Author
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TURNER, BEN - POST DOC (PREVIOUSLY ARS) |
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Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/1/2003 Publication Date: 3/1/2004 Citation: Turner, B. 2004. Optimizing phosphorus characterization in animal manures by solution phosphorus-31 nuclear magnetic resonance spectroscopy. Journal of Environmental Quality. 33:757-766. Interpretive Summary: The phosphorus composition of animal manures is important because long-term manure applications to agricultural land can lead to soil phosphorus accumulation. This may accelerate phosphorus transfer in runoff to water bodies and contribute to their eutrophication. To address this problem, management strategies are being developed increase the availability of phosphorus fed to animals and to minimize phosphorus losses in runoff. The development of robust methods to identify phosphorus compounds in animal manure is a fundamental prerequisite for the success of this dietary change and for water quality improvement. This study identified improved methods to extract and characterize phosphorus forms in broiler, swine and beef cattle manure using nuclear magnetic resonance spectroscopy. Phosphorus recovery was clearly influenced by the extraction solution. The inclusion of ethylenediaminetetraacetic acid in an alkaline extractant, sodium hydroxide, ensured the optimal spectral resolution needed to accurately quantify phosphorus compounds in the animal manures. This information will help studies better identify phosphorus balances and impacts in soil-animal-plant-water systems. Technical Abstract: A procedures involving alkaline extraction and solution phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy was developed and optimized for the characterization of P in animal manures (broiler, swine, beef cattle). Inclusion of ethylenediaminetetraacetic acid (EDTA) in the alkaline extraction solution recovered between 82 and 97% of the total P from the three manures, which represented a significant improvement on recovery in NaOH alone. Low concentrations of paramagnetic ions in all manure extracts meant that relatively long delay times (>5s) were required for quantitative analysis by solution phosphorus-31 NMR spectroscopy. The manures contained inorganic orthophosphate, orthophosphate monoesters, orthophosphate diesters, and inorganic polyphosphates, but results were markedly influenced by the concentration of NaOH in the extractant, which affected both spectral resolution and the apparent P composition of the extracts. For example, extraction of swine manure and broiler litter with 0.5 M NaOH + 50 mM EDTA produced remarkable spectral resolution that allowed accurate quantification of the four signals from phytic acid, the major organic P compound in these manures. In contrast, more dilute NaOH concentrations produced considerable line broadening that obscured individual signals in the orthophosphate monoester region of the spectra. Spectral resolution of cattle manure extracts were relatively unaffected by NaOH concentration. Improvements in spectral resolution of more concentrated NaOH extracts were, however, compromised by the disappearance of phospholipids and inorganic polyphosphates, notably in swine and cattle manure extracts, which indicated either degradation or a change in solubility. The optimum extraction conditions will therefore vary depending on the manure type and the objectives of the study. Phytic acid can be accurately quantified in swine manure and broiler litter by extraction with 0.5 M NaOH + 50 mM EDTA, while a more dilute NaOH concentration should be used for complete P characterization or comparison among different manure types. |
