Alterações físicas e químicas de um cambissolo húmico em povoamentos de Pinus taeda L. com diferentes rotações

Abstract

Starting from the assumption that changes in land use can provide changes in physical and chemical properties, influencing its quality, the study aimed to verify whether the introduction of Pinus taeda L., on soil under native grassland conditions, can degrade physical and chemical quality of Haplumbrept soil in different rotations. The study was conducted in the region of Campos de Cima da Serra - RS, Brazil, where there are large forested areas with pine trees. To this, were selected two study areas, one in the first (RT1) and another in the second rotation (RT2), with 13 years of age. For each stand, was assessed a combined area of grassland adjacent (control). In each area, five trenches were opened and collected soil samples at depths from 0.0 to 0.05, from 0.05 to 0.20, 0.20 to 0.40 and 0.40-0.60 m. Changes in physical properties were analyzed using the following parameters: particle size, particle density, bulk density, porosity, macro and micro porosity, hydraulic conductivity of saturated soil, soil air permeability and size distribution of water stable aggregates. The chemical determinations were: calcium, magnesium, phosphorus, potassium, pH, pHSMP, exchangeable aluminum, total nitrogen and total organic carbon. At RT1 was a change in the macro and microporosity, influencing the behavior of hydraulic conductivity and air permeability at 6 and 10 kPa. At RT2, the effect of pine in the macro, microporosity and hence hydraulic conductivity, occurred only in the surface layer (0.0 to 0.05 m) due to the management adopted in the area. Considering the two study areas, there was a reduction of the aggregate stability in the layer from 0.05 to 0.20 m. However, in the same layer, the RT2 presented an increase in stability of aggregates of smaller size classes, reflecting the management type. The chemical properties were altered mainly in the surface layers, with reductions of exchangeable bases (Ca and Mg) and elevation of P saturation. The pine has also promoted increased levels of Al and decrease in pH, increasing soil acidity and reducing thereby the quality of Haplumbrept soil. In RT1, the content of C and N were reduced in the surface layer, but in RT2, levels of C and N were similar to natural field, inferring in the long run, the ability to restore the levels of C in soil.