Organic Phosphorus in Soil Size Separates Characterized by Phosphorus-31 Nuclear Magnetic Resonance and Resin Extraction
1999
Rubæk, G. H. | Guggenberger, G. | Zech, W. | Christensen, B. T.
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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