Degryse, J.Ajiboye, A.Armstrong, R.McLaughlin, M.2014-02-252014-02-252013Soil Science Society of America Journal, 2013; 77(6):2050-20590361-59951435-0661http://hdl.handle.net/2440/82051There 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.enCopyright © by the Soil Science Society of America, Inc.Journal article002013363010.2136/sssaj2013.05.01650003270245000172-s2.0-8489193816416933Degryse, J. [0000-0002-4875-2944]McLaughlin, M. [0000-0001-6796-4144]