Sequestration of phosphorus-binding cations by complexing compounds is not a viable mechanism to increase phosphorus efficiency
Date
2013
Authors
Degryse, J.
Ajiboye, A.
Armstrong, R.
McLaughlin, M.
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Soil Science Society of America Journal, 2013; 77(6):2050-2059
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Fien Degryse, Babasola Ajiboye, Roger D. Armstrong, Mike J. McLaughlin
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Abstract
There is increasing interest in enhancing the efficiency of P fertilizers or mobilizing fixed P from soil. Cation-complexing ligands are claimed to increase availability of fertilizer-applied or soil P through sequestration of cations (Fe, Al, Ca) that bind P strongly. We assessed the effect of ligand addition on mobility and availability of P in four soils, using a large range of cation-complexing compounds, in batch experiments without or with added P, and found only small effects of these compounds on P solubility. Selected compounds, including two commercial polymer coatings, coated on granular monoammonium phosphate (MAP) and an organic-complexed form of single superphosphate (SSP) fertilizer were tested in diffusion experiments and in a pot trial and compared with conventional MAP or SSP. The ligand treatments, at a 1% coating rate on granular fertilizers, did not significantly affect P diffusion. The only significant difference was between the MAP and SSP treatments, with a lower rate of diffusion from SSP, presumably because of enhanced Ca-P precipitation. Only at very high, commercially unrealistic coating rates (up to 100%) of a dicarboxylic copolymer did P solution concentrations close to the granule increase in an Oxisol, but not in a calcareous soil. The pot trial also showed no effect of the ligand treatments at a 1% coating rate in any of the three soils tested. These results, as well as theoretical considerations, indicate that complexation of P-binding cations is unlikely to be an economically viable process to either release P from stored forms in soil or to increase efficiency of added fertilizer P. © Soil Science Society of America. All rights reserved.
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Copyright © by the Soil Science Society of America, Inc.