MICROMORPHOLOGICAL, PHYSICAL, AND CHEMICAL CHARACTERISTICS OF LEACHING POORLY DRAINED FLAT SOILS OF CENTRAL SPAIN

The eluviation process has been analyzed in horizons of Luvisols, Camb isols, and Acrisols on rana surfaces and in one Luvisol from the upper most terraces of the Henares River. The soils are located in the supra - and meso-Mediterranean, dry and subhumid bioclimatic areas. Some now have vegetation of Quercus rotundifolia Lam. and Quercus pyrenaicae W illd. in serial stages, while others are used for cereal crops. The mo st indicative morphological variables of the eluviation process and th eir interrelationship with laboratory variables were studied (microstr ucture, texture, porosity, organic matter, and soluble salts). The E h orizons have a loss of micromass in the thin section that coincides wi th a reduction in chlorides, sulfates, and electrical conductivity of the extract, as well as a very low ratio of Ca/Al water-soluble elemen ts. Leaching is occasionally not shown in the granulometric analyses, but the transfer of matter due to biological activity and/or soil mana gement is observed in the thin soil section. The Na+/Ca ratio greater than or equal to 1 matches a less stable microstructure, with a predom inance of planar voids over vughs and channels. Sail use must be consi dered in the interpretation of this ratio. The eluviation horizons not described morphologically as such, namely Ap, Au, and Bw horizons in the rana formations and Au2, AB, and Bt1 horizons on the terrace, are always located in the upper 40 cm of soils that are used by plants. Th ese are distinguished from the E horizons in their greater retention o f available water and, depending on the eluviation intensity, a macrop orosity higher than textural porosity.