Influência do manejo nos atributos do solo em áreas sob conversão floresta/pastagens numa topossequência em Rondônia, Brasil

Abstract

Rondônia has one of the largest cattle herds in Brazil, however most of the pastures are in some stage of soil degradation, thus reducing the carrying capacity and consequently the stocking rate. The objective of this research was to evaluate the influence of management on soil attributes in areas under forest / pasture conversion in a toposequence in Porto Velho, Rondônia, Brazil. In the field, areas with forest, brachiaria and mombaça were selected, in the areas with pastures 90 m x 60 m meshes were delimited and in the forest area 90 m x 50 m mesh, with regular spacing of 10 m between the sampling points. Samples were collected at the crossing points of the meshes, at the depths of 0.00-0.10 and 0.10-0.20 m, making a total of 70 sample points in each area with pasture and 60 sample points in the forest area. To obtain soil samples, soil samples with preserved structure in the form of clods and volumetric rings were collected in each area. These samples were used to determine the chemical and physical properties of the soil. In addition, a toposequence representative of the environments was selected in situ, where trenches were opened for soil characterization and classification. After determining the soil attributes, the data were submitted to univariate, bivariate and multivariate analyzes, and comparisons of the means of the variables within each environment were analyzed by the Tukey test at 5% probability. To complement the work, geostatistical analysis was performed, which will be used to identify the distribution and spatial pattern of the studied variables and the factors of the multivariate analysis. As a result, two soil orders were observed along the toposequence, being Latossolos and Plintossolos. The Latossolos are related to the flat, well-drained environments while the Plintossolos are related to the more undulating, moderately drained environments close to the rivers. The conversion of forest to pasture using fire is more sensitive close to the soil surface. It provides an increase in pH values and exchangeable bases, reducing the levels of exchangeable aluminum and potential acidity, however, it induces losses of phosphorus and organic carbon in the soil. The conversion of forest to pasture, had a negative impact on aggregates, compaction, porosity and accumulation of organic carbon in the soil. Among the pastures, the area cultivated with mombaça, did not degrade so much in relation to the physical attributes, approaching the forest environment.