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Genesis and Native Phosphorus Distribution in some Palexeralfs of Southern Spain

Dep. of Agronomy, Ohio State Univ., Columbus, OH 43210

J. Torrent and V. Barrón

Departmento de Ciencias y Recursos Agrícolas y Forestales, Universidad de Córdoba, Apdo. 3048, 14080 Córdoba, Spain

* Corresponding author.

ABSTRACT

Although deeply weathered soils are common on stable landscapes in Mediterranean regions, little information exists regarding the quantities and depth-distributions of native P forms in such soils. The objective of this investigation was to gather such information to determine the P status of Palexeralfs representative of southern Spain and to evaluate the applicability of current models and paradigms for describing pedogenic P transformations in such soils. Base saturation, clay distribution, absence of primary carbonates, distribution of secondary carbonates, extent of rubification, and properties of Fe (hydr) oxides all indicate that the Palexeralfs are polygenetic. Yellowishred lower sola are considered relicts attributable to deep leaching and weathering during Pleistocene pluvial periods, whereas pedogenesis is active in upper yellowish-brown B horizons. Low total and labile P contents and the dominance of reductant-soluble and organic P fractions throughout entire >3-m sola indicate that soil P distribution attained a terminal steady state during the paleo-climatic regime and has been little affected 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_o mineralization and fosters the labile P deficient state of these soils.

Received for publication November 24, 1993.