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

The eluviation process has been analyzed in horizons of Luvisols, Cambisols, and Acrisols on rana surfaces and in one Luvisol from the uppermost 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 Willd. in serial stages, while others are used for cereal crops. The most indicative morphological variables of the eluviation process and their interrelationship with laboratory variables were studied (microstructure, texture, porosity, organic matter, and soluble salts). The E horizons have a loss of micromass in the thin section that coincides with a reduction in chlorides, sulfates, and electrical conductivity of the extract, as well as a very low ratio of Ca/Al water-soluble elements. Leaching is occasionally not shown in the granulometric analyses, but the transfer of matter due to biological activity and/or soil management is observed in the thin soil section. The Na+/Ca ratio greater than or equal to 1 matches a less stable microstructure, with a predominance of planar voids over vughs and channels. Sail use must be considered 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. These are distinguished from the E horizons in their greater retention of available water and, depending on the eluviation intensity, a macroporosity higher than textural porosity.