Caracterização de uma topossequência sob cultivo de bananeira e videira na transição Mata-Agreste de Pernambuco

Abstract

Considering the importance of the relief on soil formation and differences between agricultural practices, this work has the objective of making a morphological, physical, chemical and mineralogical characterization and evaluating heavy metals contents on a toposequence of soils cultivated with banana, and in soils cultivated with grape and banana, and also under native vegetation. The study took place in the county of São Vicente Férrer, State of Pernambuco, Brazil, where high slopes represents the relief pattern. On this study we had two approaches, first were selected three soil profiles on a mountain-side cultivated with banana, and three more profiles, located each one in a different plantation system (grape and banana) and in an area under native vegetation (forest), on a similar topographic situation. In all areas the soil profiles were described morphologically and classified according to the Brazilian Soil Classification System. Samples were collected for each horizon, in triplicates, in each profile. On the comparison between the cultivated areas (grape, banana and forest), besides the samples of the profile, were collected random samples. For each plantation situation were collected three composed samples, each one obtained from twenty simple samples, in two depths (0-16 and 16-45 cm). The physical properties evaluated were grain size, clay dispersed in water, bulk density and particle density, macro, micro and total porosity, aggregate stability and specific surface. On the chemical characterization, were analyzed pH in water and KCl, cation exchange capacity, exchangeable cations, organic carbon, available phosphorus; total and available levels of cationic metallic micronutrients (Zn, Cu, Fe, Mn and Ni) and the toxic elements Cd and Pb. The mineralogy was analyzed by x-ray difratometry. The results were evaluated by variance analysis, T test and multivariate analysis with significance levels higher than 95%. The results obtained permitted conclude that, on the toposequence, the differences in soil classification were caused by crop managing and topographic position. A nitossolic Distrofic Red-Yellow Argisol(according to Brazilian Soil Classification System) was found on the top level, and then was formed a tipic Distrofic Red-Yellow Argisol on the upper slope, due to the high degree of the slope and differential erosion between A and B horizon, and then a nitossolic Eutrofic Red-Yellow Argisol was found on the down slope position, as a result of nutrient accumulation from the upper levels. The areas cultivated with banana and grape had been submitted to a high erosion process. Despite the soils were well structured and had good root development, the cultivated sites presented a decrease in physical attributes quality (bulk density, macro and microporosity, aggregate stability) on the surface layers. On the cultivated areas the principal chemical change was observed on the high pH level, as a result of liming, and on phosphorus accumulation. The metals studied along the toposequence presented such a movement down slope, specially the Mn, which appears in high level in all horizons of the down slope profile. The contents of Pb, Ni and Cd along the toposequence indicates site contamination, especially for Cd, along all the slope, with exception of the top level position, on the Ap horizon, although they don’t present high available levels. The cultivated areas presented high accumulation of Cu, Zn, Mn and Ni, and a little accumulation of Pb, but also with low available levels of these elements. The groups formed by Cluster analysis confirmed the forest site as being the original environment of the cultivated sites, when evaluated by soil physical and chemical characteristics.