Computer-assisted tomography for studies of an Albaqualf

Abstract

In order to find better techniques to evaluate the soil physical parameters applied to lowland soils, the computerized tomography has been used to measure soil density and water content with accuracy and high spatial resolution. This work was carried out in order to describe features and calibration procedures of a computerized minitomographer using X-ray and gama-rays as sources of radiation and to establish suitable statistical parameters on the study of soil bulk density and water content in a Planosol (Albaqualf) from Rio Grande do Sul State, Brazil. The minitomographer calibration was obtained from the linear regression equation among the tomography's unities (TU) presented by the image reconstruction program and the linear attenuation coefficient (m_l, cm^-1), by the measurement of direct transmission of g-rays as source of radiation in soil samples from A and B horizons, distilled water, benzin and aluminum. In order to get measures of the direct radiation transmission, containers with distilled water, benzin, soil and aluminum were used to obtain the following equations to calculate soil bulk density in the A horizon: D_s = [(TU/986.16)-(0.200xq)]/0.267 and in the B horizon: D_s = [(TU/986.16)-(0.200xq)]/0.297, where TU is the mean value in the line and q is the soil volumetric water content (m³ m^-3). The obtained configurations allowed to attain average variabilities of 2.74% and 0.73% for homogeneity and repeatability, respectively. The expected errors related to the equipment are 0.051 and 0.046 Mg m^-3, to the A and B horizons, respectively. The results showed the technique accuracy and adaptability in the studies of the physical characteristics of a Planosol.