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The state of Rondônia has several soil classes, many of which have been subjected to conversion from forest to pasture by the use of fire, causing irreversible damage. Thus, studies are needed to assess changes in soil attributes, as a way to provide information that minimizes the impacts generated. Thus, the objective was to characterize, classify and evaluate the fragility of soils when used as pastures in a toposequence in the district of União Bandeirantes, Porto Velho, Rondônia, Brazil. In the field, a toposequence was selected, where the profiles corresponding to each environment were selected based on the relief position, vegetation patterns (forest and pasture), pedological characteristics and parent material. In each environment, trenches were opened, which were morphologically characterized and samples were collected for physical-chemical analysis of the soil in the laboratory. The soils were classified according to the criteria established by the Brazilian Soil Classification System and by the World Reference Base for Soil Resources. Additionally, multivariate statistics were performed. In profiles P1 to P5, a monochromatic pattern was observed between the horizons. Soil profiles showed textural classes ranging from clayey loam to very clayey. Along the toposequence, two orders of soils, Latossolos and Plintossolos, were observed, which showed differences in the lower categorical levels. In the superficial horizons, modifications were observed in the attributes of granulometry, soil density, exchangeable bases and acidity components. By the multivariate analysis for the diagnostic horizons, three distinct groups were formed: Latossolos Amarelos, Plintossolos Pétricos and Latossolos Vermelhos. [ABSTRACT FROM AUTHOR]

In the Amazon, the change in land use, with the withdrawal of native vegetation and the implantation of agricultural crops, has caused numerous changes in the chemical properties of the soil, in addition to changing the processes that control the sustainability of its ecosystems. We aim to verify the impacts caused to soil chemical attributes as a function of the conversion of forests to cultivated area with Amazonian species in the municipality of Canutama, southern region of Amazonas. Meshes were established according to the size of the crop and, in each area, samples with a preserved structure were collected at the crossing points of the meshes, at depths of 0.00-0.05; 0.05-0.10; and 0.10-0.20 m, with 80 sampling points in each area, generating 240 samples per area and totalizing 960 samples for determination of chemical attributes and organic carbon. The multivariate analysis of soil chemical attributes is adequate to identify the nutrients that present the greatest alteration after the forest/agriculture conversion process. There were more changes in the chemical attributes in the superficial layers (0.00-0.05 and 0.05-0.10 m), which demonstrates the importance of above-ground biomass in nutrient cycling. [ABSTRACT FROM AUTHOR]

In Brazil, there are still relatively few studies involving soil erodibility, especially in areas that have undergone native forest conversion processes in agricultural areas. The objective of the present work was evaluate the impacts of native forest conversion on soil erodibility under conversion of native forest in areas of cultivation with guarana, annatto and cupuaçu in Amazonas state. Meshes were established according to the size of the crop, followed by sampling at the crossing points, at a depth of 0.00-0.20 m, with 80 sample points in each area. At each sampling point, were collected sample with a structure preserved for determination of soil texture and organic carbon, for a total of 320 samples in the four evaluated areas. The estimation of erodibility stands out as an important tool in the adoption of soil management and conservation practices, anticipating possible impacts before a crop is implanted. The areas cultivated with guarana and annatto presented greater predisposition of the soil to rill erosion and interrill. The areas of cupuaçu and forest presented high silt values, that may enhance/contribute to erodibility. In contrast, they showed high values of critical shear strength, which indicates resistance. [ABSTRACT FROM AUTHOR]