Availability and fractionation of phosphorus in soils with different physicochemical characteristics

Abstract

The total content of phosphorus (P) within soil does not reflect its availability for plants, the available form depending on the physical and chemical characteristics of the soil. The aim was to evaluate the availability of P, using Mehlich-1 and Mehlich-3 extractors, and to determine the different forms of inorganic P in different classes of soils. Samples from horizon A of five soil classes from the municipality of Lagoa Formosa, Minas Gerais, were used: Typical Dystrophic Litholytic Entisol (RLd), Typical Dystrophic Red Oxisol (LVd), Typical Dystrophic Tb Hapludox Inceptisol (CXbd), Typical Acriferic Red Oxisol (LVwf), and Typical Chernossolic Litholytic Entisol (RLm). The levels of available P, remaining P, and total P were determined. From the fractionation of inorganic P, it was determined: soluble P (“P-H2O”), P bonded to aluminum (P-Al), P bonded to iron (P-Fe), and P bonded to calcium (P-Ca). The Mehlich-1 and Mehlich-3 extractors had a high correlation coefficient, indicating that both methods could be used to extract available P from the soil. Mehlich-1 extracted more available P in the soil with a high calcium content (RLm). High levels of total P observed in LVwf and RLm were mainly due to the parent material of the soils. P-Fe and P-Al are the predominant inorganic P fractions in the most weathered (RLd, LVd, and LVwf) and acidic soils (Cxbd). In RLm, the inorganic P is predominantly P-Ca.