Compactação de dois argissolos na colheita florestal de Pinus taeda L.

Abstract

The knowledge of soil damage due forest harvest is important for adequate management of soil physical conditions, to increase wood yield and decrease soil degradation. This study evaluates the influence of different operations of forest harvest on the soil physical properties of a typical Hapludalf and an abrupt Hapludalf. The research was realized in areas under 17 years old commercial forest of Pinus taeda. The soil physical properties were evaluated before and after the forest harvest. The treatments, constituted by the different operations of Pinus harvest were as following: before the harvest; after trees cut; after wood dragging with one pass of the skidder; after wood dragging with three passes of the skidder and after removing the wood from storing place (piles). Undisturbed soil samples were taken from layers of 0.00-0.05; 0.05-0.10; 0.10-0.20; 0.20-0.30 and 0.30-0.40m to determine bulk density, microporosity, macroporosity, total porosity, gravimetric soil moisture and saturated hydraulic conductivity. Soil resistance to penetration was evaluated either. To evaluate compressive behavior of soil, undisturbed soil samples were taken from layers of 0.025-0.05m and 0.10-0.125m to determine the bulk density before and after the uniaxial compression test; soil deformation after the test; gravimetric moisture and degree of saturation of soil before the test. The precompression stress and compression index were obtained from compression curves. The soil bulk density of the typic Hapludalf presented biggest reduction after three passes of the skidder, due the superposition of the tractor passes and its pressure during wood dragging. The soil resistance to penetration had the biggest values, indicating the biggest degradation due to the forest harvest. After three steps of the skidder the compaction took place with bigger intensity in the soil surface and that had a uniform distribution in the layers of the soil profile. Before the harvest, after the forest cut, after one step of the skidder and after the wood retreat from shipyard the compaction took place more in the vertical direction. Considering the larger deformations and compression index, the soil should be trafficked with degree of saturation of 65 to 69% to avoid larger deformations and reduce susceptibility of soil to compaction. In the abrupt Hapludalf the soil compaction was smaller. Such a fact was indicated by smaller soil resistance to the mechanical penetration, which indicates a less degree of compaction. The soil saturated hydraulic conductivity was the parameter that better expressed the compaction of the Alfisols.