The effect of wetting and drying cycles on soil chemical composition and their impact on bulk density evaluation: An analysis by using XCOM data and gamma-ray computed tomography (original) (raw)
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Soil bulk density evaluation by conventional and nuclear methods
Australian Journal of Soil Research, 2005
Among the methods used to measure soil bulk density, the following have been prominent: paraffin sealed clod (PS), volumetric ring (VR), and the modern methods like gamma ray computed tomography (GCT) and the neutron/gamma surface gauge (SG). The objective of this work was to compare soil bulk density values obtained through these methods, with the aim of assisting researchers on the choice of the more appropriate method. For this, a 200 m spatial transect was chosen in an experimental area cultivated with coffee belonging to ESALQ/USP, Piracicaba, SP, Brazil. The SG readings were first taken in the field and thereafter soil samples were collected at 8 different points, spaced at 25 m, for the other methods. The lowest values of soil bulk density were obtained for the SG method (average 1.468 g/cm 3 ) and the highest for the PS (average 1.685 g/cm 3 ), which was similar to the GCT method (average 1.684 g/cm 3 ).
The physical characteristics of the soil surface are of extreme importance in relation to energy and matter transfer processes between the atmosphere and the soil. Soil internal structure changes can be due to natural or artificial causes and one important natural process is the alternation of wetting and drying (W-D) processes, which induce swelling and shrinking of soil particles, causing modifications in pore size and shape. To study the consequence of these W-D events on possible modifications in pore size distribution, pore number, and pore shape of soil samples collected in metal rings pore image analysis was used. Samples were taken from profiles of three soils of different characteristics, named as Geric Ferralsol (GF), Eutric Nitosol (EN), and Rhodic Ferralsol (RF). Confined volumetric samples (50 cm 3 ) were submitted to none (T 0 ), three (T 1 ), and nine (T 2 ) subsequent W-D cycles. Image cross sections of resin impregnated soil permitted the micrometric and macrometric characterization of changes in soil structure induced by sequences of W-D cycles. Duncan's statistical test indicated that there were significant differences (α = 0.05) among treatments for all soil samples. General conclusions indicate that total pore area increased for all soils after repeated W-D processes, specifically 19.0 to 28.9% for GF, 5.9 to 11.7% for EN, and 13.0 to 17.2% for RF. Main changes of pore diameter occurred in pores larger than 500 μm, and minor changes were observed in the total number of these pores. It is demonstrated that soil samples undergo important changes in their structures after repeated W-D cycles. The information presented here is very important for the evaluation of soil water retention curves and other soil hydric properties, because soil samples used in these procedures are collected in rings and frequently submitted to several W-D cycles.
Mass attenuation coefficients of brazilian soils in the range 10–1450 keV
Applied Radiation and Isotopes, 1994
The mass attenuation coefficients of the LRd-A, Brazilian soil has been measured at seven energies in the range of 59.5-1408.0 keV. Radioactive isotopes were used as sources of monoenergetic y radiation in a narrow-beam collimated geometry. Experimental errors were in the range from 0.4 to 3. I %. Also mass attenuation coefficients of six Brazilian soils have been calculated in the energy range from 10 keV to 10 GeV to study the influence of chemical composition.
Gamma ray computed tomography to evaluate wetting/drying soil structure changes
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2005
Wetting and drying (W-D) cycles can cause strong modifications of the structure of a soil, especially in pore distribution, which reflects the temporal and spatial distribution of soil water and, consequently, these processes can affect soil water and nutrient retention and movement. These alterations have important practical consequences when calculating soil water storages and matric potentials, widely used in irrigation management. The present paper has as objective to use gamma ray computed tomography (GCT) as a tool to investigate possible modifications in soil structure induced by W-D cycles and to analyze how these alterations can affect soil water retention. The GCT scanner used was a first generation system with a fixed sourcedetector arrangement, with a radioactive gamma ray source of 241 Am. Soil samples were taken from profiles of three different soils characterized as Xanthic Ferralsol (Fx), Eutric Nitosol (Ne) and Rhodic Ferralsol (Fr). Eighteen samples (50 cm 3 ), six from each soil, were submitted to none (T 0 ), three (T 1 ), and nine (T 2 ) wetting/drying cycles. Based on image analysis it was possible to detect modifications in soil structure in all samples after wetting/drying cycles for all treatments. Tomographic unit profiles of the samples permitted to identify an increase on soil porosity with the increase in the number of wetting/drying cycles and it was also possible to quantify the average porosity values.
2010
west Indies' Clay and organic matter both have cementing and binding abilities that play crucial roles in the formation and stability of soil aggregates. The interactions of clay and organic matter on the extent of differential swelling anri the volume of entrapped air in soil aggregates during fast wettingloth in the p-resence and in the absence of rainfall were investigated. The influence of clay mineralory was also examined. Th-e parameters assessed in the study were watei-stable aggregates (WSA), final infiltration rate (FIR), runoff(Q)r and soil loss (E). Samples frbm the surface (G-10 cm) of six agricultural soils in Trinidad with three levels of ^clay (low,' 40oh; hedium, 2F45o/o; and high, >45'/o) and two of organic matter (loq SS% and high'_>37o) were used. Generally, aggregate stability and infiltration rate increased while seal formation, runoff, and soil loss decreased witn increasing clay content. The high clay, high organic matter sample dominated-by high activity clay yielded the highest WSA (63.3%) and ihe smallest E (0.99 kg_T-.'): whilst Lhe _lowgl_ayt l.oY organic maiter Jainple dominated by tow activity clay minerals had the lowest WSAvalue (5.37o). The higl calion exchange capacity (20.2 cmot kgt) of Oropuna, a high clay, low organic matter-content soil, classified as kaolinitic, Indic:ates ihe presence bf appreciable quantities of smectites. Thereforg, the significantly lower WSA (56.5%) and FIR (3.2 mm hrland higher Q (f00.6 mm) and E (5.59 fS mr) of Oropuna over Montserrat (WSl = 61.5%o; FIR = 109.9 mm hrl Q = 6.3 mm; and E = 3.06 kg m-) and Godineal (yS4-= 68.8"/r; FIR = 60.7 mm h-r; Q = 41.3 mml and E = 0.99 kg mt) medium and high clay smectitic soils high in organic matter demonstrates the importance of organic matter in alleviating clay dispersion and stakilS 1! soils predominated by high activity expanding clays. The results also demonstrate that there is a threshold chy iontent above which the support of organic matter is required to weaken disruptive forces and below which organic matter and slow wetting are not effective in diminishing disruptive forces.
Relationship between particle density and soil bulk chemical composition
Journal of Soils and Sediments, 2015
Purpose An analytical database containing XRF chemical analyses and real density measurements of unconsolidated sediments of the Padania Plain (Northern Italy) has been used to understand the relationship that exists between the soil particle density (ρ s) and their bulk chemical composition. Materials and methods Using a linear regression, we built an equation able to link the particle density with the soil elemental composition. Results and discussion Positive correlations were found between ρ s and SiO 2 , MgO, CaO and Na 2 O and negative correlations with K 2 O, TiO 2 , Al 2 O 3 , Fe 2 O 3 and LOI, reflecting the presence in the soils of quartz and feldspars/mineral clays respectively. Conclusions Our equation is very useful because it helps to know the density properties of a soil when it is not possible to measure ρ s with a pycnometer. On the other hand, by knowing the ρ s , it is possible to have a quite precise knowledge about the chemistry of the studied soils.
2014
Correlation between grain size and activity concentrations of soils and concentrations of various radionuclides in surface and subsurface soils has been measured for samples taken in the State of Qatar by gamma-spectroscopy using a high purity germanium detector. From the obtained gamma-ray spectra, the activity concentrations of the 238U (226Ra) and 232Th (228Ac) natural decay series, the long-lived naturally occurring radionuclide 40K and the fission product radionuclide 137Cs have been determined. Gamma dose rate, radium equivalent, radiation hazard index and annual effective dose rates have also been estimated from these data. In order to observe the effect of grain size on the radioactivity of soil, three grain sizes were used i.e., smaller than 0.5 mm; smaller than 1 mm and greater than 0.5 mm; and smaller than 2 mm and greater than 1 mm. The weighted activity concentrations of the 238U series nuclides in 0.5-2 mm grain size of sample numbers was found to vary from 2.5±0.2 to ...
Adjustment of the expedite method for clay content determination in Rondônia soils
Ciência Rural, 2011
Soil clay content is an important soil attribute and has been used to classification of phosphorus status in the soil in order to determinate the needing of phosphorus amounts to be applied to crops production. The aim of this research was to adjust the method for soil clay content determination, adopted by the laboratories of Southern Brazil (ROLAS-RS/SC), for soil clay content evaluation in Rondônia soils. The study was conducted using 50 soil samples from Rondônia State with wide range clay content. It was tested shaking periods (1.5, 2.0 and 2.5h) associated with periods for soil particles decantation (1.5 and 2.0h) to correlate with the standard method for soil texture testing, known as the pipette method. Clay content determined through this method was significantly correlated with pipette method. The better treatment was the combination of 2.0h of shaking and 1.5h of decantation, resulted in total period of 3.5h, which reduced the period to determine the soil clay content wit...