Pathways of Phosphorus Transformations in Soils of Differing Pedogenesis

TLDR

The study used a sequential extraction of 168 USDA‑SCS benchmark soils into nine organic and inorganic phosphorus fractions to assess how soil development influences phosphorus composition across eight soil orders. Analyses revealed that organic matter accumulation depends partly on available P, that weathering indicators such as base saturation influence secondary P formation, and that the relative proportions of available, stable, organic, and inorganic P vary with soil chemistry and taxonomy, with Mollisols deriving most labile P from inorganic sources and Ultisols deriving it mainly from organic P.

Abstract

Abstract Nine different organic and inorganic soil phosphorus fractions were obtained by a sequential extraction of samples from 168 USDA‐SCS benchmark soils, representing eight soil orders of the Soil Taxonomy. The distribution of P across the different fractions (resin, bicarbonate, hydroxide, sonification‐2nd hydroxide, acid, and acid‐peroxide digest fractions with separate organic and inorganic P determinations) and their relationships to other soil chemical properties were used to evaluate the effects of different soil development on phosphorus composition. Correlation and regression analyses of P distribution and chemical analyses confirmed the partial dependence of organic matter accumulation on available forms of P. Weathering indicators such as base saturation were related to the formation of secondary P forms. The relative proportions of available and stable as well as organic and inorganic P forms were dependent upon soil chemical properties and related to soil taxonomy. Path analysis of relationships between labile and stable P forms showed that in Mollisols much of the labile resin extractable P was derived from inorganic bicarbonate and hydroxide extractable P forms. In more weathered Ultisols, 80% of the variability in labile P was accounted for by organic P forms, suggesting that mineralization of organic P may be a major determinant of P fertility in these soils.