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Measuring Phosphorus Release in Laboratory Microcosms for Water Quality Assessment
Published on: July 22, 2019
Extraction of soil organic phosphorus
Benjamin L Turner1, Barbara J Cade-Menun, Leo M Condron
1Smithsonian Tropical Research Institute, Balboa, Ancon, Republic of Panama. bturner@ufl.edu
Talanta
|October 31, 2008
Summary
Extracting soil organic phosphorus is crucial for understanding its role in biogeochemical cycles. A review highlights that while some methods alter its structure, a sodium hydroxide and EDTA extraction is effective for speciation analysis.
Area of Science:
- Soil Science
- Biogeochemistry
- Environmental Chemistry
Background:
- Soil organic phosphorus (P) is vital for soil biogeochemical cycles.
- Accurate extraction is necessary for soil P analysis, quantification, speciation, and bioavailability assessment.
Purpose of the Study:
- Critically review current methods for soil organic phosphorus extraction.
- Evaluate procedures for quantification, speciation, and bioavailability assessment.
- Identify limitations and suggest future research directions for ecologically relevant soil P pools.
Main Methods:
- Review of literature on soil organic phosphorus extraction techniques.
- Discussion of quantitative extraction methods using strong acids/bases and single-step procedures (NaOH-EDTA).
- Evaluation of analytical techniques like molybdate colorimetry and nuclear magnetic resonance (NMR) spectroscopy.
Main Results:
- Conventional quantitative extraction methods using strong acids/bases can alter organic P structure.
- A single-step extraction with sodium hydroxide and EDTA is suitable for most soils and aids NMR speciation.
- Molybdate colorimetry can lead to overestimation of organic P due to interference from inorganic polyphosphates and humic complexes.
- Sequential extraction schemes based on solubility may not accurately reflect bioavailability.
Conclusions:
- There is a need for improved methods to extract soil organic phosphorus that preserve its chemical structure.
- The NaOH-EDTA method shows promise for facilitating speciation analysis.
- Analytical interferences in molybdate colorimetry require careful consideration.
- Future research must focus on developing extractable soil organic P pools with clear ecological relevance.
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01:21The Phosphorus Cycle
Unlike carbon, water, and nitrogen, phosphorus is not present in the atmosphere as a gas. Instead, most phosphorus in the ecosystem exists as compounds, such as phosphate ions (PO43-), found in soil, water, sediment and rocks. Phosphorus is often a limiting nutrient (i.e., in short supply). Consequently, phosphorus is added to most agricultural fertilizers, which can cause environmental problems related to runoff in aquatic ecosystems.
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Metal ions can be separated from one another by complexation with organic ligands–the chelating agent– to form uncharged chelates. Here, the chelating agent must contain hydrophobic groups and behave as a weak acid, losing a proton to bind with the metal. Since most organic ligands used in this process are insoluble or undergo oxidation in the aqueous phase, the chelating agent is initially added to the organic phase and extracted into the aqueous phase. The metal-ligand complex is formed in...