Saturday, 15 July 2006

Influence of Soil Parent Material and Bioclimate Over the Pedogeomorphological Homogeneity in Monaicito River Microbasin, Trujillo, Venezuela.

Neida Pineda1, Edgar Jaimes2, Rosalva Arellano2, Ligia Becerra2, and José Mendoza2. (1) Soil and Water Research Group. Los Andes Univ., Ave Medina Angarita. Carmona Sector., Trujillo, Venezuela, (2) Soil and Water Research Group. Los Andes Univ, Ave. Medina Angarita. Carmona Sector., Trujillo, Venezuela

To learn the effect of three natives materials and two bioclimatics condition over the pedogeomorfological homogeneity of different landscape units distributed in the half and high part of Monaicito river microbasin, belonging to Motatán-Carache river sub-watershed in Trujillo state, Venezuela, a study was carried out. Seventy-two profiles of soils, most of them belonging to Inceptisoles were described and sampled. Six of the 72 profiles were selected in each geologic formation (Rio Negro, La Quinta and Mucuchachí) and 13 profiles by each bioclimatic condition (tropical dry forest and premontano dry forest). The considered characteristics were: a. - Physiographics (land forms, maximum slope, pedogeomorfological position, erosion and external rock fragments); b. – Morpho-physicals (Horizon thickness, sand proportion, clay proportion, textural class, color of the dry matrix and color of the humid matix, internal rock fragments and available water); c. - Chemical ([H3O+] ions, electric conductivity, organic matter, nitrogen, phosphorous, potassium, calcium and magnesium). The recovered information of the profiles was ordered by epipedon and for endopedon. A matrix of data was built to carry out the homogeneity analysis applying the Multiple Homogeneity Index (MHI) and the Automated System of Lands Homogeneity (ASLH). According to the obtained results it could be proven that the pedogeomorphological homogeneity in the study area is determined by the parental material. Indeed, the biggest pedogeomorphological homogeneity considering all the profiles is associated with the Mucuchachí formation followed by the Rio Negro formation, constituting La Quinta formation the area of smaller homogeneity. That tendency is consistent with the pedogeomorphological homogeneity determined by the epipedones and endopedones. In all the parenterals material evaluated the morfophysics characteristic was those that exhibited the more homogeneous behavior followed by the chemical ones, standing out the physiographics variable like those of smaller pedogeomorphological homogeneity. It is important to remarks that the morpho-physicals variables of the epipedon shows the following sequence of homogeneity according to the three parenteral material considered : MHI Rio Negro formation< MHI La Quinta formation < MHI Mucuchachí formation. For the case of the endopedones the MHI of La Quinta formation is the minor. Regarding the relationship between the pedogeomorphological characteristic and the bioclimatics conditions is clear the vinculation because the pedogeomorphological homogeneity tend to increase when the life zone is more humid, which is more evident in the epipedon because it is the most external layer of the soil subjected to the homogenizing action due to the combined action of all the former factors of the soil. It could be proven that the morpho-physicals variables that characterize the complete profiles (epipedon and endopedon) tend to be more homogeneous with the increment of the environmental homogeneity while the chemical ones have an inverse behavior probably due to the action of other factors (material parental, biota, topography, among other). With base to the obtained results its concludes that a very close relationship exists between the pedogeomorphological homogeneity and the petrological and petrografics characteristic of the parentales material and of the bioclimatics conditions, factors that have contributed in the soil formation in the Monaicito river microbasin. Key words: Homogeneity pedogeomorphological, Multiple Homogeneity Index (MHI), lithosequence, bioclimosequence, epipedon, endopedon, life zone.

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