Identificação e caracterização do comportamento físico de solos coesos no Estado do Ceará.

Abstract

The hardsetting soils may be found for almost the whole Brazilian coastal area of the Coastal Tablelands. They are characterized by presenting an accentuated increment in their mechanical resistance, which causes restrictions in the soil preparation and in the plants growth. These happen due to hardsetting soils become hard to extremely hard when dry, and crumbly when humid. Ceara is one of the northeast States that possess an extensive coastal area of Coastal Tablelands, with more than 10.000 km2 of hardsetting soils. Taking this into account, it was hypothesized that hardsetting soils of Ceara State had the same physical and chemical restrictions identified in hardsetting soils in other of Coastal Tablelands. The general objective of this thesis was to identify the occurrence of hardsetting soils in the Ceara State as well as to evaluate their behavior by using the morphological, physical, and micromorphological attributes, and image analysis. To accomplish the general objective three specific objectives were established. Each specific objective led to the accomplishment of one research, and is presented as a chapter of this thesis. In the first research was identified and characterized the occurrence of hardsetting soils in Ceara by using morphologic, chemical and physical attributes. In the second research, it was studied the behavior of a hardsetting Gray Argisol by using soil physical attributes, specifically: tensile strength (RT), soil resistance to penetration (RP), soil bulk density (Ds), and pore size distribution (PT). In the last research, the soil micromorphological features were studied, giving emphasis to the distribution, size and orientation of the pores in the more denser and less denser areas of the hardsetting horizon, by using image analysis. The results of the first research showed that the hardsetting horizons found in Ceara are similar to the hardsetting horizons found in other Brazilian States. The results regarding the second research indicated that the RT, RP and Ds values were higher in the hardsetting soil of Ceara than those measured in other hardsetting soils of the Coastal Tablelands. In the third research was observed that the existent natural compaction in the hardsetting horizons of Ceara influences the amount of pores as well as their shape and orientation, and that the denser areas, measured by image analysis, were the main factor that influenced the soil porosity, being responsible for the increase in the soil mechanical resistance.