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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| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Springer
2025-05-01
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| Series: | Discover Soil |
| Subjects: | |
| Online Access: | https://doi.org/10.1007/s44378-025-00059-y |
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| Summary: | 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. |
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| ISSN: | 3005-1223 |