The substitution of the native vegetation of marshlands in Paraiba, initially by sugarcane and more recently by pastures, in a strongly undulated relief, has caused serious problems of soil degradation. Currently, some of these pastures are being replaced by plantations of sabiá (Mimosa caesalpiniaefolia Benth). The objective was to analyze the effect of these changes on the soil physical and chemical properties and root development. The experiment was conducted in Areia-PB, in a dystrophic Ultisol. The three treatments were represented by three land uses:secondary native forest, sabiá plantation, and brachiaria pasture grass (Brachiaria decumbens). Soil samples were collected from three slope positions: top, middle, and bottom. For physical properties and root studies, in each position soil was collected at three different points and in four depths (0.0-2.5, 2.5-5.0, 5.0-10.0, and 10.0-20.0 cm). Composite samples were made to assess the chemical properties and clay content. The experiment was conducted in a completely randomized design with repeated measures in space. The results showed better aggregation, density, and porosity in the area of native secondary forest. The replacement of pasture by sabiá lead to a decrease in the aggregation but did not affect bulk density or soil's total porosity. Nutrient levels were higher in the sabiá area, although statistically different just for K and saturation of exchangeable bases. Changes in land use invariably degrade soil physical and chemical properties, but when a less aggressive system is introduced, changes are hardly detectable in the short term.
aggregation; carbon; nativeforest; Mimosa caesalpiniaefolia; pasture
