Sistema pedológico em um ambiente antropizado da depressão central do RS

Abstract

The present work was accomplished in a slope with a pedological system composed of Red Argisol/Gleysol, in a pasture area located in an unit of agricultural production in the municipal district of Santa Maria - RS. It aimed at the characterization morphologic and the physic-hydrical and the discretization of the variability of the loss of soil of the slope. Thirteen aligned profiles were selected in a toposequency, of a total of 57, reconstituted by the polls method. After description the approach of the pedologic system in the thirteen profiles, considering the vertical and lateral succession of the verified horizons, the samples were collected for the chemical and physical-hydrical determinations in laboratory (texture, densities, porosities, retention hydrical and availability of water, saturated hydraulic conductivity and permeability to the air), in three sampling orientations. Furthermore, the soil losses were estimated through the coupling of the Universal Equation of Loss of the Soil - RUSLE, in SIG atmosphere. In the toposequency, three profiles were classified as Gleysol and the others as Red Argisol. Argisols and Gleysols presented variated chemical and physical limitations, producing strong use limitation. The horizons Bt in Argissolos are found in different depths in the studied profiles, implicating different behaviors, depending on the thickness of the horizons upper (suprajacente) The physical-hydrical dynamics of the system is marked by a different behavior among the surface (loam) and the subsurface (clayer), and it should be understood, considering the group of the horizons of each profile, to predict the physical-hydrical behavior of the soil. The saturated hydraulic conductivity of the soil presented a variation along the horizons of the soil profiles in different positions of the landscape, with great differences among the values observed in surface in relation to the ones of the subsurface, identifying the existence of a lateral flow of water in the soil, mainly in the portion of the hillside and its space variation in a topographical sequence. In the podzolic cover, the blockade of vertical drainage occurs in the top of the horizon Bt, generating a more humid zone above. The smallest retention of water in all the profiles occured in the loam horizons, Ap and A1, in all the tensions, while in the deepest horizons, Bt1 and Bt2, there was a larger retention as a consequence of the decrease of the sand tenor and increase of the clay tenor. The transition horizons, AB and BA, presented an intermediate behavior. The available water in the soil for the plants was influenced directly by the texture, which increased with the increment of the sand fraction and it decreases with the increase of the clay fraction. With the drier of the soil the permeability to the air tends to increase due to the drainage of the water of the pores which start to conduct air, being highly dependent of the macroporosity. The animal trampling and the preparation operations promoted an increase of the soil density, resulting in the reduction of the total porosity and of the macroporosity and consequently an increase in the microporosity in the horizons Ap and A1, which suffer the direct effects of the anthropic activity. The methodology application that engagement RUSLE in atmosphere SIG, allowed the discretization of the space variability of the factors that determine the losses, as well as the soil losses in a slope of the Central Depression of RS.