Modeling of soil water retention based on 3D micro-tomographic image analysis

858-863This paper proposes the use of an algorithm based on the mercury intrusion porosimetry (MIP) method to obtain the water retention characteristic curve (pF curve) of a soil under different treatments. 3D X-ray micro-tomographic images were used to quantify pore size distribution, which was employed for the evaluation of the water retention in different matric potentials. The results showed very good agreement between the traditional method (obtained by suction tables) and that one based on the MIP algorithm. It means that the use of simulation procedures can be an interesting alternative for the measurement of soil water retention properties

A Comparison of the Differences in Soil Structure under Long-Term Conservation Agriculture Relative to a Secondary Forest

Conservation agriculture is increasingly preferred to conventional methods due to its benefits in promoting more sustainable soil management. Our study aims to compare physical and morphological properties, at the microscale, of soils under long-term no tillage (NT) and minimum-tillage (MT) to adjacent ‘natural’ soils under long-term secondary forest (SF). Soil aggregates of c. 2 cm length were imaged by X-ray Computed Tomography (XCT). The three-dimensional (3D) images were segmented and analyzed in order to assess properties such as porosity, number of pores, degree of anisotropy, pore shape, volume classifications, Euler number for pore connectivity, and pore tortuosity. The pore architecture of soils under NT and MT, for c. 40 years, was similar to that from the SF in terms of imaged porosity, pore size, and shape distributions, as hypothesized in our study. However, we observed some important differences; for instance, SF had larger, more connected, and more complex pores, likely due to the greater biological activity. In addition, SF had more isotropic pores than NT and MT, i.e., without preferential flow paths for water redistribution. Therefore, we concluded that long-term conservation agriculture was efficient at reversing structural damage typically associated with conventional, intensive agriculture, but some large differences remain, particularly concerning the pore network complexity and connectivity

Computer-assisted tomography for studies of an Albaqualf

Na busca de técnicas mais apuradas para a determinação e avaliação de parâmetros físicos do solo com aplicabilidade em várzeas, vem se destacando a tomografia computadorizada, por medir a densidade e a umidade com boa sensibilidade e alta resolução espacial. O presente trabalho teve como objetivo descrever aspectos e procedimentos da calibração de um minitomógrafo de raios-X e gama para estudo da densidade e umidade de um Planossolo no Rio Grande do Sul, bem como estabelecer parâmetros estatísticos para sua adequada utilização. A calibração do minitomógrafo foi obtida pela regressão linear entre as unidades tomográficas (UT), apresentadas pelo programa de reconstrução de imagem, e os coeficientes de atenuação linear (µl, cm-1), medidos por transmissão direta de raios gama, em amostras dos horizontes A e B do Planossolo, água destilada, benzina e alumínio. Para as medidas de transmissão direta de radiação utilizaram-se recipientes com água destilada, benzina, solo e Al, obtendo-se as seguintes fórmulas para o cálculo da densidade do solo no horizonte A: Ds = [(UT/986,16)-(0,200xq)]/0,267; e no horizonte B: Ds = [(UT/986,16)-(0,200xq)]/0,297, em que UT é o valor médio de UT em cada linha e q é a umidade volumétrica da amostra de solo, em m3 m-3. Com as configurações obtidas, verificou-se variabilidade média de 2,74% e 0,73%, respectivamente, em termos de homogeneidade e repetibilidade. Os erros atribuídos ao equipamento são de 0,051 e 0,046 Mg m-3, respectivamente, nos horizontes A e B, revelando precisão e adaptabilidade no emprego da técnica em estudos do Planossolo._________________________________________________________________________________ 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 (µl, 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: Ds = [(TU/986.16)-(0.200xq)]/0.267 and in the B horizon: Ds = [(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

Nuclear Laboratory Setup for Measuring the Soil Water Content in Engineering Physics Teaching Laboratories

Soil water content (θ) is a crucial soil parameter that is determined in many studies involving engineering, geology, and soil and environmental sciences. For instance, evaluating the soil strength, groundwater recharge, hydraulic conductivity, and soil aeration status depends on θ. The measurement of θ is fundamental for monitoring and controlling several soil processes. The gamma-ray attenuation (GRA) technique is a fast and non-destructive way of evaluating θ in soils with very contrasting compositions. Although, GRA is rarely explored in lab physics classes. The proposal of an experiment using a teaching GRA apparatus for measuring θ is presented. The experimental setup consisted of a 137Cs radioactive source, a Geiger-Müller detector, and a radiation counter. Soil samples with four distinct granulometric compositions were analyzed. Strong linear correlations were found between the transmitted gamma-ray photon intensity and θ (correlation coefficients varying from −0.95 to −0.98). The soil porosity, measured by the conventional and GRA methods, presented differences that varied from c. 7.8% to c. 18.2%. In addition, strong linear relationships (correlation coefficients from 0.90 to 0.98) were observed between the GRA and the traditional (gravimetric) method of θ measurement. It was verified that the teaching GRA apparatus is useful for measuring θ. In addition, the apparatus allows the introduction of some important aspects related to the study of modern physics for undergraduate students of many fields of knowledge

Soil Pore Network Complexity Changes Induced by Wetting and Drying Cycles—A Study Using X-ray Microtomography and 3D Multifractal Analyses

Soils are dynamic and complex systems in their natural state, which are subjected to profound changes due to management. Additionally, agricultural soils are continuously exposed to wetting and drying (W-D) cycles, which can cause modifications in the complexity of their pores. Thus, we explore how successive W-D cycles can affect the pore network of an Oxisol under contrasting managements (conventional tillage—CT, minimum tillage—MT, no tillage—NT, and secondary forest—F). The complexity of the soil pore architecture was evaluated using a 3D multifractal approach combined with lacunarity, Shannon’s entropy, and pore geometric parameters. Our results showed that the multifractal approach effectively identified and quantified the changes produced in the soil pore architecture by the W-D cycles. The lacunarity curves revealed important aspects of the modifications generated by these cycles. Samples under F, NT, and MT suffered the most significant changes. Pore connectivity and tortuosity were largely affected by the cycles in F and NT. Our findings demonstrated that the 3D geometric parameters and normalized Shannon’s entropy are complementary types of analysis. According to the adopted management, they allowed us to separate the soil into two groups according to their similarities (F and NT; CT and MT)

Soil pore system complexity and heterogeneity as affected by contrasting management practices

To better understand the changes that occur in soil systems at different scales, researchers have been using concepts from the multifractal theory for investigating intricate and heterogeneous complex structures. This analysis has also been applied to understand how complex systems such as the soil behave under contrasting management practices. This study presents the use of the three-dimensional multifractal theory, lacunarity, and normalized Shannon entropy to characterize changes in the porous system of a Rhodic Hapludox under different management practices (conventional tillage, minimum tillage, and no-tillage) compared with the same soil under a secondary forest, assumed as a reference. The results of lacunarity and multifractal spectra revealed separations between management groups in relation to their porous systems (secondary forest with no-tillage and conventional tillage with minimum tillage). These results indicate possible “degradation” in the structure of the soil under conventional and minimum tillage and its preservation when under no-tillage as the complexity of their pores is analyzed. The contrasting management practices and forest presented linear correlations between soil porosity and lacunarities, maximum normalized Shannon entropy, and the multifractal spectra. The degree of multifractal spectra asymmetries and lacunarities evidenced the variability of spatial distributions of the managements and forest pore size diameters, showing that these tools are useful for characterizing the soil pore system. The results obtained showed the potential and sensitivity of the 3D multifractal approach in the characterization and differentiation of complexity in soil management practices