GENESIS AND NATIVE PHOSPHORUS DISTRIBUTION IN SOME PALEXERALFS OF SOUTHERN SPAIN

Although deeply weathered soils are common on stable landscapes in Med iterranean regions, little information exists regarding the quantities and depth-distributions of native P forms in such soils. The objectiv e of this investigation was to gather such information to determine th e P status of Palexeralfs representative of southern Spain and to eval uate the applicability of current models and paradigms for describing pedogenic P transformations in such soils. Base saturation, clay distr ibution, absence of primary carbonates, distribution of secondary carb onates, extent of rubification, and properties of Fe (hydr)oxides all indicate that the Palexeralfs are polygenetic. Yellowish-red lower sol a are considered relicts attributable to deep leaching and weathering during Pleistocene pluvial periods, whereas pedogenesis is active in u pper yellowish-brown B horizons. Low total and labile P contents and t he dominance of reductant-soluble and organic P fractions throughout e ntire >3-m sola indicate that soil P distribution attained a terminal steady state during the paleo-climatic regime and has been little affe cted during the current semiarid climate. Although organic P (P-o) is a major component of total P, stabilization of P-o by Fe (hydr)oxides restricts P, mineralization and fosters the labile P deficient state o f these soils.