Assessing phosphate sorption by soils: toward resolving the issues
Abstract Phosphorus (P) is an essential plant nutrient and also a potential environmental pollutant, which makes its proper management an ongoing issue. Orthophosphate (PO4) may be the most important form of soil P, and its partitioning between the solid and the aqueous phase is an index of bioavail...
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Springer
2025-05-01
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| Series: | Discover Soil |
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| Online Access: | https://doi.org/10.1007/s44378-025-00059-y |
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| author | Paul J. Milham Paul Holford Natasha Carlson-Perret R. John Morrison Deirdre Harvey Karl O. Andersson Lucy L. Burkitt Damian Collins Warwick Dougherty Anthony M. Haigh Murray C. Hannah Joel Tellinghuisen |
| author_facet | Paul J. Milham Paul Holford Natasha Carlson-Perret R. John Morrison Deirdre Harvey Karl O. Andersson Lucy L. Burkitt Damian Collins Warwick Dougherty Anthony M. Haigh Murray C. Hannah Joel Tellinghuisen |
| author_sort | Paul J. Milham |
| collection | DOAJ |
| description | Abstract Phosphorus (P) is an essential plant nutrient and also a potential environmental pollutant, which makes its proper management an ongoing issue. Orthophosphate (PO4) may be the most important form of soil P, and its partitioning between the solid and the aqueous phase is an index of bioavailability and environmental pollution. This process is the basis of laboratory sorption studies in which various amounts of PO4 are spiked into soil suspensions, pseudoequilibrium residual concentrations (C) are measured using molybdate (MRP), and the sorbed PO4 (S) is estimated by difference. The partitioning can be described by the Freundlich equation: S = a C b , where a and b are fitted coefficients. In many soils, some natural or legacy PO4 (Q) is already present, which decreases the sorption of additional PO4, requiring the Freundlich equation to be modified to S = a C b – Q. It is claimed that Q can be estimated by least-squares fitting; however, there are questions over these estimates and discrepancies are reported between Q and the pool of exchangeable P (PE). The relation of our Q and PE values suggests a likely physical significance of the Q estimates. Regardless, both Q and PE have limited accessibility, prompting us to examine six readily accessible soil assays as surrogates for PE. All P assays increased with added fertiliser P and several appear promising alternatives to PE, e.g., our PE values can be estimated within ~ 6% by scaling the 1 g/100 mL 0.5 M sodium bicarbonate MRP estimates by 0.31. Should this relation apply more widely it would assist land managers estimate P fertiliser requirements and environmental risk. Lastly, filterable soil colloids contain P and the extent to which this inflates the MRP values is unknown. |
| format | Article |
| id | doaj-art-5fb8a4250d7940fd9e19c43776d5beac |
| institution | OA Journals |
| issn | 3005-1223 |
| language | English |
| publishDate | 2025-05-01 |
| publisher | Springer |
| record_format | Article |
| series | Discover Soil |
| spelling | doaj-art-5fb8a4250d7940fd9e19c43776d5beac2025-08-20T01:52:03ZengSpringerDiscover Soil3005-12232025-05-012111010.1007/s44378-025-00059-yAssessing phosphate sorption by soils: toward resolving the issuesPaul J. Milham0Paul Holford1Natasha Carlson-Perret2R. John Morrison3Deirdre Harvey4Karl O. Andersson5Lucy L. Burkitt6Damian Collins7Warwick Dougherty8Anthony M. Haigh9Murray C. Hannah10Joel Tellinghuisen11Hawkesbury Institute for the Environment, Western Sydney UniversitySchool of Science, Western Sydney UniversitySchool of Earth and Environmental Sciences, University of WollongongSchool of Earth and Environmental Sciences, University of WollongongNew South Wales Department of Primary Industries, Elizabeth Macarthur Agricultural InstituteNSW Department of Primary Industries and Regional DevelopmentFarmed Landscapes Research Centre, School of Agriculture and Environment, Massey UniversityNew South Wales Department of Primary Industries, Elizabeth Macarthur Agricultural InstituteNew South Wales Department of Primary Industries, Elizabeth Macarthur Agricultural InstituteSchool of Science, Western Sydney UniversityDepartment of Jobs, Precincts and RegionsDepartment of Chemistry, Vanderbilt UniversityAbstract Phosphorus (P) is an essential plant nutrient and also a potential environmental pollutant, which makes its proper management an ongoing issue. Orthophosphate (PO4) may be the most important form of soil P, and its partitioning between the solid and the aqueous phase is an index of bioavailability and environmental pollution. This process is the basis of laboratory sorption studies in which various amounts of PO4 are spiked into soil suspensions, pseudoequilibrium residual concentrations (C) are measured using molybdate (MRP), and the sorbed PO4 (S) is estimated by difference. The partitioning can be described by the Freundlich equation: S = a C b , where a and b are fitted coefficients. In many soils, some natural or legacy PO4 (Q) is already present, which decreases the sorption of additional PO4, requiring the Freundlich equation to be modified to S = a C b – Q. It is claimed that Q can be estimated by least-squares fitting; however, there are questions over these estimates and discrepancies are reported between Q and the pool of exchangeable P (PE). The relation of our Q and PE values suggests a likely physical significance of the Q estimates. Regardless, both Q and PE have limited accessibility, prompting us to examine six readily accessible soil assays as surrogates for PE. All P assays increased with added fertiliser P and several appear promising alternatives to PE, e.g., our PE values can be estimated within ~ 6% by scaling the 1 g/100 mL 0.5 M sodium bicarbonate MRP estimates by 0.31. Should this relation apply more widely it would assist land managers estimate P fertiliser requirements and environmental risk. Lastly, filterable soil colloids contain P and the extent to which this inflates the MRP values is unknown.https://doi.org/10.1007/s44378-025-00059-yOrthophosphate soil sorptionSoil P assaysFreundlich sorption modelEstimating presorbed soil phosphateExchangeable soil P |
| spellingShingle | Paul J. Milham Paul Holford Natasha Carlson-Perret R. John Morrison Deirdre Harvey Karl O. Andersson Lucy L. Burkitt Damian Collins Warwick Dougherty Anthony M. Haigh Murray C. Hannah Joel Tellinghuisen Assessing phosphate sorption by soils: toward resolving the issues Discover Soil Orthophosphate soil sorption Soil P assays Freundlich sorption model Estimating presorbed soil phosphate Exchangeable soil P |
| title | Assessing phosphate sorption by soils: toward resolving the issues |
| title_full | Assessing phosphate sorption by soils: toward resolving the issues |
| title_fullStr | Assessing phosphate sorption by soils: toward resolving the issues |
| title_full_unstemmed | Assessing phosphate sorption by soils: toward resolving the issues |
| title_short | Assessing phosphate sorption by soils: toward resolving the issues |
| title_sort | assessing phosphate sorption by soils toward resolving the issues |
| topic | Orthophosphate soil sorption Soil P assays Freundlich sorption model Estimating presorbed soil phosphate Exchangeable soil P |
| url | https://doi.org/10.1007/s44378-025-00059-y |
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