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Title: ANALYSIS OF POTENTIALLY MOBILE PHOSPHORUS IN ARABLE SOILS USING SOLID STATE NMR

Author
item MCDOWELL, RICHARD - AGRESEARCHLIMITED
item CONDRON, L - LINCOLN UNIVERSITY
item MAHIEU, N - UNIVERSITY OF LONDON
item BROOKES, P - IACR, ROTHAMSTED
item POULTON, P - IACR, ROTHAMSTED
item Sharpley, Andrew

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2002
Publication Date: 9/3/2002
Citation: MCDOWELL, R.W., CONDRON, L.M., MAHIEU, N., BROOKES, P.C., POULTON, P.R., SHARPLEY, A.N. ANALYSIS OF POTENTIALLY MOBILE PHOSPHORUS IN ARABLE SOILS USING SOLID STATE NUCLEAR MAGNETIC RESONANCE. JOURNAL OF ENVIRONMENTAL QUALITY. 2002. V. 31(5). P. 450-456

Interpretive Summary: Excessive fertilizer use can lead to phosphorus concentrations in topsoil that exceed those required for optimum plant growth, increase the risk of phosphorus movement to surface waters, and possibly cause environmental damage by eutrophication. The use of soil phosphorus data for environmental purposes represents an important step in the development of recommendations for farmers and policy makers. These recommendations are based on chemical extraction of soils to remove various amounts of phosphorus that may either be available for plant uptake or result in loss in runoff. Although these amounts are assumed to represent certain forms of soil phosphorus, there is little direct information on their actual chemistry. The development of Nuclear Magnetic Resonance Spectroscopy (NMR) has allowed the chemical identification of those forms of phosphorus that are available to plants or could accumulate in runoff water. By comparing chemical extraction and NMR data, we found that NMR has the potential to accurately define soil phosphorus forms and their potential mobility in the environment.

Technical Abstract: In many intensive agroecosystems continued inputs of phosphorus (P) over many years can significantly increase soil P concentrations and the risk of P losses to surface waters. This study used solid-state 31P nuclear magnetic resonance (NMR) spectroscopy (high power decoupled (HPDec)/ magic angle spinning (MAS) NMR and cross polarization (CP) / MAS NMR) to determine the chemical nature of potentially mobile P associated with aluminum (Al) and calcium (Ca) in selected arable soils. Soils with a range of bicarbonate extractable Olsen P concentrations (40-102 mg P/kg) were obtained from a long-term field experiment on continuous root crops at Rothamsted, U.K., established in 1843. This soil has a change point at 59 mg Olsen P/kg, above which potentially mobile P (as determined by extraction with water or dilute calcium chloride (0.01M CaCl2) increases much more per unit increase in Olsen P than below this point. Results showed that treatment with CaCl2 and water preferentially extracted Al-P compared with Ca-P forms, except in the high P status soil (102 mg Olsen P/kg) where water extraction removed more Ca-P relative to Al-P. Comparison between the different soils also indicated that potentially mobile P above the change point was largely present as a combination of soluble and loosely adsorbed (protonated - cross polarized) P forms associated with Ca, principally as monetite (CaHPO4) and dicalcium phosphate dihydrate (CaHPO4.2H2O). The findings of this study demonstrate that solid-state NMR has the potential to accurately define soil P species and their potential mobility.