bluuebunny/crossref_metadata_2025_split huggingface dataset:
Acquisition and analysis of three–component digital images of soil pore structure. I. Method
Authors: MORAN C. J. , McBRATNEY A. B. 
Published: July 2006

SUMMARYTechniques 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

SUMMARYTo 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

SUMMARYIn 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

SUMMARYThe 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

SUMMARYA 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

SUMMARYPhosphate (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

SUMMARYThe 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

SUMMARYThis 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

SUMMARYTime‐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

SUMMARYThe 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

SUMMARYThe 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

SUMMARYPorous 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.
Resin extraction of labile, soil organic phosphorus
Authors: RUBAEK G. H. , SIBBESEN E. 
Published: July 2006

SUMMARYIn order to develop a method for estimating labile, soil organic phosphorus (Po), macroporous anion‐exchange and adsorbent (XAD) resins were tested for their ability to extract Po from a permanent pasture soil. Experimental variables included: ionic form, soil‐water resin ratio, addition of cation‐exchange resin, extraction time, extraction temperature, continuous and stepwise extraction and soil pretreatment (chloroform and microwaves).The amounts of extracted Po and Pi (inorganic phosphorus) showed little variation between the anion‐exchange resins, when used in the bicarbonate form. In the chloride form, the amounts extracted were less and more variable. XAD resins extracted much less Po and very little Pi. The macroporous anion‐exchange resin, Lewatit MP500A in the bicarbonate form, was chosen for further studies. It extracted 21 mg Po kg−1 from air‐dried soil and 8 mg Po kg−1 from moist, incubated soil.The specific amounts of Po and Pi extracted were little affected by variations in the ratio between soil, water and resin, but increased with extraction time and temperature. Chloroform pretreatment of the soil mainly increased extracted Pi, whereas microwave pretreatment only increased extracted Po. The magnitude of these increases was approximately constant irrespective of extraction temperature, indicating that the increases came from killed micro organisms.
Root‐induced release of interlayer potassium and vermiculitization of phlogopite as related to potassium depletion in the rhizosphere of ryegrass
Authors: HINSINGER P. , JAILLARD B. 
Published: July 2006

SUMMARYThe ability of roots to weather phlogopite as shown by the release of interlayer‐K and by the concomitant vermiculitization of the mica was investigated in the rhizosphere of Italian ryegrass (Lolium multiflorum), grown for 1 to 32 d on 2–105 μm mica as sole source of both K and Mg. The K‐balance showed that ryegrass was able to induce a significant release of interlayer‐K from phlogopite after 8 d of cropping. After 32 d, this root‐induced release of K amounted to 191 g Kg−1 of total‐K and contributed a major part of plant nutrition. Concurrently, the concentration of K in solution decreased markedly in the rhizosphere and X‐ray diffractometry showed a strong vermiculitization of the phlogopite. The transformation of phlogopite into vermiculite was detected when the K‐concentration in the rhizosphere decreased below a threshold of about 80 μmol dm−3. That suggests that the roots act by depleting the rhizosphere‐K, and thus shifting the exchange equilibrium, so as to release interlayer‐K and expand the interlayer space of the phyllosilicate leading to the transformation of the phlogopite into vermiculite.
On the relation between number‐size distributions and the fractal dimension of aggregates
Authors: CRAWFORD J. W. , SLEEMANt B. D. , YOUNG I. M. 
Published: July 2006

SUMMARYNumber‐size distributions (i.e. particle‐ and aggregate‐size distributions) have historically been used as indicators of soil structure, and recent work has aimed to quantify this link using fractals to model the soil fabric. This interpretation of number‐size distributions is evaluated, and it is shown that a number‐size relation described by a power law does not in itself imply fractal structure as suggested, and a counter example is presented. Where fractal structure is assumed, it is shown that the power‐law exponent, φ, describing the number‐size distribution cannot be interpreted as the mass‐fractal dimension, DM, of the aggregate. If the probability of fragmentation is independent of fragment diameter, then the exponent may be identified with the boundary dimension, DB, of the original matrix. If, however, as is likely, this probability is scale‐dependent, then φ may over‐ or under‐estimate the boundary dimension depending on whether the fragmentation probability increases or decreases with fragment size. The significance of these conclusions is discussed in terms of the interpretation of number‐size distributions, and alternative methods for quantifying and interpreting soil structure are evaluated.
An amended functional leaching model applicable to structured soils. I. Model description
Authors: HALL D. G. M. 
Published: July 2006

SUMMARYA functional model designed to simulate the transport of non‐interactive solutes through macroporous soil is described. The concept of mobile and immobile water is used but the pore volume available for mobile water is partitioned to allow for flow through smaller water‐filled pores and rapid preferential flow through larger macropores and fissures. The general performance of the model under steady infiltration following an injection of solute is presented. The sensitivity of the output to variations in the model parameters is also discussed. A second paper compares the model with bromide and chloride leaching data on two texturally contrasting soils.
An amended functional leaching model applicable to structured soils. II. Model application
Authors: HALL D. G. M. , WEBSTER C. P. 
Published: July 2006

SUMMARYThe performance of a functional leaching model (Hall, 1993) is compared with leaching data from two lysimeter experiments with soils of contrasting texture using sodium bromide and potassium chloride as the non‐reactive solutes. The model parameters are optimized using the solute elution curves as standards and compared with the physical properties of the soil. A good match with the measured discharge of both water and solute was achieved for both soils using the moisture release characteristics to define the pore volume available for mobile and immobile water. The results indicate that preferential flow takes place through even coarse‐textured soils but that there is negligible diffusive exchange of solute between water passing through the macropores and the rest of the soil.