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This article in SSSAJ

  1. Vol. 63 No. 5, p. 1123-1132
    Received: June 22, 1998

    * Corresponding author(s): gitte.rubaek@agrsci.dk
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Organic Phosphorus in Soil Size Separates Characterized by Phosphorus-31 Nuclear Magnetic Resonance and Resin Extraction

  1. G. H. Rubæk *a,
  2. G. Guggenbergerb,
  3. W. Zechb and
  4. B. T. Christensena
  1. a Dep. of Crop Physiology and Soil Science, Danish Inst. of Agricultural Sciences, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark
    b Univ. of Bayreuth, Inst. of Soil Science and Soil Geography, 95440 Bayreuth, Germany


Land use and soil management affect soil organic C in whole soil and size separates, but knowledge of the accompanying soil organic P (Po) is limited. The objectives of this study were (i) to identify the structure of Po in soil size separates by solution 31P-nuclear magnetic resonance (NMR) spectroscopy, (ii) to determine the labile Po pool in the size separates by anion-exchange resin extraction, and (iii) to characterize the labile Po pool. We used soils from two long-term experimental sites, one in Bavaria (under spruce and deciduous forests, permanent grassland, and arable farming) and one in Denmark (with arable rotation and different fertilization strategies — unfertilized, mineral fertilizer, and animal manure). Total Po content increased with decreasing particle size. The dialyzed NaOH extracts of clay were enriched in microbial-derived teichoic acid-P and other diester-P forms compared with silt and sand. Clay from permanently vegetated soil had larger proportions of teichoic acid-P and other diester-P forms and was richer in resin extractable Po than clay from arable soil. There was a linear relationship between the proportion of the 31P-NMR spectra allocated to diester-P (including teichoic acid-P) and resin-Po Our results suggest that the highly active and easily mineralized soil Po was mainly associated with clay. The larger part of the clay-associated Po was tightly bound and not extractable. Although the composition of this Po remained unknown, it was probably inaccessible to rapid microbial utilization. The composition of NaOH-extractable Po in the clay fraction was influenced to a greater extent by land use than by fertilizer inputs.

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