Resumo

GUERRERO-ALVES, José P.; PLA-SENTIS, Ildefonso  e  CAMACHO, Rafael G.. GÉNESIS DE UN SUELO SÓDICO ALCALINO EN CHAGUARAMAS, VENEZUELA¹ . Agronomía Trop. [online]. 2004, vol.54, n.4, pp.433-460. ISSN 0002-192X.

Many soils around the world present large amounts of sodium, characteristic that leads to generate sodic soils. In these soils risks of degradation are ever present. This study was conducted to identify factors and processes in the genesis of an alkali sodic soil from the Chaguaramas Formation (Chaguaramas, Guárico State, Venezuela). Thus some morphological, physic, chemical and mineralogical soil properties and characteristics were measured. The results shown exchangeable sodium percentage (ESP) up to 89%, accumulation of alkaline salts of sodium (bicarbonates and carbonates), pH higher than 8.5, soil bulk density (Db) up to 2.27 Mg m^-3, low hydraulic conductivity (< 2 mm h^-1) and macroporosity values, precipitation of CaCO₃, and mixed mineralogy characterized by presence of smectites. It was inferred that the soil was produced from alteration of tertiary sedimentary rocks that interacted with waters rich in sodium in depressions of the Venezuelan Central High Plains during the arid phase at the end of Pleistocene. High quantities of alkaline sodium salts were favored from the accumulation of organic matter in a reduced environment; event that led up to the elimination of high quantities of sulfates as H2S. The saline sodic soil evolved during the Holocene humid climate to promote the clay migration and natric horizon formation, the progressive substitution of divalent ions by sodium in the soil exchange complex, the precipitation of CaCO₃, the elimination of salts in the deep drainage, and finally, when the total quantity of salts were diminished to critic levels, to the degradation of the soil structure.  

Palavras-chave : Alkaline hydrolysis; sodium carbonate; calcium carbonate.