Distribution and chemical species of phosphorus across density fractions in Andisols of contrasting mineralogy

Strong control of iron (Fe) and aluminum (Al) phases on soil phosphorus (P) dynamics is well established. How organic inorganic P forms are associated with Fe Al remains poorly understood, sequential density fractionation thus allows one to assess the continuum from organic-rich particles (< 1.8 g cm?3) organo-mineral (1.8–2.25 cm?3), finally mineral rich (> 2.25 cm?3). We combined approach wet extraction techniques, 31P NMR spectroscopy X-ray absorption near-edge structure (XANES) investigate distribution chemical species in relation for two Andisols: an allophanic Andisol short-range-order aluminosilicates (silandic) a non-allophanic matter (OM) organo-aluminum complexes (aluandic). fractionated soils classes 1.6–1.8, 1.8–2.0, 2.0–2.25, 2.25–2.5, > 2.5 cm?3 using sodium polytungstate solutions. Across five fractions, total were distributed low meso-density fractions (1.6–2.25 where major portions extractable found. The pool was found NaOH step low- ranges suggesting that (oxyhydr)oxides have significant roles sorption Andisols. In contrast, residual remaining after predominant heavier-density Molybdate-reactive extracted by positively correlated oxalate (Alox) (r 0.91) pyrophosphate (Alp) 0.97), stronger over phases. non-destructive XANES analysis confirmed both Andisols primarily Al, not Fe, suggested presence bound organo-Al (up 76% 1.6–1.8 fraction Alp enriched). Solution spectra NaOH-EDTA extracts showed primary group phosphomonoesters decreased increasing Myo-inositol hexakisphosphate (IHP) scyllo-IHP identified between Andisol. Our study highlights importance reservoirs