bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling the effect of adsorption of phosphate and other anions on the surface charge of variable charge oxides
Authors: BOLAN N. S. , BARROW N. J.
Published: July 2006

Adsorption of anions by iron and aluminium oxides decreases the charge on the surface. However, the negative charge conveyed to the surface by an adsorbed anion varies with the amount of anion adsorbed. This has been explained qualitatively by postulating a mixture of reactions at different surface coverage (Rajan, 1976) or by postulating different reaction mechanisms at different concentrations of phosphate (Ryden & Syers, 1975). We show that these effects may also be reproduced by the adsorption model of Bowden et al. (1974, 1977, 1980). This model does not require a mixture of equations to describe the variations in charge conveyed to the surface. Instead it describes the electrostatic consequences of adsorption. The charge conveyed to the surface by each increment of phosphate differs from that of the previous increment because each successive increment reacts with a surface with a different net charge.

The model also reproduces the observed effects of ionic strength and pH on the charge conveyed to the surface by adsorption. Further, it suggests that differences between anions on the charge conveyed to the surface are explicable in differences in the mean distance of the adsorbed anion from the original surface.
New infrared band assignments for the arsenate ion adsorbed on synthetic goethite (α‐FeOOH)
Authors: LUMSDON D. G. , FRASER A. R. , RUSSELL J. D. , LIVESEY N. T.
Published: July 2006

Infrared spectroscopy was used to show that arsenate is adsorbed on the surface of synthetic goethite (α‐FeOOH) as the acidic HAsO42‐ ion, replacing singly coordinated surface OH groups. In this respect, arsenate is analogous to phosphate, but its larger size apparently causes it to interact more strongly with some of the OH groups that remain on the surface. This has suggested an alternative assignment for the absorption bands of these OH groups.
The association of cobalt with easily reducible manganese in some acidic permanent grassland soils
Authors: JARVIS S. C.
Published: July 2006

The association of cobalt with manganese oxides was examined in some surface and sub‐soils from areas of permanent grassland in England. Hydroquinone (0.2% in ammonium acetate at pH 7.0) was used to extract easily reducible Mn oxides from the soils. Two sequential extractions with this reagent removed significant proportions of the total Co along with the Mn; no significant amounts of iron were extracted. Mn‐rich iron concretions were isolated from two of the soils and these contained from 230 to 880 μg g−1 Co. Approximately 30% of the Co in the concretions was dissolved by two sequential extractions with hydroquinone with concurrent release of considerable amounts of Mn, but, as with the soils, not of Fe. The concretions contained 20–41 mg g−1 Mn and 62–171 mg g−1 Fe that were soluble in acidified H2O2. It was concluded that significant proportions of the Co in soils is associated with Mn oxides, and will show the same sensitivity to changes in acidity and redox potential as Mn.
Distribution of allophane and organic matter in podzol B horizons: reply to Buurman & Van Reeuwijk
Authors: FARMER V.C.
Published: July 2006

The macromorphology, micromorphology and chemical nature of illuvial material in podzol B horizons and subsoils can be explained by contributions from two different migrating species: (a) a positively‐charged mixed Al2O3‐Fe2O3‐SiO2‐H2O sol incorporating minor amounts of adsorbed organic matter and silicate clay, and (b) negatively charged organic sols and solutions, carrying minor amounts of Al, Fe and clay. These species can also be generated within B horizons of high root activity. An alternative theory, that requires allophane to be formed in situ in the B horizon by microbial decomposition of precipitated organic complexes, fails to predict the observed distribution of allophane.
Evaluation of the Burns model for nitrate movement in wet sandy soils
Authors: KHANIF Y. M. , VAN CLEEMPUT O. , BAERT L.
Published: July 2006

A simple model to predict nitrate leaching developed by Burns (1974) was tested. The measured and calculated nitrate concentrations in 100 cm wet sandy soil profiles were compared: the results showed reasonably good agreement between the two values. Adjusting the initial conditions and reducing the segment size from 10 to 5 cm did not improve the accuracy of the prediction. Better agreement was, however, obtained when only the samples above the groundwater table were considered.
Optimal sampling strategies for mapping soil types. I. Distribution of boundary spacings
Authors: BURGESS T. M. , WEBSTER R.
Published: July 2006

The pattern of soil types that occur in a region can be described simply in terms of the distributions of spacings between successive soil boundaries and the probabilities of transitions from soil type to soil type. Studies of eight detailed soil maps of England and Wales, representing a very wide range of terrain patterns, showed that in all instances the interboundary spacings measured along sample transects were very satisfactorily described by the gamma distribution. In some instances the shape parameter of the distribution was sensibly 1, so that the simpler negative exponential function fitted the observed distributions well. Transition probability matrices distinguished complex and nondescript soil patterns from the more strongly repetitive ones.
Improved estimation of micro nutrients in hectare plots of the Sonning Series
Authors: WEBSTER R. , NORTCLIFF S.
Published: July 2006

The form and degree of spatial dependence in readily extractable iron, manganese, copper and zinc in the topsoil of 1 ha plots on the Sonning Series near Reading have been determined. The results have been used to calculate the sampling effort required to estimate mean values with specified precision. They show that two‐ to three‐fold economies can be achieved for iron and manganese, at least, by taking account of the known spatial dependence and optimally configuring the sampling.
Micromorphology and sub‐microscopy of allophane and imogolite in a podzol Bs horizon: evidence for translocation and origin
Authors: FARMER V. C. , McHARDY W. J. , ROBERTSON L. , WALKER A. , WILSON M. J.
Published: July 2006

In thin sections of a cemented Bs horizon, allophane is present as isotropic, or weakly anisotropic, transparent, yellow, commonly fluorescent gel deposits, which line or fill voids, cement sand and silt, and form pseudomorphs of root structures. Atomic ratios of Si: Al range from 1: 2.2 to 1: 3.7 in pale deposits, but drop to 1: 8.8 in regions of organic staining. Fe: Al atomic ratios in transparent deposits range from near zero to 0.4. The local uniformity of the gels indicates that the allophane, with associated iron oxides, is deposited from solution, and is not formed in situ from a precipitated organic complex, or by weathering of minerals in situ. Mineralogical evidence indicates that the origin of the allophane is related to intense acidic weathering of plagioclase and biotites in the Eg and Bhg horizons. A fibrous morphology indicative of imogolite is seen under the scanning electron microscope only in critical point dried specimens.

It is proposed that the cracked coatings characteristic of cemented Bs horizons can be interpreted as allophanic deposits, associated with varying amounts of clay and iron oxide, and impregnated with varying amounts of fulvic acids. Such deposits cannot be taken as evidence for the migration of Al and Fe as organic complexes.
Observations of the behaviour of large cores of soil during drainage, and the calculation of hydraulic conductivity
Authors: KNEALE W. R.
Published: July 2006

This paper reports observations on the behaviour of large cores of undisturbed clay‐loam soil during the drainage of water under an imposed step in potential. Rates of outflow and the matric potential at various points in the core were recorded during drainage. The volumes of ‘macropore‐channels’(large, continuous voids) were estimated to be 0.005 m3 m−3 in a subsoil sample, and 0.026 m3 m−3 in a topsoil sample from arable land. The calculated values of hydraulic conductivity were found to vary with the size of the step in potential imposed on the sample at the start of each drainage experiment. The available evidence suggested that the apparent K/Ψm relationship was influenced by the rate that air could enter the soil to replace water during drainage. The degree of restriction on air movement was affected by the initial drainage behaviour, and this varied with the imposed step in potential.
The inheritance of soil fabric from joints in the parent rock
Authors: HART D. M. , HESSE P. P. , MITCHELL P. B.
Published: July 2006

The origin of ped faces in subsoils has been variously ascribed to the activities of organisms, stress‐strain history and to alternating wetting and drying cycles. At three sites in the Sydney Basin the orientation of ped faces in the in situ B horizons of soils developed in dolerite and shale were measured and found to be similar to the orientation of planar joints in the parent rock. Joints in the rock, when inherited by the soil material, provided flaws which could be exploited by shrink and swell phenomena, gradually becoming permanent features. Horizontal ped faces appeared to be inherited joint or bedding planes, affected by the slope of the site to the extent that their dip increased in a downslope direction. This work confirmed previous soil fabric studies by Lafeber (1965) and demonstrated fabric anisotropy and inheritance from the parent rock.
Concepts of solute leaching in soils: a review of modelling approaches
Authors: ADDISCOTT T. M. , WAGENET R. J.
Published: July 2006

A number of conceptual models for solute leaching in soil are reviewed, quantitatively compared and classified as far as possible within a framework that makes distinction between deterministic and stochastic, mechanistic and functional and rate and capacity models. They are also discussed with reference to their purpose (viz research or management), complexity, flexibility, transferability and usefulness for field soils. The basic assumptions and structures of the models impose definite limits on the ways in which they can be used. The spatial variability of soil properties caused problems for deterministic models using rate parameters, but stochastic elements can be incorporated in these models. Simpler capacity‐type models and non‐mechanistic stochastic models offer other answers to this problem. Few data sets are available for testing a range of models and few models have been tested on a range of soil types, and very few models have much demonstrable ability to simulate transient field leaching conditions. Examples of a model being tested by someone other than the developer seem very rare.
Adsorption of phosphate by two iron oxides in relation to their porosity
Authors: MADRID L. , DE ARAMBARRI P.
Published: July 2006

Adsorption and desorption of phosphate by lepidocrocite and hematite, the latter obtained by thermal decomposition of the former, were studied and related to changes in mesoporosity of the solid surface. Differences between the oxides in the accessibility of their surfaces to phosphate seems to control the fractional amounts of ‘rapidly’ and ‘slowly’ adsorbed phosphate. Results of isotopic exchange of the phosphate adsorbed at high surface coverage can also be explained in terms of the mesoporosity of the surfaces.
Fate of fertilizer nitrogen.
Authors: BARRACLOUGH D. , GEENS E. L. , DAVIES G. P. , MAGGS J. M.
Published: July 2006

Results are presented from a three year lysimeter investigation, employing single (15NH4NO3) and double (15NH415NO3) labelled ammonium nitrate to study the uptake of soil and fertilizer nitrogen by cut ryegrass at 250, 500 and 900 kg N ha−1 a−1. Average annual recoveries of nitrogen were equivalent to 99,76 and 50% of the nitrogen added at 250, 500 and 900 kg N ha−1, respectively.

At 250 kg N ha−1 the difference between the overall nitrogen recovery and the fertilizer recovery was almost entirely attributable to pool substitution resulting from mineralization/immobilization turnover (MIT). At 900 kg N ha−1 both the low overall recovery of nitrogen and the low fertilizer recovery reflected the large excess of available nitrogen over crop requirements. No evidence of ‘priming’ was obtained.

Analysis of the results from single and double labelled lysimeters using simultaneous equations indicated that at 250 kg N ha−1,∼70% of the nitrogen in the crop was derived from the ammonium pool. At 500 kg N ha−1 this dropped to 64%, while at 900 kg N ha−1 the figure was 59%. There was a suggestion that at the lower application rates, preferential uptake of ammonium was occurring but that as N supply exceeded crop requirements, nitrate was the major N source.

Despite the preferential exploitation of the ammonium pool, at 250 and 500 kg N ha−1 pool substitution resulting from MIT resulted in lower recoveries of fertilizer ammonium compared with fertilizer nitrate.
Using soil survey information to characterize the soil‐water state*
Authors: BOUMA J.
Published: July 2006

Uses of soil for a wide variety of purposes are largely governed by interactions between soils and climatic conditions. The soil‐water state at any given moment depends on the hydraulic properties of the soil horizons, the weather and soil drainage. Emphasis in this presentation is on the manner in which the soil‐water state is being characterized in the context of land evaluation. Land evaluation is concerned with the assessment of land performance when used for specified purposes (FAO, 1976). Current and future developments in land evaluation are discussed, emphasizing the particular input of soil survey when using computer simulation models for the soil‐water regime. The soil‐water regime plays a key role in land evaluation, as it governs the soil‐water state at any given time during the year.
A model of ammonia volatilization from applied urea. III. Sensitivity analysis, mechanisms, and applications
Authors: RACHHPAL‐SINGH  , NYE P. H.
Published: July 2006

A sensitivity analysis of the model described in Part I showed that the proportion of N lost as ammonia from surface applied urea is very sensitive to the initial pH of the soil, its pH buffer capacity, the rate of urea application, and the soil urease activity. Under the conditions tested, the diffusion of bicarbonate ion to the soil surface, to neutralize the acid generated when NH4+ is volatilized as NH3, appeared to be the main process controlling the rate of ammonia volatilization.

The amount of ammonia volatilized was not very sensitive to the value of the transfer coefficient between the soil surface and the atmosphere, nor to the soil moisture status if this was around field capacity. Adsorption of ammoniacal‐nitrogen was less important than the soil pH buffer capacity in influencing the ammonia volatilization.

Further applications and extensions of the model are discussed.
Microaggregates in red earths and related soils in East and Central Africa, their classification and occurrence
Authors: TRAPNELL C. G. , WEBSTER R. , HESSE P. R.
Published: July 2006

This paper describes the microaggregate structure of residual clay soils of the red earth order in East and Central Africa, examined by low‐power microscopy, and the effects of gradual moistening and sudden wetting of the soil. Results showed a markedly angular microstructure termed fragmental, resulting from simple cleavages in the soil mass, a microgranular structure involving minute spherical bodies, either discrete or in small compound aggregates, and two types of intermediate structure. The several types of microaggregate and associated profile characteristics are described in detail, and are compared with those studied more recently in West Africa. The microgranular soils also contain larger pellet bodies originating as residual cores of rotted rock. Present evidence for the distribution of these soils is outlined and possible factors in their occurrence are reviewed, including age of land surface and termite activity.
Variation in amounts of carbon and nitrogen associated with particle size fractions of soils from the Palace Leas meadow hay plots
Authors: SHIEL R. S.
Published: July 2006

An increase in carbon (C) content of one of the more acid Palace Leas meadow hay plots (pH 4.0) is shown to occur in the >63 pm size fraction, while there is a reduction in organic matter associated with clay size fraction relative to a less acid plot (pH 5.8). Total nitrogen (N) content also is higher on the more acid plot, but the increase is smaller than for carbon, and leads to a wider overall C:N ratio in the acid plot.

The lower N accumulation in the more acid plot is due to the relative increase in coarse (> 2 mm) organic matter, with a high C:N ratio. The technique used for separation of the particle size fractions does not involve removal of coarse organic matter (> 2 mm) or drying of the soil. In the grassland soils studied, coarse organic matter is a significant component (up to 13%) of total C, yet this fraction is frequently removed before analysis. By not drying the soil, separation into particle size fractions is facilitated.
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

The 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

Two 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

A 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

Ten 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

A 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

Eleven 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

The 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

Podzols 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

The 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

Lateritic 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

Since 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

The 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

Zinc 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

Autumnal 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

The 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

Equations 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

Aggregates 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

The 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

A 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

The 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.
Evolution of porosity and changes in heat treated lepidocrocite
Authors: CORNEJO J. , HERMOSIN M. C.
Published: July 2006

The 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

The 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

In 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

Two 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

The 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

Labelled 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

CHAOS (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.