Organic phosphorus speciation and pedogenesis: analysis by solution ³¹ P nuclear magnetic resonance spectroscopy

Abstract

Summary 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 31 P nuclear magnetic resonance spectroscopy ( 31 P 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 hexa kis phosphate 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.