Silvio Crestana

X- and gamma -rays computerized minitomograph scanner for soil science

A computerized tomograph scanner system that uses X- and gamma -rays for applications in soil science is described. Use of the apparatus in measuring volumetric water content to an accuracy of +or-3% and soil bulk density to +or-2% (in grams per cubic centimeters) is discussed. The system features translation and rotation scanning modes, a 200-mm effective field of view, signal processing by pulse counting, and 1.0-mm spatial resolution. The systems advantages over classical methods are listed, principles of the tomographic method and physical considerations are presented, and the systems design is described. >

Resistência mecânica à penetração de um Planossolo submetido a diferentes sistemas de cultivo

O conhecimento das caracteristicas e propriedades dos solos de varzea do RS, utilizados atualmente com a cultura do arroz irrigado, torna-se essencial para a adocao de praticas que envolvam irrigacao, drenagem, correcao da acidez e da fertilidade, principalmente quando se deseja obter altos niveis de produtividade, com menor custo e com menores possibilidades de degradacao destes solos e do ambiente onde estao situados. Dentro deste panorama, avaliou-se a compactacao de um Planossolo cultivado sob diferentes sistemas de manejo, atraves da resistencia mecânica do solo a penetracao. Camadas compactadas foram identificadas, de forma mais acentuada, na profundidade intermediaria (0,10-0,20 m) nos sistemas com maior utilizacao da mecanizacao agricola (T2 - sistema de cultivo continuo de arroz e T3 - sistema de cultivo de arroz x rotacao de culturas). Observou-se que, em todos os sistemas, houve aumento dos valores de resistencia mecânica do solo a penetracao em relacao a testemunha (T6 - solo mantido sem cultivo), principalmente na camada intermediaria (0,10-0,20 m), quando o solo foi submetido ao sistema de cultivo continuo de arroz (T2). Os tratamentos T3 (sistema de cultivo de arroz x rotacao de culturas) e T5 (sucessao de culturas: soja (sistema convencional) x arroz (sistema de semeadura direta)) apresentaram os valores mais altos de resistencia a penetracao, provavelmente em decorrencia da baixa umidade e dos efeitos do cultivo e da utilizacao de maquinas responsaveis pela deformacao da estrutura do solo.

Electroanalytical Determination of the Herbicide Atrazine in Natural Waters

Abstract Differential pulse voltammetry at the static mercury drop electrode was used to establish an electroanalytical procedure for atrazine determinations in pure and natural waters. The cathodic peaks observed are attributed to the reduction of mono and di-protonated species and showed to be pH-dependent, with the maximum peak current values at pH 2.3. In pure water, the detection limit found was 5 μg/L at a scan rate of 2 mV/s and 11 μg/L at 10 mV/s. In natural waters the calculated detection limits at 10 mV/s were 13 μg/L and 16 μg/L for a clean dam and polluted creek waters and 38 μg/L for a typical tropical soil solution, respectively. The higher scan rate used for natural waters analysis allow to improve the detection limit by avoiding the competition of contaminants with the processes occurring at the mercury surface. Hydroxyatrazine, the main chemical and photo-degradation product of atrazine does not interfere in the determination method. The main advantage of this technique is to allow sample...

Using a computed tomography miniscanner for studying tillage induced soil compaction

Abstract Gamma-ray computed tomography (CT) is used to study thin compacted soil layers, such as millimeter thick “blades” that occur at plowing depth. The technique has the advantage, over the traditional gamma-ray attenuation techniques, of opening the possibility of measuring water contents and bulk-densities of odd-shaped samples. Being a 2-or 3-dimensional technique it is possible to detect small change of bulk-density and soil water content within the sample, even in thin layers of the order of millimeters. Results are reported for thin compacted layers in soil samples collected at the plowing depth from sugar-cane fields in Brazil, which clearly demonstrate the usefulness of this new method for compaction investigations and its quantitative evaluation.

ATTENUATION COEFFICIENTS AND TOMOGRAPHIC MEASUREMENTS FOR SOIL IN THE ENERGY RANGE 10-300 KEV

Abstract The relationship between soil parameters such as density, atomic number of the components and electron density, and mass attenuation and effective atomic number of the soil are presented. The theoretical and experimental attenuation coefficient values are compared, for Brazilian and Italian soils. The best conditions for tomographic imaging of soil, are also shown, and an example of soil tomography is given.

Thickness and size distribution of clay-sized soil particles measured through atomic force microscopy

Abstract Soil particle size distribution is a very important soil characteristic because it is related with many physical, chemical and biological processes occurring in soils. However, at the sub-micron range, where many important sorption and transformation processes occur, there are few techniques available for particle size characterization. Among the available methods are transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The classical TEM and SEM, however, are sometimes unable to clearly differentiate between agglomerates, particles and grains; and sample preparation is very difficult and tedious. To overcome these limitations, we have applied the atomic force microscopy (AFM) technique to analyze the particle size distribution of an oxisol from Sao Carlos site, in Brazil, at the sub-micron range. Thickness and diameter of soil particles deposited in freshly cleaved mica were measured for each individual particle, allowing to determine their particle size distribution. Assuming cylindrical shaped particles and a constant particle density of 2.7 g cm −3 , the mass-based soil particle distribution at the sub-micron range is obtainable.

Image processing in automated measurements of raindrop size and distribution

A rapid method for evaluating raindrop size and size distribution has been developed. It is based on image processing with correlation analysis in the frequency domain. This technique has the advantage of being a direct measurement method that automatically identifies and counts raindrops. Calibration was carried out using a standard image with known raindrop sizes. Drop sizes, ranging from less than 0.1 to over 85 mm in diameter, have been automatically recognized and successfully measured. Error was not larger than 1.5%. In addition, practical examples of use of the method for determining characteristics of raindrops in rainfall are presented.

MAGNETIC RESONANCE IMAGING AS A NON-INVASIVE TECHNIQUE FOR INVESTIGATING 3-D PREFERENTIAL FLOW OCCURRING WITHIN STRATIFIED SOIL SAMPLES

Abstract The soil fingering phenomenon was investigated using magnetic resonance imaging (MRI) as an appropriate technique. A cubic 15 × 15 × 15-cm 3 double-layer sand column was built in order to simulate the stratified soil. The column was imaged in a 500 Gauss NMR tomograph [IFQSC, USP, Sao Carlos (SP)]. After reaching the water steady-state flow several coronal, transverse and sagittal images of the column were obtained. For each case seven slices, 1.8 cm thick and separated by 2.0 cm center to center, were collected providing three-dimensional information regarding to the number of fingers, their sizes and diameters. To study the fingering dynamics employing MRI concepts, another kind of experiment was performed by following only the water front (no image reconstruction), using spin-echo signals with phase encoding along vertical axis (gravitational direction), but with phase encoding gradients switched off. Sixteen acquisitions of seven transverses of 2 cm thick slices, were performed in a 3-min experiment. After suitable treatment, the water front and the horizontal distribution at each measured time during the water infiltration process was obtained. Normalizing the signal intensities to the soil column dimensions and using computational graphic resources, made it possible to quantify the number of fingers and their spatial and temporal variability. The results elect MRI as a valuable tool for non-invasively investigating the dynamics of soil fingering phenomenon.

X-ray microtomography to characterize the physical properties of soil and particulate systems

Abstract Since many of the phenomena occurring in soil are related to grain and pore sizes and their distribution, investigation on a micrometric scale is of great importance. Also, the investigation should be non-invasive in order to avoid disturbing the region of interest of the sample. Many techniques from various areas of science have been adapted to make such investigations, but most of them are invasive or can only analyze global soil properties. Thus an X-ray tomograph was developed at Embrapa—Agricultural Instrumentation, to scan images of soil samples on a micrometric scale. A microtomographic image of a sieved soil sample, presenting aggregates from 212 μm to 250 μm and pores of 100 μm, is shown. Pores of the same size can also be seen in a microtomograph of a sand column, composed of two layers with granulometries of 106 μm to 149 μm and 297 μm to 500 μm. A microtomograph of a column composed of three layers of an orthoclasius powder is also presented. A slight variation in density along the column height can be observed.

Non-invasive instrumentation opportunities for characterizing soil porous systems

Abstract Soil is widely recognized as one of the most complex systems present in the universe. Its highly non-linear and heterogeneous nature as well as the interacted and coupled physical, chemical and biological processes and phenomena occurring in the soil environment at different spatial and temporal scales are the main reasons for such complexity. As a consequence there is a need of appropriate methodologies and instrumentation to characterize soil porous systems either in the loaboratory or in the field. Moreover, the scientists and engineers face a great challenge to non-invasively measure and follow the changes occurring in soil systems caused by the human activities. Nevertheless, despite the enormous gap still to be bridged to better understand and manage in a sustainable way the new opportunities of soil resources for its characterization are nowadays available and should be exploited in soil science research. Those new opportunities are essentially interdisciplinary and are coming from other areas of knowledge such as space science, medicine, engineering and basic sciences. This paper will present examples and results and will present challenges and potentialities of new methods and instrumentation already available at different scales of observation. Spectroscopy, microscopy and high resolution imaging techniques including X- and gamma-ray and NMR tomography, atomic force microscopy and other recent tools will be shown. The characterization of macropores and preferential water flow infiltration in two and three dimensions were performed through the employment of commercial and dedicated scanners without disturbing the soil samples. The use of fractal geometry and a modified invasion percolation theory model were also employed to describe the “fingering” phenomena.