Carlos Manoel Pedro Vaz

Contribution of water content and bulk density to field soil penetration resistance as measured by a combined cone penetrometer–TDR probe

Abstract Soil strength as measured by cone penetrometers depends on several parameters, but it is mostly affected by the soil water content ( θ ) and bulk density ( ρ ). In order to better understand the effect of the water content and bulk density on soil strength we developed a combined penetrometer–coiled TDR probe to determine simultaneously the depth distribution of penetration resistance and water content in a soil profile. Field experiments carried out for a Yolo soil allowed the fitting of the effect of θ and ρ using a combined power–exponential equation. Using the combined cone penetrometer–TDR probe data, the fitted equation may be used to estimate soil bulk density.

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.

Soil particle size fractions determined by gamma-ray attenuation

Soil texture-or the particle size fractions of sand, silt and clay-is an important characteristic of soils and is used for their characterization and classification. Textural analysis also helps agronomists and farmers in the recommendation of herbicide and fertilizer applications. Soil particle siz

Electroanalytical procedure for the determination of methylparathion in soil suspensions and its application for sorption studies with Brazilian soils

The differential pulse polarography technique was used to establish an electroanalytical procedure for the determination of the organophosphorous insecticide methyl parathion (O,O-dimethyl O-(4-nitrophenyl) phosphorothioate) in soil samples. Three reduction peaks were observed in mercury electrodes as a function of the solution pH. The more cathodic peak (Ep= -0.55V), only observed for pH values higher than 5.0, was chosen for the analytical determinations. The limit of detection was 1.93x10-8 mol L-1 for pure water and about 8x10-8 mol L-1 for soil suspensions with a scan rate of 2 mV s-1 and a pH of 6.75. The electroanalytical procedure developed was applied for the determination of sorption isotherms of methylparathion on 3 soils from Sao Paulo State, Brazil, at different pH and diverse amounts of clay and organic matter. The experimental data were fitted using the Freundlich isotherm model and the Freundlich coefficients (KF) obtained for each soil varied from 7 to 29 L kg-1, representing a low to medium sorption capacity, according to the IBAMA (Brazilian Environmental Protection Agency) standards. The amounts of organic matter and clay were the most important soil parameters controling the sorption of methylparathion by these soils.

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.

Automated soil particle size analyzer based on gamma-ray attenuation

Abstract Application of gamma-ray attenuation principles permits the determination of density and water content of a material. Moreover, this technique also allows one to determine particle size distribution, when particles are falling in a liquid medium according to Stokes’ law. Based on these principles, computerized equipment was developed to perform a fully automatic analysis of soil particle size distribution. This equipments main advantage is the capability to analyze ten soil samples automatically, each one in 18 min, the resulting output is a complete curve of soil particle size distribution, ranging from 2 μm to 2 mm. Another feature of this equipment is its fast soil granulometric fraction analysis (at ten samples per h), which determines the fractions of clay, silt, and sand. Results obtained with the gamma-ray technique showed an excellent correlation with the pipette method.

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.

Planosol soil sample size for computerized tomography measurement of physical parameters

Computerized tomography (CT) is an important tool in Soil Science for noninvasive measurement of density and water content of soil samples. This work aims to describe the aspects of sample size adequacy for Planosol (Albaqualf) and to evaluate procedures for statistical analysis, using a CT scanner with a 241Am source. Density errors attributed to the equipment are 0.051 and 0.046 Mg m-3 for horizons A and B, respectively. The theoretical value for sample thickness for the Planosol, using this equipment, is 4.0 cm for the horizons A and B. The ideal thickness of samples is approximately 6.0 cm, being smaller for samples of the horizon B in relation to A. Alternatives for the improvement of the efficiency analysis and the reliability of the results obtained by CT are also discussed, and indicate good precision and adaptability of the application of this technology in Planosol (Albaqualf) studies.