Applying 3-D X-Ray Computed Tomography for Evaluation of Soil Porosity in Tropical Ecosystems.

The X-ray computed tomography (CT) is a technique used for analysis of the factors belonging to soil properties and applications in agriculture. The technique provides cross sections images of soil. However, the soil is described as three-dimensional system, comprised of pores ranging in size and shape and are interconnected. To represent this three dimensional structure is required, evaluating a model reconstruction volume of the soil porous system. This study aims to evaluate a model for volumetric reconstruction (3-D) in soil porosity under different soil management systems. Undisturbed soil samples were collected from a Eutrophic Red Oxisol at soil layer (0.0-0.10 m), using cylinders (volumetric ring method). After the collection of undisturbed soil samples, they were brought to the Laboratory of Nuclear Techniques at the Embrapa Instrumentation in São Carlos, SP, Brazil. The acquisition of tomographic projections were obtained with a CT scanner manufactured by the SkyScan®, model 1172. This CT scanner is comprised by an X-ray tube (micro focus), power supply (100kV), a sampler holder with a precision handle system, and a detector based on a CCD camera 10MP (4000 x 2300 pixel). The acquisition of tomographic projections, tomographic control system and algorithm for reconstruction of the images are synchronized and executed based on the use of a Desktop computer. The tomographic analysis allowed to identify, quantify and differentiate the areas under tillage, under conventional tillage and under forest, with a non-evasively and non-destructive method. As a part of the validation procedure, the higher porosity was observed under forest area, indicating the effect and influence for preservation on soil structure.