Determinação do fator de erodibilidade do solo (k) para uma bacia experimental no semiárido brasileiro, utilizando geoprocessamento

Abstract

The soil erodibility factor (K) is defined as the capacity of the soil resists to erosion, being considered the most important variable of the USLE (Universal Soil Loss Equation) by treat of the physical soil parameters that order the erosion. The Wischmeier nomograph is the mostly model used worldwide for K value determination. The use of geoprocessing tools is an excellent alternative for behavior modeling of the soil erosive processes’ factors. Thus the objective of the work was determine the soil erodibility factor for the Experimental Watershed Vale do Curu, State of Ceará, Brazil, and to evaluate the suitability of the Wischmeier nomograph to determine the K factor for the studied area. Another objective was to elaborate the map of the Watershed using kriging. 35 points were sampled on a digital mesh on the study’s area, where deformed and undeformed soil samples were collected. Laboratory analyzes of physical factors (granulometric and permeability) and chemical (organic matter) were necessary to determine the soil erodibility factor. Then the occurrence of spatial dependence was determined and made the K factor interpolation by kriging. The semivariograms spherical, exponential and gaussian were tried for the generation of the soil erodibility map, choosing the best model by cross validation. The K medium value for the Luvisol was 0.0328 ton ha h ha-1 MJ-1 mm-1, for the Red-Yellow Argisol eutrophic the K medium value was 0.0258 ton ha h ha-1 MJ-1 mm-1, and 0.0424 ton ha h ha-1 MJ-1 mm-1 for the Fluvisol. The weighted average of the K values for the study area was 0.0312 ton ha h ha-1 MJ-1 mm-1. The medium value of M (related to primary soil particles) was 3817.40, 3328.81 and 4867.95, and the sum of thin sand with silt was 43.96, 37.93 and 53.71, respectively for Luvisol, Red-Yellow Argisol euthrofic and Fluvisol. The Experimental Watershed Vale do Curu is classified as highly erodible. The Wischmeier is appropriate for determine the K soil factor for the studied soils. The Gaussian model was the mostly suitable for the generation of the erodibility soils map for the studied area.