Resumen

GUERRERO-ALVES, Jose P; PLA-SENTIS, Ildefonso  y  VALERA, Angel. Morphological, physical, chemical and mineralogical characterization and genesis of an alkaline sodic pedon from papelon, Portuguesa state ¹. Agronomía Trop. [online]. 2009, vol.59, n.2, pp.189-205. ISSN 0002-192X.

Salt-affected soils are a major factor limiting plant growth and productivity of crop plants. Out of the 831 million hectares that the FAO/UNESCO reports worldwide as salt affected soils more than 50 % (434 million hectares) are alkaline-sodic soils. This study was conduced in order to identify factors and processes in the genesis of an alkalinesodic soil from the alluvial plains of Portuguesa River. Morphological, physical, chemical and mineralogical attributes were determined. Results indicated exchangeable sodium percentage (ESP) up to 43 %, NaHCO₃ accumulation, high pHs (>8.5), very high bulk densities (up to 2.03 Mg m^-3), both low hydraulic conductivity (< 0.5 mm h^-1) and macroporosity values (<3.4%) in Btn and Cn horizons, CaCO₃ precipitation, mixed mineralogy characterized by clorite, interstratified 10/14m, quartz and micas. It was inferred that the soil was produced, first, from materials grounded by glacial ice action in Venezuelan Andes during the arid phase of Pleistocene. Later, during the Holocene humid and warmer climate, sediments were transported and deposited in plains of Portuguesa River and then interacted with NaHCO₃ rich waters in micro-depressions. Alkaline sodium salts could be formed by weathering of sodic silicates in rocks from Venezuelan Andes or from accumulation of organic matter in a reduction environment with elimination of sulfates as H₂S. The soil evolved to promote clay migration, substitution of Ca-Mg by sodium in soil exchange complex, CaCO₃ precipitation, natric horizon formation, elimination of salts in deep drainage, and finally, when total salt quantities diminished to critic levels the degradation of soil structure was produced

Palabras clave : Soil genesis; alkaline hydrolysis; sodium carbonate; calcium carbonate.