Soil Pore Distribution Research Articles

The effect of soil water flow and soil properties on the motility of second-stage juveniles of the root-knot nematode ( Meloidogyne incognita)

The movement of root-knot nematode Meloidogyne incognita second-stage juveniles was investigated in a column filled with two types of fillings, andisol or sand, under a saturated condition. After incubation with or without soil water flow, the changing distribution of nematodes was monitored. As a result, we observed a tendency for different movement traits of nematodes between andisol and sand. The distance of nematodes movement in sand was always greater than that in andisol in both a percolation test and non-percolation test. In the percolation test, distance of nematodes movement in sand gradually began to increase with increasing time. We attribute this result to a gradual decrease in nematodes activity with time. Nematodes were always affected by the water flow rate, but the distance of nematodes movement did not correspond to water flow volume. We also observed that mobility of nematodes in sand were always greater than that in andisol at both percolation test and non-percolation test. These results are attributed to differences in soil structure and pore distribution of andisol and sand. This study demonstrates a difference in the movement of nematodes influenced by water flow. However, this study also presents evidence that nematodes can resist soil water flow rates that are possible in actual field conditions. Moreover, mobility of nematodes changed considerably with soil structure or pore distribution. All these may contribute to a more stable positioning of nematodes around the rhizosphere of their host plants, and therefore increase the possibility of successful parasitization.

Study of the water retention properties of a tropical soil

Some peculiarities of water retention in a tropical lateritic soil of clayey nature are presented and discussed. The typical soil microstructure is shown through thin-layer plates emphasizing soil microaggregation and pore distribution and their repercussion on the soil-water retention curve and on hysteresis. It is shown that the clayey soil has a behavior that to a large extent resembles sandy soil, which is characterized by the relatively high saturated hydraulic conductivity, low air-entry value, and small suction range at which water drainage takes place. The severe weathering processes that originated this soil have produced an altered soil that seems to be homogeneous in terms of physical indices, hydraulic conductivity, and soil-water retention characteristics, up to 4.5 m in depth.

Quantifying a soil pore distribution from 3D images: Multifractal spectrum through wavelet approach

Knowledge on soil pore geometry is important for understanding soil processes as it controls the movement and storage of fluids on various scales. With the advent of modern non-destructive tomography techniques there have been many attempts made to analyze pore space features mainly concentrating on the visualization of soil structure. Multifractal formalism or the wavelet transform has been revealed as a useful tool in these cases where highly complex and heterogeneous media are studied. The field of 3D pore space analysis opens a challenging opportunity to develop techniques for quantifying and describing pore space properties. One of these quantifications can be the maximum depth pore network (MD), analogous as the quantification of the preferential flow paths. In this paper, a variation of the wavelet transform modulo maxima (WTMM) method used to compute multifractal behavior is presented. As a wavelet transform analysis (WTA), it allows us to focus on every scale which can be useful to select the range of scales where multifractal analysis (MFA) can be applied, revealing the MD global scaling patterns. In addition, the proposed method does not make any global estimate, so it can also be used to focus on local distribution of singularities. So, in the context of multiscaling structure analysis, the proposed wavelet-based method can complement box-counting analysis in order to statistically describe preferential flow path geometry and flow processes. The methodology is applied to determine the multifractal behaviour of 3D images of soil samples with 45.1 µm resolution (256 × 256 × 256 voxels) with closer porosities (ranging from 12% to 14%) and different spatial arrangements.

Soil porous system changes quantified by analyzing soil water retention curve modifications

Soil water retention curves (SWRCs) relate soil water pressure head ( h) to soil water content ( θ) and can also be used to find information regarding soil pore distribution. To analyze SWRCs in relation to pore size distribution (PSD), changes due to wetting and drying (W–D) cycles were studied in three different tropical soils (Geric Ferralsol, GF; Eutric Nitosol, EN; Rhodic Ferralsol, RF), using three different treatments: T 0, the control with samples not submitted to W–D cycles; T 3, samples submitted to three consecutive W–D cycles; T 9, samples submitted to nine consecutive W–D cycles. Log-normal PSD equations for each treatment were obtained using the S-theory. For the GF soil, the pressure heads separating structural and matrix domains ( h s) were 17.7, 12.2 and 14.7 kPa for T 0, T 3, and T 9, respectively. These values are equivalent to pore radia of 8.4 μm ( T 0), 12 μm ( T 3), and 10 μm ( T 9). For the RF soil, h s values were 8.5 kPa ( T 0), 20.5 kPa ( T 3), and 15.1 kPa ( T 9), equivalent to radia of 18 μm ( T 0), 7.3 μm ( T 3), and 9.9 μm ( T 9); and finally, for the EN soil, h s were 18.1 kPa ( T 0), 9.1 kPa ( T 3), and 13.5 kPa ( T 9), equivalent to radia of 8.2 μm ( T 0), 16 μm ( T 3), and 11 μm ( T 9). It was found that the soil structure presented important changes in PSD due to W–D cycles for all the investigated soils. It was also observed that the W–D cycles increased the S inf (slope of SWRC) value for the GF soil for all treatments; S inf did not substantially change in all treatments for the EN soil; S inf decreased between T 0 and T 3, and T 0 and T 9 for the RF soil. According to the S-theory, it is possible to infer that W–D cycles improved the soil structure of GF, made the RF soil structure worse and did not substantially change the EN soil structure.

CHARACTERIZATION OF THE POROUS STRUCTURE OF CHILEAN VOLCANIC SOILS BY NITROGEN ADSORPTION AND MERCURY POROSIMETRY

Pore volume, specific surface area (SSA), and total intragranular porosity (TIP) of Chilean soils derived from volcanic materials were studied. Soil samples involving the 0-15 and 15-30 cm depth of virgin and cultivated Collipulli (Ultisol) and Diguillin (Andisol) soils at two particle size fractions (<1 mm and <2 µm) were considered. From mercury porosimetry and N2 adsorption, mainly mesopores (pore diameter, dpore, about 10 nm) were determined for <1 mm Collipulli samples. Diguillin <1 mm soil shows macroporosity with dpore from 70 nm to 7000 nm. The clay fraction of Collipulli has macropores (dpore from 2000 nm to 40000 nm) and mesopores (dpore from 3 nm to 23 nm), while for Diguillin clay-size fraction most of the porosity comes from macropores (dpore from 50 nm to 800 nm). For all samples the SSA linearly correlates with the mesopore volume (r2=0.781; n=16) determined by N2 adsorption, and with the mesopore + macropore volume (r2= 0.771; n=12) when Collipulli <1mm samples are excluded; an inverse relationship between SSA and organic carbon content was found (r2=0.854; n=14). Thus, the SSA defined mainly by mesopores and macropores is probably related to the soil organic matter content. Mesopores and macropores mainly give the TIP, which increases as particle size decreases. No important changes in micropore and macropore volume, and in TIP were seen as result of cultivation. Mesopore volume is more important in samples dominated by kaolinite than in samples dominated by allophane (4 to 20 times). In general the soil pore distribution, its SSA and TIP are related to its mineralogy and organic matter content

A new model for soil hydraulic properties based on a stochastic conceptualization of porous media

The nature and distribution of soil particles and pores plays a strong role in determining the soil hydraulic properties (specifically the soil water retention curve and the relative hydraulic conductivity curve) that govern water movement. A new mathematical model for these hydraulic properties was developed by conceptualizing the soil as a random assemblage of soil particles represented by randomly sized overlapping spheres (fully penetrable spheres). The spatial arrangement of the spheres was assumed to follow a homogeneous Poisson process. A stochastic analysis was utilized to obtain analytical expressions for soil water retention curves and relative conductivity at varying water contents. Unlike the existing models of soil hydraulic properties, this new model incorporates soil porosity in estimating model parameters. Furthermore, because of this conceptualization, we are able to determine the types of soils for which the model is appropriate. A quantitative evaluation of the new model was performed by examining data on hydraulic properties for several soils. In addition, quantitative and qualitative comparisons were made with currently used expressions (such as the van Genuchten model, Brooks‐Corey relationship, and Kosugi model) for the same data sets. Results show that the new model provides reasonable fits with the observed water retention curve and good predictions of the hydraulic conductivity, particularly for soils exhibiting a distinct air entry pressure.

Estimation of the water holding capacity of forest stands using soil pore distribution and an analysis of the related factors

Estimation of the water holding capacity of forest stands using soil pore distribution and an analysis of the related factors

Mathematical morphology for analysing soil structure from images

Mathematical morphology is an approach to image analysis based on set theory. It explores structures by examining the effect of transforming them by set operations. Such operations can be built up and combined into powerful tools for exploring, transforming and measuring the size, shape and connectivity of components of interest in images. Greylevel images are handled by regarding them as binary images in three dimensions. This paper reviews the basic ideas and illustrates them by application to studies of the size distribution of soil pores, the lengths and geometric patterns of cracks in drying soil, and the growth of fungal hyphae. It then extends them in an introductory way to random sets. Practical issues of scale, resolution, sampling, replication and noise in the use of images for soil measurement are described briefly.

Impact of earthworms on the diversity of microarthropods in a vertisol (Martinique)

In a study of a 15-year-old pasture in Martinique (French West Indies), abundance and organization of microarthropod communities were correlated with the spatial distribution of the earthworm Polypheretima elongata (Megascolecidae). In patches of high earthworm density (133 individuals m–2), microarthropod density was significantly higher (80000 individuals m–2) than in patches with few earthworms (31 worms m–2 and 49000 microarthropods m–2). The diversity of microarthropod communities followed a similar pattern, the Shannon index for Collembola communities being, respectively, 3.12 and 1.82 in and outside earthworm patches. These results suggest that mesofauna abundance and diversity might be at least partly determined by the activity of larger invertebrates, as a result of the dramatic effects that the latter group exerts upon soil structure, pore distribution and food resources.

Influences of soil-pore connection properties and soil pore distribution properties on the vertical variation of unsaturated hydraulic properties of forest slopes

Influences of soil-pore connection properties and soil pore distribution properties on the vertical variation of unsaturated hydraulic properties of forest slopes

Size Distribution of Dispersed and Aggregated Particles and of Soil Pores in 12 Danish Soils

Abstract Soil texture, aggregates in different size classes and water retention at several water potentials were measured in the top layers of 12 Danish soils. Size frequency curves of dispersed and aggregated soil particles and of soil pores were calculated using numerical differentiation of sum curves, which were obtained from measured data through interpolation procedures. Soils which originated from water sediments had narrow peaks with approximately lognormal distribution of dispersed soil particles and of soil pores, reflecting the sorting action of the water. Moraine soils appeared to have broad and flat frequency curves of dispersed soil particles, some of which were bimodal or skewed. These soils exhibited a typical bimodal size distribution of soil pores. Degree of aggregation was determined primarily by the soil content of clay, 10% or more creating stable macroaggregates of 2–6 mm diameter. A comparison of the frequency curves for soil pore size to a generalized four-parameter mathematical expression relating matric potential and volumetric water content revealed that the model fitted the empirical data reasonably well for the well-sorted water-sedimented soils, while in the case of the bimodal pore size soils a deviation of differing magnitude was observed. From the investigation it is recommended that in most cases, quantities of particles and pores in soil should be related to size with frequency rather than cumulative expressions.

Seasonal changes in the structure of clay soils in relation to soil management and crop type. I. Effects of crop rotation at Cruden Bay, NE Scotland

SUMMARYChanges in soil structure and macroporosity were investigated using large thin sections and image analysis of photographs taken from fluorescent resin impregnated soil blocks. In this way porosity measurements were combined with visual assessment of the distribution and type of soil pores and aggregates. Three sites were chosen on a clay soil at Cruden Bay, Aberdeenshire, and sampled throughout two growing seasons in order to characterize various stages of a 7‐year rotation.The seasonal pattern of structural change depended on the crop. During a dry period in April and May 1980, a system of cracks developed on the grass site but not on sites sown to spring barley. The changes in structure on the grass sites could mainly be attributed to changes in water content, and the resulting cycle of shrinking and swelling.After cultivation, structural changes resulting from settling were evident. Earthworm activity, especially after manure spreading, also had a pronounced effect on structure. Since many of these processes are cyclic in this environment, the resulting structural states showed a pattern of cyclic recurrence.

An index for soil pore size distribution

An index for classifying soil pore size distribution is proposed. The arithmetic mean change in percent soil water content by weight as the tension changes from zero to 1.5 bars is used as the index. This number characterizes the size distribution of pores with a radius of one micron or greater. A simple equation is presented to calculate the index from soil water contents at pressure plate settings of zero, 0.2, and 1.5 bars. Moisture release curves from 3 different soils show that the index does tend to characterize the shape of the release curve and that it is sensitive to past management which affects the distribution of large soil pores. When all other conditions are optimum, it appears that there exists a specific value of the index which indicates when the soil pore size distribution may be expected to limit plant growth. It is further suggested that the index, together with penetrometer measurements made at the 1.5-bar water content, may be used as “soil test values” for making practical management decisions and for predicting the stability of soils under varying field conditions.