Variabilidade espacial dos atributos físicos de um Neossolo Quartzarênico antropizado na bacia do rio Pandeiros

Abstract

Recent anthropic occupation of the northwest region of Minas Gerais changed the coverage and use of the sandy soils, mainly derived from the Urucuia formation. The charcoal production and the extensive cattle raising intensified the laminar erosion and furrows, culminating in large gullies, which provoked the silting of the trails, compromising the flow of important rivers of the region, such as Pandeiros. The objective of this work was to characterize the spatial variability and to map the physical attributes of the soil, identifying its relation with native plants of pequizeiro, within a microbasin in process of degradation in the region of the high Pandeiros river, affluent of the left margin of the São Francisco river. The study area has 83.89 ha, where deformed and undisturbed soil samples were collected in 47 geo - referenced points, distributed in an irregular sampling mesh. Morphometric data were also collected from 15 pequi tree plants located in the same sample mesh for covariance analysis with soil attributes. The soil samples were determined the particle density, soil density, macroporosity, microporosity, total pore volume, grain size and sand fractionation. All variables were submitted to descriptive statistics and spatial variability analysis using geostatistics with variography and kriging. The coefficient of variation was high for micropores and for height of pequi trees and very high for macropores, very coarse sand, height of the canopy of the pequi trees and diameter of the trunk at the height of the chest. All variables presented a spatial dependence structure, being classified as weak for coarse sand, strong for total pore volume, macropores, micropores, particle density, very coarse sand and medium sand, and moderate for other attributes. The range of the semivariograms was of 26 m for height of the crown of the pequis to 2050 m for macroporos, defining the minimum distance for independent samplings in the field. The absence of the pure nugget effect in the semivariograms indicates that the minimum distances between the sampling points were within the sample dependency region. The maps of the physical attributes indicate that the voicoramento in the region of the high Pandeiros river is a result of the disordered occupation that promoted the suppression of the native vegetation and increased the soil compaction, degrading the Quartzarenic Neosol. The declivity of the terrain coupled with low infiltration, cattle trampling and inefficient management of the soil, caused surface sealing and increased runoff, silting the trails in the lower regions. The study of spatial variability of physical attributes was able to determine spatial dependence of all attributes analyzed. The size of the pequi trees and the distribution of the granulometric fractions in the study area are directly influenced by slope relief. There was a very clear relation between the pore size and other physical attributes of the soil, observing this correlation mainly in the part of higher altitude of the slope with predominance of the micropores. The dynamics of the slope area degradation process can be better understood through the spatial analysis of soil physical attributes. The voicoramento in the region of study is the result of the anthropization that promoted the withdrawal of the native vegetation leaving the fragile soil exposed.