Uso e degradação do solo em áreas sob diferentes sistemas de manejo, município de Reserva - PR

Abstract

This study aims to evaluate the use and degradation of soils under differente management system with emphasis on soils under black beans (Phaseolus vulgaris L.) in the watershed of the Palmeirinha stream, in Reserva city, Paraná state. Five areas were chosen to pair this study, being three areas cultivated with beans, one with grassland, and one with the forest. Was collected 12 undisturbed soil samples at each depth (0-5, 5-15, 15-30 cm), totaling 36 samples per area measurement of physical parameters (density, porosity, aggregate stability), we used a tension infiltrometer for measurement of infiltration and hydraulic conductivity and impact penetrometer for evaluating penetration resistance. Three samples were collected in each area and depth for analysis of macro-nutrients, organic matter and soil pH. After collecting the samples were cataloged and sent to an accredited laboratory for analysis. Soil density showed no critical values in any of the areas studied, the total porosity was close to the ideal values considered in the literature ranging from 40 to 60% for all areas and depths. The mechanical strength of the soil did not vary significantly between areas cultivated with beans and forest area, these areas showed higher values than those considered critical (2.0 Mpa) only in the layer of 15-30 cm. The pasture (Pt) area was the only present above the critical values in all layers evaluated. The aggregate stability indices were higher in areas bean 2 (F2), forest (Ft) and Pt demonstrating the influence of organic matter and roots of grasses in the formation and stabilization of aggregates. Infiltration and hydraulic conductivity at different voltages applied to the tension infiltrometer were the physical parameters that showed greater difference between the forms of management, demonstrating that the area bean 1 (F1) structure has degraded due to destruction of macropores, which are responsible for most of circulation of water and air into the soil. Generally it is observed that the area F2 to have suffered burns in a stage of time more recent than the other areas showed better chemical conditions, upper and/or similar to the forest area, with elevation of pH, organic matter , P, CTC and base saturation. The area F1 in comparison with other areas had lower chemical indicators, especially the pH, organic matter content and base saturation, which arrived in the present differences of about 50% in the values of the other areas cultivated with beans . Regeneration time (F2) was not sufficient to alter the physical parameters, but the mowing and burning of vegetation accelerated the release of soil nutrients contributing to the improvement of soil chemical conditions. The conclusion is thus that the shape of soil tillage has a greater effect on the chemical than the time (age) of handling, since the area bean 3 (F3) chemical conditions presented above the area F1 which is being managed for a period of 10 years, or 20 years difference in time between the two management areas. We also conclude that the watershed of the Palmeirinha stream land use for pasture has caused greater soil physical degradation compared with the areas cultivated with beans, which can compromise the environmental quality of the basin, since the pastures occupy more than 50% of its total area.