bluuebunny/crossref_metadata_2025_split huggingface dataset:
34S natural abundance variations in prairie and boreal forest soils
Authors: SCHOENAU J. J. , BETTANY J. R. 
Published: July 2006

SUMMARYThe systematic nature of the 34S natural abundance variations (δ34S) in a prairie and boreal forest ecosystem enabled construction of hypotheses regarding the origin and cycling of S in the two soil‐plant systems. By considering the 34S abundance variations in relation to soil S transformations, a better understanding of S isotope fractionation in soils was also achieved.The δ34S values suggest that atmospheric S becomes increasingly more important as a S input as pedogenesis proceeds in these soils. The origin and movement of sulphate salt in a saline seep was evaluated using δ34S values, demonstrating the usefulness of the δ34S technique in soil salinity studies. The 34S‐enrichments and depletions found in soil organic S fractions were consistent with postulated differences in lability, mobility, and turnover rate. Wheat plants growing on the saline, sulphate‐saturated prairie soil were found to be enriched in 34S relative to surrounding S sources, providing indirect evidence for release of 34S‐depleted H2S by the plants as a S‐stress relief mechanism.
Effects of lime applications to parts of an upland catchment on soil properties and the chemistry of drainage waters
Authors: ADAMS W. A. , EVANS G. M. 
Published: July 2006

SUMMARYThe liming of soils in the lower part of an upland catchment was found to have a major effect on both soil properties and the chemistry of drainage waters. Exchangeable Al was closely correlated with soil pH and showed a very steep rise from 2.6‐4.8 meq 1−1 over the pH range 5.5‐4.5. As streams flowed from unimproved through improved land there was an increase in pH and the concentration of all major anions and basic cations. The greatest increase was in Ca (approximately 3.5‐fold). The concentrations of all dissolved Al species decreased, with inorganic monomeric Al falling to near zero. Leachates were examined from soils representative of the most acidic and the least acidic. Calcium concentrations differed by almost tenfold. Aluminium was present in leachates from the limed soil, but most was unreactive and none was inorganic monomeric. Most of the Al leached from the acid soil was monomeric.A model of soil acidification is proposed in which soil Ca is depleted at a rate of 8% of the exchangeable Ca per annum. The model predicts that liming a soil to neutrality would be likely to influence drainage water chemistry for 30‐40 years and that the most acidic soils of the catchment show no net loss of Ca to drainage.
Potassium and magnesium in some Kenyan soils: their mineral sources and release to Ca‐resin
Authors: ONCHERE J. , GOULDING K. W. T. , WOOD I. G. , CATT J. A. 
Published: July 2006

SUMMARYFive soil types from Kenya were examined for their ability to release K and Mg to crops by extracting them with a calcium‐saturated cation exchange resin, and for the mineral sources of K and Mg. Amounts and rates of release of exchangeable, short‐ and long‐term reserves of K and Mg were determined. This was done for K before and after one, two and 10 wetting and drying (WD) cycles, designed to mimic the effect of the local climate on K release. The order of decreasing K and Mg contents of the soils was Muguga > > Katumani > Kampi‐ya‐Mawe (KYM) ∼ Ithookwe ∼ Kwale. In the case of K, wetting and drying increased the exchangeable fraction in all of the soils. The Muguga, Ithookwe and KYM soils have the capacity to release a great deal of K in the long‐term, but at very different rates; the Kwale soil has few reserves and fixes K on WD.The K and Mg contents of the soils were closely related to the mica contents of the clay + silt fractions. Exchangeable and non‐exchangeable K was released from soil micas primarily by ion exchange, with some contribution to non‐exchangeable K from dissolution. Release of exchangeable Mg was primarily by ion exchange, whilst that of non‐exchangeable matrix Mg was by dissolution of trioctahedral mica in the clay + silt and the sand fractions of the soils. Response would be expected only to K fertilizers and only with the Kwale soil. However, all the other soils should, in the interests of good husbandry, receive maintenance dressings of K and Mg at convenient times in the crop rotation.
Evidence for aliphatic mixed mode coordination in copper(II)–fulvic acid complexes
Authors: GREGOR J. E. , POWELL H. K. J. , TOWN R. M. 
Published: July 2006

SUMMARYA comparative approach based on ion–selective electrode measurements is presented for studying Cu(II) complexing by fulvic acids. Metal binding curves (% free metal vs pH) and complexation capacity curves (% free metal vs total metal at fixed pH) for copper(II) fulvic acid systems are compared with those for appropriate model ligands.It is inferred that citrate, malonate and amino acid moieties could dominate complexing to Cu(II) at pH 3 to 7. The involvement of amino acid moieties is supported by fluorescence quenching and by anodic stripping voltammetry (ASV) studies. The proportion of ASV–non labile complexes is reported for Cu(II) and Pb(II) fulvic acid systems at pH 4.8.A mixed mode of coordination is proposed, with the dominant binding sites varying with pH and metal:ligand ratio.
A rapid method for predicting the lime requirement of acidic temperate soils with widely varying organic matter contents. I. Development of the lime requirement model
Authors: BAILEY J. S. , STEVENS R. J. , KILPATRICK D. J. 
Published: July 2006

SUMMARYA model to describe the shapes of soil pH‐CaCO3 neutralization curves is presented. The model can be used to predict lime requirement in soils with widely varying organic matter contents. Parameters of the model are predicted from the easily measured soil properties of sample density and initial pH. The results suggest that soil titratable acidity is primarily related to soil organic matter content, and that soil organic matter content may be predicted from measurements of soil sample density. The proposed method for predicting lime requirement should be superior to other established quick‐test methods for routine soil testing both in terms of speed and versatility.
Roughness of soil fracture surfaces as a measure of soil microstructure
Authors: GRANT C. D. , DEXTER A. R. , HUANG C. 
Published: July 2006

SUMMARYThe examination of soil fracture surfaces that are created under tensile stress may reveal a great deal about the internal structural condition of the soil. A simple technique for quantifying the roughness of soil fracture surfaces from a measurement of their topography in cross‐section is described. The technique involves calculating the standard deviation of the differences between the measured elevations of soil fracture surfaces and their corresponding running‐mean values. The standard deviation, σR, is used as a measure of the fracture surface roughness. Advantages of this technique over others are discussed.Two methods for measuring the topography of soil fracture surfaces are presented: a bisection (single transect) method, and a laser scanning (multiple transects) method. The laser scanning method is to be preferred because it requires no sample preparation and enables greater and more rapid replication. Also, fracture surfaces created by applying direct tension in the hands produced values of σRthat were statistically indistinguishable from those created using indirect tension in a loading frame. This result makes the technique of fracture surface analysis usable for both laboratory as well as field investigations of soil structure.An example of the technique is presented to illustrate the role that air‐filled pores play in the brittle fracture of unsaturated soil (air‐filled pores are closer together in drier soils and further apart in wetter soils.) A strong positive linear correlation was found between the gravimetric water content,wand σRof natural soil clods, which supports the contention that brittle fracture of unsaturated soils under tensile stress occurs at least partly because of the propagation of air‐filled pores.
The power‐function model for the soil moisture characteristic
Authors: BUCHAN G. D. , GREWAL K. S. 
Published: July 2006

SUMMARYThe minimum number of parameters required to model the unsaturated soil moisture characteristic, relating volumetric water content (θ) and matric suction (χ), is shown to be two. A third parameter, θ=θs at saturation, is required to define its saturation limit. The popular power‐function χ/χe, = (θ/θs)b is the most general three‐parameter model, with χ normalized by a notional air‐entry potential, χe. When log‐transformed, e.g. as In χ= a + bln(θ/θs), it gives a good fit to observations over varying ranges of χ. We show, using US, Australian, UK and NZ data, that a,b and θs, in this formulation are uncorrelated across a wide range of textures, thus providing a ‘basis set’ of independent parameters. Gregson et al. (1987) used the alternative formulation In χ= a″+ bln(100θ), with χ rescaled to a percentage. Their reported correlation between a″ and b, which led to their ‘one‐parameter model’ of the characteristic, is shown to be a mathematical artefact, arising from absorption of the term – b[ln(100)+ ln θs] into a″.
Forest soil chemical changes between 1949/50 and 1987
Authors: BILLETT M. F. , PARKER‐JERVIS F. , FITZPATRICK E. A. , CRESSER M. S. 
Published: July 2006

SUMMARYSoil profiles from the Alltcailleach Forest in north‐east Scotland originally sampled in 1949/50 were resampled in 1987. Soil pH, exchangeable Ca, Mg, K and Na, extractable Al and cation exchange capacity were measured on the original stored and resampled soils. Chemical changes were characterized by decreases in pH, base cations, base saturation and cation exchange capacity. Extractable amounts of Al increased. Sequential leaching experiments showed a significant increase in the amount of extractable sulphate in mineral soil horizons.Changes in soil chemistry were interpreted to result from a combination of nutrient depletion caused by tree growth, natural pedogenic processes and atmospheric pollution effects.
Effect of liming and added phosphate on charge characteristics of acid soils
Authors: NAIDU R. , SYERS J. K. , TILLMAN R. W. , KIRKMAN J. H. 
Published: July 2006

SUMMARYThe effects of liming‐induced pH changes on surface charge were studied with four acid Fijian soils. All the soils possessed both positive and negative charge. Much of this charge was pH‐dependent, but some negative charge was present at pH values as low as 4.0 and small quantities of positive charge were detected at pH values as high as 8.2.Adsorption of phosphate (P) reduced positive charge at low pH and increased negative charge at high pH. The net amount of surface charge per unit of P adsorbed varied with pH and appeared to depend on the mineralogy of the soil.
Calibration and validation of a model of non‐interactive solute leaching in a clay‐loam arable soil
Authors: VINTEN A. J. A. , REDMAN M. H. 
Published: July 2006

SUMMARYA capacity‐type approximate leaching model (Addiscott et al., 1986) with a simple treatment of soil matrix permeability was tested, using field tracer experiments with CaBr2, on hydrologically isolated plots. The model predictions are sensitive to the value of the soil matrix permeability factor, a, and four methods of estimating this parameter were evaluated: (1) using a calibration based on soil texture; (2) least‐squares fitting of the model to successive neutron probe measurements of the water content profile; (3) least‐squares fitting to daily drainage outflow; (4) least‐squares fitting to cumulative drainage outflow. The best independent method (method 3) led to slight (20–30%) under‐prediction of leaching losses for two of the four experiments, but in one experiment leaching was much less than predicted. As a management model the approach seems promising but more attention needs to be paid to estimation of the value and variability of the permeability parameter, a.The convective‐dispersion equation, using steady‐state assumptions and a fitted dispersion length, gave as good a prediction of cumulative leaching losses as the approximate model studied here.
The use of air‐filled porosity and intrinsic permeability to air to characterize structure of macropore space and saturated hydraulic conductivity of clay soils
Authors: BLACKWELL P. S. , RINGROSE‐VOASE A. J. , JAYAWARDANE N. S. , OLSSON K. A. , MCKENZIE D. C. , MASON W. K. 
Published: July 2006

SUMMARYIntrinsic permeability to air of macropore space (ka) is related to macroporosity (ɛ) and organization of macropore space (O). Organization is defined as ka/ɛ. The use of ka for estimating saturated hydraulic conductivity (Ka) is also considered. The relationship between Log (O) and ɛ (Oɛ characteristic) can be used to describe changes to the macropore space of clay soils by amelioration and compaction. The effects of dominant macropore shape can also be identified and calculated as an empirical index of the efficiency of the pore organization E (E=log (O)/ɛ). Intrinsic permeability can then be related to E in a E:ka characteristic. Intrinsic permeability is the parameter most sensitive to structural change and E is mainly influenced by the dominant shapes of the macropores. Thus, the E:ka characteristic is suggested as a basis for studying differences in macropore space as may occur in response to external and internal stresses upon the soil and different systems of soil management, for example increases of packing pores by cultivation or of fissures by gypsum application and loss of packing pores by compaction. Empirical data indicate that Ks of the B horizons of Australian red‐brown earths can be estimated from ka of macropore space at a standard potential.
Nutrient changes in decomposing beech leaf litter assessed using a solution flux approach
Authors: JOERGENSEN R. G. , MEYER B. 
Published: July 2006

SUMMARYThe decomposition of beech (Fagus sylvatiea L.) leaf litter was examined in lysimeters. The experiment allowed comparison of data from mass changes of bioelements in leaf litter and the solution flux balance of through fall input and lysimeter output over a two‐year period (1983 and 1984). The annual C loss from the leaf litter was 19%. Na and K concentrations in this leaf litter decreased in the first year and remained constant in the second, while those of Ca and Mg showed no significant changes. N and S amounts per ha increased during the first year by about 7 kg N ha−1 and 0.5 kg S ha−1. Ash, Fe, Mn and Al amounts per ha increased to 470, 130 and 240% of their initial levels. These net increases in the first year of decomposition are discussed.The mean annual water and element input by through fall during the experiment corresponded approximately to the long‐term average. Thirty to 40 mm more water was evaporated from the litter layer in the drier year (1983) than in 1984. Total N, NO, Na and C1 flux rates of through fall inputs and lysimeter outputs were equal. NH, input rates were greater and organic N smaller than the output rates of the lysimeters. Water balance data indicated that the lysimeter output of K, Mg, Ca and SO, exceeded through fall input. Probable reasons for these differences are discussed.
Mechanism of sulphate adsorption by two tropical SoilS
Authors: CURTIN D. , SYERS J. K. 
Published: July 2006

SUMMARYThe mechanism of sulphate (SO4) adsorption was investigated using two highly‐weathered soils with contrasting surface‐charge characteristics (one with a net negative charge and the other with a net positive charge). The addition of SO4caused a release of OH and increased the adsorption of cations, in keeping with the widely‐held view that SO4is chemisorbed by replacing ‐OH and ‐OH2ligands. On the other hand, adsorbed SO4was completely recovered by washing with an indifferent electrolyte solution (1 M KC1), an extractant which is usually taken to be specific for ‘exchangeable’ ions. The amounts of SO, adsorbed were several times higher than those of non‐specifically adsorbed Cl. It is suggested that the experimental observations can be interpreted in terms of a model in which SO4adsorbs in a plane closer to the surface than monovalent anions (e.g. in the Stern layer). The consequence of higher counter‐ion valence and proximity to the surface is that additional positive charge is induced onto the surface by OH release. Charge reversal in the diffuse layer allows more cations to be adsorbed. This type of adsorption may involve forces other than the purely electrostatic but, in contrast to chemisorption, the adsorbed anion does not become chemically coordinated to the surface metal atoms.
Evaluation of porous ceramic cups for monitoring soil‐water aluminium in acid soils: comment on a paper by Raulund‐Rasmussen (1989)
Authors: HUGHES S. , REYNOLDS B. 
Published: July 2006

SUMMARYFollowing recent observations by Raulund‐Rasmussen (1989) implicating A1 contamination of soil solutions isolated by suction‐cup samplers, A1 release from porous ceramic cups in acid solutions was investigated. In our studies a flush of Al, followed by a gradual decrease in leaching over successive extractions was observed. The amount of Al released was retarded by the presence of 37 μmol dm−3 of A1 in solution. Gibbsite solubility controls were not observed; all solutions isolated by the cups were undersaturated with respect to amorphous gibbsite. The cups evaluated in this study are appropriate for sampling acidic soil solution, provided they are suitably pretreated and then equilibrated in the field before use.
Humic substances in acid organic soils: modelling their release to the soil solution in terms of humic charge
Authors: TIPPING E. , WOOF C. 
Published: July 2006

SUMMARYBatch titration experiments were carried out with organic soil samples in order to investigate the release to the solution phase of humic substances (HS). Measurements were made of pH, dissolved organic carbon (DOC) concentration, and the concentration of mono‐meric (inorganic + organic) aluminium, as functions of added acid or base. DOC was taken to be entirely due to HS. The results can be interpreted in terms of a model in which the soil is considered to contain two types of HS–mobile or potentially mobile (HSM), and immobile (HSI). The binding of inorganic ions by the HS is calculated using humic ion‐binding model IV, previously developed in this laboratory. Model IV allows the charges on the HS (ZHSM, ZHST) to be calculated; these are determined mainly by the binding of H+ and A13+. Concentrations of HS in solution, [HSaq], are given by the equation:

image
where |ZHSM| is the modulus of ZHSM, nHSM is the carboxyl group content of HSM, cHSM is the soil content of HSM, β is a fitting parameter, and square brackets, [ ], indicate concentrations. For most of the soils a value for β of 3 gives acceptable agreements between measured and calculated values of [HSaq], indicating a major influence of charge on release. The optimized value of cHSM differs considerably among soils, whereas cHIS varies by only a factor of about two. Total humic contents (cHSM+ cHSI estimated by model optimization are in approximate agreement with values estimated by extraction of the soils with NaOH.
Phosphate sorption in allophanic soils and release of sulphate, silicate and hydroxyl
Authors: PARDO M. T. , GUADALIX M. E. 
Published: July 2006

SUMMARYPhosphate (P) sorption and the concomitant release of sulphate (SO,), silicate (Si) and hydroxyl ion (OH) were determined on three allophanic soils from Spain, at different P concentrations. P effectively replaced SO4, Si and OH. However, at every stage of P sorption, the molar ratios of the total amounts of anions released (SO4+ Si + OH) to that of the sorbed P were low.The amount of added P affected the relative proportions of SO4, Si and OH exchanged. At low concentrations of P, phosphate sorption was accompanied mostly by release of the adsorbed SO4 with some Si. As more P was sorbed an increasing displacement of OH was also observed.
A comparison of the surface impedance factors of Ca, Na, Rb and Cs derived from their self‐diffusion coefficients in various soils
Authors: STAUNTON S. 
Published: July 2006

SUMMARYSelf‐diffusion coefficients of calcium, sodium, rubidium and caesium on the topsoils and subsoils of contrasting soil series are presented. The distribution ratios of each cation on each soil, at the moisture content of the diffusion experiments, have been calculated by extrapolation from series of suspensions.Diffusion coefficients were found in each case to be greater than expected by considering the liquid phase alone. Surface‐phase impedance factors, fs, were calculated. Although impedance factors are considerably smaller on the surface than in solution, the surface flux may exceed the flux in the liquid phase. Differences of an order of magnitude separated average values of fs for each cation. For a given cation, variations between soils were considerably less. No correlation was found between fs and soil mineralogy or composition.Values of fs were found to decrease with increasing distribution ratio. Reasons for this observation are discussed, in particular the energy of adsorption of the cations. The possibility of extrapolating these findings to other soils, to potassium and to other cations is discussed.
13C NMR characterization of humic acids from soils of a development sequence
Authors: NEWMAN R. H. , TATE K. R. 
Published: July 2006

SUMMARYHumic acids were isolated from nine topsoils in New Zealand tussock grasslands. Cross‐polarization 13C NMR spectra of solid samples were used to estimate fractions of carbon contained in different types of chemical functional groups. The degree of oxygen substitution of aromatic rings showed a strong negative correlation with soil development. Aromaticities greater than 0.25 were found in humic acids from only the two least‐developed soils.
Use of force‐deformation curves to estimate Young's modulus and its applications to soil aggregate breakdown
Authors: OKUNLOLA A. , PAYNE D. 
Published: July 2006

SUMMARYSoil aggregates from a clay and a sandy loam were subjected to uniaxial compression and their force‐deformation relationships determined. From these relationships the elastic deformation was identified, and estimates were made of Young's modulus, elastic strain energy and work of fracture. Also estimated were the increases in surface area produced on breakdown and hence surface energies. The results were interpreted in terms of Griffith's crack theory, and apparent crack lengths were calculated. The calculated values were high, but the variability of the data prevented a full assessment of this approach to the study of brittle failure of aggregates.
Comparison of soil solution chemistry in zero tension and ceramic‐cup tension lysimeters
Authors: HENDERSHOT W. H. , COURCHESNE F. 
Published: July 2006

SUMMARYThe chemistry of soil solutions collected from plastic 0‐tension and ceramic‐cup tension lysimeters was compared. Except for NO−3 there was no systematic difference in the chemistry of major cations, anions, pH or Al speciation of the solutions collected by the two types of lysimeter. although there were some differences at both 25 and 75 cm depths, on such occasions the difference at the other depth was either in the apposite direction or non‐significant. The concentration of NO−3 was significantly lower in the 0‐tension lysi meters and, although the mechanism is not clearly understood, this may be due to uptake by micro‐organisms feeding on fine organic matter particles in these solutions. The choice of lysimeter can be based on the objectives and constraints of the research project, rather than on the fact that the soil solution is more representative with one type of lysimeter than another.