bluuebunny/crossref_metadata_2025 huggingface dataset:
Extractability and adsorption of sulphate in soils
Authors: CURTIN D. , SYERS J. K.
Published: July 2006

Virtually all of the indigenous sulphate (SO4) in a range of UK soils with moderately high pH values (> 6) was found to be present in the soil solution and, as a consequence, was highly susceptible to leaching. For acid soils containing adsorbed SO4, the extractability of SO4in NaCl and CaCl2solutions was dependent on both the ionic strength and cation species. Addition of small amounts (<∼ 10−2M) of either NaCl or CaCl2actually decreased the amount of SO4extracted, but SO4extractability increased sharply with concentrations of NaCl or CaCl2higher than about 0.1 M. At a similar ionic strength, more SO4was extracted by NaCl than CaCl2. Sequential extraction with 1 M NaCl removed essentially all of the absorbed SO4. The release characteristics of SO4were very different to those of phosphate and this difference in behaviour is not easily reconciled with the view that SO4is chemisorbed, as is phosphate. Except for a few acid soils with high oxide contents, the capacity of the soils to adsorb added SO4was quite small. None of the soils with pH values higher than 6 adsorbed a significant amount SO4. The results raise questions regarding the efficiency of SO4‐containing fertilizers in correcting and preventing S deficiency in situations where leaching is important.
Modelling water and solute transport in macroporous soil. II. Chloride breakthrough under non‐steady flow
Authors: JARVIS N. J. , BERGSTRÖM L. , DIK P. E.
Published: July 2006

A model of water and solute transport in macroporous soils (Jarvis et al., 1991) has been evaluated in column breakthrough experiments under field conditions. Hydraulic properties were first measured in replicate soil monolith lysimeters sampled from grass ley and continuous barley treatments in a clay soil. A pulse input of 0.05 M KCl was then supplied by drip irrigation and measurements made of the water discharge and chloride leaching resulting from the natural rainfall over a 1‐month period.

The results showed that the macropores constituted the dominant flow pathway (accounting for 80% of the total water outflow) and that diffusive exchange of chloride between the two flow domains was the main factor causing variability in leaching. Larger hydraulic conductivities and macroporosities in the lower topsoil and at plough depth in the grass ley monoliths were taken as evidence of structural amelioration. Less of the applied chloride was leached in the grass monoliths than in the barley (means of 20% and 31% respectively). This was mainly due to a smaller effective aggregate size and thus a more efficient diffusion‐controlled retention.
A statistical approach for predicting accuracies of soil properties measured by single, double and dual gamma beams
Authors: MIYAZAKI T. , KASUBUCHI T. , HASEGAWA S.
Published: July 2006

A statistical analysis is developed to describe the accuracies of soil properties measured through single, double and dual gamma‐beam methods. The gamma sources are 137Cs for the high‐energy beam (662 keV) and 241Am for the low‐energy beam (60 keV). The theoretical confidence intervals of the thicknesses or water contents of samples are determined using a modification of the method of Gardner el al. (1972), who derived theoretical variances using standard error propagation formulae. The finding of Gardner et al. that, in the double‐beam method, errors in the soil bulk density and water content measurements are primarily caused by random emission from the sources, is confirmed by the theoretical confidence intervals and is applied to the single‐beam and dual‐beam methods. The effects of interferences between gamma rays in the dual‐beam method on the accuracies of estimations are examined. The minimum measurement time to attain a required accuracy can be predicted from the theoretical confidence intervals.
A basis for soil mesomorphological analysis
Authors: KOPPI A. J. , McBRATNEY A. B.
Published: July 2006

To bridge the gap between description of soil in the field, i.e. macromorphology (which is usually qualitative), and micromorphology (which may be quantitative), a technique for mesomorphological description is presented. Undisturbed vertical soil monoliths are impregnated with epoxy resin and features of interest are quantified using image analysis. Resin is applied, in the field, to the soil profile. A monolith is excavated and resin is applied to the reverse side which is then ground flat with a disc grinder. The prepared surface is then presented to a video camera for image capture. In general, the resolution is > 0.2 mm and the field of view is 100 × 500 mm. This scale permits details of horizons to be quantified and the relationship between features of interest in different horizons to be discerned. The technique is illustrated by quantifying the pore structure and distribution of manganese/ iron‐rich material (nodules and some rock fragments) in the first three horizons of a Paleustalf. The attributes measured on each of these features are the volume proportion and surface area. The three horizons may be distinguished by the quantity and two‐dimensional pattern of the pore structure. The macroporosity (volume proportion of pore space) and surface area are greatest in the surface horizon, smallest in the second horizon and intermediate in the third horizon. The concentration of manganese/iron‐rich nodules is at a maximum in the second horizon which corresponds to the region of least macroporosity.
Use of 137Cs measurements to investigate soil erosion on arable fields in the UK: potential applications and limitations
Authors: WALLING D. E. , QUINE T. A.
Published: July 2006

Recent awareness of the potential hazard of soil erosion on arable land in the UK has highlighted the lack of reliable data concerning actual rates of soil loss. This lack of information reflects both a low level of interest, and the lack of a simple and generally applicable method of documenting long‐term rates of soil loss. Existing methods involving the use of hazard classification procedures and direct measurement techniques, including erosion plots and field surveys, all possess significant limitations. The use of 137Cs measurements to provide information on rates of soil loss and deposition averaged over the past 30 years would appear to offer considerable potential. The results of applying this approach to three arable fields on contrasting soil types in Britain are reported. These results confirm the viability of the technique and its potential for providing information on patterns and rates of erosion and deposition within individual fields and their overall sediment budgets. Limitations include the restricted size of the areas that can be investigated and the need to take account of additional inputs of 137Cs derived from the Chernobyl accident.
Aggregation of soil particles by iron oxides in various size fractions of soil B horizons
Authors: BARBERIS E. , MARSAN F. AJMONE , BOERO V. , ARDUINO E.
Published: July 2006

Quantitative relationships between aggregation of soil particles and the content of haematite and goethite were studied by removing iron oxides, with dithionitetrate‐bicarbonate (DCB) and oxalate reagents, from various sizes of soil separates which were stable to sodium hexametaphosphate, and then determining the particle‐size distribution. Significant quantitative relationships were found between DCB‐extractable oxides and particles obtained from the separates up to 20 pm, whereas oxalate‐extractable oxides were correlated only with < 0.2‐μm particles. Oxalate‐extractable oxides were observed to aggregate a greater quantity of fine clay and a larger surface area of particles per gram of oxide than DCB‐extractable oxides, A more efficient mechanism of aggregation was postulated for the oxalate‐extractable oxides than for the DCB‐extractable oxides. There were fewer aggregated particles in soils containing haematite and goethite than in soils containing only goethite. This was attributed to differences in pedoenvironment, rather than to a difference in the behaviour of the oxides. Although various clay minerals were identified in the soils studied, no preferential aggregation of any mineral was observed.
Two models for the leaching of a non‐reactive solute to a mole drain
Authors: SCOTTER D. R. , HENG L. K. , WHITE R. E.
Published: July 2006

Two models of solute leaching to a mole‐pipe drainage system are described. The first model is research‐oriented. It simplifies two‐dimensional water and solute flow to a mole drain by dividing the soil between the mid‐mole plane and the mole into notional compartments. Solute movement between compartments is assumed to occur by convection and

mechanical dispersion. Within each compartment a mobile and immobile solute phase is defined, with diffusion occurring between them. Rainfall intensity (over approximately hourly intervals) and basic soil hydraulic data are needed as inputs. An explicit finite‐difference solution to the water and solute mass‐balance and flux equations is used.

The second simpler model is management‐oriented. It uses daily time steps, and assumes the soil solution behaves as if it were well‐mixed system. It requires only daily rainfall and evaporation data, the drainage coefficient of the mole‐pipe system, and the soil macroporosity as inputs. In both models a source/sink term accounts for additions of solute in rainfall and fertilizer, and extraction by plant uptake.

The models were used to simulate leaching losses of chloride to a mole‐pipe drainage system in a silt loam under pasture, following the application of potassium chloride to the soil surface. The first model simulated leaching better immediately after ertilizer application, and during bypass flow induced by heavy rain. However, both models were able to simulate the measured losses over a 2‐year period equally well.
Characteristics of membrane filters in relation to aluminium studies in soil solutions and natural waters
Authors: MENZIES N. W. , BELL L. C. , EDWARDS D. G.
Published: July 2006

Potential vitiative effects of Millipore 0.45‐, 0.22‐, 0.05‐ and 0.025‐pm filter elements on aqueous samples were investigated. All the filter elements evaluated exhibited a cation exchange capacity (CEC); in the case of 0.025‐pm filter elements, the CEC increased with pH. Filtration of 20 μM AlCl3/1.65 mM CaCl2, solutions (I∼0.005 M) to 0.45, 0.22 and 0.05 pm resulted in no significant change in solution A1 concentration. Filtration through 0.025‐μm filter elements significantly reduced the total A1 present in solutions adjusted to pH 4.5 and 5.0; the A1 concentration of solution adjusted to pH 4.0 was not altered. The removal of A1 from pH 4.5 and pH 5.0 solutions was attributed to the retention of A1 hydroxide micro‐particulates formed during pH adjustment of the AlCl3/CaCI2, solution. Adsorption of A1 by the filter element was not significant.

Soil solutions were analysed without filtering and after filtration to 0.45,0.22,0.05 and 0.025 pm. Filtration had no effect on the concentration of the major anions (Cl−, SO24 ‐, NO13) or cations (Ca++, Mg++, Na+, K+). However, filtration to 0.05 and 0.025 pm resulted in significant reductions in the concentration of Al, Fe, Si and organic C in some samples. In soil solutions for which filtration resulted in the removal of large amounts of particulate material, the solution appeared less coloured after filtration and exhibited lower absorbance in the visible spectrum (4O(MOO nm). However, the absence of colour did not preclude the presence of colloidal particles.
The effect of alternate freezing and thawing on aggregate stability and aggregate size distribution of some Prince Edward Island soils
Authors: EDWARDS L. M.
Published: July 2006

The effect of 1–15 daily freeze/thaw cycles on aggregate stability (S) and aggregate‐size distribution measured as mean‐weight diameter (MWD) was investigated for loam, sandy loam and fine sandy loam (FSL) soils; and two aggregate‐wetting procedures, spray‐wetting and vacuum‐wetting, were compared. Initially, S and MWD decreased rapidly until about the fifth freeze/thaw cycle, thereafter change occurred progressively less rapidly reaching a minimum value at about the 10th cycle. Sand MWD in the loam, which had the greatest content of clay and iron oxides, decreased significantly less rapidly than in the other soils. The sandy loam, with the least clay but the most organic matter, was intermediate in behaviour. Macro‐aggregate (>4.75 mm) content of the FSL decreased from 40% initially to 12% of total mass by the 15th cycle, while the micro‐aggregate (<0.5 mm) content increased from 19% to almost 70% of total mass. In contrast, the loam retained many macro‐aggregates, with a decrease from an 80% macro‐aggregate content to 60% of total mass by the 15th cycle. With an average of about 40 freeze/thaw cycles occurring during a Prince Edward Island winter, S and MWD in both the sandy loam and the FSL will reach minima by the end of winter. In contrast, Sand MWD in the loam will not have reached a minimum by the end of winter. These results are related to the erosive behaviour of the three soils.

Data on S and MWD of samples exposed to the two wetting procedures followed similar trends with number of freeze/thaw cycles (r=0.84 to 0.99); but spray‐wetting gave less variable results than did vacuum‐wetting and was a simpler procedure.
Soil mechanical properties as influenced by exchangeable cations
Authors: DEXTER A. R. , CHANT K. Y.
Published: July 2006

The tensile strengths of dried, undisturbed aggregates and of dried, artificial aggregates and the shear strengths of freshly‐moulded, moist soils were investigated as functions of their contents of exchangeable cations.

Tensile strength increased with increasing exchangeable sodium and decreased with increasing exchangeable calcium. Shear strength of moist soil, as assessed through the Atterberg limits, increased with increasing exchangeable calcium, potassium and sodium. The influence of exchangeable magnesium was variable in that it tended to increase the tensile strength of the soils when dry, whereas it tended to decrease the shear strength of one of the sets of soils in the moist state.

It is concluded that the exchangeable cations which give rise to greater repulsion between, and dispersion of, clay particles in water also give rise to greater strength in the dried soil. It is proposed that this is because greater particle repulsion in the soil water during drying enables particle rearrangements to take place more readily and this results in denser packing arrangements and increased strength.
method for assessing the goodness of computer simulation of soil processes
Authors: WHITMORE A. P.
Published: July 2006

Any satisfactory computer simulation model of a soil process must match actual behaviour in the laboratory or field; a model can be evaluated by how well it does so. This paper describes a method for assessing models using anion diffusion and nitrate leaching as examples. The method partitions the sum of squares of the differences between measurement and simulation into two components, one calculated from the differences between the simulation and the mean of replicate measurements (the ‘lack of fit’), and the other calculated from the variance within each set of replicate measurements (the ‘pure error’). If the former is not significantly larger than the latter than the data present no grounds for rejecting the model. Where a model simulates the change in a process with time the method can also take account of how experimental error in the initial measurements affects the goodness of fit of the simulation of subsequent measurements.

The method is particularly valuable where it is difficult or costly to take many replicate measurements, such as often happens in soil science or agriculture; nonetheless, some replicates must be taken.
Effect of heating on phosphate sorption and availability in some north‐east Nigerian soils
Authors: KWARI J. D. , BATEY T.
Published: July 2006

Studies on phosphate sorption and availability in some north‐east Nigerian soils showed that phosphate adsorption and inorganic‐P concentrations increased considerably after the soil was heated either in a furnace or during the field‐burning of straw. The increase in phosphate adsorption after heating was thought to be caused by an increase in free Fe and A1 oxides, whereas the high contents of exchangeable Ca and possibly carbonates and hydroxyl ions in the ash were probably responsible for the increase in phosphate sorption after field‐burning of straw.

Investigations into the availability of P to maize over a 7‐d period of growth showed that there was no significant nutritional benefit from the P released after soil heating. The effect of heating was to increase P sorption and so reduce P in solution and P availability.
Empirical evaluation of the relationship between soil dielectric constant and volumetric water content as the basis for calibrating soil moisture measurements by TDR
Authors: ROTH C. H. , MALICKI M. A. , PLAGGE R.
Published: July 2006

The paper is addressed to soil scientists who use Time‐Domain Reflectometry (TDR) technology to measure soil moisture. The practical aspects of the measurement calibration are discussed, and an empirical approach to establishing the existence of a universal calibration function is presented.

Samples of 11 mineral soil horizons and seven organic soil horizons with different chemical and physical properties (including magnetic properties) were selected with the aim of determining their dielectric constant‐volumetric water content relationship as calibration functions for TDR soil moisture measurements. These samples were supplemented by other, soil‐like, capillary‐porous reference materials (montmorillonite, glass beads, washed sand and a sand from a C horizon).

The study showed that a unique calibration function for mineral soils and another distinct calibration function for organic soils can be established.
The influence of soil clay constituents on surface free energy of clay fractions
Authors: JAŃCZUK B. , BIALOPIOTROWICZ T. , ZDZIENNICKA A. , HAJNOS M. , JÓZEFACIUK G.
Published: July 2006

Measurements were made of the contact angle for glycerol, di‐iodomethane and cis‐decalin drops settled on the surface of pellets prepared from sodium forms of clay fractions of soils before and after successive removal of organic matter, iron and aluminium. On the basis of contact angles thus measured and a modified Young equation, the dispersive and non‐dispersive components of the surface free energy of the clay fractions were calculated. It was found that the non‐dispersive component decreased linearly with an increase in organic matter content, and with Fe and Al in the clay fractions of the soils studied. However, the dispersive component was not dependent on organic matter content, but decreased with increasing content of Fe and Al in the clay fractions studied.
A continuum approach to soil classification by modified fuzzy k‐means with extragrades
Authors: McBratney A. B. , de Gruijter J. J.
Published: July 2006

The need for a more continuous approach to soil classification is discussed, and methods based on the mathematical constructs known as fuzzy sets are considered most appropriate for this. A centroidal grouping method, fuzzy k‐means with extragrades, which quantifies the intragrading and extragrading of soil individuals is described. An example of the application of this technique to an area of 4800 ha at Wesepe in The Netherlands is presented. The results show that the technique could create a classification that reflects the main pedological features of the area in a continuous way. Although there may be problems in selecting the optimal number of groups and degree of fuzziness, we conclude that the method is most promising and worthy of consideration when any type of quantitative soil classification is required.
Fuzzy classification methods for determining land suitability from soil profile observations and topography
Authors: BURROUGH P. A. , MACMILLAN R. A. , van DEURSEN W.
Published: July 2006

Because conventional Boolean retrieval of soil survey data and logical models for assessing land suitability treat both spatial units and attribute value ranges as exactly specifiable quantities, they ignore the continuous nature of soil and landscape variation and uncertainties in measurement which can result in the misclassification of sites that just fail to match strictly defined requirements. This paper uses fuzzy classification to determine land suitability from (i) multivariate point observations of soil attributes, (ii) topographically controlled site drainage conditions, and (iii) minimum contiguous areas, and compares the results obtained with conventional Boolean methods. The methods are illustrated using data from the Alberta Agricultural Department experimental farm at Lacombe in Alberta, Canada. Data on site elevation and soil chemical and physical properties measured at 154 soil profiles were interpolated by ordinary block kriging to 15 m × 15 m cells on a 50 × 50 grid. The soil property data for each cell were classified by Boolean and fuzzy methods. The digital elevation model created by interpolating the elevation data was used to determine the surface drainage network and map it in terms of the numbers of cells draining through each cell on the grid. This map was reclassified to yield Boolean and fuzzy maps of surface wetness which were then intersected with the soil profile classes. The resulting classification maps were examined for contiguity to locate areas where a block of minimum size (45m × 45m) could be located successfully. In this study Boolean methods reject larger numbers of cells than fuzzy classification, and select cells that are insufficiently contiguous to meet the aims of the land classification. Fuzzy methods produce contiguous areas and reject less information at all stages of the analyses than Boolean methods. They are much better than Boolean methods for classification of continuous variation, such as the results of the drainage analysis.
Neoformed aragonite in clay soils on Keuper materials from east‐central Spain
Authors: LAYA H. A. , DE LA PEÑA J. A. , BENAYAS J.
Published: July 2006

Fibrous radial aragonite nodules occur in a toposequence developed in the Triassic (Keuper) in a subhumid mediterranean climate (Soria, Spain).

Neoformation in situ of the nodules in these soils is proposed, on micromorphological and physico‐chemical grounds, such as their fragility, the inclusion of material from the groundmass, their occurrence along cracks and their high Mg: Ca ratio.
The effects of sulphate and fluoride on the sorption of aluminium by an oxisol
Authors: GIBSON J. A. E. , WILLETT I. R. , BOND W. J.
Published: July 2006

The sorption of aluminium by an Oxisol in the presence of sulphate or fluoride was studied to determine the effects of these co‐ordinating anions on the distribution of aluminium between the solid and solution phases. Addition of sulphate increased aluminium sorption, probably due to a sulphate‐induced increase in negative surface charge. In contrast, fluoride was found to depress sorption due to the decrease in the average charge of the aluminium‐containing species resulting from the formation of fluoro‐aluminium complexes.

The pH of the equilibrium mixtures was linearly related to the pAl3+. This relationship held regardless of the concentrations of fluore or sulphato‐aluminium species. Equilibrium pH and pAl3+ appeared to be controlled by gibbsite.
Importance of proton supply and calcium‐sink size in the dissolution of phosphate rock materials of different reactivity in soil
Authors: ROBINSON J. S. , SYERS J. K. , BOLAN N. S.
Published: July 2006

The dissolution of a range of phosphate rock (PR) materials (Gafsa, GPR; Jordan, JPR; North Florida, NFPR; and Tundulu, TPR) was evaluated in three UK soils (Nercwys, Davidstow and Withnell) which differed in proton supply and P‐buffer capacity. The Ca‐sink size was adjusted by adding different amounts of a cation‐exchange resin (CER) to the soils. In the presence of a large proton supply (pHw 3.8–4.8, pH‐buffer capacity 52.5–36.5 mmol OH− kg−1 pH unit−1), the dissolution of GPR, JPR and NFPR in the Nercwys and Davidstow soil‐CER mixtures was strongly influenced by the size of the Ca sink. A twofold increase in Ca‐sink size in these two soils caused an increase in PR dissolution of 44–120%. Except for TPR, the increase in PR dissolution per unit increase in Ca‐sink size was the same for the three PR materials. In the Withnell soil‐CER mixtures, where the initial proton supply was relatively small (pHw 4.8–6.1, pH‐buffer capacity 23.7–21.4 mmol OH− kg−1 pH unit−1), the increase in PR dissolution with increasing Ca‐sink size was less (24–68%) than in the other two soils (44–120%). Also, for the Withnell soil, the increase in PR dissolution with increasing Ca‐sink size decreased in the order GPR (68%) > JPR (49%) > NFPR (24%), a trend consistent with the decrease in PR reactivity. The maximum dissolution of TPR was only 8–22% under favourable conditions of proton supply and Ca sink, and was little affected by Ca‐sink size.
The influence of humus fractionation on the chemical composition of soil organic matter studied by solid‐state 13C NMR
Authors: KROSSHAVN M. , KÖGEL‐KNABNER I. , SOUTHON T. E. , STEINNES E.
Published: July 2006

Four samples of soil organic matter and their humic acids, fulvic acids and humin were studied with solid‐state 13CP MAS NMR. The whole soil samples were fractionated using NaOH and HCl in order to extract humic acids, fulvic acids and humin. This investigation indicates that conventional humus fractionation does not significantly change the content of different functional groups in soil.
The contribution of lignin to the composition of humic acids from a wheat‐straw amended soil during 3 years of incubation in pots
Authors: AMALFITANO C. , PIGNALOSA V. , AURIEMMA L. , RAMUNNI A.
Published: July 2006

An Andisol from the Vesuvian volcanic area, low in organic matter, was treated with wheat straw (20/1 w/w) and urea (500/1 w/w) in pots, and maintained at 60–90% of field capacity in an open greenhouse in order to study the yields and properties of humic acids after 30, 122 and 224 d, and 1, 2 and 3 years of incubation.

During the first year the yields increased, but subsequently they showed a decrease. However, the chemical and spectroscopic properties of humic acids remained substantially constant.

The chemical characteristics of modified lignin from added wheat straw were recognized in the properties of humic acids by UV‐visible, FT‐IR and 13C CP‐MAS NMR spectroscopic analysis. Evidence was obtained that these modifications included the microbial removal of carbohydrates, the oxidative destruction or transformation of the side chains of lignin units, the demethylation of mainly guaiacyl, and subsequent oxidation of catechol‐like structures to o‐quinone. The latter can be postulated to promote the nucleophilic addition of amino compounds with formation of aromatic amines in humic acids.
Laboratory experiments on surface seal development and its effect on interrill erosion processes
Authors: SLATTERY M. C. , BRYAN R. B.
Published: July 2006

Despite extensive research, the processes involved in seal and crust formation are not yet fully understood. This paper provides detailed information on the dynamics of surface sealing and its effect on the erosion process. Seal development of an artificial soil mixture was investigated by measuring changes in splash detachment, soil bulk density and near‐surface soil strength, and by detailed observation and analysis of thin‐section photomicrographs taken at different sealing stages.

Raindrop impact was found to be the principal force governing the formation of the surface seal. The sequence of seal development was as follows: (i) rapid disruption of surface aggregates by direct raindrop impact; (ii) rearrangement of disrupted fragments and textural separates; and (iii) compaction of surface material by continued drop impact. Eventually, an ‘equilibrium’ complete seal of the surface was established. Other micro‐morphological characteristics included (i) a mean seal thickness of 0.3–0.8 mm, (ii) a complex void structure dominated by compound packing voids and vughs, (iii) an absence of any ‘washing‐in’ of fine material, and (iv) development of miniature soil pedestals (micro‐hoodoos), micro‐depressions and micro‐knolls formed by drop impact. Measured changes in splash detachment and soil bulk density were consistent with the observed fabric changes. Splash detachment increased during the early seal stages but thereafter decreased rapidly with incorporation of material into the developing seal. The decrease was matched by an overall increase in soil bulk density. Contrary to expectations, soil shear increased only during the initial wetting phase, and subsequently decreased to give minimum values coincident with maximum seal development. After the initial wetting phase shear strength had a negative linear relationship with soil moisture content. It is concluded that soil shear strength may not be a reliable indicator of seal development.
Acquisition and analysis of three–component digital images of soil pore structure. I. Method
Authors: MORAN C. J. , McBRATNEY A. B.
Published: July 2006

Techniques for examining pore structure as a three–component system, most notably dye–staining of pore space, are reviewed. A method for analysing digital images of pore structure with three components is presented. The method is a direct extension of earlier work on the description of pore structure using two‐component digital images in which the two components represented pore space and soil solid. A previously published method for preparation of an undisturbed, vertically oriented, planar face through soil with pore space in the field condition is used. Field impregnation with opaque epoxy resin is followed by sawing, completion of the impregnation under vacuum and grinding of the sawn face to a smooth finish. In the method presented here the resin used for the laboratory impregnation contains a different‐coloured dye from that used in the field. The ground face is then video‐digitized. Three components are represented in the resulting digital grey level image, namely, field‐impregnated pore space, laboratory‐impregnated pore space and soil solid. The image–processing steps required to segment the grey level image into the three required components are described. Image analysis, for quantitative assessment of the pore structure, consists of generation of 11 pore‐structure attributes from the segmented image. Interpretation of these attributes and use of the method are discussed.
Strategies for updating soil survey information: a case study to estimate phosphate sorption characteristics
Authors: BRUS D. J. , de GRUIJTER J. J. , BREEUWSMA A.
Published: July 2006

To support future decisions on alternative strategies of updating soil survey information, we have studied the efficiency of four strategies, viz. revision, upgrading, revision plus upgrading and upgrading by two‐phase sampling. Revision results in a new soil map. Upgrading gives statistical information about means and variances within mapping units of the soil map.

The merits of these strategies were measured in terms of the increase in accuracies of the spatial estimates of the values at unvisited points and of the spatial means of a study area of several soil characteristics. Point values were estimated by assigning an estimate of the mean value to any point in a given mapping unit. In the first strategy, the estimator was derived from the representative profile description of that mapping unit. In the other strategies, the estimator was derived from the statistical sample.

Although the mapping units of the revised map were more homogeneous for some characteristics, the point estimates using the values of the representative profile description were no more accurate. This was due to the bias of this estimator, which rules out the reduction in spatial variance. If revision was followed by sampling this bias could be eliminated. As a result, for some characteristics the point estimates became more accurate than those based on the original map.

Estimates of the spatial means of the study area via upgrading by two‐phase sampling were more accurate, for all characteristics, than estimates via revision plus upgrading. Using the estimates of the spatial variance within the mapping units of the original map for allocation was apparently more effective than reducing the variance itself.
Fragipan formation in argillic brown earths (Fragiudalfs) of the Milfield Plain, north‐east England. I. Evidence for a periglacial stage of development
Authors: PAYTON R. W.
Published: July 2006

In this first of three papers, the parent materials, morphology and field relationships of soils with fragipans, similar to those in north‐eastern United States, are described and analyses of their chemical and physical properties are presented to support a periglacial stage of development. The soil materials have been affected by periglacial processes, including ice‐wedge formation, the age of which has been established by reference to a buried paleosol. The fine earth bulk density of the fragipans is between 1.75 and 1.91 g cm−3 whereas the density of overlying Eb horizons is < 1.40 g cm−3. The formation of the compact lenticular structures and polygonal fissuring of fragipans is ascribed to the former presence of permafrost during the Loch Lomond Stadia1 11 000 to 10 000 years B.P. The polygonal fissures, after subsequent infilling with illuvial material, have determined the position of the greyish polygonal zones which have formed by the eluviation of Fe and Mn from fissure infill and fissure walls by redox processes. Clay migration from the Eb horizon into the fragipan is well marked. Clay and silt have also been locally removed from the upper parts of the greyish zones and redeposited towards their lower parts. Similar textural degradation has affected eluvial pockets in the upper fragipan. It is concluded that periglacial processes fully explain the genesis of macrostructural features but not the distinctive consistence of the fragipan.
Measurement of the potentially available charge and the dissociation behaviour of humic acid from cobaltihexammine adsorption
Authors: MAES A. , TITS J. , MERMANS G. , DIERCKX A.
Published: July 2006

The use of a new method for characterizing humic acids based on the measurement of the cobaltihexammine cation exchange capacity (CEC) vs. pH is examined. The method was first verified on a macroporous weak‐acid cation exchange resin: charge vs. pH curves and pK values from cobaltihexammine adsorption identify with results from discontinuous acid‐base titrations at high ionic strength (5 M). Similar agreement was obtained for humic acids from a Podzol soil: the cobaltihexammine‐CEC identifies with the macromolecular charge (from continuous acid‐base titrations) at ionic strength of 3 and 5 M, but slightly underestimates (5%) the humic acid charge at 1 M ionic strength. The cobaltihexammine method is suitable for determining the potentially available charge in the pH range 2 to 12 and the intrinsic pK values of humic acids.
Assessment, based on a climosequence of soils in tussock grasslands, of soil carbon storage and release in response to global warming
Authors: TATE K. R.
Published: July 2006

A soil climosequence in tussock grasslands in South Island, New Zealand, encompassing climates ranging from cold to warm temperate provided a spatial analogue of climate change for investigating the effects of global warming on soil C contents and turnover. Mean annual temperature (T) and annual precipitation (P) ranged from 2 to 10°C, and 350 to 5000 mm, respectively. Soil C contents were curvilinearly related to T/P across the sequence (r=−0.95, significant at P<0.0l), indicating that east of the Southern Alps, increased decomposition of organic matter with global warming would provide a positive feedback to further increase atmospheric CO2. This decrease in New Zealand's soil C, estimated to be up to 10% of the current content for a global temperature rise of 0.03 K a−1 to 2050, could contribute about 0.5 × 1015 g C to the atmosphere over the next 60 years. These conclusions were generally supported by changes in soil C turnover estimated from ‘bomb’14C enrichment. The unexpectedly slow turnover found for two soils was explained by a ‘memory’ effect from the former southern beech forest that grew on these soils in prehistoric times. Accumulation of Al‐humus under the forest may be responsible for the slow C turnover observed.
The reaction between phosphate and dry soil. I. The effect of time, temperature and dryness
Authors: BRAMLEY R. G. V. , BARROW N. J. , SHAW T. C.
Published: July 2006

Phosphate (P) was added to soil in solution. The soil was air‐dried or freeze‐dried and then incubated at a range of temperatures for periods of up to 110 d. The rate of the continuing reaction between the P and soil was measured using the null‐point method, and by measuring the amount of desorption induced by filter paper impregnated with iron oxide (Pi test). The reaction between soil and P continued in both air‐dried and freeze‐dried soil, albeit more slowly than in moist soil. Freezing the soil, whether moist or dry, virtually stopped the reaction.

These results are consistent with the hypothesis that the continuing reaction between P and soil involves a solid‐state diffusive penetration of the soil particles by the sorbed P ions. They also indicate that the common practice of storing soil air‐dry, even for short periods at low temperature, will not preserve the P status of the soil as at sampling. It was estimated that for a sample of soil which remained moist at 25°C for 100d after the addition of 335 μg P g−1 soil, before being sampled and stored air‐dry at 4°C for 16 years, the measured Pi test value would be about 15 μg P g−1. This compares with 46 μg P g−1 which is the estimated Pi test value measured on the same day as sampling.

When samples cannot be analysed for P status immediately following sampling, they should be stored at the lowest convenient temperature, preferably below 0°C.
Studies of the soil atmosphere and related physical site characteristics in mineral forest soils
Authors: MAGNUSSON T.
Published: July 2006

The composition of the soil atmosphere in mineral soils was studied for 3 years, by regular sampling from gas equilibrium chambers followed by gas chromatographic analysis. In sandy loam till soils with different groundwater levels, the mean growing season concentrations of O2 decreased and CO2 increased as site wetness increased. Similarly, O2 decreased and CO2 increased with increasing soil depth on freely drained sites. On sites where the subsoil was often waterlogged, concentration gradients between 20 and 50 cm below the mineral soil surface were often reversed, i.e. O2 increased and CO2 decreased with increasing depth. Periods of rapidly falling O2 and rising CO2 concentrations were the most conspicuous characteristic of the annual pattern in the mor and the upper mineral soil layers. The main cause is suggested to be impeded gas exchange, due to near–saturation water content. Such periods often started after snowmelt in May and ended after the disappearance of soil frost in June. The porosity of the frozen topsoil in spring, which is affected by the climate in early winter and spring, is proposed as a particularly important ecological factor in these soils. A silt soil and the subsoils of tills with high groundwater levels showed growing season trends, with minimum O2 and maximum CO2 contents in the late autumn. Concentrations changed temporarily, towards those of the free atmosphere, in the till subsoils during summer droughts. Clearfelling caused a rise of the watertable. O2 concentrations decreased and CO2 concentrations increased in the humus layer, while the changes in the mineral soil were less clear. The soil atmosphere, represented by the mean growing season concentrations and the minimum O2/maximum CO2 concentrations during each growing season, were significantly different on all main sites, and also differed between clearfelled and forested plots.
A constant cell volume triaxial testing technique for evaluating critical state parameters of unsaturated soils
Authors: HETTIARATCHI D. R. P. , O'SULLIVAN M. F. , CAMPBELL D. J.
Published: July 2006

This paper describes the development of a constant cell volume triaxial compression testing machine. This apparatus features a method for applying the deviator load to a soil specimen contained in a conventional triaxial testing machine without altering the volume of the fluid jacket. The technique utilizes the stiffness or compliance of the closed hydraulic system to monitor the volume changes taking place in the soil sample during shear failure. This information is obtained from the pressure changes taking place in the closed fluid system.

The behaviour of a prototype apparatus of this type in testing a normally consolidated soil sample is analysed in some detail. These results, and others not discussed in the paper, demonstrate that the method has considerable scope in the rapid acquisition of quantitative data on the strength and volume change behaviour of unsaturated soils. A mathematical model of the system is developed and used to evaluate its performance and exhibits good agreement with experimental observations. The model also highlights how the provision of a variable compliance facility extends the range of state paths that can be achieved by the system.
Considerations on the use of time‐domain reflectometry (TDR) for measuring soil water content
Authors: WHALLEY W. R.
Published: July 2006

Time‐domain reflectometry (TDR) is becoming an increasingly popular technique for measuring soil water content. It is based on measuring the dielectric constant of soil from the propagation velocity of a pulse travelling along an electromagnetic transmission line embedded in the soil. Although various designs of transmission line have been proposed, there have been no attempts to contrast these designs to enable the experimenter to select an appropriate system. A second area which needs consideration is the choice of calibration function, as the use of an empirical calibration with no physical basis persists. In this paper, transmission line design (balanced and unbalanced) is discussed and a simple linear calibration function based on refractive index is developed.
The role of organic acids in the soil solution chemistry of a podzolized soil
Authors: LUNDSTRÖM U. S.
Published: July 2006

The soil solution chemistry of a podzolized soil in the north of Sweden was monitored for four years using percolation lysimeters. Weak organic acids were a major constituent of the soil solution and are important because of their ability to form complexes with aluminium. Dissolved organics leached from the mor layer enhance the weathering rate in the eluvial horizon by forming complexes with aluminium, especially during the autumn when the leaching of dissolved organics was greatest. The weak organic acids were titrated and their pKa values were evaluated. Aluminium was speciated with an ion‐exchange method and by applying equilibrium calculations. Formation constants for the organic aluminium complexes were calculated to be log KAlong=5.42±0.32 m−1 (n=13) in spring and summer and log KAlorg=4.87±0.14 m−1 (n=6) in autumn. Equilibria of Al3+ with solid phases were also examined using solubility constants. Percolation lysimeters below undisturbed and cut‐off mor layers were compared.
Weathering patterns in representative soils of Guanxi Province, south‐east China, as indicated by detailed clay mineralogy
Authors: SINGER A.
Published: July 2006

The mineralogy of five soils situated on a south‐west to north‐east transect of Guanxi Province, south‐east China was determined by X‐ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA) and chemical composition. One soil had formed on granite under tropical conditions, the others on sedimentary rocks under subtropical conditions. In all soils, kaolinite dominates the clay fractions, and is accompanied by vermiculite or chloritized vermiculite. In the saprolites of the granite‐derived and sandstone‐derived soils, the kaolinite has a morphology close to that of hydrated halloysite. The formamide and hydrazine/water tests suggested the presence of both poorly‐crystalline (dehydrated halloysite) and well‐ordered kaolinite. Gibbsite was identified in the saprolites of the granite‐derived and sandstone‐derived soils but not in the soils themselves. Gibbsite was also identified in the lowermost horizon of a soil derived from Pleistocene sediments. The upper horizon clay of a Rendzina soil formed on Permian limestone contains much more gibbsite and is much more weathered than the corresponding lower horizon clay. Only in the more humid, southernmost soil can the mineral composition be explained by present‐day climatic conditions. In the soils from drier areas, the clay mineral composition reflects weathering that had taken place under moister, paleoclimatic conditions. Some of these paleoclimatic conditions had been conducive to lateritic weathering, as is indicated by the presence of goethite‐containing pisolitic nodules in one of the soils and in its parent material. Two of the soils appear to be polymorphic, with one part of the soil having weathered more strongly than the other part.
Developments in the use of porous ceramic cups for measuring nitrate leaching
Authors: LORD E. I. , SHEPHERD M. A.
Published: July 2006

Porous ceramic cups are widely used for measuring nitrate leaching from agricultural land, but it is not fully clear what procedures give the most reliable results, or what factors could limit the validity of their use. This paper reports improvements in methodology made during tests of the technique when it was first used on a large scale, on light soils.

Porous cup assemblies must be installed carefully to avoid preferential flow through the disturbed soil around them, and to maximize contact between cup and soil. Newly‐installed and well‐established porous cups could give differing results. Sampling must start as soon after return to field capacity as possible, when concentrations are often highest. The estimate of nitrate loss can be greatly affected by the calculated date of start of drainage, and some independent check on this date is advisable. Sampling frequency must be sufficient to define the shape of the curve of concentration against drainage, but this curve is normally fairly smooth. Methods of calculating nitrate loss are discussed. The spatial variability between cups in arable soils is typically 30–60% of the mean, less than between individual soil samples. Because porous cups can be left in situ, changes over time are not confounded with changes due to sampling from differing locations, as they are with successive soil samples.