bluuebunny/crossref_metadata_2025_split huggingface dataset:
The preparation of unsmeared soil surfaces and an improved apparatus for infiltration measurements
Authors: KOPPI A. J. , GEERING H. R. 
Published: July 2006

summaryA method is described for using a quick setting epoxy resin to prepare a soil surface for infiltration measurements. It gives an unsmeared soil surface where the biological pores and structural surfaces are revealed. Experiments with an alluvial Prairie Soil and a Red Podzolic Soil, comparing steady state infiltration rates through cut smeared surfaces and resin treated ones, showed that the resin‐prepared surface permits 2.5–6 times more rapid entry of water. It is postulated that the greater rate more closely reflects the field structural condition. Apparatus, with a water reservoir remote from the hole, is also described for measuring constant head subsoil infiltration through a specially prepared auger hole.
Testing a mechanistic model. I. The effects of time and temperature on the reaction of fluoride and molybdate with a soil
Authors: BARROW N. J. 
Published: July 2006

SUMMARYA mechanistic model that had been developed to describe the reaction of phosphate with soil was applied to the reactions of fluoride and molybdate with soil. The model assumes that: there is an initial adsorption reaction between ions and charged surfaces; that the surfaces are not uniform in their properties; and that the initial adsorption is followed by diffusive penetration.The model was developed beyond that previously published to permit the rate of the initial adsorption reaction to be included. The model reproduced the effects of solution concentration, and of increasing period and temperature of incubation, on the retention of both fluoride and molybdate. Increasing the temperature of incubation increased the retention, or decreased the solution concentration, and this was reproduced by the effect of temperature on the rate of diffusive penetration. Desorption of fluoride was also reproduced. This supports the argument that slow desorption is mostly due to the need to reverse the diffusive penetration. After incubation at constant temperature, increasing the temperature at which solution concentration of molybdenum was measured, increased the concentration. The direction of this effect of temperature was also reproduced. It arises because of the effect of temperature on the position of the equilibrium between adsorbed molybdate (in the strict sense of the term) and molybdate in solution.
Testing a mechanistic model. III. The effects of pH on fluoride retention by a soil
Authors: BARROW N. J. , ELLIS A. S. 
Published: July 2006

SUMMARYThe pH of a soil was altered by incubating it with either lime or acid at 60°C for 1 day. Subsamples were then mixed with fluoride solutions in order to measure the effects of pH on fluoride retention. The results were compared with those previously obtained with phosphate on the same soil.At equal concentration of total fluorine in solution, fluoride retention was greatest at about pH 5.5 and decreased at both lower and higher pH. The decrease at low pH appeared to be caused by the formation of complexes between fluoride and aluminium in solution. As a result, only a small proportion of the total fluorine in solution was present as fluoride ions. At equal concentrations of fluoride ions, fluoride retention decreased with increasing pH. It was shown that this decrease could be explained by decreases in the electrostatic potential of the variable charge materials. The decrease in potential was steeper than that required to describe phosphate retention. This is consistent with the plane of adsorption of fluoride ions being closer to the plane of adsorption of H+ and OH− ions.
Testing a mechanistic model. VI. Molecular modelling of the effects of pH on phosphate and on zinc retention by soils
Authors: BARROW N. J. 
Published: July 2006

SUMMARYBoth phosphate and metal cations such as zinc can be retained by oxides of iron and aluminium. Yet the phosphate‐retaining and zinc‐retaining materials in soil appear to differ in their behaviour from that of pure oxides of iron and aluminium. In most soils, the electrostatic potentials of retaining materials appear to be negative at normal soil pH values. The changes in potential with pH, and consequent change in retention, also appear to differ from those of pure oxides. A model of a pure oxide was modified in an attempt to simulate the observed behaviour of soil. The most effective modification was to include a negative charge in the oxide. Such a charge could have arisen from solid–state diffusion of anions into the oxide, or by close association with permanently charged clays. The inclusion of this charge changes the direction of the effect of pH on phosphate retention. If the amount of negative charge is large enough, the paradoxical situation can arise in which the potential of a ‘variable‐charge’ surface is not affected by pH. This is consistent with observed effects of pH on zinc retention by soils.
Determination of erodibility of a subtropical clay soil: a laboratory rainfall simulator experiment
Authors: ELWELL H. A. 
Published: July 2006

SUMMARYErodibility of tropical soils changes according to land use and management. It is important to monitor these changes so that farming practices can be designed to conserve the soil.On a fersiallitic clay soil in Zimbabwe, the mean weight diameter of water‐stable aggregates was highly significant in explaining variations in both soil loss and runoff. Percent water‐stable aggregates > 2 mm diameter was also significant and had the practical advantage of being easier to measure. Organic carbon in the soil largely explains the proportion of water‐stable aggregates. These indices will aid management decisions on arable and grazing lands on this soil type, within the limits of the ranges tested.
Desorption of potassium from five soils of North India using electro‐ultrafiltration
Authors: BRAR M. S. , SEKHON G. S. 
Published: July 2006

SUMMARYSamples were collected from five soil series, developed on different parent materials and occurring widely in intensively cultivated areas of Northern India. Potassium in these soils was desorbed by electro‐ultrafiltration, and collected in different fractions by applying successively higher voltages and temperature. K was also determined by extraction with M neutral ammonium acetate and M boiling nitric acid. Potassium desorption using EUF differentiated between soil series and between low K and high K soils. The K‐buffering capacity of the soil was associated with soil texture.
Mechanisms controlling zinc solubility in soils
Authors: PULFORD I.D. 
Published: July 2006

SUMMARYThe removal of zinc from solution has been studied for seven soils of varying properties. The presence of a background electrolyte as an ionic strength buffer and the nature of the anions and cations in solution have also been examined. This process has been considered as both a surface adsorption and a precipitation mechanism. Evidence presented suggests a role for a precipitation mechanism involving zinc and iron, which is independent of pH. Iron concentration in solution decreased with increasing zinc concentration; the ion product pZn+2pFe was constant (15.00, SD 1.00) over all seven soils. A further indicator of a precipitation mechanism was the shape of the Langmuir plot at low equilibrium concentrations of zinc in solution.
Acid pyrophosphate extraction of soil fulvic acids
Authors: GREGOR J. E. , POWELL H. K. J. 
Published: July 2006

SUMMARYA simple three step method is described for isolation of soil fulvic acids in high yield. The complexing agent H2P2O72− (at pH 2) is used to release soil‐bound fulvic acids. Extraction of humic acids is minimal. Selective separation of the protonated fulvic acids from the ionic extractant is achieved on a non‐ionic polyacrylate resin (Amberlite XAD‐7); after washing the resin, fulvic acids were retrieved in >98% yield by adjusting the pH to 6.5. Two problems associated with the classical alkali extraction method are avoided: possible alkaline oxidation of phenolic components, and their oxidation by Fe3+ under the acidic conditions employed to precipitate humic acids. The product typically has an ash weight of <0.6% after one XAD treatment. The method has been applied to three soils and one IHSS peat sample.
Changes in the mineralogy of a cultivated marsh soil caused by simulated weathering
Authors: DE ARAMBARRI P. , TALIBUDEEN O. 
Published: July 2006

SUMMARYDifferential heats and isotherms for K‐Ca exchange and CEC values show that simulated weathering by grinding and NaTPB treatment of the coarse clay fraction of a rice‐growing marsh soil exposed vermiculitic layers to reaction with ions in solution, and also created more montmorillonitic layers and uncharged clay. Calcium selectivity was also increased, especially at K saturations > 50%. Changes in the CEC values of the fine clay, fine silt and coarse silt by such treatment, compared with that in the coarse clay fraction, were used to predict changes in the layer charges of their component phyllosilicates.
A retentivity function for use in soil–water simulation models
Authors: HUTSON J. L. , CASS A. 
Published: July 2006

SUMMARYA sigmoidal, non‐hysteretic two‐part retentivity function having only two constants in addition to porosity was developed for use in soil‐water flow simulation models. Values of the constants, shapes of the retentivity curves, and soil textural properties were related by fitting the retentivity function to retentivity data generated using regression equations. Two sets of regression equations, which relate water content at specific matric potentials to soil texture and bulk density, were used, one for British soils and one for South African soils. Hydrologically inhomogenous soils may be modelled by varying the values of the retentivity constants through the profile to reflect changing soil properties.
A comparison of the convection‐dispersion equation and transfer function model for predicting chloride leaching through an undisturbed, structured clay soil
Authors: DYSON J.S. , WHITE R.E. 
Published: July 2006

SUMMARYThe transfer function mode) (TFM) and convection‐dispersion equation (CDE) were compared for predicting Cl − transport through a calcareous pelosol during steady, nearsaturated water flow. Large, undisturbed soil cores were used at constant irrigation intensities (q0) between 0.3 and 3 cm h−1, with a step‐change in Cl− concentration. The assumption of a lognormal distribution of travel times–characterized by the mean (μ) and variance (σ2)–permitted the flux‐averaged breakthrough curves (BTCs) to be modelled very accurately by the TFM. The BTCs could be modelled equally well by the CDE when both the mean pore water velocity (v) and dispersion coefficient (D) were optimized simultaneously by the method of least squares, but not when v was put equal to q0/v, where V was the mean volumetric water content.The best estimate of v was consistently > q0/v, which suggested that not all the pore water was effective in chloride transport. An operationally defined transport volume (θst) was calculated from the mean () or median (τm) travel times derived from the TFM. Chloride exclusion was not solely responsible for θst() being <V: immobile water also contributed. The positive skewness of the travel time distributions meant that θst(τm) < θst(), indicating the effectiveness of macropore flow in solute transport. Dαv1.42 (from the CDE), and σ2αv (from the TFM), confirmed that Cl− dispersion increased as flow velocity increased.Flux‐averaged concentrations were used to calculate the volume‐averaged resident concentrations. They matched the measured Cl− concentrations most closely when there was a gradual decrease in measured Cl − concentration with depth, but not when Cl − decreased sharply below c. 10 cm. Calculations assuming that all the water was effective in chloride transport gave less accurate results. Comparison of the measured and predicted concentrations of solute demonstrated that this must be a critical part of the evaluation of any model of solute transport.
Comparison of several spatial prediction methods for soil pH
Authors: LASLETT G. M. , McBRATNEY A. B. , PAHL P. J. , HUTCHINSON M. F. 
Published: July 2006

SUMMARYA survey of topsoil pH has been designed specifically to compare the performance of several two‐dimensional spatial prediction methods. These methods have been classified as global or local, and interpolating or non‐interpolating, and smooth or non‐smooth predictors. The techniques tested were global means and medians, moving averages, inverse squared distance interpolation, Akima's interpolation, natural neighbour interpolation, quadratic trend surface, Laplacian smoothing splines and ordinary kriging. All methods showed some deficiencies; for example, prediction sums‐of‐squares were higher than expected for all methods. Interpolating methods either were very poor predictors, or suffered from theoretical drawbacks, or both. Of the non‐interpolating methods, Laplacian smoothing splines and kriging generally performed best. Estimates of variance derived from models which assume independent errors were greater than estimates of variance derived from neighbouring pairs of data sites, suggesting that short range correlations definitely exist, and should be taken into account in any predictive modelling.
A one‐parameter model for the soil water characteristic
Authors: GREGSON K. , HECTOR D. J. , McGOWAN M. 
Published: July 2006

SUMMARYThe two‐parameter model In φ= a+b ln θis widely accepted in the literature as providing a good fit to the soil moisture characteristic for a wide variety of soil types. This model is examined and it is shown that the parameters a and b are not independent, and hence that the SMC may be represented by a one‐parameter model with little loss of accuracy. Thus it is possible to define the SMC from one paired measurement of soil water content against potential. Because this single paired measurement is all that is required it also avoids the necessity of classification of the soil type–indeed it may provide an additional means of soil identification.
Retarded leaching of nitrate measured in monolith lysimeters in south‐east Nigeria
Authors: WONG M. T. F. , WILD A. , JUO A. S. R. 
Published: July 2006

SUMMARYAt Onne in South‐east Nigeria, drainage water was collected from four monolith lysimeters and analysed for nitrate. The lysimeters contained an acid sandy loam. At the start of the first rainy season two lysimeters received urea labelled with 15NO3– and two received no nitrogen fertilizer; all four were uncropped in the first year.The peak concentrations of 15NO3– and of unlabelled (soil) NO3– were found after 2.5 pore volumes of water had passed through the lysimeters. Using the same soil in the laboratory after fine sieving, the peak concentration of tritiated water was found at 1 pore volume whereas nitrate leaching was retarded. The pattern of nitrate leaching was well described by miscible and immiscible models which included an adsorption coefficient for nitrate. Over the 2 years 81.4% of the 15N added at the start of the first rainy season was recovered in the drainage water.
Hydraulic and soil mechanical aspects of rill generation on agricultural soils
Authors: RAUWS G. , COVERS G. 
Published: July 2006

SUMMARYAn attempt is made, using literature data, to clarify the relationship between the detachment capacity of overland flow and its hydraulic characteristics. Attention is paid to the influence of sediment properties and rainfall.Using these relationships and the concept of effective shear velocity, it was possible to establish a relationship for rill prediction which covers a variety of soils and a wide range of field conditions. Raindrop impacts do not seem to have an important influence on rill generation on cohesive materials.
Dependence of tensile strength of soil aggregates on soil constituents, density and load history
Authors: HADAS A. , LENNARD G. 
Published: July 2006

SUMMARYThe compressive‐tensile stress ratio at failure under unidirectional loading of air‐dry samples of 10 soils was compared with their clay and CaCO3 contents, and their surface areas. Deviations from the commonly assumed Griffith theory were found for two soils. No special relationships were found between soil constituents and associated compressive tensile stress ratio, even though this ratio tends to decrease slightly with increasing clay percentage.
The effect of sodium and calcium on physical properties and micromorphology of two red‐brown earth soils
Authors: GREENE R. S. B. , RENGASAMY P. , FORD G. W. , CHARTRES C. J. , MILLAR J. J. 
Published: July 2006

SUMMARYThe effect of treatment with either gypsum or sodium chloride on the saturated hydraulic conductivity (Ks) of repacked soil columns and modulus of rupture (MOR) was studied on surface samples of two red‐brown earth soils from SE wheat belt in Australia.When the exchangeable sodium percentage (ESP) of the two soils was increased to >80, KS was substantially reduced and MOR increased relative to the untreated soil; the values of the parameters were nearly equal for these pairs of high ESP soils. However, after treatment with gypsum the Raywood soil had a Ks twice, and a MOR less than half, the corresponding values for the Glenloth soil.Micromorphological and scanning electron microscope (SEM) observations suggest that the increase in Ks following gypsum treatment is associated with an increase in visible macropores and reduced clay dispersion; Na treatment increased dispersion at the soil surface, with the clay particles forming an impermeable surface seal and illuviation argillans.
The influence of earthworms and cranefly larvae on the decomposition of uniformly 14C labelled plant material in soil
Authors: CHESHIRE M. V. , GRIFFITHS B. S. 
Published: July 2006

SUMMARYAmounts of the individual carbohydrate components derived from uniformly 14Clabelled grass added to soil were monitored in incubations lasting for up to 2 years. Decomposition was enhanced by the presence of the earthworms. Allolobophora caliginosa and Lumbricus rubellus and the cranefly larvae Tipula paludosa. After 28 d larvae had increased the loss of 14C‐arabinose by 8.8% (compared to soil without larvae), ‐xylose by 15%, ‐non cellulose glucose by 5.3% and ‐cellulose glucose by 12.5%. Earthworms had increased the loss of 14C‐xylose by 5%, ‐galactose by 21% and ‐total glucose by 11% after 6 months, and by another 29%, 14% and 8% respectively after 12 months. The losses of 14C, initially about 60% from soil with tipulid larvae after 1 month, and 50% from soil with earthworms after 3 months, became progressively less. Total 14C losses in the presence of earthworms were 66% after 12 months and 60% after 2 years, respectively. Increased decomposition is considered to be the result of the mixing of soil and substrate by the invertebrates, rather than an effect of their digestive capabilities.
On the role of expert systems and numerical taxonomy in soil classification
Authors: DALE M. B. , McBRATNEY A. B. , RUSSELL J. S. 
Published: July 2006

SUMMARYExpert systems and numerical classification in general are reviewed and their relative ability to improve soil classification systems are discussed. The inductive and deductive elements of expert systems are seen as corresponding to the class establishment and class assignment phases of classification; computerized expert systems have so far been set up only for very simple assignments. To date, numerical classification has been useful in the analysis and organization of local low‐level soil data but has been largely untried at the higher global levels of soil classification because of a lack of suitable data and scientific commitment. It is concluded that numerical classification has a potentially useful part to play in establishing soil classes and generating rules for assignment in expert systems. The inference procedures and user interface of expert systems should allow more integration and realistic assignment of available data and increase the usefulness and predictability of soil information, especially if presented in a user‐friendly mode.
Seasonal changes in the structure of clay soils in relation to soil management and crop type. II. Effects of cultivation and cropping at Compton Beauchamp
Authors: MACKIE‐DAWSON L. A. , MULLINS C. E. , GOSS M. J. , COURT M. N. , FITZPATRICK E. A. 
Published: July 2006

SUMMARYThe effects of direct drilling and ploughing on the structure and macroporosity of a clay soil at Compton Beauchamp, Oxfordshire, growing winter wheat, were studied using large thin sections (10 * 5 * 3.5 cm) and image analysis of photographs of fluorescent resin impregnated soil blocks.Composite coarse angular to subangular blocky and medium to fine granular aggregates were present in the top 3 cm of the direct drilled soil and in the top 10 cm of the ploughed soil. Settling of the soil and coalescing of these aggregates took place throughout the year under both treatments, but was most marked in the ploughed soil. In the subsoil (20 to 30 cm) most of the structural changes could be attributed to changes in the soil water content. Swelling in the winter led to the closure of the most macropores and shrinking in the spring and summer led initially to the development of vertical planar macropores and then to large cracks. Freezing and thawing in the winter created many very small subcuboidial aggregates at the soil surface which later coalesced as a result of raindrop impact.
Interaction of methyl nitrite with the inorganic and organic fractions of soils
Authors: MAGALHÃES A. M. T. , CHALK P. M. 
Published: July 2006

SUMMARYThe reactions of methyl nitrite (CH3ONO), a gaseous product of NO−2decomposition in soils, were studied by exposure of soils in closed vessels to the gas. The N transformations occurring in soils at different soil‐water states were assessed by measuring CH3ONO and other gaseous forms of N in the gas space, soil inorganic N (NH4+, NO−2, NO3−) and incorporation of CH3O15NO into the soil organic N fraction.The initial rate of uptake of CH3ONO increased with decreasing soil‐water content, but the rate of hydrolysis decreased as soil‐water content decreased below – 33kPa matric potential. Uptake was not affected by y‐irradiation of soils. Adsorption isotherms conformed to the Langmuir equation in each of 22 oven‐dry soils studied. Langmuir adsorption maxima were positively correlated with the clay contents of the soils, and adsorption was reversible to some extent at all soil‐water states.Small amounts of added CH3ONO were recovered as N2and N2O and as15NH4+in γ‐irradiated soils. From 60 to 72% of added CH3O15NO was recovered by Kjeldahl digestion; this was indicative of a chemical reaction with soil organic matter.The results suggest that the physical process of adsorption of CH3ONO by clay minerals and the chemical fixation of CH3ONO by soil organic matter are key factors controlling the atmospheric concentration of CH3ONO, and that the combined effect of these processes, together with hydrolysis in the soil solution, will inhibit the emission of CH3ONO formed in N‐fertilized soils.