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  • 1
    Electronic Resource
    Electronic Resource
    Prediction of water retention properties of clayey soils: validity of relationships using a single soil characteristic (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 10 (1994), S. 0 
    Details
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. Regression equations successfully allowed the calculation of water retained at—0.3 × 105 Pa and–15 × 105 Pa matric potentials from single soil characteristics, such as bulk volume or clay content, in clayey horizons derived in similar ways from a single parent material. It is possible to use these regression equations on other soils with similar clay fabrics. The fabric is expressed numerically using the pore volume associated with clay particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1475-2743.1994.tb00467.x
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  • 2
    Electronic Resource
    Electronic Resource
    Use of class pedotransfer functions based on texture and bulk density of clods to generate water retention curves (2003)
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 19 (2003), S. 0 
    Details
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. Water retention properties of 219 horizons were measured in Cambisols, Luvisols and Fluvisols, mainly from the Paris basin. We derived class pedotransfer functions (class PTFs) based on texture alone and in a second stage class PTFs based on classes combining texture and clod bulk density. The performance of these two types of PTFs were discussed at −330 and −15000 hPa water potential on an independent set of 221 horizons. Results showed that PTFs based on sets grouped by texture and clod bulk density provide estimates with an accuracy that is (i) greater than with class PTFs based on texture alone, and (ii) similar to the estimation accuracy recorded with continuous PTFs. As a consequence, the lack of interest in class PTFs should be reconsidered to bridge the gap between the available basic soil data and hydraulic properties which are generally missing, particularly when pertinent soil characteristics can be derived from the data available in soil databases. The two types of class PTFs providing gravimetric water contents at seven water potentials ranging from −10 to −15 000 hPa were converted to volumetric water content using the soil bulk density. Finally, the parameters of van Genuchten's water retention curve model were computed for every class PTF.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1475-2743.2003.tb00309.x
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  • 3
    Electronic Resource
    Electronic Resource
    Particle packing and organization of the textural porosity in clay–silt–sand mixtures (1998)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 49 (1998), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The packing of elementary particles in soil largely determines the properties that depend on the textural soil pore space, but is studied little. The relations between packing and size and nature of soil particles were studied using fractions of clay, silt and sand, mixed when wet and then dried. Ternary mixtures (clay:silt:sand) were compared with binary mixtures (clay:silt, clay:sand). The pore space of the mixtures was studied using mercury porosimetry and scanning electron microscopy. In all the mixtures the textural pore space was divided into two compartments: (1) lacunar pores due to the presence of skeleton particles and to the shrinkage of the clay phase between these particles, and (2) the clay–fabric pores due to the packing of the clay. In the ternary mixtures, lacunar pores could be divided into two classes: (1) those due to sand particles within the clay–slit phase considered as a single phase, and (2) those due to silt particles within this same phase. For certain mixtures, lacunar pores, referred to as hidden lacunar pores, were not interconnected but were occluded. This occurred both for hidden pores caused by the presence of sand and occluded by the clay–slit phase, and for hidden pores caused by the presence of silt and occluded by the clay phase. The relations between these types of textural pores and the proportions of different size fractions in the mixtures provide guidelines for making optimum use of the particle-size characteristics of the soil to determine its properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.1998.4940557.x
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of clay content and silt—clay fabric on stability of artificial aggregates (1998)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 49 (1998), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The influence of clay content and silt–clay fabric on aggregate stability was investigated. Two silt—clay fabrics were produced in the laboratory by mixing silt particles with a clay phase: (i) a loose packing of the silt particles with clay aggregates, and (ii) a close packing of the silt particles with the dispersed clay phase, the latter coating and bridging the silt particles. Porosity and pore size distribution were measured, and the silt—clay fabric was described using scanning electron microscopy. The aggregate stability was measured under three treatments corresponding to different wetting conditions and energy levels: fast wetting, mechanical breakdown and slow wetting. Our results show that aggregate stability is related to both clay content and silt—clay fabric. Comparison of fragment size distributions and their mean weight diameter amongst the three treatments enabled identification of mechanisms responsible for the variation of aggregate breakdown. The compression of trapped air was the predominant breakdown mechanism for both fast and slow wetting and was related mainly to porosity characteristics. For the mechanical breakdown, the degree of disintegration depended on the cohesion of the silt–clay fabric, which is related to the continuity of the solid phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.1998.4940569.x
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  • 5
    Electronic Resource
    Electronic Resource
    Water retention properties of the clay in soils developed on clayey sediments: significance of parent material and soil history (2000)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 51 (2000), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: We have investigated the water retention properties of clayey subsoil horizons according to the variation of clay characteristics. The horizons studied developed on a large range of age and facies of calcareous or calcium-saturated clayey sediments. The water retention properties were studied from −10 hPa to −15 000 hPa water potential using small clods collected in winter when swelling is at a maximum and water content close to field capacity. The specific water content and volume of the clods at field conditions, their specific volume at −15 000 hPa water potential, the clay content, the organic carbon content, the cation exchange capacity, the N2-BET surface area and calcareous content were measured. The clay fabric, which is the spatial distribution of the elementary clay particles, was quantified when the soil was close to field capacity and we could attribute the whole pore volume to the porosity of the clay fabric. Our results show that the water retention properties of the clay vary greatly from one soil to another with respect to the clay fabric. The variation of the latter depends on the cation exchange capacity, the size of elementary particles and hydric stress history of the clay. We show that the water retention properties of the studied clayey soils vary according to the clay content and fabric, the latter being related either to parent material fabric or to both the hydric history of the soil and size of the elementary clay particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2389.2000.00338.x
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  • 6
    Electronic Resource
    Electronic Resource
    A hard sandy-loam soil from semi-arid Northern Cameroon: I. Fabric of the groundmass (1997)
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 48 (1997), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: In semi-arid tropics soil hardening may reduce both water infiltrability and biological activity, thus inducing the development of large almost bare areas. A sandy-loam soil with contrasting loose and underlying hard horizons was studied in the southern plain of the Chad basin. The fabrics of these horizons were studied using combined sieving and sedimentation techniques, mercury porosimetry and scanning electron microscopy. The horizons had similar particle size distributions of the skeleton grains. The hard horizon differs by a small increase in its fine clay (〈 0·2 μm) content. The hardness is closely related to a fabric with clay coatings on the skeleton grains and clay wall-shaped bridges linking the latter. This induces a strong continuity of the solid phase. This fabric requires a minimum of clay content (6%) to make the coatings and the wail-shaped bridges, and it can be 30% less porous than the loose horizon, without any change in the packing of the skeleton grains. These characteristics of the fabric of the hard horizon are like those of fragipans elsewhere. The continuity of the solid phase, from the microscopic to the macroscopic scale, as well as the absence of a network of cracks explains the considerable strength of the hard horizon, and consequently the difficulties for water infiltration, root penetration and tillage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2389.1997.tb00542.x
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of compaction on the porosity of a silty soil: influence on unsaturated hydraulic properties (2001)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 52 (2001), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Tillage and traffic modify soil porosity and pore size distribution, leading to changes in the unsaturated hydraulic properties of the tilled layer. These changes are still difficult to characterize. We have investigated the effect of compaction on the change in the soil porosity and its consequences for water retention and hydraulic conductivity. A freshly tilled layer and a soil layer compacted by wheel tracks were created in a silty soil to obtain contrasting bulk densities (1.17 and 1.63 g cm−3, respectively). Soil porosity was analysed by mercury porosimetry, and scanning electron microscopy was used to distinguish between the textural pore space and the structural pore space. The laboratory method of Wind (direct evaporation) was used to measure the hydraulic properties in the tensiometric range. For water potentials 〈 −20 kPa, the compacted layer retained more water than did the uncompacted layer, but the relation between the hydraulic conductivity and the water ratio (the volume of water per unit volume of solid phase) was not affected by the change in bulk density. Compaction did not affect the textural porosity (i.e. matrix porosity), but it created relict structural pores accessible only through the micropores of the matrix. These relict structural pores could be the reason for the change in the hydraulic properties due to compaction. They can be used as an indicator of the consequences of compaction on unsaturated hydraulic properties. The modification of the pore geometry during compaction results not only from a decrease in the volume of structural pores but also from a change in the relation between the textural pores and the remaining structural pores.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.2001.00357.x
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  • 8
    Electronic Resource
    Electronic Resource
    Increase in the bulk density of a Grey Clay subsoil by infilling of cracks by topsoil (2001)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 52 (2001), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Increases in soil bulk density beyond the optimum reduce land productivity and, where soil is affected, may be difficult to remedy. Elucidating the mechanisms causing compaction is a prerequisite to sustainable management of fragile soils. We examined a dense grey soil in Western Australia in which the dominant physical feature of the subsoil was coarse prismatic structure. The prisms were approximately hexagonal in horizontal section with an average side length of 0.66 m. The top of the prisms reached to within approximately 0.07 m of the soil surface, their sides becoming indistinguishable below approximately 0.9 m. The vertical faces of the prisms were coated by material similar in composition to the topsoil and separated from it by a transition material of intermediate composition. Soil within the prisms had a bulk density at maximum swelling which reached a maximum of 1.86 g cm−3 in the upper subsoil. We investigate the hypothesis that such a high bulk density could have developed as a result of a simple three-stage process: (i) soil shrinkage as the profile dries over summer leading to widening of cracks between prismatic peds, (ii) infilling of cracks by detached topsoil which adds to coating thickness, and (iii) swelling during the winter, now partially restricted by coating material, leading to compression of the prismatic peds. We present a model which accounts quantitatively for this process and explain how soil physical characteristics might facilitate it. The dense upper subsoil (7–60 cm) limits root penetration and prolongs the period of transient waterlogging of the topsoil during winter, adversely affecting subsequent crop performance. Our work suggests that stabilizing surface soil to minimize soil detachment could be a relevant management objective on these structurally unstable soils in order to prevent subsoil compaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.2001.t01-1-00365.x
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  • 9
    Electronic Resource
    Electronic Resource
    Three-dimensional crack monitoring by electrical resistivity measurement (2004)
    Oxford, UK; Malden, USA : Blackwell Science Ltd
    European journal of soil science 55 (2004), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Soil cracks formed by natural processes play a key role in water and gas transfer. Patterns of soil cracks are, however, difficult to characterize. Our aim here is to assess the effectiveness of three-dimensional electrical resistivity surveys in detecting soil crack networks. A three-dimensional electrical survey was carried out by a square array quadripole with Cu–CuSO4 electrodes (electrode spacing of 3 cm). The measurements were made with two orientations (0° and 90°) on a block (26 cm × 30 cm × 40 cm) of soil while it dried for 18 days under controlled conditions. Two indexes, calculated from the apparent resistivity values, were evaluated to detect the degree of soil heterogeneity: (i) an anisotropy index based on the ratio between the apparent resistivity at 0° and that at 90°; and (ii) the angle-array orientation corresponding to the preferential anisotropic orientation (maximum resistivity). The anisotropy index provided information on the presence of cracks and the orientation for crack width 〉 1 mm in the first pseudo-depth (i.e. depth of investigation), while the angle-array orientation provided information on crack extension for the whole pseudo-depth. Information about the presence, position, orientation and extension of cracks can be obtained from an analysis of apparent resistivity obtained by a three-dimensional electrical survey. Such direct analysis will help the resistivity inversion to detect the crack network.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2389.2004.00632.x
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  • 10
    Electronic Resource
    Electronic Resource
    A hard sandy-loam soil from semi-arid Northern Cameroon: II. Geochemistry and mineralogy of the bonding agent (1997)
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 48 (1997), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The hardening of soils containing little clay content has often been related to the cementing of skeleton grains. In sandy-loam soils from the southern plain of the Chad basin the skeleton grains of the hard horizon are coated and bonded by wall-shaped bridges. We have studied the bonding agent by X-ray diffraction on extracted fractions (〈 0·5 pm) and by quantitative in situ electron microprobe analysis on thin sections. The coatings and the wall-shaped bridges are composed mainly of SO2 (mean = 60%), Al2O3 (29%) and FezO3 (7%). The TiO2 and K2O contents were small (1–2%), and the MgO, Na3O and CaO contents were less than 1%. The composition of the coatings and the wall-shaped bridges is almost homogeneous, even if the Si/Al atomic ratio varies weakly with the morphology of the bridges. The bonding agent constituting the coatings and the wall-shaped bridges seems to be a mixture of predominantly Al-Fe beidellite with small contents of kaolinite, illite and quartz. A small content of fine clay minerals plays the major role of bonding agent and is responsible for hardness in sandy or sandy-loam soils.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2389.1997.tb00543.x
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