bluuebunny/crossref_metadata_2025 huggingface dataset:
Charge characteristics and exchangeable cation status of Korean Ultisols and Alfisols and Thai Ultisols and Oxisols
Authors: WADA S.‐I. , WADA K.
Published: July 2006

The charge characteristics of A1 or Ap and B2 horizon samples of total 23 Ultisols, Alfisols and Oxisols in Korea and Thailand were studied by measuring the retention of NH4+ and NO3− at different pH values (4–8) and NH4NO3 concentrations (0.1–0.005 m). The magnitude of their negative charge (σ−; meq/100g) was dependent on pH and NH4NO3 concentration (C; m) as represented by a regression equation: log σ−=apH +blogC +c. The values of the coefficient a (0.04–0.226), b (0.03–0.264) and c (–0.676–1.262) were correlated with the kinds of the soil and horizon and with the region where the soil exists. The retention of NO3− was less than 1 and 2–3 meq/100 g for the A1 or Ap and B2 horizon samples, respectively.

The sum of exchangeable base and Al (‘effective’ CEC) was close to and higher than the magnitude of permanent charge (=σ− measured at pH = 4.3 and at C = 0.005 m) for one‐third and two‐thirds of samples, respectively. A σ− value of 16 meq/100 g clay at pH = 7 and C = 0.01 m was found appropriate to separate the B2 horizons of Thai Ultisols and Oxisols from those of Korean Ultisols and Alfisols. Korean Alfisols and Ultisols and Thai Ultisols were distinguished from each other on the status of exchangeable base and Al
Extractable copper concentrations in Scottish soils
Authors: BERROW M. L. , REAVES G. A.
Published: July 2006

The distribution of ethylenediaminetetraacetic acid (EDTA)‐extractable Cu concentration levels in 3653 samples from 725 Scottish soil profiles is reported. The derived mean for the full set of data is 0.86 mg kg−1 and the normal range 0.08–9.8 mg kg−1. The relation of extractable Cu concentration to that of total Cu and to some other soil variables is also examined. Extractable Cu contents decrease with increasing depth over the first 50 cm and are almost constant below this.

The correlation between total and extractable copper (r=+ 0.453) is statistically highly significant (P<0.001). The extractability (i.e. the percentage of total Cu extractable by EDTA) has also been considered in relation to the other soil variables. Extractability is inversely related to ash content though the relationship is not linear. Extractability is enhanced under conditions of impeded drainage but there is no indication that it is related to clay or sand contents.

Approximately 18% of the arable topsoil samples contain levels of extractable Cu which are inadequate to supply the nutritional requirements of cereal crops and approximately 79% contain levels inadequate to support herbage with a Cu content sufficient to supply the requirements of grazing cattle.
Describing the effect of time on sorption of phosphate by iron and aluminium hydroxides
Authors: BOLAN N. S. , BARROW N. J. , POSNER A. M.
Published: July 2006

Iron and aluminium hydroxides were precipitated both in the presence and absence of kaolinite. The reaction between phosphate and these hydroxides was measured for periods which ranged from 5 min to 72 h. The effect of time on phosphate sorption was examined by plotting the sorption data according to different, simple, kinetic equations such as the first order, second order, the parabolic diffusion equation, the Elovich equation and the modified Freundlich equation. The effect of time on sorption was also examined by the mechanistic model recently developed by Barrow (1983b) for the sorption and desorption of phosphate by soils.

The sorption of phosphate by iron and aluminium hydroxides increased with time and the reaction continued through the period of observation without reaching a true equilibrium. Curvilinear relationships were obtained when the data were plotted according to the simple kinetic equations. These simple kinetic equations fail to describe the effect of time on sorption partly because the mechanism is different from that postulated and partly because they do not consider electrostatic effects when phosphate ions react with a charged surface. The mechanistic model of Barrow (1983b), which takes this effect into account, described effect of both concentration and time on phosphate sorption. According to this model, the increase in phosphate sorption with time was caused by a redistribution of adsorbed phosphate into the interior of the particles of iron and aluminium hydroxides by solid‐state diffusion.
A survey of clover and Lotus rhizobia in Northern Ireland pasture soils
Authors: WOOD M. , COOPER J. E. , CAMPBELL D. S.
Published: July 2006

192 sites covering the main soil types in Northern Ireland were analysed for numbers and effectiveness of clover and Lotus rhizobia, and chemical properties. Peat sites were generally highly acid (pH <5.5) and mineral sites near neutral (pH 5.5–7.8). Clover rhizobia were generally absent from peat sites and present in mineral sites as large populations (> 106 g−1 dry soil). 79% of isolates were effective on T. repens var. Grasslands Huia. Lotus rhizobia were generally absent from peat sites, less often present than clover rhizobia in mineral sites, and as smaller populations. They were mainly effective on L. pedunculatus var. G4705 and were all of the slow‐growing type belonging to the genus Bradyrhizobium. Numbers of clover rhizobia were significantly correlated with soil pH, exchangeable Ca, base saturation and Al saturation, but effectiveness of clover rhizobia and numbers of Lotus rhizobia were not correlated with any soil chemical property.
The dissolution and dispersion of dicalcium phosphate dihydrate in soils.
Authors: KIRK G. J. D. , NYE P. H.
Published: July 2006

A model of the dissolution of a planar source of dicalcium phosphate dihydrate (DCPD) in soil is developed, with which to predict the calcium, phosphate and pH profiles formed by DCPD dissolving in an acid soil. The model comprises numerical solutions of partial differential equations describing the diffusion and reaction of calcium, phosphate and base in soil. The concentrations of calcium, phosphate and hydrogen ions in the soil solution at the mineral/soil boundary are found from the ion activity product of DCPD and by equating the fluxes of calcium, phosphate and base across the boundary. The derivation of the equations, the other boundary conditions, and the simplifying assumptions necessary for the solution of the equations, are discussed. The sensitivity of the model to its input parameters is assessed. The model provides a basis from which to advance to more complex geometries, and more complex fertilizers.
Gas diffusion in structured materials: the effect of tri‐modal pore size distribution
Authors: CURRIE J. A. , ROSE D. A.
Published: July 2006

Coefficients of gas diffusion (hydrogen through air) were measured on packings of Portland stone chips over a range of water contents. The chips were obtained by crushing blocks of Portland stone on which similar gas diffusion measurements had been previously made. The packings had a tri‐modal pore‐size distribution: pores between the stone chips; pores within the chips but between ooliths; pores within the chips and within ooliths. As the water content of the packings was progressively decreased, the diffusion coefficient for the packings increased in three steps corresponding to successive drainage of the three pore modes. The previous results for the blocks were used to give good theoretical prediction of the three steps obtained by measurement. These results support earlier speculation that a similar stepwise increase in diffusion coefficient in soils might have been caused by micro‐pedal structure within soil crumbs.
Simultaneous nitrification and diffusion in soil. III. The effects of the addition of ammonium sulphate
Authors: DARRAH P. R. , NYE P. H. , WHITE R. E.
Published: July 2006

The simultaneous nitrification and diffusion of NH4+, applied as ammonium sulphate to laboratory columns, was followed experimentally and with a simulation model. Ammonium was applied as a fertilizer band at levels equivalent to 69 kg N ha−1 to a 1 cm depth. The concentration profiles of NH4+, NO3−, SO2−4 and pH were measured in two columns for incubation times of 214 and 286 h. The simulation model provided for the precipitation and ion pair formation of CaSO4, the adsorption equilibria of NH4+ and soil acid with the soil solid phase, and nitrifier growth and activity. In general, good agreement was found between the experimental and simulated concentration profiles. The effect of CaSO4 precipitation on the diffusion of N was investigated using model simulations of the diffusion of NH4+ in the absence of nitrification. The simulations suggested that the reactions of SO2−4 in the soil could markedly affect the spread of NH4+ from a band of (NH4)2SO4.
Effect of liming levels and Ca:Mg ratios on yield, nitrogen content and nodulation of soyabeans grown in acid Cerrado soil
Authors: MUCHOVEJ R. M. C. , BORGES A. C. , NOVAIS R. F. , THIEBAUT J. T. L.
Published: July 2006

The effect of four lime levels and of five ratios of Ca: Mg on nodulation, nitrogen fixation and yield of soyabean var. UFV‐1 was studied under greenhouse conditions, using a Typic Haplorthox soil. Dry matter production of top growth was relatively constant for soil Ca: Mg ratios ranging from 0.26: 1 to 24: 1 and a similar production level was sustained for A1 saturation values from 0 to 43%. Nodulation (number and dry weight of nodules) increased with increasing A1 saturation from 0 to 43%. The greatest increase was observed when Al saturation was raised from 0 to 2 or 3%. The N accumulated in the shoots, decreased with the increase in the percent A1 saturation, showing that the largest number of nodules does not necessarily result in greatest accumulation of N in shoots.
The possible effect of soluble silicon on the lepidocrocite content of gley soils from England and Bangladesh
Authors: KARIM Z. , NEWMAN A. C. D.
Published: July 2006

Nine different gley profiles from England and Bangladesh were studied; out of these, four English soils contained variable amounts of lepidocrocite. The amounts of lepidocrocite present in various layers of these soils decreased with increasing concentrations of Si(OH)4 in the soil solution. The amount of lepidocrocite formed was negatively correlated (r= ‐0.78) with the atomic ratios of Si/Fe in the citrate/dithionite extracts.

Lepidocrocite was absent from the other five profiles, including three surface water gley soils from Bangladesh. These soils contained relatively large concentrations of Si(OH)4 in soil solution, ranging between 0.7 mm and 1.0 mm. The atomic ratio of Sid/Fed in the citrate/dithionite extracts was higher in these soils. Enborne soil contained maximum amount of citrate/dithionite extracted silicon (2.30 mg g−1) with no X‐ray crystalline iron oxides in the profile.
Testing a mechanistic model. IV. Describing the effects of pH on zinc retention by soils
Authors: BARROW N. J.
Published: July 2006

Samples of two soils were incubated at 60°C for 24 h with several levels of either calcium carbonate or hydrochloric acid. Zinc retention was then measured on subsamples of the treated soil over 24 h at 25°C. The results were compared with published experiments (Bar‐Yosef, 1979; Harter, 1983) in which zinc retention was also measured over a range of concentrations and pH values, but using different experimental conditions.

Zinc retention increased as pH increased. In all cases, this effect could be described by assuming that the ZnOH+ ion was retained and the effect of pH was due to the increased proportion of this ion in solution. Over most of the pH range it was not necessary to assume any contribution from a decrease in the electrostatic potential of the reacting surfaces with increasing pH. This contrasts with the effects of pH on phosphate and fluoride retention and suggests that the materials that react with zinc differ from those that react with anions.

The shape of plots of zinc retention against ZnOH+ concentration was reproduced using a model in which it was assumed that there was a range of values of electrostatic potential. A similar model had previously been used for anions. Zinc would tend to react with the most negative end of this range and phosphate with the least negative end. This further suggests that zinc and anions may react with different materials.
Simultaneous nitrification and diffusion in soil
Authors: DARRAH P. R. , NYE P. H. , WHITE R. E.
Published: July 2006

A short‐term nitrification assay was used to investigate the relationship between pH and nitrification rate. The resulting pH relation was included in a model that simulated the time‐course of nitrification over a 16–day period. The predictions from this model corresponded closely with measured nitrate concentrations in contrast to a similar model that did not include the response of the nitrifiers to pH change.

The simultaneous nitrification and diffusion of ammonium sulphate, applied as a band of fertilizer equivalent to 69 kg N ha‐1 to a 1 cm depth, was followed experimentally in a soil column incubated for 382 h. The measured concentration profiles of ammonium, nitrate and pH agreed well with those predicted by a simulation model that included the effect of pH on nitrification, while profiles predicted by a model that neglected the effect of pH agreed poorly with the experimental results.
The dissolution and dispersion of dicalcium phosphate dihydrate in soils
Authors: KIRK G. J. D. , NYE P. H.
Published: July 2006

The model developed in part I to describe the dissolution of a planar source of DCPD in soil is extended to deal with the dissolution of particles, allowing for diminution of the particles as they dissolve and the interaction of neighbouring particles. The model has nine input parameters: concentrations of calcium and phosphate in the unamended soil solution, unamended soil pH, phosphate and lime potential buffer capacities of the soil, volumetric moisture content, diffusion impedance factor, and rate of application and particle size of the DCPD. A sensitivity analysis of the model showed that the rate is particularly dependent on particle size, rate of application, and the pH and concentration of calcium in the soil solution. If the particles are so far apart that they do not influence each other, after the very early stages the rate of dissolution is independent of the soil buffer terms. But for typical rates and methods of application, neighbouring particles will influence each other, and the consequent interactions between the rate‐determining variables are complex.
The dissolution and dispersion of dicalcium phosphate dihydrate in soils
Authors: KIRK G. J. D. , NYE P. H.
Published: July 2006

The model of the dissolution of particles of DCPD in soil, presented in part III, was tested against experimentally determined rates of dissolution in soil at two pHs, 4.6 and 6.0. To measure the rates, 45Ca dissolved from labelled DCPD was recovered from the soil by shaking the mixture of soil and undissolved DCPD in a CaCl2, extractant. There was good agreement between the observed and predicted rates of dissolution.
Stability of aggregates of different size grades in allophanic soils from volcanic ash in New Zealand
Authors: CHURCHMAN G. J. , TATE K. R.
Published: July 2006

Samples from six ash soils were chosen with a range of Fe and C contents. Stabilities over the aggregate size‐range from < 1 †m to > 2 mm were measured by selectively removing aggregating agents from fresh soil samples. Wet‐sieving was also carried out on both field‐moist and air‐dried 3.4–2.0 mm macroaggregates.

Macroaggregate stabilities were closely related to C contents and were also enhanced by high contents of allophane and/or Feox. High water contents decreased the stability of field‐moist macroaggregates.

Clay‐sized material was most readily dispersed with Na resin after pretreatment with hydrogen peroxide; removing the latter alone was usually ineffective in dispersing clays.
Plant uptake of exchangeable and non‐exchangeable potassium. I. Measurement and modelling for onion roots in a Chalky Boulder Clay soil
Authors: MITSIOS I. K. , ROWELL D. L.
Published: July 2006

Uptake of K was measured using a single onion root technique with four soil cylinder diameters, and measuring changes in exchangeable K in the soil. Baldwin's model fitted the measured uptake when only exchangeable K was taken up, but that of Heming & Rowell allowed predictions of uptake of both exchangeable and non‐exchangeable K (Knes) after fitting the necessary parameters. Release of Knex occurred in both 3 mm and 6 mm cells (root densities of 14cm cm”−3 and 3.5 cm cm−3) in 10 days. Predictions were made for longer times and differing soil water contents: after four weeks at a water content midway between field capacity and wilting point the contribution of Knex to total uptake was significant (up to 60%) for plants with high root densities.
Characteristics of soil organic matter in temperate soils by Curie‐point pyrolysis‐mass spectrometry. II. The effect of drainage and illuviation in B horizons
Authors: BRACEWELL J. M. , ROBERTSON G. W.
Published: July 2006

B horizons from a set of 23 Scottish soils were examined by Py/MS multivariate analysis. These soils comprised phaeozems, cambisols, podzols and gleysols.

The principal components analysis of 52 mass ion intensities partitioned the set of soils successfully according to morphological classes Bw, Bg and Bs, and established characteristic differences of organic composition between them. Reconstructed factor spectra for the factors effecting this partition showed distinct homologous groups of products to be responsible. These were principally pyrroles, alkenes and aromatic hydrocarbons of low molecular mass. Possible organic origins of these are discussed and related to the organic patterns found in the A horizons.

The Bh (humus B) horizons of podzols gave pyrolysates richer in polysaccharide and lignin products than those of other B horizons, suggesting a less decomposed organic matter.
Effects of green manure on isotopically exchangeable phosphate in a dark‐red latosol in Brazil
Authors: LEMARE P. H. , PEREIRA J. , GOEDERT W. J.
Published: July 2006

In a field experiment on a dark‐red latosol (haplustox) in the Cerrado of Brazil, green manure, including maize residues, increased yield of maize grain. Samples of soil from the experiment were investigated in the laboratory. Green manure caused no effect on amounts of phosphate extracted by Bray's solutions, nor by anion exchange resin. Adsorption measurements showed that green manure did not affect the total amount of phosphate adsorbed by the soil, in relation to the amount added nor to the concentration of phosphate in solution. However, green manure increased the proportion of added phosphate that became isotopically exchangeable so that after desorbing some phosphate in two stages, 99% of the adsorbed added phosphate was exchangeable in soil with green manure, but 89% was exchangeable in soil without it. Green manure increased the concentration of phosphate in solution that was maintained by a specific amount of exchangeable phosphate held by the soil. Buffer power increased with time, without and with green manure; but it was less in its presence indicating that phosphate was less strongly held, and would be more mobile in soil in the field.

The results indicate that easily decomposable organic material, such as green manure and crop residues, makes fertilizer phosphate more effective for crops growing in an oxisol.
Salt effect in a multicomponent variable charge system: curve of zero salt effect, registered in a pH‐stat
Authors: MEIJER E. L. , BUURMAN P.
Published: July 2006

Measurement of the effect of KC1 addition to a soil suspension in pH‐stat experiments indicates that the pH titration curves of such a multicomponent system are characterized by a Curve of Zero Salt Effect (CZSE) rather than a Point of Zero Salt Effect (PZSE). This curve is most accurately measured as a functional relation between pH and KC1 molarity. The described method is very accurate and, by its rapidity, precludes long‐term changes in the sample which are the bane of classic batch experiments. In analogy, multicomponent soil systems will probably be characterized by a Curve rather than a Point of Zero Net Charge (PZNC).
A scheme for the quantitative description of soil macrostructure by image analysis
Authors: RINGROSE‐VOASE A.J.
Published: July 2006

Images prepared from impregnated samples showing a range of structures were classified structurally. A Quantimet 720 image analyzer and the ANOPOR system separate the pore space in each image into its fissure, channel and packing pore/vugh components. Measurements are derived for each type.

Overall structure is determined by the structural pore space consisting of fissures and packing pores/vughs. Paramenters relating to these types indicate the size and shape of structural units and their degree of development. Two scheme are proposed which describe several structural spectra.One treats fissures and packing pores as modifications of the same structural pore space, whereas the other treats the two separately.The effects of various processes of structural parameters are discussed, and the reliability of pore measurements is discussed.
Multi‐orientation thin sectioning for the determination of 3‐D morphology
Authors: SULLIVAN L. A. , KOPPI A. J.
Published: July 2006

A new soil thin sectioning technique which gives thin cross‐sections (called sliver sections) of thin sections, is described. Optical analysis of soil thin sections and soil sliver sections, using plain, crossed polarized and circularly polarized light provides three‐dimensional information on the micromorphology of clay coatings. This new technique is applied to a common type of clay plug and shows that these features consist of a stack of bowl‐shaped clay coatings.
The effect of subsoil cracking on moisture deficits of Pleistocene and Holocene fluvial clay soils in the Netherlands
Authors: KOOISTRA M. J. , MIEDEMA R. , WÖSTEN J. H. M. , VERSLUIS J. , BOUMA J.
Published: July 2006

Computer simulation of the soil water regime was used to calculate moisture deficits for Pleistocene and fluvial Holocene clay soils for a 30‐year period. Hydraulic conductivity (K‐h) and moisture retention (h‐θ) data were derived for major horizons in both soils as well as functions to characterize bypass flow and effects of horizontal planar voids on upward unsaturated flow of water from the water‐table to the root zone. Calculated moisture deficits in Holocene soils occurred earlier during the year and were more pronounced during the summer period. Differences between the two soils could be attributed to more pronounced formation of horizontal planar voids in the Holocene soil, which was associated with more pronounced swelling and shrinkage of the undisturbed soil material. The relatively low swelling and shrinkage of the undisturbed Pleistocene soil material was attributed to very dense packing of the elementary soil particles.
The basaltic soils of SE Nigeria: properties, classification and constraints to productivity
Authors: ESHETT E. T.
Published: July 2006

Four basaltic profiles located in northern Cross River State of Nigeria are described and characterized. The soils are classified as Typic Tropohumult and show strong acidity, low effective CEC, low N and available P. Organic matter levels of the surface soils are high. All the soils are well drained in spite of high YO clay, which is apparently kaolinitic, with moderate to high A1 saturation. Higher agricultural productivity of these soils is restricted by low effective CEC and strong acidity. Measures to combat these problems are suggested.
The use of tension infiltrometers to assess routes and rates of infiltration in a clay soil
Authors: JARVIS N. J. , LEEDS‐HARRISON P. B. , DOSSER J. M.
Published: July 2006

This paper describes the design and operation of a simple tension infiltrometer which imposes pressure potentials at the soil surface (hb) of –0.5, – 2 and –9 cm water, corresponding to equivalent diameters (ed) of the largest conducting pore of 6, 1.5 and 0.3 mm respectively. Infiltration measurements obtained in Evesham series clay soil were fitted to Philip's (1957) two‐term infiltration equation. Results were interpreted using information on the number, type and size of conducting macropores obtained in a dye tracing experiment. Significantly larger values of effective hydraulic conductivity at hb=–0.5 cm were attributed to the flow of water in large shrinkage cracks which constituted nearly 90% of the total conducting macroporosity. Measured fluxes at hb=–9 cm were related to sorption and swelling in the clay matrix, since within the range of infiltration times considered (t<0.5 h), the gravity or steady state component of infiltration was negligible. Rainfall intensity/duration data for a large number of storms at Silsoe were used to demonstrate that in dry soil nearly 70% of rainfall infiltrates in the clay matrix, and that the infiltration capacity of macropores of ed≤1.5 mm is only rarely exceeded.
The contribution of sorbed sodium and calcium to the self‐diffusion of these cations in soils with different clay mineralogies
Authors: STAUNTON S. , NYE P. H.
Published: July 2006

Self‐diffusion coefficients of sodium and calcium were measured on a range of moist subsoils. The ratio of concentrations of each isotope in the liquid phase and on the surface at the water content of the diffusion run was obtained from both the extrapolation of ratios measured at a range of soil:solution ratios, and, where possible, by measurement on expressed soil solution.

The diffusion coefficients were considerably greater than would be predicted if only the liquid phase contributed to diffusion. Surface phase impedance factors, fs, were calculated for each soil. fs for sodium was between 1/5 and 1/2 of the liquid phase impedance factor, fL; fs for calcium was between 1/9 and 1/20 of fL. Values of fs were not obviously related to the clay mineralogy, the proportion of internal to external cation adsorption, the volumetric water content, or the pH.
Chemistry of pedogenesis in Indo‐Gangetic alluvial plains
Authors: TOMAR K. P.
Published: July 2006

Five soil pedons–two aquic and two udic Haplustalfs and one petrocalcic Natrustalf–from the Indo‐Gangetic alluvial plain of Western Uttar Pradesh were investigated to evaluate the pedogenetic processes. Sand/silt ratios indicate that parent material discontinuities are insignificant. Higher K content and lower SiO2/R2O3 ratios of the non‐clay fractions in Bt, rather than in the A, horizons suggest maximum weathering at or near the surface.

An almost linear relationship between decrease in molar SiO2/R2O3 and % increase in clay to about 100cm depth in all the pedons, presence of clay argillans in Bt horizons (where % clay, fine/coarse clay ratio and bulk density values are greatest), all indicate that the development of argillic horizons in these soils was due, at least partly, to lessivage of clay. Fe in clay fractions decreases with depth whilst Al increases, but in the fine earth both increase steadily with depth. This, together with crystalline iron concretions in the lower Bt horizons, suggests that in Haplustalfs these horizons are gaining clay by neoformation/ reorganization of illuviated constituents, especially A12O3.
Effect of soil compaction by tractor traffic on soil structure, denitrification, and yield of wheat (Triticum aestivum L.)
Authors: BAKKEN L. R. , BØRRESEN T. , NJØS A.
Published: July 2006

In a field experiment with soil compaction by tractor traffic on a loam soil, the denitrification rate (using the C2H2 inhibition method), the soil structure, and the wheat yield were investigated. Tractor traffic on wet soil (> – 50 mbar matric potential) reduced the pore volume, doubled the percentage of large aggregates (> 20 mm), reduced the wheat yield by about 25%, and increased the N‐loss through denitrification by a factor of 3–4. Neither of these parameters were affected by tractor traffic at low soil moisture content. The weight of the tractor (1800 kg vs 4800 kg) did not significantly alter the effect of compaction on the measured parameters. There was a factor of 2–6 between the measured denitrification rate in compacted and that in uncompacted soil, and this factor showed little dependence on the average activity level on each date of measurement. Accumulated values for the measured denitrification during 75 days (May 23‐August 9) were 3–5 kg N ha–1 in uncompacted soil and 15–20 kg N ha–1 in soil which was compacted in wet condition.
Caesium and strontium diffusion through sodium montmorillonite at elevated temperature
Authors: JENSEN D. J. , RADKE C. J.
Published: July 2006

Counter ionic migration rates of dilute Cs+ and Sr2+ against sodium in a Na‐montmorillonite gel are measured using a radially perfused diffusion cell. Enhanced or surface diffusion for caesium is observed both at ambient and elevated temperature. To quantify these surface diffusivities the ion‐exchange properties of the diffusing species are required. Thus, exchange isotherms for caesium against sodium on montmorillonite at 22 and 90°C are given for 10−1, 10−2, and 10−3M background NaCl concentrations. Caesium counterion surface diffusivities at 22 and 90°C are 2.2*10−6 and 8.0 * 10−6 cm2 s−1, respectively. These values are found to be essentially independent of background ionic strength over the range 10−3 to 10−1m NaCl. Experimental evidence of enhanced transport through Na‐montmorillonite for the divalent cation Sr2+ is also confirmed with a surface diffusivity of 2 * 10−6 cm2 s−1 at 22°C and in 10−1m NaCl.
The numerical classification of soils: a case study using data from West Sussex, England
Authors: WICKRAMAGAMAGE P. , FISHER G. C.
Published: July 2006

A set of numerical clustering strategies was applied to soil data for 65 profile descriptions from profiles in West Sussex. The numerical classifications were compared to an original (1967) traditional classification, and at the higher categorial levels the composition of groups was found generally to be different. Such differences were ascribed to attribute weighting, missing information and restrictions on the types of data which could be employed by certain methods. Wilks’ Criterion, A, was used to find the classification producing the most homogeneous groups and, on the basis of tests using a restricted number of quantitative variables, numerical methods were found to give better groupings. An agglomerative, heirarchical procedure based on similarities calculated by Mahalanobis D2 and clustering by minimizing error sums of squares was found most satisfactory, however, the difficulty of defining a best classification is discussed.
Ochre deposits and associated bacteria in some field drains in Scotland
Authors: WHEATLEY R. E.
Published: July 2006

Drainage systems installed in highly organic soils, with the ground water pH near to neutral and affected by iron ochre deposition, were studied at six sites in Scotland. The iron ochre was composed of iron–encrusted filamentous bacteria entrapping amorphous material. The filamentous bacteria were identified as Gallionella spp., Sphaerotilus natans, Leptothrix ochracea and Leptothrix pseudo–ochracea. Heterotrophic iron–oxidizing bacteria were also present in the iron ochre, but Thiobacillus ferroxidans was not isolated. Differences in the proportion of species could not be correlated with peat type or the age of the drainage system. Sulphate reducing bacteria and bacteria capable of reducing Fe3+ were also isolated from the drainage water.

A preliminary investigation of the importance of biotic factors in the kinetics of Fe2+ oxidation showed that the rate of Fe2+ oxidation in unfiltered drainage water, was about twice the rate in filtered water, at 10°C. Incubations over a range of temperatures showed that the differences in rates were greatest at low temperatures.
Gaseous nitrogen losses from soil under Sitka spruce following the application of fertilizer 15N urea
Authors: HULM S.C. , KILLHAM K.
Published: July 2006

Gaseous N loss, through denitrification and NH3−volatilization, was monitored throughout the growing season after spring application of 15N labelled urea fertilizer to peaty gley soils supporting N‐deficient Sitka spruce. From the 15N data, it was calculated that only about 0.28% of applied N was lost through NH3‐volatilization, almost all within the first few days after fertilizer application. Approximately 0.05% of applied N was calculated to be lost through denitrification. Denitrification decreased slowly over a 4‐month period after fertilizer application. Rates of NH3‐volatilization correlated with available NH4+ in the litter layer, while for the early part of the study when N‐losses were highest, denitrification rates correlated with available NO3− in the litter layer. Observations of gaseous N‐loss are also discussed in relation to data from lysimetry, changes in soil pH, and the soil moisture regime.
Testing a mechanistic model. VIII. The effects of time and temperature of incubation on the sorption and subsequent desorption of selenite and selenate by a soil
Authors: BARROW N. J. , WHELAN B.R.
Published: July 2006

Several levels of both selenite and selenate were incubated with separate samples of soil for periods of up to 30 d and at temperatures between 5 and 60°C. The concentrations of selenite or of selenate which caused neither desorption nor further sorption–that is, the null‐point concentrations–were then measured at 25°C. In addition, the rate of desorption was measured after incubation at 60°C for 10 d. The ability of a mechanistic model to describe the results was tested.

There were large decreases in the null‐point concentrations of selenite with both increasing period and increasing temperature of incubation. These effects were modelled as due to a relatively rapid diffusive penetration and a large activation energy for diffusion. Only a small proportion of the sorbed selenite was desorbed within 3 d but, at large solution:soil ratios, desorption appeared to be still continuing. These effects were fairly well predicted by the model applied to the sorption data. For example, the continuing desorption was ascribed to the slow reversal of the diffusive penetration. For selenate, the effects of period and temperature of incubation were much smaller. These effects were modelled as due to a slower diffusive penetration and a lower activation energy. Desorption was quicker and was more nearly complete. According to the model, a large proportion remained in the adsorbed form and was more quickly removed when desorption was induced. It is argued that the behaviour of selenite is consistent with diffusion into a crystal and the large activation energy is required to enable jumps over energy barriers. On the other hand, the lower activation energy for selenate is consistent with diffusion being limited to pores or cracks.

It is suggested that the residual value of selenite fertilizers would decrease because of the continuing reaction, but that this effect would be unimportant for selenate.
Measurements of the yield surfaces and critical state of some unsaturated agricultural soils
Authors: KIRBY J. M.
Published: July 2006

Yield surfaces and the critical‐state condition have been measured on unsaturated agricultural soils using a standard uniaxial compression test and a constant‐volume direct shear test. The yield surfaces and critical‐state line are all readily described in terms of applied or total stresses, and such an approach offers practical advantages over approaches based on effective stresses. Four soils were tested, these being a silt, a tilth with aggregates mostly from 5‐15 mm, a cracking clay and a red‐brown earth.

Each soil was tested at a single constant moisture content in all tests, although the moisture content differed from soil to soil. The range of saturation covered by the four soils was approximately 20‐98%. All the soils displayed yield and deformation behaviour qualitatively consistent with the critical‐state concept. All approach a condition of shear with no volume change (the critical state) under continuing shear. All show collapse with shear in states looser than critical, and expansion with shear in states denser than critical. The silt, being a non‐cohesive soil, cannot support shear stresses much above the critical‐state line, whereas the other three soils can support much higher shear stresses in the overconsolidated condition. The yield surfaces of the silt and the tilth, which were tested at low saturation, are similar in shape with increasing stress level. However, the other two soils, tested when near saturation, display yield surfaces that are not constant in shape with increasing stress level. While the critical‐state concept is applicable both qualitatively and quantitatively, unsaturated soils may be considered to have properties that differ in detail from those of saturated soils.
Determination of the exponential unsaturated hydraulic conductivity function by parameter identification
Authors: BRANDYK T. , ROMANOWICZ R. , SKAPSKI K.
Published: July 2006

The parameter identification technique for the evaluation of the exponential unsaturated hydraulic conductivity function is described. The identification is performed using the indirect approach with an output error criterion for steady soil moisture flow through peat‐muck soil columns. The identification procedure uses the Levenberg‐Marquardt algorithm to the solution of the stated least‐square optimization problem. Examination of the evaluated parameters from laboratory experiments justifies the use of this simple identification method for the whole soil profile when the variation of the soil properties in the soil profile is not too large. For layered soil profiles with relatively large differences of soil properties between layers, the parameters of the exponential function must be evaluated separately for each layer.
Fuzzy mathematical methods for soil survey and land evaluation
Authors: BURROUGH P. A.
Published: July 2006

The rigid‐data model consisting of discrete, sharply bounded internally uniform entities that is used in hierarchical and relational databases of soil profiles, choropleth soil maps and land evaluation classifications ignores important aspects of reality caused by internal inhomogeneity, short‐range spatial variation, measurement error, complexity and imprecision. Considerable loss of information can occur when data that have been classified according to this model are retrieved or combined using the methods of simple Boolean algebra available in most soil and geographical information systems. Fuzzy set theory, which is a generalization of Boolean algebra to situations where data are modelled by entities whose attributes have zones of gradual transition, rather than sharp boundaries, offers a useful alternative to existing methodology. The basic principles of fuzzy sets, operations on fuzzy sets and the derivation of membership functions according to the Semantic Import Model are explained and illustrated with data from case studies in Venezuela and Kenya.
A rapid method for predicting the lime requirement of acidic temperate soils with widely varying organic matter contents. III. A lime‐quality correction model
Authors: BAILEY J. S. , STEVENS R. J. , KILPATRICK D. J.
Published: July 2006

A correction factor for lime quality (F), is described, which can be used to convert CaCO3 requirements into recommendations for commercially available liming materials. A model is presented that relates values of F to the properties of both the liming materials and the soils to which the materials are applied. The results of independent tests demonstrate that the model is capable of predicting suitable values of F for a wide variety of different soil‐lime treatments.

A procedure is described for estimating the amount of liming material required to adjust the pH in soils with widely varying organic matter contents. The procedure incorporates all the models and relationships developed in this study and appears to provide a more comprehensive method of evaluating the lime requirement of temperate acidic soils than any other method currently available.
Structure of soil carbohydrates resistant to periodate oxidation
Authors: CHESHIRE M. V. , LOMAX J. A. , MUNDIE C. M.
Published: July 2006

Permethylation has been applied to the polysaccharide in soil, which has been oxidized with 0.2 m NaIO4 and treated with 0.1 m Na2B4O7. The amounts and types of methylated sugar obtained on hydrolysis have been compared with those from unoxidized soil.

As well as a number of derivatives corresponding to 1 ‐3 linked glucose, arabinose and xylose, considerable proportions of 1‐4 linked glucose and xylose also persisted. The polysaccharides appear to persist for both chemical and physical reasons.
Electron paramagnetic resonance in humic substances
Authors: GUTSZE A. , PACEK M. , DZIADOWIEC H.
Published: July 2006

Electron spin resonance (ESR) measurements of soil and its fractions (humic acids, fulvic acids, post‐extraction residues and bitumens) were performed and particular attention given to free radicals of organic origin. For such radicals in soil, two lines with g factors 2.004 and 2.002 were observed. For all four fractions one line was observed. To obtain more information on the radical structure, the samples were carbonized. This allowed the different chemical structures of each of the two organic radicals to be differentiated. However, it was not possible to ascribe any definite structure to these radicals. Heat‐treatment measurements indicated that the humification process shows some similarity to the process of carbonization at low temperature.
Labelled and native sugars in particle‐size fractions from soils incubated with 14C straw for 6 to 18 years
Authors: CHESHIRE M. V. , CHRISTENSEN B. T. , SØRENSEN L. H.
Published: July 2006

Four soils of different texture (6% to 46% clay and 6% to 32% silt) were incubated with 14C‐labelled barley straw for periods ranging from 16 to 18 years. Incubations were either under laboratory (three soils, 20°C) or field conditions (one soil).

Soil samples were separated into clay‐size (< 2 μm), silt‐size (2–20 μm) and sand‐size (20–2000 μm) fractions using ultrasonic dispersion and gravity sedimentation. Whole soils and size fractions were hydrolysed with 12 M sulphuric acid, the released neutral sugars isolated and their amounts and specific activities determined.

The proportion of C present as carbohydrate decreased in the order clay, silt and sand, but the sugar compositions of the various fractions were similar. No relationship could be discerned between the soil particle‐size distributions and the persistence of sugars.

The specific activity of xylose remained higher than that of any major sugar, indicating the persistence of straw polysaccharides. This was true for all soils and size fractions. Galactose and mannose retained a greater proportion of their initial activity than did arabinose, xylose or glucose. This was ascribed to synthesis of microbial polysaccharides.

Total activity present in whole soils decreased in the order glucose, xylose and arabinose, galactose and mannose. The total activity of individual sugars in size fractions decreased in the order clay, silt, sand. The hexose to pentose ratio (galactose+mannose to arabinose + xylose) tended to be higher for silt than for clay, but the trend was not consistent for all soils.
Gel filtration chromatography of humic substances in soil solutions using HPLC‐determination of the molecular weight distribution
Authors: BERDÉN M. , BERGGREN D.
Published: July 2006

The molecular weight distribution of humic substances in soil solutions from a dystric cambisol and an orthic podzol were determined by high‐performance gel filtration chromatography (Toyo Soda TSKgel G2000 SWXL column). The retention volumes of humic substances were compared to those of narrow molecular weight distributed poly‐styrenesulphonates with known molecular weight.

A change in mobile phase pH or ionic strength usually resulted in an almost identical change in retention volume for the polystyrenesulphonates and the bulk of humic substances. The possibility of using the former to calibrate the column is discussed. The molecular weight at peak maximum was 1120–1190 and 1800 for the cambisol and podzol samples, respectively, using polystyrenesulphonates as molecular weight standards. No pretreatment of samples was used, but ion exchange is recommended for samples with high Al concentrations.
Dual water flow pattern in the unsaturated zone under a gypsum‐amended soil
Authors: GVIRTZMAN H. , MAGARITZ M. , NADLER A.
Published: July 2006

Sediment samples were obtained from boreholes down to c. 20 m in a gypsum‐treated, saline‐water irrigated soil and from nearby uncultivated fields at two locations (Nir Oz and Nahal Oz). Measurements of tritium concentrations in the soil solution enabled the determination of water flow rates in the unsaturated zone. Two types of flow, fast and slow, were identified in the profiles. The slow component, the ‘piston‐flow type’ in the sandy loess section in Nir Oz and in the clayey loess section of Nahal Oz, had a vertical velocity of 0.16 and 0.23 m a−1, respectively. The faster component typically transported the solution through fractures and other preferred paths. The percentage of the slow component in the sandy and in the clayey loess was 40% and 60% respectively. A previous prediction of delayed transport of salts was verified and is related to the interaction between chemical composition of irrigation water and the agro technical practices of gypsum application.
Aspects of transport processes in aggregated soils
Authors: YOUNGS E. G. , LEEDS‐HARRISON P. B.
Published: July 2006

The way in which water and solutes move in aggregated soils depends on the mode of saturation of the pore space that is made up of the micropore region within the aggregates and the macropores surrounding them. When both regions are saturated, a hydraulic‐head gradient causes water to flow preferentially in the macropores with little flow within the aggregates, so that movement of solutes into or out of the aggregates is mainly by diffusion caused by the difference between the solute concentrations of the water in the two regions. When macropores full of water surround unsaturated aggregates, water is imbibed by the aggregates giving rise to convective movement of solutes with the moving water. When the macropores are empty, the aggregates become almost isolated so that redistribution of water and solutes occurs only within the aggregates with very little transport of water and solutes between them. The movement of water and solutes in the micropore region within the aggregates can be considered to behave as if in a continuum, and can be described by Darcy's law and the dispersion equation, with boundary conditions imposed by conditions in the macropores.

These physical considerations of transport behaviour in aggregated soils can be used to give guidance on soil management practices concerning drainage and leaching.
Incorporation of natural hydrocarbons from plant residues into an hydromorphic humic podzol following afforestation and fertilization
Authors: JAMBU P. , AMBLÈS A. , DINEL H. , SECOUET B.
Published: July 2006

The content and composition of natural hydrocarbons from plant residues (Pinus maritima sp.) of a hydromorphic humic podzol were investigated following the addition of NPK and P fertilizers. L and F layers and the A, horizon from non‐fertilized and fertilized soil were analysed for total lipids and hydrocarbons, and non‐linear and linear hydrocarbons. The decrease in non‐linear hydrocarbons extracted following the addition of fertilizers was attributed to the incorporation of non‐linear hydrocarbons into humus, rather than to their biodegradation by soil micro‐organisms. Short‐ and medium‐chain linear hydrocarbons from plant residues or of microbial origin were rapidly biodegraded or fixed by soil micro‐organisms, resulting in a very low concentration in the A, horizon. In contrast, long‐chain linear hydrocarbons of plant origin accumulated in the non‐fertilized soil, while the addition of P fertilizer slightly stimulated their biodegradation. oration is needed before firm conclusions can be drawn.