bluuebunny/crossref_metadata_2025_split huggingface dataset:
Testing a mechanistic model. V. The points of zero salt effect for phosphate retention, for zinc retention and for acid/alkali titration of a soil
Authors: BARROW N. J. , ELLIS A. S. 
Published: July 2006

SUMMARYThe pH of samples of a soil was altered by adding acid or lime and incubating the moistened soil at 60°C. The effect of varying the concentration of salt on pH, retention of phosphate, and retention of zinc was then measured.At low pH, increasing the concentration of salt decreased phosphate retention; at high pH, it increased it. The pH at which the effects crossed over (that is, the point of zero salt effect on phosphate retention) was higher than the point of zero salt effect on pH. This is opposite to effects observed with uniform surfaces. These results were described by a model in which it was assumed that individual sites varied in their electrostatic potential and that phosphate was retained preferentially by sites with the highest potential.Zinc retention was decreased by high concentrations of salt. This was partly because of effects of salt in decreasing the pH of solutions in contact with soil. There was no indication of a crossing‐over of effects at low pH. This suggested that the electrostatic potential of zinc‐retaining sites did not vary much with pH.
Ionic strength effects on surface charge and adsorption of phosphate and sulphate by soils
Authors: BOLAN N. S. , SYERS J. K. , TILLMAN R. W. 
Published: July 2006

SUMMARYTwo surface soils (Patua and Tokomaru) of contrasting mineralogy were incubated with several levels of either CaCO3 or HC1. The effects of ionic strength on pH, on surface charge, and on the adsorption of phosphate and sulphate were measured in three concentrations of NaCl.The pH at which the net surface charge was zero (point of net zero charge—PZC) was 1.8 for the Tokomaru soil and 4.6 for the Patua soil: differences that can be related to mineralogical composition. There was an analogous point of zero salt effect (PZSE) that occurred at pH 2.8 for the Tokomaru soil and at 4.6 for the Patua soil. The presence of permanent negative charge in the Tokomaru soil resulted in an increase in PZSE over PZC.The effect of ionic strength on adsorption varied greatly between phosphate and sulphate. For phosphate, there was a characteristic pH above which increasing ionic strength increased adsorption and below which the reverse occurred. This pH (PZSE for adsorption) was higher than the PZC of the soil and was 4.1 for the Tokomaru soil and 5.3 for the Patua soil. In contrast, increasing ionic strength always decreased sulphate adsorption and the adsorption curves obtained in solutions of different ionic strengths converged above pH 7.0. If increasing ionic strength decreases adsorption, the potential in the plane of adsorption must be positive. Also, if increasing ionic strength increases adsorption, the potential must be negative. This suggests that, depending upon pH, phosphate is adsorbed when the potential in the plane of adsorption is either positive or negative, whereas sulphate is absorbed only when the potential is positive.
A simple model for predicting the rates of dissolution of sparingly soluble calcium phosphates in soil
Authors: KIRK G. J. D. , NYE P. H. 
Published: July 2006

SUMMARYA simple model is developed for predicting the rates of dissolution of particles of sparingly soluble calcium phosphates in acid soils. The model comprises analytical solutions to equations describing the steady‐state diffusion of phosphate and hydrogen ions in soil. The concentrations of the ions in solution at the boundary between soil and mineral are found from the solubility product of the calcium phosphate and by equating the fluxes of the ions across the boundary. The diminution of the mineral particles as they dissolve, and the effect of neighbouring particles on each other, are allowed for. The model's predictions for dicalcium phosphate agreed very well with those of the more complex model, tested experimentally (Kirk & Nye, 1986a), but only one‐thousandth of the computer time was necessary to simulate equivalent conditions. he extension of the model to predict the rates of dissolution of the apatites in rock phosphates is described, and examples of the predicted rates of dissolution are given.
Effect of liming on extractable Zn, Cu, Fe and Mn in selected Scottish soils
Authors: JAHIRUDDIN M. , CHAMBERS B. J. , LIVESEY N. T. , CRESSER M. S. 
Published: July 2006

SUMMARYTen naturally acidic Scottish soils have been limed with CaCO3 at 0,0.25, 0.50, 0.75, 1.00 and 1.25 times the recommended lime requirement, and then subjected to three cycles of alternate wetting to field capacity at 20°C for 1 month and drying for 1 month. The Zn, Cu, Fe and Mn extracted by DTPA solution, both at pH 7.3 and also after adjustment to match the final soil pH, were measured by flame AAS. The same elements were determined in ammonium acetate extracts, for extractants buffered at pH 4.8, pH 7.0 or at the final soil pH. The effect of extractant pH upon the amounts of trace elements removed is discussed for the two extractants, with particular reference to Zn. The influence of soil pH upon the amounts of trace elements extracted is also considered. There appears to be a distinct relationship between rate of decrease of DTPA‐extractable Fe with increasing soil pH and the effect of pH upon DTPA‐extractable Zn, high rates of decrease of extractable Fe being associated with a more continuous decline in extractable Zn with increasing soil pH. Possible reasons for this relationship are discussed, in the light of an experiment conducted to examine the effect of Fe and A1 on loss of Zn from solution at high pH. DTPA‐extractable Cu varied little with increasing soil pH.
The design, limitations, and use of a portable tensiometer
Authors: MULLINS C. E. , MANDIRINGANA O. T. , NISBET T. R. , AITKEN M. N. 
Published: July 2006

SUMMARYA digital reading, portable, pressure‐transducer tensiometer, accurate to ± 100 Pa is described and compared with a dial gauge version. Both tensiometers deform the soil on insertion and the time to obtain a reliable measurement was found to depend on how long it took for disturbed soil around the sensing tip to re‐equilibrate with undisturbed soil. At matric potentials greater than −5 kPa the digital tensiometer equilibrated within a few minutes but a t potentials less than −30 kPa both tensiometers required more than 2 h. Two examples are given in which digital tensiometers are used to investigate spatial variation in water‐table height.
Influence of iron oxides on cobalt adsorption by soils
Authors: BORGGAARD O. K. 
Published: July 2006

SUMMARYEleven soils from Denmark and Tanzania were extracted with ammonium acetate (controls), EDTA, and dithionite‐EDTA (DE) to fractionate iron (and manganese) oxides. The amounts of cobalt adsorbed and acidity desorbed by the extracted soils as well as by two synthetic iron oxides were determined, using 0.85 mM cobalt in 0.2 m NaNO3.No significant correlations were found between cobalt adsorption and the contents of extractable manganese or organic matter, presumably because of their low contents. The major part of the cobalt adsorption (by DE‐extracted samples) was due to the clay fraction and was associated with the release of approximately one proton per adsorbed Co. The remaining cobalt adsorption was attributed to the iron oxides. This portion of adsorbed cobalt was well described by considering soil iron oxides composed of only two fractions, an EDTA‐extractable fraction of high reactivity and a less reactive fraction corresponding to the difference between DE‐extractable iron and EDTA‐extractable iron. Approximately 1.7 protons were released per Co adsorbed by these iron oxide fractions and by the synthetic iron oxides.The amounts of cobalt adsorbed by the soil iron oxides were well predicted from the contents and specific surfaces of the two iron oxide fractions together with the specific cobalt adsorption of synthetic iron oxides.
The elucidation of soil pattern in the Wyre Forest of the West Midlands, England. I. Multivariate distribution
Authors: OLIVER M. A. , WEBSTER R. 
Published: July 2006

SUMMARYThe soil of the eastern 6 km2 of the Wyre Forest in the West Midlands of England was surveyed by recording the soil profile at 36 points per km2 chosen by stratified random sampling. Ordination by principal component analysis revealed an unclustered multi‐variate distribution, which nevertheless was classified profitably into six fairly stable groups. The groups lacked spatial coherence when mapped, and a novel method of spatially weighted classification was devised to increase the spatial coherence. To be effective the spatial weight had to be very large and produced very heterogeneous groups of soil profile. Sampling was too sparse to delineate homogeneous parcels of soil, and the spatial scale of variation was not identified.
A hardpan podzol at Yarner Wood, Devon
Authors: LOVELAND P. J. , CLAYDEN B. 
Published: July 2006

SUMMARYPodzols under sessile oak at Yarner Wood National Nature Reserve have extraordinarily hard and compact grey subsurface (Ea) horizons. The parent material is solifluxion debris from sandstones and siltstones of the Culm Measures (Lower Carboniferous) into which small amounts of loess have been incorporated. The general morphological, micro‐morphological and chemical features of these soils, which are classified as hardpan stagnopodzols, are outlined and compared with those of adjoining brown podzolic soils. The evidence shows that the compaction is due only to close packing of particles and not to cementation. The genesis of the hardpan stagnopodzols and their relationship to other hardpan soils elsewhere in the world is discussed and the creation of a‘Densi‐’Great Group within Soil Taxonomy is proposed.
Mechanics of mole drainage channel deterioration
Authors: SPOOR G. , FORD R. A. 
Published: July 2006

SUMMARYThe nature of the soil disturbance caused by standard mole ploughs is described and the major types of failure mechanism causing channel deterioration are identified. Direct links have been established between the kinds of mole plough disturbance and many of the channel failure mechanisms, opening up possibilities for the future for modifying the implement to improve channel stability.Following mole channel observations on six different clay soil sites, the influence of soil conditions at channel installation and subsequent weather patterns on long‐term channel stability were determined. The extent of the ageing period between channel formation and its first significant wetting and weather extremes later, were identified as being particularly important influences on the subsequent life of the channel.
Iron oxides in lateritic soils from Western Australia
Authors: ANAND R. R. , GILKES R. J. 
Published: July 2006

SUMMARYLateritic soils developed from dolerite contained larger amounts of goethite and haematite than those developed from granite. The goethite/(goethite + haematite) ratio in granitic soils ranged from 0.55 to 1 and from 0.29 to 0.83 in doleritic soils. Maghemite ranged in abundance from 0 to 10% and it only occurred in duricrust. Mole % Al substitution ranged from 16 to 33% in goethite and from 2.5 to 10% in haematite and was similar for both granitic and doleritic soils. Al substitution in maghemite was <5%. A significant, positive correlation (P<0.01) occurred between Al substitution in goethite and the amount of gibbsite in the soil. The dehydroxylation temperature of goethite ranged from 292 to 334°C and was positively correlated with the mole % Al substitution. Goethite crystals varied in size from 16 to 26 nm and haematite crystals from 18 to 59 nm. Goethite and haematite crystals occurred as aggregates of subrounded platy crystals.Iron oxides obtained by NaOH treatment contained much of the minor element contents of the soils; mean concentrations (μg g−1) were: Zn 19.9, Cu 31, Mn 68, Ni 140, Co 32, Cr 394 and V 696. These minor elements were most abundant in iron oxides derived from dolerite, but were not preferentially associated with goethite or haematite.
13C NMR of humic substances: pH and solvent effects
Authors: PRESTON CAROLINE M. , SCHNITZER M. 
Published: July 2006

SUMMARYSince the concentration of free radicals in humic subtances increases at high pH the use of basic solutions for 13C NMR spectroscopy may cause broadening and loss of aromatic signals, with distortion of intensity distributions. No such effects were found in 13C spectra of soil humic and fulvic acid, an aquatic fulvic acid, and two phenolic polymers run in aqueous solutions at different pH values, and in dimethylsulphoxide. With increasing pH, the peak in the carboxyl region shifted in a manner consistent with greater dissociation of carboxyl and phenolic groups, and also certain features in the aliphatic and carboxyl regions were enhanced under some solution conditions. Elevated solution temperature (70°C) caused only slight improvement in the resolution of some lines. Chemical shifts were determined for some known phenolic and benzenecarboxylic acid compounds in DMSO and NaOD. The range for phenolic carbons extended to 173 ppm in NaOD, while some aromatic carbons occurred around 105 ppm, in the same region as anomeric carbons. Thus, even under quantitative acquisition conditions, relative areas may be used only to estimate proportions of different types of carbons and functional groups.
Laboratory studies of effects of lime on soluble Al, Ca, Mg and Mn in a pelostagnogley soil
Authors: JARVIS S. C. 
Published: July 2006

SUMMARYThe cation composition of solutions and leachates from small‐diameter laboratory soil columns was examined over a 23‐week period after the addition of lime (0, 3 and 6 t ha–1) and/or nitrogen fertilizer (0 or 200 kg N ha–1) to an acid soil (pH 4.2). Water was applied at regular intervals to the surface of the columns and 17 leachate samples collected. Initially, the pH of the leachate was high (6.6) in all treatments (including those without lime) but fell rapidly to approach a steady value of 3.8. Large losses of calcium occurred from all columns; the total equivalent amounts of lime lost ranged from 0.88 (no addition) to 2.38 (with added lime) t CaCO3 ha–1 High concentrations of aluminium (181–325 μM) were present in leachates from all treatments; the addition of 200 kg N ha–1 increased the leaching of Al by 94%; addition of lime also increased the amounts of Al leached (by 52%).The pH of the soil solution (separated by centrifugation) was influenced by treatment, especially in the top 0–40 mm of the column. Aluminium concentration was related to pH, but the form of the relationship differed amongst the treatments.
The effects of phosphate on zinc sorption by a soil
Authors: BARROW N. J. 
Published: July 2006

SUMMARYZinc sorption curves were obtained after treatment of a soil with several rates of phosphate and with two rates of lime. The lime permitted evaluation of the effects of phosphate on Zn sorption via its effects on pH. The phosphate was either incubated with the soil at a high temperature before reaction with Zn or was supplied at the same time as the Zn. This produced treatments with similar concentration of phosphate in solution but different amounts of sorbed phosphate.Two distinct effects of phosphate addition on Zn sorption were detected. One arose from effects of phosphate on pH. This effect could be large and could either increase or decrease Zn sorption depending on the direction of the pH effect. A second effect was correlated with the amount of sorbed phosphate and was assumed to operate through the effects of phosphate on charge. The effects were small at low levels of Zn but larger at higher levels. This suggested that Zn and phosphate were sorbed at opposite ends of a spectrum of electrostatic potentials and overlap only occurred when the level of application was high. A third possible effect, due to reaction of the soil with zinc phosphate complexes in solution, was not proved.
Winter water regimes of clay soils
Authors: REID I. , PARKINSON R. J. 
Published: July 2006

SUMMARYAutumnal recharge of water in a clay soil is prolonged, taking >3 months. Once thoroughly re‐wetted, mean winter water contents lie within 0.5% v/v year by year at each site, and variability during the winter period is low, with SE = 0.2%. The uniformity of winter soil water content reflects the important part played by macropores as rapid transmission pathways for the disposal of rainwater. Weekly changes in water content are small but are inversely related to antecedent levels and the soil may become marginally drier from one week to the next despite substantial falls of rain if the soil begins the period at moisture contents higher than the seasonal mean. This behaviour has been observed in other clays and in lighter textured soils. The constancy of the mean winter soil water content provides a practical measure of the upper limit of plant‐available water, i.e. field capacity. It can be established by field sampling on as few as six occasions, and is free from the problems associated with plot irrigation and tension table methods of determining field capacity.
Aluminium speciation and pH of an acid soil in the presence of fluoride
Authors: MOORE C. S. , RITCHIE G. S. P. 
Published: July 2006

SUMMARYThe aim was to determine whether the addition of F to an acid soil reduces the concentration of free Al3+ and other forms that have been shown to be toxic to plants. The ability of two different extracts to reflect Al speciation in the soil solution was also investigated. Addition of F (0‐5.2μmolg−1) to an acid soil (pH 4.15, soil solution) increased the pH and total concentrations of Al and F in the soil solution whereas Al3+ remained constant or decreased. Soil solution pH, total soluble Al and Al extracted by 0.01 m CaCl2 are not good predictors of the likelihood of aluminium toxicity in soils containing soluble fluoride.
A model of ammonia volatilization from applied urea. IV. Effect of method of urea application
Authors: SINGH RACHHPAL , NYE P. H. 
Published: July 2006

SUMMARYEquations are given for calculating the initial distribution when a solute is (a) applied at the surface (b) placed below the surface and (c) mixed uniformly in a given depth of top soil. These equations are plugged into a predictive model developed by the authors (Rachhpal‐Singh & Nye, 1986a) to compare the concentration profiles of ammoniacal‐nitrogen and soil pH, and ammonia volatilization losses under the three methods of urea application. Placement of urea gave smaller ammonia losses than uniform mixing in the same depth of soil, which in turn gave smaller losses than surface application. Half‐time for ammonia volatilization was about 6 days irrespective of the method and depth of urea application. Concentration profiles of ammoniacal‐nitrogen and soil pH were more affected by variation in the depth of placement than by depth of mixing. The experimental ammonia volatilization losses and the concentration profiles of ammoniacal‐nitrogen and soil pH agreed very well with those predicted by the model.
The effect of successive wet/dry cycles on aggregate size distribution in a clay texture soil
Authors: SHIEL R. S. , ADEY M. A. , LODDER M. 
Published: July 2006

SUMMARYAggregates of a fine textured (61% clay, 33% silt) soil with a high coefficient of linear expansion (20%) were exposed to successive wet/dry cycles in their natural state and after mechanical reworking. In both cases aggregate size decreased; the reworked sample initially consisted of larger aggregates, but their size fell more rapidly, and after four cycles both the reworked and natural aggregates had a similar size distribution. A model was developed which successfully predicts the proportion of aggregates in each size grade at the nth cycle from that present at the outset. The rate of decrease in aggregates size declined with aggregate size and on both reworked and natural samples the dispersion ratio was low (≤5%).
Crystallinity of soil kaolinites in relation to clay particle‐size and soil age
Authors: CHITTLEBOROUGH D. J. , WALKER P. H. 
Published: July 2006

SUMMARYThe crystallinity of soil kaolinites as a function of clay particle‐size and soil age was investigated in soil chronosequences of the Shingle House Creek and Hawkesbury River alluvial terraces in south‐eastern Australia. The youngest soils (late Holocene) in each sequence are texturally uniform Entisols containing kaolinite and illite. The oldest soils (Pleistocene to late Tertiary) are Ustalfs with strong textural differentiation and are predominantly kaolinitic. With increasing age, textural B horizons are increasingly enriched in kaolinite and in particles of fine clay (< 0.2 μm) size. In two sub‐fractions of the fine clay (0.2‐0.06 μm; < 0.03 μm), no corresponding changes were observed in the crystallinity of kaolinites (as measured by the index, Ck) with age. However, values of Ck were significantly higher in the coarse clay (2‐0.2 μm) than for both fine clay fractions in all except the Ultic Paleustalf of the oldest, possibly late Tertiary, terrace of the Hawkesbury River sequence. In this soil, Ck values are low in all three clay‐size fractions.In these sequences, the effects of both clay particle‐size and soil age were identified in the crystallinity of kaolinites. Disorder as a result of pedogenesis, however, was associated only with the most prolonged weathering and the strongest soil textural differentiation.
Description of titration curves of mixed materials with variable and permanent surface charge by amathematical model. 1. Theory. 2. Application to mixtures of lepidocrocite and montmorillonite
Authors: MADRID L. , DIAZ‐BARRIENTOS E. 
Published: July 2006

SUMMARYA model to describe titration curves of mixed materials with variable and permanent charge surfaces is based upon published proposals, but includes the adsorption of potential‐determining ions on both kinds of surface, and the influence of the permanent charge. It also considers the interface formed by a system of capacitors in parallel and series. Some typical outputs of the model are given.The model was tested for mixtures of an iron oxyhydroxide and montmorillonite. The best fit of the model to titration data of the pure materials gave a set of values for the parameters that were used to predict the behaviour of the mixtures. It was concluded that most of the parameters estimated in this way reproduced the behaviour of the mixtures. However, the maximum density of sites on the oxide decreased when the latter was mixed with montmorillonite, and the binding constants of the clay mineral for the p‐d ions reached values, intermediate, between those of both minerals when the oxide was present in low proportion. These results suggested that some kind of association occurs between the solid surfaces, which would block part of the oxide surface. However, there is insufficient evidence to confirm this hypothesis.
Response of soil microbial biomass to straw incorporation
Authors: ALLISON M. F. , KILLHAM K. 
Published: July 2006

SUMMARYThe response of the soil microbial biomass to cereal straw incorporation was assessed for three sites in Eastern Scotland. Increases in the C:N ratio of the biomass, due to straw inputs, were greater for soil with a history of straw incorporation than soil with no previous incorporation history. The biomass C:N ratio response to straw inputs was associated with increases in the fungal component of soil microbial respiration, fungal plate count (total and cellulolytic) and FDA‐active lengths of fungal hyphae.