bluuebunny/crossref_metadata_2025_split huggingface dataset:
A comparison of measured and theoretical soil acidity diffusion coefficients over a wide range of pH
Authors: NYE P. H. , AMELOKO A. 
Published: July 2006

SUMMARYThe soil acidity diffusion coefficients have been measured at two Pco2 levels with values in the range 2–70 × 10−9 cm2 s−1. The coefficient passed through an ill‐defined minimum in the pH range 5–6.5. Theoretical values, calculated on the basis that the only significant acid‐base carriers in the soil were the H3O+ ‐H2O and H2CO3‐HCO−3 pairs, agreed well with the experimental values over the whole pH range at Pco2= 0.005 atm. Agreement was not so good however at a CO2 pressure of 0.0003 atm., especially in the neutralalkaline pH range. This was thought to be due to difficulties in maintaining this level of CO2 throughout the soil samples.
Competitive adsorption of humus acids and phosphate on goethite, gibbsite and two tropical soils
Authors: SIBANDA H. M. , YOUNG S. D. 
Published: July 2006

SUMMARYCompetition in adsorption between humic acid (HA) or fulvic acid (FA) and phosphate on synthetic goethite, gibbsite and two tropical soils was studied. The results for both goethite and gibbsite showed that HA and FA competed strongly with phosphate for adsorption sites at low pH values. The soils showed a similar result with a reduction in phosphate adsorption resulting from the addition of HA at the pH of the soils. The competition between HA and phosphate at different pH levels is illustrated by comparing the adsorption envelopes for phosphate on goethite, gibbsite and the two soils in the presence and absence of HA. The trends observed may be explained by the relative positions of the maximum buffer‐power (buffer capacity) of the organic acids and of phosphoric acid which are shown to lie in different pH ranges.
Forms of aluminium in some acid permanent grassland soils
Authors: JARVIS S. C. 
Published: July 2006

SUMMARYThe more labile forms of aluminium in a range of soils from areas of permanent grassland were determined with a number of selective extractants. The amounts of exchangeable A1 extracted with molar KCl were dependent upon pH, while the amounts exchangeable with 0.3 M LaCl3, although much greater, were not well correlated with pH. There were good correlations between soil organic C content and A1 extracted by (i) 0.5 M EDTA and (ii) 0.1 M potassium pyrophosphate. Pyrophosphate extracted greater amounts than any of the other extractants (sodium citrate/dithionite, ammonium oxalate (dark), acid oxalate (UV radiation), as well as those already mentioned). It was concluded that much of the extractable A1 in soils was associated with organic matter. Addition of lime to one of the soils reduced the amount of A1 extracted by all reagents except dithionite and acid oxalate solutions. There were considerable differences between soils in their release of A1 to continuous leaching with 0.01 M CaCl2. Despite these differences between the soils in organically bound extractable Al, the differences in the amounts and patterns of release of A1 with CaCl2did not appear to be related to organic matter contents, nor to the other determined properties.
The forms of cobalt in some Scottish soils as determined by extraction and isotopic exchange
Authors: McLAREN R. G. , LAWSON D. M. , SWIFT S. 
Published: July 2006

SUMMARYThe results of fractionation and correlation studies provided evidence that cobalt in soils is associated predominantly with the soil oxide fraction, particularly the manganese oxides. Only a small proportion of the total cobalt present in soils was extracted by acetic acid, EDTA, pyrophosphate or hydroxylamine. Cobalt extracted with these reagents was considered to be derived principally from easily reducible manganese oxides, although the origin of the cobalt extracted by acetic acid in particular was not well defined. The bulk of the cobalt present in soils appeared to be occluded by more highly crystalline oxide materials or was present in the structures of primary and secondary minerals.Labile cobalt in soil was assessed by extraction with acetic acid and EDTA and by determination of isotopically exchangeable cobalt. The amounts of cobalt extracted by both EDTA and acetic acid were highly dependent on the length of extraction period and on the temperature of extraction. Neither of these reagents appeared likely to give good estimates of the quantity or intensity factors of soil cobalt supply to plants as defined by the isotopic exchange determinations.
Anisotropic shrinkage of clay cores, and the interpretation of field observations of vertical soil movement
Authors: TOWNER G. D. 
Published: July 2006

SUMMARYAn anisotropic state was induced in saturated clay cores by unidirectional compression. The cores were allowed to dry slowly in the laboratory and the resulting linear shrinkage was measured in all three dimensions. The rate of shrinkage was less in the precom‐pressed direction than in the other directions. An analysis is given for characterizing the anisotropic shrinkage.An analysis is made of the vertical soil movement occurring in response to wetting or drying within the profile in which volume changes are anisotropic. It is shown that for saturated clays the ratio of added water (expressed as a depth) to the vertical soil displacement is greater than or equal to unity, though it is unlikely to exceed 5. When the soil volume properties are isotropic, the ratio has one of two integer values: 1 when the soil is constrained to move only vertically, and 3 when it is free to change volume in three dimensions. The measured value should be used for modelling changes in crack geometry.
The self‐diffusion of sodium in soil: factors affecting the surface mobility
Authors: STAUTON S. 
Published: July 2006

SUMMARYA study is presented of the self‐diffusion of sodium in a sub‐soil. Impedance factors (fs)associated with the surface phase have been derived, representing the mobility of sorbed sodium ions relative to mobility in an ideal solution. Effects of drying, of cationic com‐position and of enrichment with either native clay fraction or ‘pure’ clay minerals were investigated. The liquid phase impedance factor (fL) without added clay was 0.29: clay enrichment affected soil structure and hence fL. Values of fs were in the range 0.19–0.05, and were about one‐third of fL. The value off, decreased as clay content increased, being halved when 50% native clay or 10% clay mineral was added. In a sodium saturated soil fs was 0.06, less than half that in a calcium saturated soil.
Water and oxygen regimes under conifer plantations and native vegetation on upland peaty gley soil and deep peat soils
Authors: KING J. A. , SMITH K. A. , PYATT D. G. 
Published: July 2006

SUMMARYConcentrations of oxygen and carbon dioxide were measured in an upland peaty gley soil during two growing seasons and a deep peat during one season. Measurements were compared with the soil water regimes on both soils. Comparison was also made between planted areas of Sitka spruce and Lodgepole pine, and areas of the native vegetation (Molinia grassland on the peaty gley, and Calluna heath on the deep peat). In 13 m tall pure stands of the pine and spruce on the peaty gley soil about 28% of the rainfall was intercepted by the canopy and evaporated without reaching the soil, and the watertable was deeper and matric potentials were lower than under grass. When the matric potential fell below −5 kPa in the upper soil layers, high oxygen concentrations prevailed. In undisturbed peat, waterlogged conditions produced an anaerobic regime virtually to the surface, but a 1 m deep drainage ditch lowered the watertable and created an aerobic regime within the top 0.3 m of peat. The presence of tree crops on drained plots increased the depth of drying during the summer months, and aerobic conditions reached 0.4 m depth under Sitka spruce and 0.5m under Lodgepole pine. On the peaty gley also, Lodgepole pine dried and aerated the soil to a greater depth than Sitka spruce during the summer, but no difference in water regime was evident in the winter.
Use of the Kubelka—Munk theory to study the influence of iron oxides on soil colour
Authors: BARRON V. , TORRENT J. 
Published: July 2006

SUMMARYThe Kubelka–Munk theory, which is commonly applied to ‘pigment mixtures’, adequately predicted the colour of mixtures of synthetic haematite, synthetic goethite and deferrated soil powders. The theory illustrated the higher pigmenting effect of haematite compared with goethite. In mixtures containing haematite the calculated colour coordinates could be combined into simple ‘redness’ indices that were highly correlated with haematite content and were not appreciably influenced by goethite.The theory was also applied to the study of the chromatic characteristics of 98 soils, differing widely in their origin but having an organic matter content <2% in which haematite or goethite was the dominant Fe oxide. The theory showed that the average ‘soil’ haematite and ‘soil’ goethite had colours similar to those of their synthetic counter‐parts, whereas the rest of the soil components could be considered as an essentially ‘grey’ matrix. It was also useful in predicting the haematite and goethite contents of soils either from several reflectance measurements of soil‐white standard mixtures or from the indices of redness developed for the synthetic mixtures.
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

SUMMARYThe effect of non‐uniform distribution of particles in the soil on the rate of dissolution of calcium phosphate particles was investigated, using a negative binomial distribution to describe the degree of clumping of the particles. A randomly distributed sample dissolved about 10% more slowly than a regularly distributed one. For a degree of clumping in which the sum of the spherical volumes influenced by particles was about 10% of the whole soil volume, the predicted rate of dissolution was reduced by about 85%. The effect of a range of particle sizes in the applied material was also investigated. Typical grades of commercial rock phosphate contain a high proportion of fine particles, resulting in a rapid initial rate of dissolution of the applied material, but the rate trails off as the small particles are exhausted.The effect of the presence of plant roots was also considered, using average root characteristics and assuming the root effects to be spread over the whole soil volume. The rate of calcium phosphate dissolution was increased by root uptake of dissolved phosphate ions, by an amount depending on the rooting density and the rate of calcium phosphate application, and by secretion of acid by the roots. In many circumstances where rock phosphates are applied as fertilizers, plants are likely to be rhizosphere acidifiers; sufficient acid may be secreted to render rock phosphates soluble where they would other‐wise be insoluble. Generally, calcium uptake will not greatly affect the rate of calcium phosphate dissolution.
The fractionation of soil polysaccharide by electrofocusing
Authors: CHESHIRE M. V. , MUNDIE C. M. 
Published: July 2006

SUMMARYSoil polysaccharide isolated from alkali extracts of Countesswells and Insch series soils has been submitted to electrofocusing with ampholyte in dextran gel. To aid detection, polysaccharide which had been dyed with either Procion Red or fluorescein or labelled 14C by prior incubation of the soil with 14C‐labelled substrates, was also used.After electrofocusing, polysaccharide was distributed in the gel over the entire range of pH used, 1.9–10, with the greatest concentration occurring within the pH 1.9–4 region. The distribution was partly the result of adsorption and diffusion. Re‐electrofocusing of material isolated from particular regions of the bed located most of it in the original position, although considerable dispersion occurred, particularly with the less strongly charged material and there was evidence for association/dissociation reactions. This was also observed in a medium containing 8 M urea.The proportion of uronic acid was greatest in the polysaccharides fractions from the pH 3.0–4.0 region of the bed. The increased acidity of the fraction nearest to the anode appeared to relate to the presence of other organic acids, such as succinic, fumaric and levulinic acids. No difference could be detected between the separation of polysaccharide from the two different soils or between the labelled polysaccharides derived from an incubation of 14C‐glucose with soil and those from an incubation of 14C‐plant material.
Effects of season and management on the vane shear strength of a clay topsoil
Authors: DOUGLAS J. T. 
Published: July 2006

SUMMARYVane shear strength, water status and bulk density were measured at various times in a growing season at two depths in a swelling clay topsoil. The site comprised experimental plots that had been ploughed annually, or direct‐drilled for 10 years; short‐term fallow areas, created on adjacent long‐term grassland, were compared with the arable plots. In the middle of the topsoil layer (nominally 120 mm depth) of all three treatments shear strength was linearly related to water content, and similarly to bulk density in the direct‐drilled and ploughed soils. Closer to the soil surface (nominally 40 mm), relationships between strength and wetness or density were less distinct, particularly in the spring, when drying was not accompanied by an increase in strength; possible reasons for this anomaly are considered. The shear strength of the untilled soils was greater, at both depths, than that of the ploughed soil. Other factors including density, water potential, soil structure and organic constituents, differed with time or between treatments, and their contribution to variations in shear strength are discussed.
The preparation of soil thin sections for biological studies
Authors: TIPPKÖTTER R. , RITZ K. , DARBYSHIRE J. F. 
Published: July 2006

SUMMARYA method is described that permits the preparation of soil thin sections up to 6 × 8 cm in approximately 14 days without any discernable artefact. Soil samples are fixed in buffered glutaraldehyde, dehydrated rapidly in a graded series of acetone: water mixtures and impregnated with a polyester resin. The method effectively preserves biological material, such as delicate protozoan cells and root tissues. A range of stains were tested for staining roots in soil blocks and in soil thin sections.
Interaction forces between soil particles: shear moduli of the < 2 μm size fraction
Authors: PIPER J. 
Published: July 2006

SUMMARYThe shear moduli of the < 2 μm size fraction of three soils have been measured for samples of 10–35% w/w solid. Samples were thixotropic, the shear modulus increasing with time. This increase can be described by simple models and visualized in terms of the formation of links between particles. For a given soil the shear modulus increases with ionic form in the order Ca2+∼Mg2+ <K+ <Na+ < Li+ and varies in a complex manner with electrolyte concentration.
Adsorption of sulphate and fluoride by variable charge soils
Authors: ZHANG G. Y. , ZHANG X. N. , YU T. R. 
Published: July 2006

SUMMARYThe adsorption of sulphate and fluoride by three variable charge soils was studied. Adsorption increased with increase in the amount of sulphate added at constant pH, and decreased with increase of pH.The ratios of the amount of released OH−to that of the adsorbed SO2‐4 at pH 5–0 were 0.12, 0.14 and 0.20 for the three soils, respectively, much lower than the corresponding OH−/F− ratios which ranged from 0.3 to 1.0. For a ferric acrisol the OH− released accounted, on average, for only 15% of the SO2‐4 adsorbed, leaving more than 60% to be explained by the decrease in positive charge and the increase in negative charge carried by the soil.
The solution chemistry of podzolic soils from the eastern Canadian shield: a thermodynamic interpretation of the mineral phases controlling soluble Al3+andH4SiO4
Authors: MANLEY E. P. , CHESWORTH W. , EVANS L. J. 
Published: July 2006

SUMMARYThirty‐one soil solutions were extracted by immiscible displacement with CCl4 under high speed centrifugation from sub‐horizons of three podzolic soils from north‐eastern Ontario, Canada. The solutions were analysed for major cations and anions and a speciation of dissolved Fe and Al was attempted to distinguish ‘free’, ‘organically bound’ and ‘inorganically bound’ species. Results indicated that the Ae (E) horizon solutions were of low pH and contained mainly organically bound Fe and Al. With depth, pHs increased, ionic strengths decreased and the relative proportion of inorganically bound Fe and Al increased. Although application of phase diagrams permitted only a semi‐quantitative interpretation of the data, all horizon solutions, with the exception of some Ae solutions, appeared supersaturated with respect to likely occurring crystalline and amorphous aluminosilicates [kaolinite, halloysite, allophane (Al:Si=l) and imogolite]. Of the phases considered, reactions involving imogolite‐allophane, gibbsite‐halloysite, gibbsite‐allophane and gibbsite‐imogolite all appeared reasonable in controlling the content of Al3+ and H4SiO4 in solution, although the presence of gibbsite and imogolite could not be definitely confirmed in these soils.
Plant uptake of exchangeable and non‐exchangeable potassium. II. Influence of soil type on uptake by onion roots
Authors: MITSIOS I. K. , ROWELL D. L. 
Published: July 2006

SUMMARYMeasurements and predictions of uptake of non‐exchangeable K have been made for three soils. Exchangeable K is important in controlling the extent to which non‐exchangeable K is used; rate of diffusion of exchangeable K seems less important. Rate of release of non‐exchangeable K did not vary much between soils, but critical release concentrations in solution varied from 33 to 85 μM with little obvious effect on the extent of use of non‐exchangeable K.
Composition and properties of poorly ordered minerals in Welsh soils. II. Phosphate adsorption and reactivity towards NaF solution
Authors: ADAMS W. A. , GAFOOR S. N. , KARIM M. I. 
Published: July 2006

SUMMARYEleven horizons of acidic soils developed from Lower Palaeozoic sedimentary rocks in mid Wales contained varying amounts of poorly ordered minerals. In nine of these over 70% of the phosphate adsorption capacity was attributed to poorly ordered minerals. Iron oxide with substituted Al, and a separate Al oxide, together accounted for the phosphate adsorption of the poorly ordered fraction. Aluminium‐substitution had no major effect on the adsorption capacity of Fe oxide, but since Al occurred in both active minerals it masked the effect of Fe on phosphate adsorption in simple correlations. The relative contribution of the two mineral forms to phosphate adsorption varied widely between soils. Aluminium as a substituent in Fe oxide and in ‘free’ oxide form was responsible for the soils’ reactivity towards NaF, but no distinction could be made between these poorly ordered forms. For certain horizons both poorly ordered Al and Si were correlated with OH− release, but Al oxides were more important than silicates.
The effect of the frequency of sampling on the observed concentration of oxygen in an afforested peat soil
Authors: RAY D. , PYATT D. G. , WHITE I. M. S. 
Published: July 2006

SUMMARYSamples of air or water were extracted daily from porous pots buried within the rooting zone of trees planted on a deep peat soil. For most pots, the O2 concentration in the fluid increased with the number of samples taken each day, presumably because air was drawn into the pot from shallower depths. Sampling frequency should therefore be chosen as a compromise between the needs to increase precision and to minimize introduced bias.
Weathering of a mica introduced into four acidic forest soils
Authors: HATTON A. , RANGER J. , ROBERT M. , NYS C. , BONNAUD P. 
Published: July 2006

SUMMARYA mica was inserted into the soil at four sites to try to identify, in situ, the physico‐chemical changes in the soil caused by the introduction of different tree species, and especially conifers. Changes in the chemistry and mineralogy of the mixed‐layered mica, mica‐chlorite, vermiculite, after 1 1/2 and 31/2 years in the soil, showed good differentiation between soil horizons and between soil types. Differences due to tree species were present, but small. The mechanisms of mineral evolution can be defined with reference to experimental data obtained in the laboratory. In litter layers, the mica‐chlorite sheet was transformed into a mica‐vermiculite, and exchangeable cations predominated on the exchange sites. In the organo‐mineral horizons, changes varied depending on the soil type: in the podzol, transformation was similar to that in the litter layers, but in the sol brun acide, changes were dominated by the Al fixation on the exchange sites and its rapid hydroxylation which blocks these sites, leading to the formation of Al intergrade minerals.Different tree species produced deviations linked to their ability to cycle cations, and also to the different organic materials produced which can attack the mineral.The method has the potential to define the present soil environment and weathering processes, but it needs a more complete experimental design and the use of statistics to clarify the effects of the parameters and their interactions.
A constant potential titration method for studying the kinetics of Cu2+ desorption from soil and clay minerals
Authors: JOPONY M. , YOUNG S. D. 
Published: July 2006

SUMMARYThe kinetics of Cu2+ desorption from a contaminated Malaysian padi soil, English Supreme kaolinite and Wyoming bentonite are studied using a constant potential titration method. This technique involves maintaining a constant Cu2+‐sensitive electrode potential corresponding to a Cu2+ ion activity below that which would naturally be supported by the soil in suspension. This is achieved by the controlled addition of complexing agent. Desorption occurs in response to the artificially reduced solution activity and the rate of the desorption reaction is revealed by the rate of addition of the complexing agent.The desorption results were fitted to three established kinetic equations, all of which showed reasonable agreement with the data. In particular, a two‐constant rate equation demonstrated some consistency between different materials. Both first‐order and ‘diffusion’ kinetic equations appeared to apply within specific titration conditions. Each equation is discussed in terms of its implied desorption mechanism and the inconclusive nature of such mechanisms for short term (< 1 hour) desorption reactions is illustrated.
The fate at several time intervals of 15N‐labelled ammonium nitrate applied to an established grass sward
Authors: BRISTOW A. W. , RYDEN J. C. , WHITEHEAD D. C. 
Published: July 2006

SUMMARY 15N‐labelled ammonium nitrate solution was applied in late April to circular, enclosed micro‐plots prepared by pressing open‐ended polypropylene cylinders into an established sward of perennial ryegrass. Cylinders were removed from the ground at intervals between 2 and 370 days after the application and assessments made of the distribution of 15N in plant and soil components. Of the added labelled N, 54.7% was recovered in the herbage which was cut four times during the growing season and again at the final sampling date. After two days, 37% of the labelled N was recovered in the soil microbial biomass. Large fluctuations occurred in the amount of 15N recovered in the soil microbial biomass over the next 14 days suggesting that rapid cycling of 15N occurred between this fraction and the mineral N fraction. After the first cut in late May, translocation of15N occurred more slowly from the roots into the stubble than from stubble into new herbage, so that the amount in the stubble declined more rapidly than did that in the roots. During the winter, there was no net transfer of N from the roots to above‐ground components of the sward. By the end of the growing season, half the 15N remaining in the sward was immobilized in the humified fraction of the soil organic matter; some of this was mineralized in the following spring.