bluuebunny/crossref_metadata_2025_split huggingface dataset:
The use of cation activity ratios to estimate the intensity of soil acidity
Authors: CONYERS M. K. , MUNNS D. N. , HELYAR K. R. , POILE G. J. 
Published: July 2006

SUMMARYSoil solution extracts can be relatively difficult to obtain and to handle. The aim of this study was to investigate whether a simple 0.01 M CaCI, extraction could be used to estimate the intensity factor of soil acidity by employing the Schofield Ratio Law. Activity ratios of H, Ca and A1 were compared in soil solutions and in 0.01 M CaCI, extracts on four soils adjusted to a range of pH values with acid and lime. The ratios pH‐1/2pCa (0.01 M CaCl2) and pH‐1/2p(Ca + Mg) (soil solution) were not statistically significantly different. The ratio pH‐1/3pAl was less strongly correlated, but again was not significantly different between the soil solution and extractant. The Schofield Ratio Law did not hold over the entire range of data for pCa‐+2/3pAl, but the values in the two solutions correlated closely. Cation activity ratios in 0.01 M CaCl2 can be used to estimate the intensity factors of acidity in a soil, even though the extractant has a higher ionic strength than many soil solutions in variable charge soils. Therefore pH and A1 as measured in 0.01 Cacl2 extracts may be useful tests for routine diagnostic purposes and soil surveys.
Organic matter available for denitrification in different soil fractions: effect of freeze/thaw cycles and straw disposal
Authors: CHRISTENSEN S. , CHRISTENSEN B. T. 
Published: July 2006

SUMMARYThe 0 to 20‐cm surface layer of a sandy loam soil was sampled in early autumn from plots where straw had either been removed or incorporated annually for 22 years. Denitrification in whole soils, 1–2‐mm wet‐stable aggregates, clay and silt size fractions was determined by acetylene blocking during anaerobic incubation with excess nitrate. Thus available organic matter was the limiting factor. Samples were exposed to one or two freeze/thaw cycles, or used unfrozen. K2SO4‐extractable carbon (C) was determined before and after CHCI, fumigation.Freeze/thaw increased denitrification in whole soils and in aggregates. In aggregates and in whole soil without straw the increase in denitrification was similar following two freeze/thaw cycles, and well above the amount that could be fed by extractable soil C. In whole soils with straw addition, an extra denitrification increase occurred at first thaw only. This straw‐induced denitrification surplus was matched by a decline in soil microbial biomass. For other samples and treatments, the freeze/thaw released C from additional organic matter sources.The availability of C in clay for denitrification was twice that of silt‐associated C. Straw disposal generally had no effect on the bioavailability of particle‐bound C. In contrast to whole soils and aggregates, the availability of organic matter in clay and silt after one freeze/thaw cycle was only half that observed from unfrozen samples.The effect of freeze/thaw on whole soils and aggregates may be to release organic matter available for denitrification by killing the microbial biomass and by disintegrating aggregates. However, the impact of freeze/thaw on completely dispersed samples such as clay and silt may be to promote the formation of granular structures (micro‐aggregation) in which organic matter may become less accessible to denitrifiers.
Potassium release and fixation in Ferralsols (Oxisols) from Southern Togo
Authors: POSS R. , FARDEAU J. C. , SARAGONIT H. , QUANTIN P. 
Published: July 2006

SUMMARYPotassium release and fixation were studied on Ferralsols (typic Eutrustox) of Southern Togo both by isotopic exchange with 42K+ ions and by exchange with 1 M ammonium acetate. Experiments were conducted on soil samples taken from surface (0–30 cm) and subsoil (80–100 cm) layers of four plots. These plats, with the same soil type, were subjected to various kinds of use: forest and crops, with or without fertilizers. A single wetting and drying of the soil samples increased the amounts of exchangeable K. This exchangeable K release could stem from clay protonation during drying. However, the K release is insufficient to allow permanent intensive agriculture without K fertilizer addition. Soil samples were therefore treated with KCI in order to study K fixation. About 20% of the applied K was fixed and the percentage increased with wetting and drying. The fixation can be explained by the presence of about 2% of interstratified clay minerals in these kaolinitic soils. Comparison of the kinetic characteristics of the isotopically exchangeable K with the amounts of ammonium exchangeable K revealed the existence of several kinds of exchange site for K ions.
Assessing the fixation and availability of sorbed phosphate in soil using an isotopic exchange method
Authors: HE Z. L. , YUAN K. N. , ZHU Z. X. , ZHANG Q. Z. 
Published: July 2006

SUMMARYAn isotopic exchange method was used to characterize quantitatively the fixation and plant availability of phosphate previously sorbed by soils. In general, the exchangeability of the sorbed phosphate was much higher than its desorbability for both soils and clay minerals. Isotopic exchangeability of the sorbed phosphate increased with sorption saturation during the initial stage (15–60% saturation), but the increase was less with increasing saturation from 60–90% for all soils tested. Therefore a sorption saturation of 60% was recommended as the upper limit of P fertilization in terms of economical efficiency. For clay minerals, with increasing sorption saturation, the isotopic exchangeability of the sorbed P increased significantly for kaolinite and sesquioxides, but decreased for montmorillonite. Most of the phosphate sorbed by montmorillonite and kaolinite was found to be isotopically exchangeable, but only a small amount of the P sorbed by goethite could be exchanged. The P sorbed by Al oxide exhibited isotopic exchangeability between that of kaolinite and Fe oxide. The isotopically exchangeable phosphate pool could readily account for the P uptake of plants and the available P determined by some commonly used chemical methods, such as Olsen‐P and Bray‐P.
Development of a technique for the measurement of root geometry in the soil using resin‐impregnated blocks and image analysis
Authors: COMMINS P. J. , McBRATNEY A. B. , KOPPI A. J. 
Published: July 2006

SUMMARYA method is described that permits the measurement of roots in situ in the soil using computerized image analysis to process images obtained from planar faces cut from a resin‐fixed pot. Soil sample pots are initially impregnated with rapid‐curing epoxy resin. Blocks are then cut from the impregnated pot with a diamond saw to expose a planar face. Modification of the present resin‐impregnation procedure is necessary as impregnation results were mostly unsatisfactory. Roots are contrasted from the soil matrix by enhancing autofluorescence using longwave ultraviolet light and appropriate filters. After image capture and segmentation to show regions of root material, measurements of volume fraction of roots, volumetric surface area, horizontal root length and horizontal root separation, were made with a larger resolution with soil depth than previously.
Validation of a model of the transport of zinc to an artificial root
Authors: BAR‐TAL A. , BAR‐YOSEF B. , CHEN Y. 
Published: July 2006

SUMMARYZinc movement in soils is influenced by soil pH, the presence of organic chelators, the total quantity of Zn in the soil and by root exudates. The effect of these factors on Zn uptake by a single plant root was simulated mathematically by Bar‐Yosef et al. (1980). The objective of this paper was to validate this simulation model and evaluate the relative importance of soil chemical properties, the stability of Zn complexes and the soil pH in determining Zn transport in soil and absorption by plant roots. To avoid problems of soil and plant variability, an artificial root, namely a ceramic tube through which solutions of known composition flowed, was used. The soil was a montmorillonite‐sand mixture of known Zn adsorption characteristics. The model satisfactorily described the decline in net Zn influx into the root (Fzn as soil pH increased or as total Zn in soil (Qzn) decreased, and also described Fzn, as a function of time. Addition of fulvic acid (FA) to the soil decreased Fzn. The decreased uptake rate stemmed from the lower permeability of the root to the large Zn‐FA molecule. When the pH of the solution that flowed inside the tube was decreased from 5.0 to 2.0, thus generating a greater efflux of H+ by the roots, Fzn, increased four‐to six fold, depending on the time. The model satisfactorily described the decline in Fzn, as the clay fraction in the soil increased, while maintaining the same quantity of Zn per volume of soil.
Properties of sub soils in relation to various measures of surface area and water content
Authors: CHURCHMAN G. J. , BURKE C. M. 
Published: July 2006

SUMMARYNeither the specific surface area values (from N2 sorption) nor the ethylene glycol monoethyl ether (EGME) retention values of 21 soil samples from New Zealand and Fiji could all be accounted for by the sum of the contributions from their component minerals. Much EGME is probably retained by internal surfaces of inter layered and interstratified clay minerals. EGME retention correlated well with cation exchange capacity (CEC) and a number of measures of water content of these soils. The water contents of air‐dried soils (measured as ‘moisture factors’ or the ratios of air‐dry and oven‐dry weights) showed almost as close a relationship to CEC as EGME retention for this set of 21 subsoils. Moisture factors and CEC were closely related, within groups defined by dominant clay mineralogies, for a much wider selection of 1318 New Zealand soil horizons with low carbon contents. The relationships between surface area and a number of other soil properties including dispersibility of soils were also examined.
A brief discussion on the effect of temperature on the reaction of inorganic ions with soil
Authors: BARROW N. J. 
Published: July 2006

SUMMARYPublished reports on the effect of temperature on the sorption of ions by soil, or soil constituents, are in conflict with regard to the direction of the effect and its interpretation. It is argued that, in many cases, increased sorption with increased temperature is due to an increased rate of the reaction that follows adsorption. The effects of temperature on the adsorption reaction itself are complex because of separate effects on the ions in solution, on the charge on the surface, and on the affinity of the ions for the surface. On balance, adsorption of anions should decrease with increasing temperature, and adsorption of cations should increase. However, decreased adsorption of cations is possible, particularly at high pH. With one exception, these conclusions are consistent for all published reports seen.
Interactions between peat and sodium acetate, ammonium sulphate urea or wheat straw during incubation studied by 13C and 15N NMR spectroscopy
Authors: Benzing‐Purdie L. , Cheshire M. V. , Williams B. L. , Ratcliffe C. I. , Ripmeester J. A. , Goodman B. A. 
Published: July 2006

SUMMARYTransformations of sodium acetate, ammonium sulphate, urea and wheat straw in peat have been studied by determining the distribution of 15N‐labelled material, and by 13C and 15N nuclear magnetic resonance spectroscopy (NMR) using cross polarization (CP) and magic‐angle spinning (MAS). Samples of an oligotrophic blanket peat were incubated for 6 months at 15°C with 15N ammonium sulphate, 15N urea, 13C15N urea, 15N‐labelled wheat straw or 13C sodium acetate. The incubated samples were separated into fractions of >1 mm, 1–0.5 mm, 0.5–0.25 mm, 0.25–0.15 mm, 0.15–0.05 mm, 0.05–0.005 mm and a water‐soluble fraction by wet sieving, and were then freeze‐dried. The distribution of 15N between the fractions was obtained after isotope‐ratio analysis by mass spectrometry, and the 0.5–0.25 mm, 0.05–0.005 mm and water‐soluble fractions from the incubations were examined by 13C and 15N NMR. 13C‐labelled acetate increased carbohydrate resonances in the 0.05–0.005 mm and soluble material, but an organic acid derived from the substrate was still present 6 months later. Incorporation of 15N from ammonium sulphate into the peat was low, and more than 50% of the added N was detected in the soluble fraction still present as 15NH+4. As carbohydrate and soluble organic matter were detected in the peat, it was concluded that microbial activity and N immobilization were restricted by poor aeration and low pH. Urea, in contrast, interacted with all the fractions examined, with some 15N being incorporated into a range of compounds that included protein, peptides, amides, amino acids and carbamates or lactam derivatives. A small proportion of labelled 15N from wheat straw, orginally present in the > 1 mm and 14.5 mm fractions, had moved into the 0.05–0.005 fraction during incubation and sieving. The 13C spectra suggested that the presence of the straw may have stimulated decomposition of the peat components.
Acoustic determination of air‐filled porosity and relative air permeability of soils
Authors: MOORE H. M. , ATTENBOROUGH K. 
Published: July 2006

SUMMARYTwo acoustic techniques for determining the air‐filled porosity and air permeability of soil surfaces, and the near‐surface variation of these properties with depth, have been applied to several soils in situ. The techniques depend upon an inversion process using data on sound propagation near to the soil surface and through the soil surface. The measured difference in acoustic spectra received by two vertically separated microphones above the ground surface and by probe microphones beneath the surface were matched theoretically to deduce the porosity of air‐filled connected pores and an effective air permeability which depends on pore shape and size distribution. This modified permeability parameter and the acoustically deduced porosity varied realistically with surface sealing and compaction. The acoustically deduced porosities were within 10% of those obtained conventionally. Changes in acoustically deduced parameters occurred with changes in moisture content both in soil bin and field experiments. The acoustic techniques were successful in monitoring surface sealing and near‐surface layering on a fine scale.
A physically based model for surface sealing of soil
Authors: BONSU M. 
Published: July 2006

SUMMARYA physically based model describing the mechanism of surface seal formation of soil from a suspension of soil in flowing water was formulated on the basis of the principle of conservation of mass and Darcy's equation for the flow of water through a layered soil column. The model shows that, for sufficiently large times, the flux density of the filtrate is proportional to the inverse square root of time. The proportionality constant is a function of the saturated hydraulic conductivity and bulk density of the seal, and the concentration of the suspension. The components of the proportionality constant suggest that the constant could be used as an index of structural stability of soil. For the three suspensions used in testing the validity of the model, log‐log plots of the flux densities of the filtrates and time showed linear relationships with slopes approximately equal to –0.5, as predicted by theory. However, using calculated components of the model to predict flux densities of the filtrates failed to show agreement for two out of the three suspensions used. This was attributed to some over‐simplified assumptions used in the model, such as constant concentration and no sedimentation effects during the filtering process. It is suggested that incorporation of a time‐dependent concentration and sedimentation factors could perhaps improve the efficacy of the model.
Gypsum applications to aggregated saline—sodic clay topsoils
Authors: ARMSTRONG A. S. B. , TANTON T. W. 
Published: July 2006

SUMMARYGypsum application was highly efficient as a treatment for reducing amounts of exchangeable sodium and inhibiting clay dispersion in highly structured saline‐sodic clay topsoils.Phosphogypsum, applied to the surfaces of aggregates in soil columns treated with simulated rainfall, was dissolved efficiently by frequent intermittent ‘rainfall’. The calcium released by dissolution displaced sodium on the exchange complex within soil aggregates ranging from 7.5 mm to 45 mm in diameter. Of the applied calcium, 64–74% was transferred to ion exchange sites; however, almost one‐third of this adsorbed calcium displaced exchangeable magnesium.Comparison of three gypsum treatments, phosphogypsum, rock gypsum, and a saturated gypsum solution (representing a top dressing of highly soluble gypsum), showed that the effectiveness of calcium uptake on the exchange complex followed the order: rock gypsum < saturated solution < phosphogypsum, but differences were small.Application of phosphogypsum caused a 90% reduction in the total amount of dispersed clay released in column leachates, and decreased the maximum clay concentration in the effluents by at least 80%, when compared to soils leached without gypsum treatment.
The effects of pH and chloride concentration on mercury sorption. I. By goethite
Authors: BARROW N. J. , COX V. C. 
Published: July 2006

SUMMARYThe effects of mercury concentration, pH, and chloride concentration on mercury adsorption by goethite were measured. With increasing pH, mercury adsorption increased rapidly at first, until a maximum was reached, and then decreased slowly. In the absence of chloride, the maximum was just below pH 4. With increasing chloride concentration, the maximum moved to higher pH values. This behaviour contrasts with that of the other heavy metals for which, beyond a certain pH, adsorption increases rapidly with further increase in pH.The results were described by a model in which HgOH+ and HgCl+ ions were adsorbed and the electric potential of the reacting surfaces decreased with increasing pH. The maxima in the adsorption corresponded to maxima in the concentration of HgOH+. Although a good description of the results was obtained, there were consistent discrepancies. These suggested that the charge component of the model was unable to produce the correct relationship between electric potential and pH.The results indicated that mercury adsorption was controlled by the same principles as adsorption of the other heavy metals. However, mercury's lower pK for dissociation and its higher affinity for chloride mean that the effects of pH on the ions present in solution are different, and this is the cause of the different behaviour.
Chemical extractability of heavy metals during and after long‐term applications of sewage sludge to soil
Authors: McGRATH S. P. , CEGARRA J. 
Published: July 2006

SUMMARYSequential extractions were used on soils from a long‐term experiment treated with either metal‐contaminated sewage sludge or inorganic fertilizers between 1942 and 1961. The four extracts employed were CaCl2, NaOH, EDTA and aqua regia. These showed that large increases in the proportions of Pb, Cu, Zn, Ni and Cd in at least one of the first three fractions occurred during the first 10 years of sewage sludge additions. Cr always remained predominantly in the aqua regia‐soluble fraction. For 30 years after this, including a period of more than 20 years after application of sludges to the field had ceased, there was very little change in the percentage of each metal extracted by each reagent.Although the ‘residual’ (aqua regia‐soluble) and EDTA fractions usually contained the largest amounts of metals in either sludge‐ or fertilizer‐treated soils, there were clear differences between the metals: Pb represented the largest fraction of any metal extracted by EDTA, Cu of any metal extracted by NaOH and Cd of any metal extracted by CaCl2. The same extractions were made of the sewage sludges that were applied to the field, and the distributions of the metals differed from those found in the treated soils. It was particularly apparent that more Pb and Cu was present as the ‘residual’ (aqua regia) fraction in sludges than in the soils.
b‐Fabric of some benchmark Vertisols of India in relation to their mineralogy
Authors: KALBANDE A. R. , PAL D. K. , DESHPANDE S. B. 
Published: July 2006

SUMMARYAt present precise information on the b‐fabric of Vertisols is inadequate for gaining a comprehensive knowledge about such soils formed in alluvium of basic igneous and metamorphic rocks and spread in varying agro‐climatic zones of peninsular India. The aim of the present study, on five benchmark Vertisol series (Sarol, Aroli, Nimone, Bellary and Kovilpatti), was to assess the possible reasons for differences in the b‐fabric of the subsoils despite their common shrink‐swell properties, as evidenced by the presence of sphenoids and/or slickensides, and similar clay contents and amounts of fine clay smectite. In Sarol and Aroli soils from the sub‐humid region, the b‐fabric is porostriated, whereas in Nimone and Kovilpatti soils of the semi‐arid and Bellary soils of the arid regions the fabric is either mosaic‐speckled or granostriated, indicating weak plasma separation, a result of restricted swelling of clays. The related distribution pattern of the s‐matrix in all these soils was open porphyric.Recent literature has suggested that weak plasma separation is an effect of dissolution and crystallization of calcite. However, generally low concentrations of soluble calcium (c. 1 mmol dm−3) in soil solutions of Vertisols in arid and semi‐arid agroclimates suggest that the presence of calcite does not guarantee the presence of sufficient soluble calcium to impair swelling of clays by contracting the diffuse double layer. Weak plasma separation in Bellary and Kovilpatti soils compared with Sarol and Aroli soils is explained in terms of a decrease in the internal surface area of fine smectite, as evident from a very high degree of chloritization in smectite interlayers, and smaller proportions of coarse smectite. In Nimone soils the weak plasma separation is primarily due only to a decreased internal surface area of fine smectite.
The influence of vegetational origin and degree of humification of organic soils on their chemical composition, determined by solid‐state13C NMR
Authors: KROSSHAVN M. , SOUTHON T. E. , STEINNES E. 
Published: July 2006

SUMMARYOrganic soil samples with different vegetational background and others with variation in the degree of humification, were investigated with solid‐state13C NMR. This work indicates that the vegetational origin and degree of humification of the organic matter appear to influence the distribution of functional groups in organic soils considerably, but one year of decomposition under controlled laboratory conditions gave only small changes in the chemical composition.
Oriented and random sedimentation of plate‐like clay particles in high centrifugal fields
Authors: WHALLEY W. R. , MULLINS C. E. 
Published: July 2006

SUMMARYPlate‐like particles can sediment in an oriented manner or completely randomly. The hydrodynamic conditions that lead to an oriented sedimentation are reviewed. The tendency for plate‐like clay particles to adopt oriented sedimentation in high centrifugal fields is demonstrated. Maximum centrifugal fields that still permit random sedimentation are suggested on the basis of experimental observation.