bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evolution of porosity and changes in heat treated lepidocrocite
Authors: CORNEJO J. , HERMOSIN M. C. 
Published: July 2006

SUMMARYThe thermal decomposition of lepidocrocite in air has been studied by X–ray powder diffraction, IR spectroscopy, transmission electron microscopy and N2 adsorption isotherms. Three consecutive processes may be differentiated with increasing temperature: (a)<200°C; no structural change is observed, but a surface dehydration gives rise to an increase in surface area besides a change of mesopore shape from cylindrical to slit–shaped, (b)200–300°C; the maghaemite phase is obtained with a high increase in surface area mainly due to the formation of micropores, because of water losses from inner positions that produce lattice disruption, and (c)≥ 350°C; the transformation of maghaemite to haematite takes place decreasing the specific surface area as the temperature increased. At 450°C microporosity is destroyed and a change of slit–shaped to cylindrical mesoporosity is observed. Porosity dissappeared at ≥600°C, mainly due to interparticle sintering which produces well crystallized haematite samples of low surface area.
The topology of pore structure in cracking clay soil I. The estimation of numerical density
Authors: SCOTT G. J. T. , WEBSTER R. , NORTCLIFF S. 
Published: July 2006

SUMMARYThe numerical density, Nv, of the pore structure of soil is the number of disjoint networks of pores per unit volume of soil. A method is described for estimating Nv of patterns of cracks that dominate in many clay subsoils. The cracks are photographed from numerous close‐spaced parallel sections and skeletonized; by comparing the skeletonized photographs sequentially, individual networks are tracked from one section to another and counted. The average number of networks that appears or disappears per section in the sequence is a measure of the numerical density and is obtained by regressing the counts on the volume of soil spanned by the sections. The regressions for appearances and disappearances converge on one another and stabilize within 10 to 20 sections, so that Nv can be estimated for a sample of soil with moderate effort.Estimates of Nv for cracks wider than 60 μm in subsoil of the Windsor series, sampled at two nearby sites and 5 years apart in time and determined from sections at 50 μm intervals, were approximately 32 cm−3 and 36cm−3. That of Nv in the Swanwick series subsoil nearby was about 75 cm−3.
The effects of chemical weathering on the morphology and strength of quartz grains–an example from S.W. Australia
Authors: ASUMADU K. , GILKES R. J. , ARMITAGE T. M. , CHURCHWARD H. M. 
Published: July 2006

SUMMARYIn soils in south‐western Australia rounded quartz pebbles and sand grains have been greatly modified by chemical dissolution. Evidence of dissolution was provided by thin sections, scanning electron microscopy and measurements of quartz grain strength. Dissolution is initiated at fractures and intercrystalline boundaries so that dissolution along intersecting microfractures produces various surface etch features including tessellated pyramidal surface textures. The alteration of quartz grains by dissolution prevents the use of quartz as a stable reference mineral in studies of pedogenesis in these soils.
Clay‐mineral contribution to the weathering mechanisms in two contrasting watersheds
Authors: OLSON CAROLYN G. 
Published: July 2006

SUMMARYTwo mountain watersheds in eastern USA showed sensitivity of their bedrock type to acidification from changes in atmospheric input: they were a Catoctin Mountain watershed on Precambrian metabasalt, and a Massanutten Mountain watershed developed on Silurian metaquartzites and shales. The role of clay minerals to neutralize potential increases in acid deposition was examined. Landscape position and drainage characteristics influence the clay mineral suites present at Catoctin, and an expandable clay component enables this watershed to adequately buffer the hydrochemical systems. A 14 Å hydroxy‐interlayer vermiculite provided a sink for A13+, and also a possible neutralizing effect in the second watershed which was highly sensitive to acid deposition.
Dredged materials–problems associated with their use on land
Authors: BRAMLEY R. G. V. , RIMMER D. L. 
Published: July 2006

SUMMARYThe use of river and harbour dredgings in reclamation projects worldwide is reviewed. Potential land uses are considered where the emphasis is placed on the growth of plants, such as agricultural and public recreation areas. Physical and chemical problems associated with the use of dredgings in such projects are identified, and crop responses on these materials are discussed. Health risks to man and animals associated with using dredged materials are also considered.Physical problems such as high water‐holding capacity do not limit the use of dredged materials provided that the period of ripening is of sufficient length. High heavy metal contents, nutrient imbalance and unfavourable pH are seen as the major constraints to the use of dredged materials as growth media. It is concluded that with careful ripening, and monitoring of chemical parameters, dredged materials may be of considerable use in many reclamation projects.
Recovery of 15N‐labelled fertilizer in crops, drainage water and soil using monolith lysimeters in south‐east Nigeria
Authors: VAN DER KRUIJS A. C. B. M. , WONG M. T. F. , JUO A. S. R. , WILD A. 
Published: July 2006

SUMMARYLabelled urea was applied to monolith lysimeters in the 1st year of a 2‐year experiment at Onne in south‐east Nigeria. On eight lysimeters maize and rice were grown in each of the 2 years. Four lysimeters were similarly cropped in the 2nd year after being uncropped in the 1st year. Measurements were made over the 2‐year period of labelled and unlabelled mineral nitrogen in the drainage water, and labelled and unlabelled nitrogen in the crops. At the end of the experiment, weeds and the soil were also analysed for labelled and unlabelled nitrogen.The total recovery of 15N in crop, soil and leachate varied between 70 and 93%. It was lowest when applied to the second season rice crop, which recovered only 15%, and highest when it was leached in the 1st year or was taken up by the maize crop. The highest crop uptake was 31%. The results indicate that, depending on the treatment, between 10 and 30% of the 15N was immobilized in the soil, lysimeters cropped in the 1st year lost between 22 and 29% of the 15N in drainage water, and between 7 and 30% was lost by denitrification. The accuracy of these figures is discussed.
A model of solid‐solution interactions in acid organic soils, based on the complexation properties of humic substances
Authors: TIPPING E. , HURLEY M. A. 
Published: July 2006

SUMMARYCHAOS (Complexation by Humic Acids in Organic Soils) is a quantitative chemical model of organic soils that incorporates complexation by the functional groups of humic substances and non‐specific ion‐exchange reactions. The two types of interaction are linked by the net humic charge, Z, which depends on the extents of proton and metal complexation, and which in turn determines ionic concentrations in the diffuse part of the electrical double layer, by a Donnan equilibrium. CHAOS was found to account satisfactorily for the results of acid‐base titration experiments (pH range 3–5) with soil samples, giving reasonable simultaneous predictions of solution pH and concentration of A13+. Predictive calculations with CHAOS suggest that organic soils acidified by acid rain would respond on a time‐scale of years‐to‐decades to reductions in rain acidity. An associated effect might be an increase in the concentration of dissolved organic matter in the soil solution.
Clay and iron minerals in soils of the clay plains of Central Sudan
Authors: YOUSIF A. A. , MOHAMED H. H. A. , ERICSSON T. 
Published: July 2006

SUMMARYSurface soil samples from seven profiles from the central plains of Sudan were investigated using XRD, chemical analysis and Mössbauer spectroscopy measured at 15K. Dioctahedral montmorillonite was the main constituent with different proportions of kaolinite and chlorite. Goethite was found as fine iron oxyhydroxide in all the samples, with haematite detected in two pedons. Crystallinity of the clays was observed to correlate negatively with the amount of free iron oxide in the soil. The influence of the climatic factors on the soil and its formation is discussed.
The reactions of copper and zinc with calcium carbonate surfaces
Authors: PAPADOPOULOS P. , ROWELL D. L. 
Published: July 2006

SUMMARYThe reaction of copper and zinc were studied by adding the metal nitrate to a 4g:50ml suspension of calcite and water which had been equilibrated for two days, and then equilibrating for a further three days. Zinc behaved in a similar manner to cadmium in forming a surface‐solid solution of ZnχCa1‐χCO3 as a result of adsorption, and the pIAP of the equilibrium solutions were close to those expected from the Thorstenson & Plummer equation. However, the continuity from adsorption to precipitation was broken by the formation of Zn5(OH)6(CO3)2 which has a higher stability than ZnCO3. The CaCO3 surface appears to constrain the adsorbed Zn to conform to a carbonate structure despite its lower stability than the hydroxy carbonate.The adsorption data for Cu can also be explained in terms of a surface‐solid solution of CuχCa1‐XCO3, but CuCO3 is not found naturally because of much greater stability of Cu(OH)2, and so there is no independent value for the solubility of a CuCO3 end‐member if a surface‐solid solution is formed. Secondary reactions are more likely to occur for Cu, especially close to the adsorption‐precipitation boundary. Continuity from adsorption to precipitation again was not found. Theory predicts that Cu is less likely to form a surface‐solid solution than Zn.Upper Chalk (calcite with 4% other minerals, mostly quartz) behaved in a similar way but with increased adsorption due to its higher surface area.
Seasonal changes in Cu, Mn, Zn and Co concentrations in soil in the root‐zone of barley (Hordeum vulgare L.)
Authors: LINEMAN D. J. , SINCLAIR A. H. , MITCHELL M. C. 
Published: July 2006

SUMMARYSoil solutions were isolated by centrifugation of moist soil taken from the root‐zone of field‐grown barley plants and bulk soil from adjacent fallow areas. Low concentrations of Cu, Mn, Zn and Co were found in soil solutions in late winter with increases in spring and early summer. Discrete maxima are generally achieved at some time between May and early July. The precise timing of such maxima appears to depend on the extent of the development of the growing crop and on seasonal influences. The extent to which micronutrient concentrations increase in fallow soils is less than in the root‐zone soil solutions although similar trends occur. It is suggested that the increased micronutrient concentrations might result from their mobilization from insoluble forms by biologically produced chelating ligands.
The variation of soil water regime, oxygen status and rooting pattern with soil type under Sitka spruce
Authors: NISBET T. R. , MULLINS C. E. , MACLEOD D. A. 
Published: July 2006

SUMMARYSoil water regime, oxygen status and rooting pattern under Sitka spruce were characterized in five soil types: a waterlogged peaty gley, a peaty gley, a flushed peaty gley, a surface water gley and a brown forest soil during 1982. The waterlogged peaty gley had a high water‐table which only dropped below 30 cm depth for 46 d during the summer. Below the water‐table the profile was anoxic and rooting was restricted to a depth of 12cm. The peaty gley experienced seasonal waterlogging with a winter water‐table around 15cm depth. Roots that grew further down the profile during the summer as the topsoil dried to –100 kPa matric potential were later killed when the water‐table rose. The top 30 cm of the flushed peaty gley remained oxygenated even below the water‐table. Roots survived below the winter water‐table. The top 30 cm of the surface water gley and brown forest soil were freely draining and remained aerated throughout the year. The platinum electrode polarographic method demonstrated that there was a sharp transition to anoxic conditions just above the water‐table at the first two sites.
The effect of wet cultivation on the structure and fabric of a Vertisol
Authors: McGARRY D. 
Published: July 2006

SUMMARYChanges in soil structure and fabric of a Vertisol in northern New South Wales, Australia following pre‐sowing cultivation at two different soil water profiles (dry and wet) were investigated. Both the dry and wet cultivated plots had similar, intensive pre‐sowing cultivation typical of commercial practice for irrigated cotton. For thin section analysis two profiles were sampled prior to this cultivation, and three from each of the dry and wet plots were sampled after cultivation. Samples were also available from soils in the area which had never been cultivated. All soils had porphyric fabric with vo‐ma‐skel‐insepic plasmic fabrics and a wide range of pedological features. The cultivated soils had other pedological features not present in the ‘never’‐cultivated soils, i.e. zones within which the plasma exhibited a moderately‐ to strongly‐striated orientation pattern. The more strongly‐striated units included occasional, very fine to fine joint planes. These zones were domi‐nantly equant to planar with sharp boundaries. Internally, they consisted of layer silicate plasma and mineral skeleton grains most commonly similar to the enclosing material. The proportion of these features differed between treatments especially in the 0.05‐0.25 m layer. Soil cultivated dry, and land prior to cultivation had < 1 % of their area composed of zones of striated clay, compared to up to 17% in the wet cultivated soil. This may be related to a greater incidence of shearing of soil in a plastic state by tillage implements and tractor wheels. In the dry cultivated soil shear appears to be of minimal significance.
Soil scientists as members of the scientific community*
Authors: WILD A. 
Published: July 2006

SUMMARYI have tried to show in this paper that there is a need for our expertise in areas outside agriculture, though in the immediate future employment is likely to remain largely through applications to agriculture. At the same time, in broadening our interests we must not neglect to develop our understanding of the properties of soils, their behaviour and the processes that occur in them, because it is fundamental knowledge which finds applications. A related requirement is for us to be aware of innovation in other sciences and technologies. We also have the difficult task of selling our subject to the public while maintaining our scientific integrity. I believe that our image will improve if we can do all this.As interests broaden and the range of applications increases, as I expect they will, there is a danger of a Society like ours becoming fragmented. If one part isolates itself it can become sterile because soil biology, chemistry, mineralogy, physics and pedology interact with each other. In this narrow sense we should all be holists at heart even though developments in science require us to specialize.
Testing a mechanistic model. X. The effect of pH and electrolyte concentration on borate sorption by a soil
Authors: BARROW N. J. 
Published: July 2006

SUMMARYBorate sorption by a soil was measured with 0.01, 0.1, or 1.0 M sodium chloride as background electrolyte and samples of soil with a range of pH values achieved by incubating with either calcium carbonate or hydrochloric acid for 24 h at 60°C.Borate sorption generally increased with increasing pH. The more concentrated the electrolyte, the steeper the increase. At low pH, increasing the salt concentration decreased borate sorption; at high pH, it increased sorption. There was an intermediate pH at which salt had no effect on borate sorption. The point of zero salt effect on borate sorption was at a higher pH than the point of zero salt effect on pH. This result was explained by a mechanism in which borate ions react with variable charge surfaces which are heterogeneous and for which part of the heterogeneity is in the electric potential of the surfaces. It cannot be explained by mechanisms which do not take into account the effects of the electric potential of the reacting surfaces on the reaction with borate ions. Although the behaviour of borate was broadly consistent with that of other anions, it differed in that about half of the heterogeneity had to be allocated to the binding constant for borate ions. It was suggested that this was because reaction with organic matter was more important for borate than for other anions.
Reaction kinetics of the adsorption and desorption of nickel, zinc and cadmium by goethite. II Modelling the extent and rate of reaction
Authors: BARROW N. J. , GERTH J. , BRÜMMER G. W. 
Published: July 2006

SUMMARYA model of the reaction of metal ions with a variable charge surface was modified and applied to goethite that had been formed in the presence of silicate. The data included the effects of initial concentrations of Ni, Zn and Cd ranging from 1 to 100 μm, of periods from 2 h to 42 d, of temperatures from 5 to 35°C, of pH from about 4 to about 8, and of background electrolyte from 0.01 to 1.0 M.The observed effects of concentration and pH were explained by assuming that the reacting surface sites were heterogeneous and that they reacted with the MOH+ ions in solution. The heterogeneity was described by assuming that the affinity of the sites for MOH+ ions decreased logarithmically as the log of the amount adsorbed increased. This gave a Freundlich relation between sorption and surface activity. The effects of increasing the concentration of the background electrolyte were explained as being caused by decreased activity of MOH+ ions in solution counteracted by decreases in the electric potential of the surface. To explain the effects of time and temperature, it was assumed that an initial rapid adsorption reaction was followed by slow diffusion of metal ions into the goethite. Using these assumptions, a comprehensive description of the data was obtained.
Depletion and movement of water beneath cereal crops grown on a shallow soil overlying chalk
Authors: GREGORY P.J. 
Published: July 2006

SUMMARYChanges in water storage and gradients of water potential were measured beneath cereal crops grown on Andover soil series for three seasons. The measurements showed that depletion of water from the soil (0‐0.3 m) was 20–29% of the total profile depletion and that from the chalk/soil and chalk layers was 71–80%. Rain showers rewet the soil so that depletion from the non‐soil layers contributed about 35% of the total water use despite containing only 12% of the roots.Water in the chalk/soil and chalk layers was held at matric potentials between – 200 and – 800 kPa and gradients of hydraulic potential indicated upward movement from depths of almost 3 m. Comparisons of measured water depletion beneath the root zone with estimates of upward movement to the rooting zone indicate that substantial upward movement is possible, although the estimates were generally larger than the measured depletion.The estimated contribution of the water moved to the root zone for shoot dry matter production was 8% and 22% for winter and spring cereals respectively.
A usable mechanistic model of nitrate leaching I. The model
Authors: BARRACLOUGH D. 
Published: July 2006

SUMMARYA mechanistic model to simulate the leaching of nitrate in soil is described. Three flow patterns are accommodated: conventional convective‐dispersion; preferential flow, in which water and solute moving in the larger water‐filled pores fails to equilibrate with that in the smaller pores; and by‐pass flow, in which water (and solute) moves rapidly down cracks and fissures without displacing the soil water. The pattern of flow depends on the rainfall intensity and the hydraulic conductivity of the water‐filled pore space. The performance of the model is examined in terms of its ability to reproduce solute profiles calculated from analytical solutions to transport equations, and in the sensitivity of the output to changes in the main parameters. A second paper (Barraclough, 1989) illustrates the use of the model to reproduce nitrate leaching patterns observed in the field.
Exchange‐induced dissolution of gypsum and the reclamation of sodic soils
Authors: FRENKEL H. , GERSTL Z. , ALPEROVITCH N. 
Published: July 2006

SUMMARYA study was undertaken to define the dissolution kinetics of gypsum in the presence of ion exchange resins and to study sodic soil reclamation in laboratory soil columns.Gypsum pellets were prepared at 1.5 MPa pressure and the time course of their dissolution followed by measuring the electrical conductivity of the solution. Dissolution experiments were carried out in distilled water with and without Na‐ and Cl‐saturated exchange resins or a combination of the two. The results indicate that in the presence of resin the reaction is first order as calcium and/or sulphate are removed from solution by the resin driving the reaction to completion. In water alone the reaction follows second‐order kinetics and depends on the rate of mixing as the reaction is transport controlled.The effect of gypsum placement (uniformly mixed with the entire soil, mixed with the top third of the soil, applied to the soil surface or applied as a saturated gypsum solution) on the efficiency of exchangeable sodium removal, leaching of soluble salts and soil hydraulic conductivity was studied. In addition, the effect of various flow rates on reclamation efficiency was investigated.The amount of leachate required for reclamation was found to be dependent on gypsum placement, tending to decrease in the order mixed < top third mixed < saturated gypsum solution < gypsum surface application < water. Soil hydraulic conductivity was much higher in the mixed gypsum column than in the gypsum applied on the surface; a result of the higher effective gypsum solubility. Sodic soil electrical conductivity in the presence of solid‐phase gypsum is linearly related to the total amount of exchangeable sodium expressed in mol dm−3.
Carbon mineralization in soil size fractions after various amounts of aggregate disruption
Authors: GREGORICH E. G. , KACHANOSKI R. G. , VORONEY R. P. 
Published: July 2006

SUMMARYAggregates (1–2mm) were subjected to shaking, increasing intensities of ultrasonification, or a peroxide treatment and then physically fractionated into sand‐, silt‐ and clay‐size fractions. CO2 evolution was measured during a 20‐day incubation of the sand‐, silt‐ and clay‐size fractions and was used to assess the decomposability of the organic matter within aggregates and associated with these size fractions.All of the size fractions showed a large increase in the amount of readily decomposable C when the ultrasonic energy input increased from 300 to 500 J ml−1 and disruption of microaggregates occurred. The data suggest that some readily decomposable organic matter is sequestered within microaggregates and protected from microbial attack.Following complete dispersion, the C mineralized (mg C g−’C) upon incubation was greatest in the sand particles and least in the clay. The levels of potentially mineralizable C (C0) in the sand‐size fraction increased with increased dispersion energy whereas the mineralization rate (k) remained about the same. The levels of C0 in the clay‐size fraction decreased and the estimates of k increased abruptly upon the disruption of micro‐aggregates.