld 4068, Australia.

D Corresponding author. Email: cguppy@une.edu.au

Australian Journal of Soil Research 43(2) 189-202 https://doi.org/10.1071/SR04049
Submitted: 6 April 2004  Accepted: 27 October 2004   Published: 1 April 2005

Abstract

The incorporation of organic matter (OM) in soils that are able to rapidly sorb applied phosphorus (P) fertiliser reportedly increases P availability to plants. This effect has commonly been ascribed to competition between the decomposition products of OM and P for soil sorption sites resulting in increased soil solution P concentrations. The evidence for competitive inhibition of P sorption by dissolved organic carbon compounds, derived from the breakdown of OM, includes studies on the competition between P and (i) low molecular weight organic acids (LOAs), (ii) humic and fulvic acids, and (iii) OM leachates in soils with a high P sorption capacity. These studies, however, have often used LOAs at 1–100 mm, concentrations much higher than those in soils (generally <0.05 mm). The transience of LOAs in biologically active soils further suggests that neither their concentration nor their persistence would have a practical benefit in increasing P phytoavailability. Higher molecular weight compounds such as humic and fulvic acids also competitively inhibit P sorption; however, little consideration has been given to the potential of these compounds to increase the amount of P sorbed through metal–chelate linkages. We suggest that the magnitude of the inhibition of P sorption by the decomposition products of OM leachate is negligible at rates equivalent to those of OM applied in the field. Incubation of OM in soil has also commonly been reported as reducing P sorption in soil. However, we consider that the reported decreases in P sorption (as measured by P in the soil solution) are not related to competition from the decomposition products of OM breakdown, but are the result of P release from the OM that was not accounted for when calculating the reduction in P sorption.

Additional keywords: low molecular weight organic acids, mineralisation.


Acknowledgments

The authors would like to thank the Australian Centre for International Agricultural Research (ACIAR Project LWR1/1994/014) for funding research associated with this paper. The authors would also like to thank the two referees for constructive comments on the manuscript.


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