Long-Term Effects of P Fertilization on Organic Phosphorus Species Determined by 31P NMR Spectroscopy.

Phosphorus (P) is one of the most limiting nutrients in forest soils.  Phosphorus fertilization increases labile P after fertilization; however, it is uncertain how inorganic P fertilization influences soil organic P pools over time in forest soils.  The goal of this project is to determine how fertilization affects organic P pools 28 years after fertilization in the southeastern US.  Surface soil samples (0-5 cm) were collected in a Pinus taeda plantation established in poorly drained acid sandy soil.  We used solution ³¹P nuclear magnetic resonance (NMR) spectroscopy to characterize NaOH-EDTA extractable P.  Total NaOH-EDTA extractable P ranged from 0.1 mg P L^-1 in the control plots to 5.1 mg P L^-1 in fertilized plots.  The extracts in both treatments were dominated by inorganic orthophosphate.  Orthophosphate monoesters were the dominate organic P species present in both treatments.  Control plots had very low quantities monoester P in comparison to fertilized plots.  Mehlich-3 extractable P was significantly higher in the fertilized plots compared to control plots.  Results from this research will help our understanding on the long-term affects of forest fertilization prescriptions on organic P pools in southeastern US soils.