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Analysis of Potentially Mobile Phosphorus in Arable Soils Using Solid State Nuclear Magnetic Resonance
Author(s) -
McDowell R.W.,
Condron L.M.,
Mahieu N.,
Brookes P.C.,
Poulton P.R.,
Sharpley A.N.
Publication year - 2002
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2002.4500
Subject(s) - soil water , magic angle spinning , chemistry , solid state nuclear magnetic resonance , nuclear magnetic resonance spectroscopy , arable land , environmental chemistry , phosphorus 31 nmr spectroscopy , analytical chemistry (journal) , soil science , environmental science , nuclear magnetic resonance , ecology , physics , organic chemistry , biology , agriculture
In many intensive agroecosystems continued inputs of phosphorus (P) over many years can significantly increase soil P concentrations and the risk of P loss to surface waters. For this study we used solid‐state 31 P nuclear magnetic resonance (NMR) spectroscopy, high‐power decoupling with magic angle spinning (HPDec–MAS) NMR, and cross polarization with magic angle spinning (CP–MAS) NMR to determine the chemical nature of potentially mobile P associated with aluminum (Al) and calcium (Ca) in selected arable soils. Three soils with a range of bicarbonate‐extractable Olsen P concentrations (40–102 mg P kg −1 ) were obtained from a long‐term field experiment on continuous root crops at Rothamsted, UK, established in 1843 (sampled 1958). This soil has a threshold or change point at 59 mg Olsen P kg −1 , above which potentially mobile P (as determined by extraction with water or 0.01 M CaCl 2 ) increases much more per unit increase in Olsen P than below this point. Results showed that CaCl 2 and water preferentially extracted Al‐P and Ca‐P forms, respectively, from the soils. Comparison among the different soils also indicated that potentially mobile P above the threshold was largely present as a combination of soluble and loosely adsorbed (protonated–cross polarized) P forms largely associated with Ca, such as monetite (CaHPO 4 ) and dicalcium phosphate dihydrate (CaHPO 4 ·2H 2 O), and some Al‐associated P as wavellite. The findings of this study demonstrate that solid‐state NMR has the potential to provide accurate information on the chemical nature of soil P species and their potential mobility.