Abstract

OCHOA, Guido R; MALAGON, Dimas  and  OBALLOS, Jajaira. Parent material and bioclimate influence on the river motatán medium and upper basin pedogenesis. Mérida-trujillo. Venezuela. Agronomía Trop. [online]. 2008, vol.58, n.2, pp.125-140. ISSN 0002-192X.

This study aims to characterize soils from high and medium basin of Motatán river (located at the Venzuelan Andes) and to offer genesis-related information. Fourteen representative soil types from various pedologic conditions (Entisols, Inceptisols, Mollisols, Ultisols) were selected. Mineral composition of parent material is known to have a great influence on soils, especially on those soils located at 1 500-2 000 m above sea level or higher due to high slopes, soil rejuvenation because of. Erosion, and low evolution rates (domination of Inceptisols and Entisols). Soils textures are mainly sandy loam, sandy clay loam, clay loam, and clay. Soil reaction goes from acid to strongly acid, except some soils based on lime material at Mucuchachí Formation. Surface horizons have medium to high organic matter content, and humus types go from chernozem with mull to moder. Three classes of soil formation are observed: (1) Incipient, characterized by having an incomplete, partial and non-advanced organic/mineral mixture, (most soils under the study are included under this classification). Processes have not become to develop specific actions and/ or events mainly because of erosion. (2) Pseudo-calci­1fication, distinguished by high Ca and/or Mg saturation, neutral/basic pH, absence of clay illuvation, and calcic or chernozem with mull humus. Since no HCL reaction is observed, this is not a calcification process. (3) argilluviation, characterized by clay migration occurring under acid conditions, low base saturation of alkaline and alkaline earthy cations, high exchangeable acidity under Al influence, abundance of resistant minerals, and accumulation of stable products.

Keywords : Mountain soils; parent material; soil forming class; soil genesis and classification; clay texture; humus; Venezuela.