Organic phosphorus speciation and pedogenesis: analysis by solution 31P nuclear magnetic resonance spectroscopy |
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Authors: | R W McDowell B Cade-Menun & I Stewart |
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Institution: | AgResearch, Invermay Agricultural Centre, Private Bag 50034, Mosgiel, New Zealand; , Department of Geological and Environmental Science, Stanford University, Building 320, Room 118, Stanford, CA 94305–2115, USA; , and Department of Chemistry, University of Otago, PO Box 56, Dunedin, New Zealand |
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Abstract: | Changes in phosphorus (P) during soil development are central to the understanding of labile P for plant productivity and soil P management. We used NaOH‐EDTA extraction with 31P nuclear magnetic resonance spectroscopy (31P NMR), sequential P fractionation, and general soil chemical characterization to better our understanding of P dynamics within two chronosequences (Manawatu and Reefton) and one Basalt maturity sequence under original native vegetation. With time, orthophosphate and orthophosphate monoesters tended to increase with organic C to a maximum of about two‐thirds of NaOH‐EDTA‐extractable P in young soils (16 000 years in the Reefton chronosequence), but gradually declined thereafter to about one‐third of NaOH‐EDTA‐extractable P in the oldest soils (130 000 years old). This coincided with a depletion of P from primary minerals (e.g. apatite) and readily available P for plant production. This depletion of inorganic P resulted in a greater reliance on organic P cycling via mineralization, hence the depletion of the normally recalcitrant monoester‐P pool. Concomitantly, the build‐up of labile P species (diesters and pyrophosphate) and scyllo‐ over myo‐inositol hexakisphosphate occurred as soils developed, and might be attributed to microbial activity, including scavenging for P. This work highlights the importance of organic P cycling during pedogenesis. |
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