Geoestatística aplicada ao estudo das características físico-químicas do solo em áreas de floresta estacional decidual

Abstract

It was used methods of classic statistics, exploratory data analysis and geostatistics in the identification of size and structure of space variability of some physiochemical attributes of soils under seasonal deciduous forest areas, which was called mature forest, secondary forest and capoeirão . The areas, located in Santa Tereza, RS State, were sampled during the period from 2002 to 2003, comprising the soil classes: Argiluvic Chernosol, Cambisol Ta and Litholic Neosol. Systematic sampling was performed with regular spacing grid of points varying of 30 m for capoeirão and 40 m for mature and secondary forest, in an amount of 80 sample points in a total area of 7.34 ha. In each point measurements "in situ" were made of the soil bulk density, clay content, pH, potassium, organic matter and phosphorus. The magnitudes of the space variability were given by the variation coefficients, while the structure was identified through the variograms, being defined the needed parameters for the Kriging. The most variable attribute was the organic matter, didn t being adjusted to any model of variogram, while the pH was the less. In the analysis of structure of the space variability through the geostatistics, the clay and bulk density, both in area of secondary forest, and pH in the experimental areas had showed the biggest space dependence. The gauss model for the clay attribute obtained the largest reach (a), being respectively 400 m and 388 m in the areas of secondary and mature forest respectively. The crossed validation showed accuracy in the variographic models adjustment, being the pH variable the one which presented the optimum performance, 0.87; 0.94 and 0.92 in the areas of mature forest, secondary forest and capoeirão respectively. The ordinary Kriging of the interest variable allowed the detailing of distribution of these variable from the isoline maps. All of the variograms models for most of the studied attributes, presented anisotropic influence zones, being the larger space variability in perpendicular direction to the slope of these areas.