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The scaling properties of fractals are formally defined only in the limit of infinite or infinitessimal length scales, while measurements are necessarily restricted to finite scales. The implications of this limitation are studied from the perspective of characterising the heterogeneity of a fractal and its complement. An examination of the scaling properties of the solid and pore space of soil...
In many agricultural soils in the semi-arid and and mediterranean climates, exposure to cyclic wetting and drying (WD) can reduce aggregate stability. The extent to which soil pretreatment with coal-derived humic substances (HS) can increase aggregate stability in soils exposed to cyclic wetting and drying (WD) was evaluated in this study. The soils studied are an Acireale silty clay loam from Sicily,...
Morphological investigations can be used to reveal the nature and distribution of solid matter and pore space within a porous medium, such as rock, soil or milled peat. When sampling milled peat, it is necessary to ensure that disturbance during sample collection and transportation is minimised, and a field impregnation is required to preserve the structure of the milled peat as it exists in the stockpile...
Macroporosity influences the dynamics of water and dissolved solutes in the soil. Size, shape and continuity of macropores is affected by soil management. In this study, dye staining technique, followed by digital image processing, are used to quantify macroporosity under field conditions in a short time at low cost. We compared 17 macroporosity parameters, in 55 staining patterns from three fields...
A finely structured (self-mulching) Vertisol from Zimbabwe was sampled to 150 mm (bulk samples) or 30 mm (undisturbed samples) in order to provide material for an investigation of the effects of wet/dry cycles on microstructure. Bulk samples were worked in the plastic state and then taken through a number of wet/dry cycles using flood, slow and fast capillary and simulated rainfall wetting. Thin sections...
A new method for the acquisition of undisturbed in situ samples of milled peat (non-cohesive particulate material) suitable for image analysis was developed. Samples were obtained in the field by dripping Endura epoxy resin onto a stockpile surface. Blocks of material (160 mmx120 mm) with original pore structure up to 140 mm deep were removed to the laboratory and re-impregnated with Crystic resin...
We review a generalized approach to modeling soil structures, which exhibit scale invariant, or self-similar local structure over a range of scales. Within this approach almost all existing fractal models of soil structure feature as special albeit degenerate cases. A general model is considered which is shown to exhibit either a fractal or nonfractal pore surface depending on the model parameters...
A simple description of soil respiration is combined with a three-dimensional random fractal lattice as a model of soil structure. The lattice consists of gas-filled pores and soil matrix that is a combination of the solid phase and water. A respiration process is assumed to take place in the soil matrix. Oxygen transport occurs by diffusion in the gas-filled pores and, at a much slower rate, in the...
This paper describes the application of fractal geometry to the study of the structure and dynamics of tilled silty topsoil. The soil structure of each topsoil sample has been experimentally quantified directly by image analysis and indirectly by both water retention and mercury porosimetry. Any fractal scaling laws were mostly determined within a relevant common pore radius yardstick scale. Their...
The objective of this study was to relate the major chemical and mineralogical properties of soils formed on sedimentary deposits in southeastern Nigeria to the stability of their aggregates at both the macro and micro (colloidal) levels. Five profiles and twenty-five topsoil samples representing four major geological formations were studied. The soils are classified as Entisols and Ultisols. The...
This study concerned an experimental truffle bed of downy oaks infected by the ectomycorrhizal fungus Tuber melanosporum and planted in 1983. The presence of T. melanosporum creates rounded areas with little herbaceous cover, termed ''brulis'', where carpophores are found. The investigation was aimed at relating the occurrence and carpophore production of T. melanosporum to soil properties, i.e.,...
Common irrigation procedures in many parts of the world involve flood irrigation. Observations during recent years have, however, indicated that preferential flow may be an important phenomenon that could affect the outcome of both irrigation and fertilizer application for this irrigation type. To analyze and visualize solute transport by preferential flow mechanisms, field experiments were carried...
There is limited information on the application of fractal concepts to Vertisols. The objectives of this study were to: (i) test the applicability of the fractal fragmentation theory to Vertisols and (ii) see whether the parameters of fractal models reflect differences in soil management and with depth. The soil was sampled at 0-10, 10-20, and 20-40 cm depths in early May 1998, 15 days after the rice...
The effects of the activity of seed harvesting ants (Messor bouvieri) on the fertility, rainfall infiltration, structural properties and water repellency of top soils were investigated in a semi-arid rangeland in SE Spain. The soil surfaces had a low vegetative cover and bare areas had a sieving crust. Rainfall simulation experiments were carried out over ants' nest mounds and on control areas without...
Two sets of shrinkage data for a Norwegian clay Topsoil and Subsoil provided in the literature by Olsen and Haugen [Geoderma 83 (1998) 67] were re-evaluated by fitting them to the Groenevelt and Bolt [Soil Science 113 (1972) 238] constitutive shrinkage equation. The shrinkage curves were differentiated to obtain the slopes, and the slope curves were subsequently differentiated to obtain the curvatures...
Macropore transport of chemicals in soil often causes unexpected contamination of groundwater. The effect of soil structure on the functions of various sized macropores was assessed, investigating transport of nonreactive bromide (Br) under matric heads of 0, -2, -5 and -10 cm using undisturbed soil columns from A, B w and E horizons of a Thatuna silt loam soil (fine-silty, mixed, mesic Xeric...
Evaporation is a major component of the water loss from the soil whose structure is modified by traffic and tillage. This study was undertaken to analyse, in field conditions, the effect of tillage and traffic on soil structure and evaporation, and to determine the role of the change in hydraulic properties on soil drying using water transfer model. Three structures of the ploughed layer were formed...
Soil structure exerts important influences on the edaphic conditions and the environment. It is often expressed as the degree of stability of aggregates. Aggregation results from the rearrangement, flocculation and cementation of particles. It is mediated by soil organic carbon (SOC), biota, ionic bridging, clay and carbonates. The complex interactions of these aggregants can be synergistic or disruptive...
Measuring fractal dimensions has become a common practice for describing structural properties of porous media. Depending on the object of interest, different features of the structure can be measured: solid matrix, pores, and the interface between them. However, when measuring the fractal dimension of all these features, the question arises whether these dimensions are independent from each other...
Examination of soil structure often requires that analysis takes place on samples that are representative of field conditions. A new method for the acquisition of undisturbed in situ soil samples for morphological analysis was developed. Small volumes (c. 100 cm 3 ) were impregnated in the field by infiltrating a household varnish into the soil. Results indicated that the varnish readily penetrated...
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