bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of non‐instantaneous exchange on the self‐diffusion of phosphate in soil
Authors: STAUNTON S. , NYE P. H. 
Published: July 2006

SUMMARYThe kinetics of isotopic exchange of phosphate in a soil were studied using three techniques: (a) in shaken suspension, (b) in a system where solution circulated through a thin disc of soil, and (c) in moist soil from which solution was extracted by centrifugation with a dense immiscible liquid.The exchange kinetics of isotope diffusing in moist soil were inferred from the concentration profile of the isotope after diffusion periods of 10‐60 days. The proportion of the exchange that is effectively instantaneous in this diffusion system was much lower than in systems in which isotope is uniformly applied to the soil.It is postulated that the difference arises because exchange of diffusing isotope is limited by access to exchange sites and not, during the period considered, by slow exchange at the solid‐liquid interface.
The effects of pH and drying on adsorption of phosphate by aluminium‐organic matter associations
Authors: HAYNES R. J. , SWIFT R. S. 
Published: July 2006

SUMMARYThe effects of pH value and of drying on phosphate adsorption by Al‐peat and Al‐humate associations were investigated. Raising the pH of the Al‐organic matter associations from 3 to 7, by addition of Ca(OH)2, greatly increased their phosphate adsorption capacity. There was a pronounced increase in phosphate adsorption as a result of drying the limed, Al‐organic matter associations, but when equilibration time was increased phosphate adsorption by moist Al‐peat samples approached that of the dried samples, indicating that the drying effect was at least partially caused by incomplete equilibration of P in the moist samples. In contrast, increasing the equilibration time did not alter the magnitude of the pH effect.A detailed study was made of the adsorption of phosphate both by Al‐peat limed to pH 7.0, and by its constituent components Ca‐peat (pH 7.0) and hydroxy‐Al (pH 7.0), synthesized separately then mixed together. For limed Al‐peat, drying increased phosphate adsorption, whereas for the individually synthesized components in combination the reverse was true. Thus, the limed Al‐peat behaved differently to its components.The increasing adsorption of phosphate by Al‐organic matter complexes with rising pH was attributed to increasing hydrolysis and polymerization of hydroxy‐Al associated with the organic matter. However, the interaction of organic matter with hydroxy‐Al would block many phosphate adsorption sites on the hydroxy‐Al. Upon drying, it is suggested that the organic matter condenses and the accessibility of phosphate to adsorption sites on the hydroxy‐Al is increased. Thus, drying resulted in increased phosphate adsorption.
Release of potassium from some benchmark soils of India
Authors: DHILLON S. K. , SIDHU P. S. , BANSAL R. C. 
Published: July 2006

SUMMARYRelease of potassium from 15 surface samples of benchmark Alluvial, Red and Black soils of India to 0.01 M solutions of BaCl2, CaCl2, NH4Cl and NaCl was studied in soils either untreated or pretreated with 5 × 10−3 M KCl. In the untreated soils, the efficacy of the extractants declined in the sequence: BaCl2 > NH4Cl > CaCl2 > NaCl. Cumulative K‐release was greatest from Black soils, followed by Red and Alluvial soils. From soils pretreated with 5 * 10−3 M KCl, more K was released than retained, and more ‘native’ K was released than that from untreated soils. Increase in the release of ‘native’ K decreased in the sequence: Red > Alluvial > Black soils. The amounts of surface and internal K, desorption rate constants and parabolic diffusion constants were calculated from K release to the various electrolytes.
Description of titration curves of mixed materials with variable and permanent charge by a mathematical model. 3. Influence of the nature of the permanent charge mineral
Authors: MADRID L. , DIAZ‐BARRIENTOS E. , SÁNCHEZ‐SOTO P. J. 
Published: July 2006

SUMMARYA mathematical model, previously developed, is tested here for various clay minerals and their mixtures with iron oxides. The model yields good predictions of the permanent charge for non‐swelling clay minerals, but clearly underestimates the permanent charge of montmorillonite. This result is interpreted as being caused by partial accessibility of the internal surface of the mineral.In all cases, the values estimated for the permanent charge of the clay minerals fit the data for their mixtures with iron oxides. Nevertheless, important differences are found between the values of maximum densities of adsorption sites of potential‐determining ions of the various minerals estimated when they are alone and when they are in mixtures, particularly in the case of montmorillonite mixtures. The differences are explained in terms of an intimate association between the particles in the mixtures, and some SEM and EDX results point to the same conclusion.
Chemical change in organic matter decomposing in and on a forest Rendzina under beech (Fagus sylvatica L.)
Authors: JOERGENSEN R. G. , MEYER B. 
Published: July 2006

SUMMARYThe chemical characteristics of the organic matter of five horizons from a Terra fusca Rendzina under beech were compared by fractionation. Two litter layers, sampled in autumn, were compared: fresh leaf litter and the remains of the previous years’ litter. Three mineral horizons, A, B and C were also sampled.While decomposition in the litter layer led only to slight redistribution of the fractions, much greater changes occurred when the organic matter became incorporated into the mineral soil. The proportion of C and N in amino sugars rose markedly down the profile. The percentage of more readily soluble substances, such as the hot water‐soluble fraction or the unidentified, hydrolysable component, in the mineral soil was twice the amount found in the leaf litter. The percentage of non‐hydrolysable compounds in the mineral horizons was nearly half that found in the leaf litter. The C/N ratio fell from 44 in fresh leaf litter to 10 in the C horizon. The amino acid C/amino sugar C ratio fell from 45 in fresh leaf litter to 3.0 in the B horizon. The glucosamine/galactosamine ratio fell from infinite in galactosamine‐free fresh leaf litter to 1.2 in residual litter and increased again to 2.5 in the C horizon. The hexose/pentose ratios were virtually the same in all horizons. The glucose/ mannose ratio showed a steady fall down the profile, from 7.7 to 1.6. The glucuronic/ galacturonic acid ratio increased from 0.1 and 0.2 in the two litter layers to 4.7 in the C horizon.
An evaluation of some oxidative degradation methods of humic substances applied to carbohydrate‐derived humic‐like polymers
Authors: ALMENDROS G. , LEAL J. A. 
Published: July 2006

SUMMARYArtificial polymers prepared by acid‐catalysed dehydration of glucose were examined by 13C nuclear magnetic resonance (NMR), and subjected to degradation procedures frequently used in the study of humic substances: acid hydrolysis, persulphate degradation, alkaline permanganate oxidation, perborate depolymerization and cupric oxide oxidation. The ethyl acetate–soluble degradation products were identified by combined gas chromatography‐mass spectrometry. The compounds released in the perborate and in the cupric oxide treatments are as would be expected from a polymer derived from glucose dehydration products. Such degradation patterns contrasted with those obtained by alkaline permanganate oxidation, which resembled those of humic‐ or lignin‐like substances.
Aluminosilicate phases during initial clay formation: H+‐Al3+–oxalic acid–silicic acid–Na+ system
Authors: BILINSKI H. , HORVÁTH L. , INGRI N. , SJÖBERG S. 
Published: July 2006

SUMMARYThe solid phases and the precipitation boundary characterizing the system H+‐Al3+‐oxalic acid‐silicic acid‐Na+ are discussed. Model experiments have been used to throw more light on two environmental problems: the formation of sparingly soluble aluminium silicates in oceans and alkaline lakes, which could be determining aluminium and silicate concentrations in pore waters of sediments, and the validity of inorganic and organic mechanisms of podzolization and their significance for soil science.pH and Tyndallometric measurements were performed at constant ionic strength of 0.6 M NaCl at 25°C. Three phases Al(OH)4, H4SiO4 (phase Via), Al2, (OH)6.H4SiO4 (phase VIb) and NaAl(OH)4.(H4SiO4), (phase VIII) determine the precipitation boundary. Phase NaAl(OH)4.H4SiO4 (phase VII precipitates at 0.4pH units above NaAl(OH)4.(H4SiO4)2. Using a set of previously determined binary and ternary complexes, and phases of the subsystems, the following formation constants were deduced:

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Phases VIa and VIb are described as end‐members of the allophane series with Si: Al ratios of 1:1 and 1.2. Phase VIb was identified with protoimogolite allophane. These two phases are good model clays for podzolic soils and are extremely soluble at pH < 4. Sodium phases could be hydrous feldspathoids. These phases are possible in sediments of seawater or saline lakes.It is suggested that organic and inorganic mechanisms of podzolization operate sequentially and that neither of them alone can completely describe the process.
Effect of liming on phosphate sorption by acid soils
Authors: NAIDU R. , SYERSY J. K. , TILLMAN R. W. , KIRKMAN J. H. 
Published: July 2006

SUMMARYThe sorption of phosphate (P) by four strongly acid Fijian soils from 0.01 M CaCl2 decreased with increasing pH up to pH 5.5–6.0 and then increased again. The initial decrease in P sorption with increasing pH appears to result from an interaction between added P, negative charge, and the electrostatic potential in the plane of sorption. The results of a sorption study, involving KCl or CaCl2 of varying concentrations as the background electrolyte and using Nadroloulou soil incubated with KOH or Ca(OH)2, suggested that the increase in P sorption at pH values > 6.0 was caused by the formation of insoluble Ca‐P compounds. For some soils this is consistent with the results of an isotopic‐exchange study in which incubation with lime caused marked reductions in the amounts of exchangeable P at high pH.
The development, calibration and field testing of a soil loss and a runoff model derived from a small‐scale physical simulation of the erosion environment on arable land in Zimbabwe
Authors: ELWELL H. A. 
Published: July 2006

SUMMARYSoil loss and runoff prediction models were developed for a clay soil from a five‐factor small‐scale physical simulation of the field environment by following a central composite rota table experimental design.The uncalibrated models efficiently ranked observed annual soil losses and runoff over a 4–year period between nine field treatments consisting of two bare fallows, two weed fallows and five plots cropped to soyabeans.When calibrated against the field data, the soil loss model predicted the 4–year mean losses from cropped and bare fallow treatments to within 6% for two of the plots, to within 12% for five of the plots and to within 14% for all seven treatments.Over the same period, the runoff model predicted mean annual runoff for the cropped and bare fallow treatments to within 4% for four of the plots and to within 16% for all seven treatments.Percentage vegetal cover proved to be an adequate parameter for describing the role of the soyabean crop in runoff and soil loss processes for a wide range of planting densities of the crop. However, it did not prove to be an efficient index for weed fallows and it was apparent that factors other than simple above‐ground cover became important soon after germination.
Paragonite in Spanish ‘raña’ soils
Authors: GARCÍA‐GONZÁLEZ M. T. , ARAGONESES F. J. 
Published: July 2006

SUMMARYThis study reports the presence of paragonite in the fine fraction of soils developed from Pliocene‐Quaternary aged formations (raña) in central Spain and investigates the factors that determine its presence. Paragonite was found in two of the four areas studied. These two areas had a lesser degree of alteration, although of the two, the more altered area had a higher proportion of paragonite. No significant correlation was found between paragonite and illite content, although the areas which contain paragonite generally had a higher illite content. The presence of paragonite was determined by the origin of the materials in each of the zones.
Effect of tillage on soil organic carbon mineralization estimated from 13C abundance in maize fields
Authors: BALESDENT J. , MARIOTTI A. , BOISGONTIER D. 
Published: July 2006

SUMMARYThree methods of cultivation, conventional tillage (CT), superficial tillage (ST) and no‐tillage (NT), were applied for 17 years to continuous maize. Their effect on soil organic carbon content was investigated through measurements of carbon and 13C/12C ratios, using the natural difference in 13C content between C3 plants and maize, which is a C4 plant. Because the soil had carried C3 plants before the experiment started, the organic carbon remaining from that time (C3,‐carbon), was distinguished from the carbon derived from maize. Comparison between continuous wheat and maize plots showed that organic matter from both maize and wheat decomposed without significant 13C enrichment, whereas older C3‐carbon was enriched by 1.5% compared to that of fresh wheat material. From the initial 3.6 kg C m−2 in the topsoil (0–30 cm), 0.95 were mineralized in the CT treatment, but only 0.45 in NT. The mineralization was the same in the tilled layer of ST as in CT. The CT treatment accumulated 1.1 kg C m−2 of maize‐derived carbon and the NT treatment 0.8. The mineralization of initial C3‐carbon was the same at all depths between 0 and 30 cm in the NT treatment; 75% of the carbon derived from maize was found in the 0–5 cm layer.
Soil controls on recharge to aquifers
Authors: COOPER J. D. , GARDNER C. M. K. , MACKENZIE N. 
Published: July 2006

SUMMARYCase studies are presented of the use of soil water measurements to determine the pathways, timing and quantities of natural recharge to groundwater at sites on the Chalk and Triassic Sandstone aquifers in England. Water content and potential have been monitored for several years at seven sites and unsaturated hydraulic conductivity measured in situ at three of the chalk sites. Recharge was estimated using a combination of the zero flux plane (ZFP) method and a simple water balance. Examples of the water balance are presented for three sites.It is shown that a shallow (∼1 m) depth of permeable drift and soil increased the annual drainage from the soil to the underlying formation by about 34% at a pair of sites on the Chalk aquifer. Effects upon drainage timing are equally dramatic. On thin soil directly on chalk, drainage responds quickly to rainfall and, once evaporation starts to exceed rainfall, declines rapidly. On drift‐covered sites, the drainage continues for a much longer period, as it does from the loamy soil overlying the sandstone site.
The effect of volatilization on the mass flow of a non‐aqueous pollutant liquid mixture in an inert porous medium: experiments with kerosene
Authors: GALIN T. , McDOWELL C. , YARON B. 
Published: July 2006

SUMMARYKerosene, an industrial petroleum product characterized by the presence of a large number of petroleum hydrocarbons (C9‐C15), was selected as an example of a non‐aqueous pollutant liquid (NAPL) mixture for our studies. Three inert materials (fine, medium and coarse sand) were used in the experiments and the initial amount of kerosene applied ranged from residual to saturated retention capacity.Volatilization in the air phase and saturated mass flow of kerosene in the three sands were studied in the laboratory under controlled conditions. The volatilization was the major physicochemical process affecting the fate of kerosene in the inert porous medium. During volatilization the liquid kerosene changed its composition by gradually losing its light components (C9‐C13), and the viscosity of the remaining liquid kerosene increased. The increase in viscosity led to a decrease in the infiltration rate, for example, by about 20% when the viscosity increased from 1.3 × 10−3 to 2.0 × 10−3 Pa s. The relationship between the composition of the residual kerosene following volatilization and its mass flow in a sand illustrates the behaviour of non‐aqueous pollutants in inert porous media.
Sulphate sorption by variable charge soils
Authors: GUADALIX M. E. , PARDO M. T. 
Published: July 2006

SUMMARYThe sorption of sulphate (SO2−4) by three variable charge soils from the Canary Islands (Spain) was studied. Sulphate sorption decreased with increasing pH. Only negligible amounts of SO2−4 were sorbed above pH 6.5. When the soils were washed with an indifferent electrolyte (0.01 M KCl), more SO2−4 was recovered than had been sorbed. This indicated a release of native SO2−4 Sulphate replaced hydroxyl ions (OH) and co‐ordinated H2O molecules, as well as very small amounts of silicate (Si). No measurable amount of phosphate (P) was released. On average hydroxyl release accounted for 50% of SO2−4 sorbed, the rest being accounted for by the increase in negative charge as measured by K+ adsorption. The results presented here are consistent with the sorption of SO2−4 through a ligand exchange mechanism, but in a different plane of sorption to that of phosphate.
Testing a mechanistic model. XI. The effects of time and of level of application on isotopically exchangeable phosphate
Authors: BARROW N. J. 
Published: July 2006

SUMMARYA model for the reaction of ions with soil was improved to permit time trends to be followed at a given level of phosphate addition. Difference equations were also developed to describe the rate of reaction of ions with both vacant sites and occupied sites, while diffusive penetration of the surface was occurring. The model was applied to data for the effects of time and of level of application on exchangeable phosphate.Many of the observed values for isotopically exchangeable phosphate could be well‐described if it was assumed that equilibration of 32P with surface sites was very rapid and this was followed by a diffusive penetration into the adsorbing particles. However, for short periods of contact between soil and 32P, it was necessary to also take into account the rate of the reaction between 32P and surface sites. This reaction was largely with vacant sites. Reaction with occupied sites–that is, true exchange–was unimportant.It is suggested that the electric potential of the surface may determine whether reaction is with occupied or vacant sites. In contrast to reaction of 32P with occupied sites, reaction with vacant sites involves a net transfer of charge. Reaction with vacant sites would be slow if the potential was large and negative. It is shown that when reaction with vacant sites is slow, the proportion of previously added 31P recorded as exchangeable increases with level of addition of 31P. This may explain published observations of slow and non‐linear exchange in some soils.
The distribution of humic substances between the solid and aqueous phases of acid organic soils; a description based on humic heterogeneity and charge‐dependent sorption equilibria
Authors: TIPPING E. , WOOF C. 
Published: July 2006

SUMMARYA description of the partitioning of humic substances (HS) between the solid and solution phases of acid organic soils is proposed, based on the opposition of hydrophobic and hydrophilic properties. Soil HS are considered to be of two types, mobile, i.e. potentially transferable to the soil solution (HSM), and immobile (HSI). The HSM consist of a series of fractions, each with the same ion‐binding properties, but differing in hydrophobicity. Partitioning of HSM between the solid and solution phases depends upon the net humic charge (Z), which is determined by the binding of protons and other cationic species. For each fraction, the extent of transfer to the solution phase increases as Z becomes more negative. The most hydrophilic HSM require only a small negative charge for transfer to the solution phase to be favoured, while the most hydrophobic require the development of a large negative charge. A mathematical version of the model, combined with an existing model of ion‐binding by HS, can explain reasonably well the release of HS from agitated aqueous suspensions of organic soil samples. The model also explains the release of HS when the solution phases of organic soil suspensions were repeatedly replaced with NaCl solution.
Factors affecting the formation of dark, thick epipedons beneath forest vegetation, Michigan, USA
Authors: SCHAETZL R. J. 
Published: July 2006

SUMMARYExtremely gravelly, coarse‐textured soils (frigid Udorthents and Rendolls) with different thicknesses of Oa+A horizon sequences were studied to identify factors that have influenced their genesis. These well‐drained, forested soils occur on geomorphic surfaces that range in age from 3200 to 6000 years BP. The soils all have more than 500 g kg−1 coarse fragments by mass; most contain less than 300 g kg−1 fine earth. In the lower solum of most pedons, content of cobbles increases and amount of fine earth decreases. Most coarse fragments are dolomite and chert.Thick, gravelly Oa and A horizons are weakly correlated with parent material characteristics such as high pH and carbonate contents. Organic matter concentrations in, and thicknesses of, upper horizons are enhanced by an abundance of coarse clasts, as soils with the most gravel exhibited the thickest and darkest epipedons. Relatively high amounts of crystalline clasts in the fine gravel fraction, as well as feldspathic minerals in the fine sands, also appear to promote the development of mollic epipedons.
The use of region partitioning to improve the representation of geo statistically mapped soil attributes
Authors: McBRATNEY A. B. , HART G. A. , McGARRY D. 
Published: July 2006

SUMMARYAn attempt to improve the representation of a geo statistically mapped soil attribute, clay content of the surface soil, through partitioning of the study area into two new regions was made. A topographic boundary divided the study area into hill and plain regions.Possible global non‐stationarity or non‐stationarity within the two newly defined regions was dealt with through the use of intrinsic random functions (IRF) of order k. Cross‐validation of generalized covariance functions suggested that ordinary kriging might also have been appropriate. Exponential variogram models were subsequently fitted to the experimental variograms for each region.IRF‐k block kriging and ordinary block kriging were then used as the primary methods of estimation. Both IRF‐k and ordinary kriging performed badly in the vicinity of the topographic boundary when global models were used. This discontinuity was removed, at the expense of the introduction of some additional edge effects, when the hill and plain regions were kriged using models appropriate to each region.Independent zero‐order generalized covariance functions with nugget and linear terms and exponential variogram models produced similar representations of clay content within each region, when used with their respective estimators. Splitting the region resulted in a 6% reduction in mean absolute deviation and a 14% reduction in mean squared deviation of predicted clay contents compared with a global model.