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This article in JEQ

  1. Vol. 31 No. 2, p. 450-456
     
    Received: June 2, 2000
    Published: Mar, 2002


    * Corresponding author(s): richard.mcdowell@agresearch.co.nz
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doi:10.2134/jeq2002.4500

Analysis of Potentially Mobile Phosphorus in Arable Soils Using Solid State Nuclear Magnetic Resonance

  1. R.W. McDowell *a,
  2. L.M. Condronb,
  3. N. Mahieuc,
  4. P.C. Brookesc,
  5. P.R. Poultonc and
  6. A.N. Sharpleya
  1. a USDA-ARS Pasture Systems and Watershed Management Research Laboratory, University Park, PA 16802-3702
    b Soil, Plant & Ecological Sciences Division, P.O. Box 84, Lincoln University, Canterbury, New Zealand
    c IACR, Rothamsted, Harpenden, Hertfordshire AL5 2JQ, UK

Abstract

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 31P 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 CaCl2) increases much more per unit increase in Olsen P than below this point. Results showed that CaCl2 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 (CaHPO4) and dicalcium phosphate dihydrate (CaHPO4·2H2O), 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.

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Copyright © 2002. American Society of Agronomy, Crop Science Society of America, Soil Science SocietyPublished in J. Environ. Qual.31:450–456.