bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of ionic strength and nature of the cation on the desorption of fluoride from soil
Authors: BARROW N. J. , SHAW T. C. 
Published: July 2006

SummaryThe reaction between soil and added fluoride was accelerated by incubating at a high temperature. Desorption of the fluoride was then studied using solutions of chloride salts of several cations at a range of solution : soil ratios and for periods which ranged from 1 h to 4 days. Fluoride desorbed was related to the experimental variables by a regression equation.When the solution : soil ratio was small and hence only small amounts of fluoride were desorbed, decreasing the concentration of salts increased the concentration of fluoride in the solution. The concentration in the solution was lower for calcium chloride than for sodium or potassium chloride. Amongst the monovalent cations, the concentration of fluoride was highest for salts of the cations of lowest atomic number. Thus the greater the average distance between the charge conveyed to the surface by the adsorbed fluoride and the cation which balanced it, the higher the fluoride concentration in the solution.As the solution : soil ratio was increased, the differences between the cations in their effects on fluoride desorption decreased and seemed to disappear as the solution : soil ratio became very large. This contrasts with previously observed effects on phosphate. It is suggested that the difference may have arisen because appreciable desorption of fluoride occurs by exchange with hydroxyl ions rather than by escape of the fluoride ion together with its counter ion.
The resistance patterns to metals of bacterial populations in contaminated land
Authors: OLSON B. H. , THORNTON I. 
Published: July 2006

SummaryThe resistance of populations of soil bacteria to heavy metals is determined using a dilution technique with media containing a range of metal concentrations. Metal resistance patterns are quantitatively related to ‘total’ concentrations of Cd, Zn and Pb in surface soils from historical mining areas in Somerset and Derbyshire. It is proposed that the tolerance of bacteria to metals may be used to determine their bioavailability and potential toxicity to other forms of life.
The use of gypsum for preventing soil sodification: effect of gypsum particle size and location in the profile
Authors: GOBRAN G. R. , DUFEY J. E. , LAUDELOUT H. 
Published: July 2006

SummaryLaboratory studies were conducted on a mixture of surface soils from the Nile Delta (Egypt). Twenty‐two soil columns, initially saturated both with respect to their water‐holding capacity and to their base exchange capacity with calcium, contained 0.0, 0.25, 0.5, 1.0 and 2.0 per cent solid gypsum in the total weight of the solid material in the column. Three particle sizes of gypsum (>0.5, 0.5–1 and 1–2 mm) were mixed either with the top layer or with the whole soil column. The result of leaching these columns with saline water (36 meq 1−1 NaCl+4 meq 1−1 CaCl2) at 0.1 cm h−1 was compared with a mathematical model based on thermodynamic equilibria.The three different particle sizes gave the same experimental results. Applying a given amount of gypsum to the surface soil was more effective in reducing the exchangeable sodium percentage (ESP) than mixing the same quantity through the soil. The mathematical model adequately predicted the changes in the soil column.
Analysing one‐step outflow experiments to calculate soil‐water diffusivities, using Gardner's Equation
Authors: TOWNER G. D. 
Published: July 2006

SummarySoil‐water diffusivity values, calculated using Gardner's analysis of measurements of water‐content changes with time of a horizontal soil column losing water from one end, are approximate. An iterative method is developed to improve their accuracy. Using the approximate values, computer simulations are made of the water‐content measurements. Gardner's analysis is then applied to these simulated values, thus giving the result of applying the analysis when the diffusivity function is known. This ‘calibration’ is used with the approximate values to infer the actual diffusivity function. The process is repeated until there is agreement between the simulated and the measured water contents.The method is demonstrated, using computer modelling of the experiments, for four functions of diffusivity versus water contents: two linear and two exponential, increasing and decreasing with water content. The procedure is an improvement on recent alternative analyses in being applicable to decreasing as well as increasing diffusivity functions.
The influence of iron oxides on the surface area of soil
Authors: BORGGAARD O. K. 
Published: July 2006

SummarySoils from Denmark and Tanzania have been extracted with ammonium acetate (controls), EDTA to dissolve amorphous iron oxides, and dithionite‐EDTA (DE) to dissolve crystalline iron oxides. The surface areas of the extracted soils have been determined by applying the BET equation to nitrogen adsorption and by water adsorption at 19 percent relative humidity. High correlations (P < 0.001) were found (i) between EDTA‐extractable iron (amorphous iron oxides) and the decrease in the surface area following EDTA extraction, and (ii) between the difference between DE‐extractable iron and EDTA‐extractable iron (crystalline iron oxides) and the further decrease in the surface area following DE extraction. The calculated specific surfaces of both the amorphous and the crystalline iron oxides varied from soil to soil but without any definite trend. The means of all the soils investigated may therefore serve as reasonable estimates of the specific surfaces of amorphous and crystalline iron oxides in soil.
Modification of soil physical properties by manipulating the net surface charge on colloids through addition of Fe(III) polycations
Authors: SHANMUGANATHAN R. T. , OADES J. M. 
Published: July 2006

SummaryThe addition of 0.07 per cent Fe in the form of polycation of molecular weight 10000–50000 flocculated soil suspensions. Higher concentrations of Fe(III) caused redispersion of the clay. Electrophoretic and electron microscopic studies confirmed the flocculation‐dispersion phenomena. The soil suspensions with higher concentrations of Fe(III) gave points of zero charge (PZC) between pH values 5.0 and 6.0. The flocculation resulted in microaggregation and created pores 40–100 μm in diameter. This led to an increased water‐holding capacity and hydraulic conductivity and lower bulk densities and modulus of rupture. The soils treated with Fe(III) polycations were shown to be more friable than untreated soils.
The effect of lime on the response of soils to sodic conditions
Authors: SHAINBERG I. , GAL M. 
Published: July 2006

SummaryThe role of CaC03 in preventing clay dispersion and losses in hydraulic conductivity (HC) of sodic soils was determined directly by mixing two lime‐free soils with 0.5 and 2.0 per cent CaCO3. Whereas the HC of the lime‐free soils dropped sharply when 0.01 n solutions of SAR 20 were displaced with distilled water, mixing the soils with powdered lime prevented both HC losses and clay dispersion. The response of a sandy soil mixed with lime was similar to that of a calcareous sandy soil. The beneficial effect ofCaC03 was not so pronounced in soils equilibrated with solutions of SAR 30. The increase in electrolyte concentration, due to CaCO3 dissolution, was suggested as the mechanism responsible for the beneficial effect of lime.
Direct field measurement of N2 and N2O evolution from soil
Authors: LIMMER A. W. , STEELE K. W. , WILSON A. T. 
Published: July 2006

SummaryA gas lysimeter has been designed and used to measure directly the evolution of N2and N2O in a soil profile under field conditions. Concentrations of N2 in the soil atmosphere within the lysimeter as low as 2000–5000 p.p.m. have been achieved by flushing with N‐free gas. A flow of gas into the base of the lysimeter forms a barrier against diffusion of soil air into the lysimeter during measurements.After reducing the N2 concentration in the soil core, a low concentration of N2enriched in N‐15 is introduced. By monitoring changes in the 8 N value using a high‐precision isotope mass spectrometer, rates of N2 evolution down to 6 kg N2‐N ha−1 a−1 can be detected. N2O evolution was determined at the same time using the mass spectrometer in the single‐beam mode.
The variability introduced by various subsampling techniques
Authors: MULLINS C. E. , HUTCHISON B. J. 
Published: July 2006

SummarySubsamples of a granular material contain a finite number of grains. Practical methods of subsampling do not select these grains on an entirely random basis. Both of these features contribute to the observed variability between subsamples. As an example, the theoretical coefficients of variation attributable to statistical variation between 10‐g random subsamples taken from four different (<2 mm) air‐dry soils have been calculated. These are calculated to give CVs of between about 0.002 and 1 per cent between particle size analysis results. In an actual comparison between four different subsampling methods, CVs of between 4 and 18 per cent were observed in the proportion of coarse sand (2–0.2 mm) in 15‐g soil subsamples. Rotary sub‐sampling and chute splitting were found to be more reliable methods of subsampling than cone and quartering or random spoon sampling. Variability between subsamples is shown to depend not only on subsampler design, but also on the precise details of the procedure adopted, and the physical properties of the sample itself.
Soil strength and crop emergence in direct drilled and ploughed cereal seedbeds in seven field experiments
Authors: BALL B. C. , O'SULLIVAN M. F. 
Published: July 2006

SummaryCone resistance and vane shear strength were measured in the top 50–100 mm of seven soils. Bulk density and water content were also measured in the same layer by coring. At each site cone resistance and vane shear strength tended to decrease with increasing water content and decreasing bulk density down to 1300 kg m‐3, but at lower densities they were not related to bulk density. Cone resistance and vane shear strength tended to decrease with increasing coarseness of texture but also depended on soil structure and organic matter content.Plant populations, mainly spring barley, were reduced in soils with cone resistances and vane shear strengths greater than 2500 kPa and 65 kPa respectively. Such high strengths in undisturbed soils were associated with wheeling during harvesting, were apparently independent of soil type and, at the only site of measurement, apparently decreased during weathering in the subsequent season.In contrast to the cone penetrometer, the vane shear tester has minimal shaft friction in undisturbed soils and is more sensitive to soil differences and less sensitive to water content differences than the penetrometer. It is apparently more suitable for indexing the suitability of undisturbed soils for the penetration of direct drill coulters and for subsequent plant establishment.
Prediction of solute leaching under field conditions: an appraisal of three methods
Authors: CAMERON K. C. , WILD A. 
Published: July 2006

SummaryThe analytical equation of Rose was more successful than the models of Burns and Addiscott in predicting movement of chloride through a soil on Upper Chalk under irrigation and winter rainfall. The two models required water inputs to be divided into 5 mm increments. When this was done the model of Addiscott was more successful than that of Burns although both then gave predictions of acceptable accuracy for practical purposes. The analytical equation of Rose requires a value for solute dispersivity. This was obtained from the experimental measurements, but the value used (3 cm) was found not to be critical.
The effect of pH upon the copper and cupric ion concentrations in soil solutions
Authors: SANDERS J. R. 
Published: July 2006

SummarySoil samples whose pH had been adjusted to between 4.5 and 7.5 either for long periods in the field or short periods in the laboratory were incubated after wetting with water or 0.01 m CaCl2. Copper concentrations in the soil solutions decreased only slightly as the solution pH increased, but free cupric ion concentrations decreased considerably. The copper concentrations were smaller and the proportion of copper present in solution as cupric ion at a given pH was larger when CaCl2 rather than water was used. Complexed organic species made up most of the copper in all solutions. The duration of pH adjustment did not affect these results.Copper adsorption isotherms were determined on the soils using low equilibrium solution concentrations. As a given copper concentration the quantity of copper adsorbed increased and the proportion of copper in solution present as cupric ion decreased with pH increase; again the duration of pH adjustment did not affect the results.
Sorption of isotopically exchangeable and non‐exchangeable phosphate by some soils of Colombia and Brazil, and comparisons with soils of southern Nigeria
Authors: LEMARE P. H. 
Published: July 2006

SummaryFourteen soils from Colombia and Brazil provided a wide range of sorption characteristics. Curves of sorbed phosphate that was exchangeable to 32P were described by Freundlich's equation, and of non‐exchangeable phosphate by Temkin's equation. Exchangeable phosphate was associated with aluminium in poorly‐crystalline oxides and in organic complexes. Non‐exchangeable phosphate was related to aluminium in organic complexes, and especially to the ratio of AI/C in them. In Nigerian soils similar mechanisms controlled sorption of phosphate but oxides and organic complexes of iron were important.The concentration of phosphate in solution when affinities of soil for exchangeable and non‐exchangeable phosphate are equal, and the importance of organic matter, are discussed in relation to soil management and to responses of crops to fertilizer phosphate.The results indicate that sorption curves should not be split into sections.
Effect of wetting and drying of soils on phosphate adsorption and resin extraction of soil phosphate
Authors: OLSEN R. G. , COURT M. N. 
Published: July 2006

SummarySixteen topsoils from Denmark and the UK were subjected to two wetting and drying treatments: (i) moist incubation (wet), (ii) eleven wetting and drying cycles (W/D). The W/D treatment resulted in larger P adsorption and resin extraction of soil P than the wet treatment. The differences in P adsorption at the final concentration of 800 μM P were mainly above 20 per cent, whereas the differences in amount of resin‐extracted P were mainly less than 20 per cent. The effects were positively correlated with the cation exchange capacity of inorganic components. Furthermore, the increase in rapidly released P was positively correlated with pH. It is suggested that wetting and drying effects on P adsorption and desorption are associated with changes in soil structure caused by rewetting of dry samples.
The origin of oxygen in soil humic substances
Authors: DUNBAR J. , WILSON A. T. 
Published: July 2006

SummaryThe 18O/16O ratios of a number of soil humic and fulvic acids were measured and compared with those of lignin and cellulose samples originating from the same area. The average enrichments above ground water were: cellulose 32%0 humic and fulvic acid 29%0 and lignin 14%0, suggesting that the oxygen in humic and fulvic acid originates pricipally from cellulose or other plant carbohydrates and not lignin as has been suggested.
Nitrogen fixation by white clover (Trifolium repens) in grasslands on soils contaminated with cadmium, lead and zinc
Authors: ROTHER J. A. , MILLBANK J. W. , THORNTON I. 
Published: July 2006

SummaryThe nitrogenase activity (potential nitrogen fixation) of a mixed white clover‐grass sward growing on a range of soils containing up to 216 μg g−1 Cd, 30 000μg g−1 Pb and 20 000 μg g−1 Zn was determined using the acetylene‐reduction assay. The plants were incubated in situ using an intact soil‐core technique. Little change in the rate of C2H2 reduction was observed during the daylight hours although a marked seasonal fluctuation was found, the maximum activity during the spring and declining to 20% of this by the autumn. Some reductions of nodule and plant size, and in nitrogenase activity, was observed in the most heavily contaminated sites. These effects were small; the plants and nodules otherwise appeared healthy. The potential for nitrogen fixation was equally high in all the sites at up to 80 g N ha−1 h−1 in the spring.
N.M.R. spectroscopy of soils: structure of organic material in sodium deuteroxide extracts from Patua loam, New Zealand
Authors: WILSON M. A. , GOH K. M. 
Published: July 2006

SummaryThe structure of the organic matter from the ‘A’ and ‘B’ horizons of Patua loam (New Zealand) which is soluble in sodium deuteroxide has been investigated by conventional 13C‐nuclear magnetic resonance spectroscopy. Experiments using inverse gated 1H‐decoupling and a variety of pulse delays and weighting functions for Fourier transformation are reported. Sufficient number of transients have been collected for quantitative estimates of the aromaticity of the extract. The results complement an earlier qualitative study on this soil (Wilson & Goh, 1977) and illustrate conditions under which conventional 13C‐n.m.r. spectra of humic materials should be obtained.The sodium deuteroxide soluble material from Patua loam ‘A’ and ‘B’ horizons has an estimated aromaticity of 33%. Different carbon types are not well resolved. However, there appear to be seven distinct resonances in the carboxyl region of the A horizon of which at least six are not derived from inorganic sources. Together with results already recorded in the literature, the results illustrate the variability of humic acids isolated from different soils. The nature of this variability is discussed.
Micromorphometric and micromorphological investigations of a clay loam soil in viticulture under zero and conventional tillage
Authors: PAGLIAI M. , LAMARCA M. , LUCAMANTE G. 
Published: July 2006

SummaryPorosity, pore size distribution and the orientation pattern of pores were measured on thin sections prepared from undisturbed soil samples by means of electro‐optical image‐analysis. Total porosity was significantly higher at all sampling times in conventionally tilled plots, but the proportion of pores ranging from 30 to 500 μm, which are considered the most important both in soil‐water‐plant relationships and in maintaining a good soil structure, was higher in no‐tilled plots. Modifications of pore orientation pattern were also observed. Micromorphological observations revealed some differences between the two series of soil samples; the formation of surface soil crusts was strongly reduced in no‐tilled plots.
Management of the Cerrado soils of Brazil: a review
Authors: GOEDERT W.J. 
Published: July 2006

SummaryA large proportion of the world tropical region is covered by savannas, which have been little used for agriculture. Locally known as Cerrado, this ecosystem occupies about 20% of Brazilian territory. Preliminary surveys indicate that at least 50 × 106 ha of the Cerrado are of potential use for intensive mechanized agriculture, but development has been limited by soil‐related constraints. Most soils are acid and with very low native fertility, especially in terms of phosphorus. Chemical barriers to root growth may cause severe yield losses during dry periods. Field crop responses to lime and fertilizers, obtained during the last 5–8 years, show that once soil‐related constraints are removed, high yields can be achieved. This review gives an account of the main lines of research which are leading to economic methods of developing the agricultural use of the Cerrado, and gives future research needs.
Effective stresses in unsaturated soils and their applicability in the theory of critical state soil mechanics
Authors: TOWNER G. D. 
Published: July 2006

SummaryCricital state soil mechanics, which expresses relationships between deformation and effective stresses, has not yet been established for unsaturated soils. Effective stresses in unsaturated soils are not only complicated functions of the applied stress and the pore‐water pressure, but are also hysteretic. Furthermore, they cannot yet be determined independently, because present theories are inadequate, and they must be obtained by the less satisfying method of comparing the deformation of unsaturated and saturated soils subjected to similar stress paths. The paper discusses the further measurements that need to be made to validate the extension of critical state soil mechanics to unsaturated soils, and concludes that unless the effect of hysteresis proves to be small, the theory may be too difficult, if not impossible, to apply quantitatively.
Fate of fertilizer nitrogen applied to grassland. I. Field leaching results
Authors: BARRACLOUGH D. , HYDEN M. J. , DAVIES G. P. 
Published: July 2006

SummaryResults are presented from a 3 year investigation into nitrate leaching from isolated 0.4 ha grassland plots fertilized with 250, 500 and 900 kg N ha−1 a−1. Cumulative nitrate leaching over the 3 years was equivalent to 1.5%, 5.4% and 16.7% of the fertilizer applied at 250, 500 and 900 kg N ha−1 rates respectively. Over a whole drainage season, mean nitrate leachate concentrations at 250 kg N ha−1 did not exceed 4 mgl−1, although maximum values of 13.3 mgl−1 were observed. In contrast, at 900 kg N ha−1, the mean nitrate leachate concentration in two of the years exceeded 90 mgl−1. Mineral nitrogen balances constructed for the 1979 growing season indicated that leaching at 250 kg N ha−1 was low because net mineralization of soil organic nitrogen was small, and crop nitrogen uptake almost balanced fertilizer application. Although the pattern of nitrate leaching suggested that by‐passing occurred in the movement of water down the soil profile, it was not possible to confirm this using simulation models of leaching. Possible reasons for this, including the occurrence of rapid water flow down gravitationally drained macropores, are discussed.
Nitrate loss in soil drainage waters in relation to by‐passing flow and discharge on an arable site
Authors: SMETTEM K. R. J. , TRUDGILL S. T. , PICKLES A. M. 
Published: July 2006

SummaryIn a well‐structured soil at or close to pedal saturation, rainfall intensity in excess of pedal Ksat is predicted to result in by‐passing flow through well connected structural voids.The depth of solute penetration (tracer dye and nitrate) under by‐passing flow has been predicted by Df=(P‐Cp)/θf, where Df is the depth of penetration of the leading edge of solute in by‐passing flow, P is gross precipitation, Cp is the input volume transmitted through the soil peds and θf is the operational volumetric moisture content in by‐passing. The timing of surface applied nitrate arrival at a channel bank is demonstrated to be related to by‐passing flow rather than uniform displacement.The relationship between nitrate load in soil drainage waters (Y, mg s‐1) and water discharge (X, dm3 s−1) was Y∼6X after nitrate fertilizer application but subsequently declined to Y 0.5X It is deduced that the decline resulted from inefficient leaching under by‐passing conditions once surface applied nitrate had become relocated within the soil peds.