bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proto‐imogolite and the process of podzol formation: a critical note
Authors: BUURMAN P. , VAN REEUWIJK L. P. 
Published: July 2006

SUMMARYThe presence of imogolite or other poorly crystalline aluminosilicates in the lower B horizons of podzols can be explained by neoformation from silica in the percolating soil solution and aluminium species liberated from their organic bond by activity of micro‐organisms. There are physicochemical arguments refuting the alternative concept that iron and aluminium are transported down the profile as short range order aluminosilicates such as proto‐imogolite which would thus play an important role in podzol formation. There is ample evidence to attribute the mobilization, translocation and precipitation of sesquioxides to complexing organic compounds.
Depolarization of a platinum electrode in soils and its utilization for the measurement of redox potential
Authors: ZHI‐GUANG LIU , TIAN‐REN YU 
Published: July 2006

SUMMARYThe platinum electrode was polarized by a current flowing through the electrode‐soil solution interface, and then the change in electrode potential caused by soil constituents diffusing from the bulk soil to the electrode surface (depolarization) was monitored. The speed of depolarization was dependent on the kind and concentration of depolarizers, and was affected by some physical conditions of the soil. Within the time interval of 3–10 min the change in electrode potential with the logarithm of time followed a straight line, and the intersection point of the two lines after anodic polarization and cathodic polarization was taken as the equilibrium electrode potential, i.e. the Eh of the soil.
Diffusion of urea, ammonium and soil alkalinity from surface applied urea
Authors: SINGH RACHHPAL , NYE P. H. 
Published: July 2006

SUMMARYA model for predicting the concentration profiles of urea, ammonium and soil pH in a soil column following diffusion from a surface application of urea is developed, using independently derived parameters, and tested experimentally.The following processes within the model were studied separately under the same conditions as those in the diffusion run. The rate of urea hydrolysis as a function of substrate concentration and pH in the soil solution, and the sorption of urea and ammonium by the soil from solution. A theory for the propagation of changes of pH in soils was applied to describe the diffusion of soil alkalinity arising from urea hydrolysis.These processes were linked by three diffusion equations—for urea, NH4 and soil alkalinity, which were solved numerically using finite difference methods. There was good agreement between experimental and predicted concentrations of urea and NH4, and soil pH values at the two times tested.
Clay migration in upland soils of Malaysia
Authors: TESSENS E. 
Published: July 2006

SUMMARYClay movement was studied in a large number of well‐drained soils from Peninsular Malaysia, with a kaolinite mineralogy and an udic or perudic moisture regime. Dispersion in subsoils was found to be related to the net charge on the clay, while in topsoils it was virtually independent of charge or weathering status, and all but one topsoil dispersed well. Accumulation of the dispersed clay is thought to be mainly through flocculation, and as such accounts for the absence of clay coatings in many subsoil horizons.A number of criteria are proposed to distinguish between highly weathered Ultisols and Oxisols, in an effort to improve on the currently used inconclusive properties, such as fine clay to total clay ratio.
Optimal sampling strategies for mapping soil types. II. Risk functions and sampling intervals
Authors: BURGESS T. M. , WEBSTER R. 
Published: July 2006

SUMMARYThis paper develops the concept of the quality of a soil map in terms of the proportion of soil boundaries that have remained undetected as a result of point sampling. This proportion is equated to the risk of omitting such boundaries during survey. A risk function is defined, and the optimal strategy is such that the risk is maintained at some predetermined acceptable level.In general the risk depends on the distribution of boundary spacings, the distance travelled from the last boundary and the projected sampling interval. Where the distribution is exponential, the position of the last encountered boundary is immaterial, and for a constant risk the sampling interval is also constant. The optimal strategy is a regular grid. The same principles enable the total sampling effort for a survey of constant risk to be forecast once the distributions of boundary spacings have been estimated from reconnaissance. The sampling effort for a risk of 0.1 is shown to be within the range of traditional practice.
A quantitative analysis of the relationships between root distribution and nitrogen uptake from soil by two grass species
Authors: ROBINSON D. , RORISON I. H. 
Published: July 2006

SUMMARYTwo grass species, Holcus lanatus and Deschampsia flexuosa, were grown in soil containing available nitrogen at 4 μg g−1 (‘Low N’) or 58 μg g−1 (‘High N’), in a controlled environment. Water was supplied via an auto‐irrigation system, which also minimized the vertical redistribution of soil nutrients, particularly NO3−. Growth, root morphology and distribution, and N uptake were measured during a 70‐day period. H. lanatus produced more dry matter than D.flexuosa in the high N treatment. Yields were similar in both species in the low N treatment. The growth of H. lanatus in the low N treatment was not limited by a complete exhaustion of soil N. Root density of H. lanatus was likely to have been inadequate to allow this species to attain its maximum potential N‐inflow rate. Thus, N uptake per plant and dry matter production were restricted. The growth of D.flexuosa was not limited by the low N treatment, compared with that in the high N treatment. This was attributed to its low maximum potential relative growth rate and, hence, its low demand for N compared with H. lanatus, rather than to any major ‘compensatory’ adjustments in root morphology or N absorption efficiency.
Aluminium release in relation to the determination of cation exchange capacity of some podzolized New Zealand soils
Authors: LEE R. , BACHE B. W. , WILSON M. J. , SHARP G. S. 
Published: July 2006

SUMMARYIn upper mineral horizons, CEC by compulsive and isotopic exchange methods, using Ba2+ as the saturating cation, gave higher values than the effective CEC at natural soil pH, and much higher values than CEC determined with m NH4OAc at pH 7. Cumulative Al release during leaching was considerably higher using Mg2+ and Ba2+ chlorides than K+ and NH4+ chlorides, and gave a different shape extraction curve. Basal spacing of the dominant dioctahedral vermiculite in the soil clays contracted from 14.5Å to 10.0–10.9 Å when saturated with NH4+ and K+, restricting release of interlayer Al. Lower horizons, containing a large proportion of Al‐chlorite in the clay fraction, which did not contract with any of the cations, showed more normal exchange behaviour. On leaching, Al release was slightly greater with K+ and NH4+, than with Mg2+ and Ba2+, chlorides. The implication of the results for CEC measurements is discussed.
Aluminium‐organic complexation: formation constants and a speciation model for the soil solution
Authors: YOUNG S. D. , BACHE B. W. 
Published: July 2006

SUMMARYStability constants describing Al3+ combination with soil polycarboxylates were measured using the methods of Gregor et al. (1955) and Tanford (1961). It is suggested that the high stability of such complexes is derived largely from the electrostatic energy associated with the high surface charge of soluble humus acids. Chemically, the affinity of fulvic acids for Al3+ appeared to be no greater than that of a weak complexant such as adipic or acetic acid. A species distribution model was constructed showing the proportion of soluble Al that is bound by organic complexes. The model uses certain approximations regarding the degree of dissociation of the humus acids, but from measurements of soluble humus and Al in soil solutions it was suggested that these approximations were reasonably valid. The range of the model falls within conditions likely to occur in agricultural topsoils and demonstrates the importance of organic complexants in limiting Al3+ concentrations in natural aqueous systems.
Soil colour: its measurement and its designation in models of uniform colour space
Authors: MELVILLE M. D. , ATKINSON G. 
Published: July 2006

SUMMARYThe principles of colour perception are outlined and applied to the problems of soil colour measurement using ‘Munsell Soil Color Charts’. As care is needed in using these charts to make an accurate assessment of soil colour, recommendations for the correct methods for soil colour measurement are outlined. The three soil colour characteristics of Munsell Hue, Value and Chroma are commonly used in multivariate analyses as orthogonal, equi‐dimensional, linear variables that describe perceived colour space. Such an approach may be inappropriate because the angular separation of Hue and an approximately 2.5:1 scaling relationship between Value and Chroma should be accounted for in any model of perceived colour space. An appropriate and simple polar transformation of Munsell colour data is compared with some other coordinate systems for representing colour space, including the CIELAB system. This polar transformation is recommended for processing colour data in multivariate analyses.
Trace elements in surface soils from the mineralized area of Madison County, Missouri, U.S.A.
Authors: DAVIES B. E. , WIXSON B. G. 
Published: July 2006

SUMMARYDuplicate, bulked surface soil samples, from sites 10m apart, were collected at 97 locations 1000 m apart on a regular grid measuring 8x11 km. Data were obtained for Ag, Ba, Be, Cd, Co, Cr, Cu, Li, Mn, Ni, Pb, V and Zn. One field sample was a good predictor of its nearby duplicate for Co, Cu, Ni and Pb, satisfactory for Ba, Be, Cr, Mn and Zn, but poorer for Cr, Li and V. Maps of the variation in precision of the field samples did not reveal any association between abandoned mine sites and high variability. The median coefficient of variation for trace elements in the field duplicates was between 8 and 19.5%.The duplicated field data were averaged to yield a mean soil metal concentration at each sample location. Concentrations of Ba, Be, Cr, Li, Sr and V were comparable with other published values for similar soils in Missouri. Concentrations of Co, Cu, Mn, Ni, Pb and Zn were higher which was explained by pollution from mining activities. A graphical technique was used to calculate background levels for metals in the second group. Samples of forest litter were collected at 12 locations: Ag, Ba, Cd, Mn, Sr and Zn concentrations were higher in the litter whereas Li and V concentrations were higher in the subjacent mineral soil. Computer isoline maps of the distribution of elements revealed an association between areas of high soil Cu, Co, Ni, Pb and Zn and abandoned mines or mineralized rocks.
The pedogenic effects of different species and vegetation types and the implications of succession
Authors: MILES J. 
Published: July 2006

SUMMARYThe paper surveys the changes in pH, organic matter type and degree of podzolization of poorly buffered, freely drained, siliceous soils in Britain caused by the predominant plant species and semi‐natural vegetation types. Changes in vegetation with succession, especially with varying grazing and burning regimes, and also with stand regeneration, are outlined, and their implications for soil change noted. Many cyclic changes in species a bundance seem to occur naturally which cause an alternation of contrasting trends in soil acidity and podzolization, thus tending to maintain a long term equilibrium.
Soil organic C, N, S and P after forest clearance in Nigeria: mineralization rates and spatial variability
Authors: MUELLER‐HARVEY I. , JUO A. S. R. , WILD A. 
Published: July 2006

SUMMARYMeasurements were made in southern Nigeria of soil organic C, N, S and P after forest clearance and cultivation of the site over a period of 22 months. Sampling depth, initially 0–10 cm, was adjusted as soil bulk density increased. Assuming a first order decay equation, the resulting mineralization constants for C, N, P and S were 0.179, 0.193, 0.136 and 0.262, giving half lives of 3.5, 3.3, 4.7 and 2.3 years. The amounts of N and P mineralized in the surface soil layer were equal to or exceeded the uptake of N and P by one crop of soybeans and three crops of maize. The observations are discussed in relation to a model that might be used for the more effective use of nutrients after a forest fallow.Also reported is the spatial variability of the soil C, N, S, organic P and total P at the time of forest clearance. Total and organic P had a high long‐range variability which is related to the clay content. C, N and S had high short‐range variability which is attributed to the vegetation.
Effects of inorganic speciation on the interpretation of copper adsorption by soils
Authors: RITCHIE G. S. P. , JARVIS S. C. 
Published: July 2006

SUMMARYA previous study with a range of soils indicated that adsorption of copper could not be adequately described by the Freundlich equation. Adsorption curves for all but a highly calcareous soil could be divided into two straight lines with a marked increase in slope at low solution concentrations.A computer program (QELIOS) has now been used to calculate the effects of pH, CO, partial pressure and different inorganic anions on the chemical equilibria of the systems used in the adsorption experiments. At pH 6–8.5, hydrolysed species play a major role in Cu speciation whereas CO2−3 species become important only at pH > 8.0. The sensitivity of Cu hydrolysis to pH changes and to total Cu concentration in solution provides a possible explanation for the two surface Freundlich curves for soils of pH 6–7, and for the lack of such double surfaces for soils of pH > 7.
Testing a mechanistic model. II. The effects of time and temperature on the reaction of zinc with a soil
Authors: BARROW N. J. 
Published: July 2006

SUMMARYSamples of a soil were mixed with zinc nitrate solutions and incubated from 1 to 30 days at temperatures from 4 to 60°C. The solution concentration of zinc, which would not have changed on brief mixing with the soil at 25°C, was measured. Background electrolytes for this measurement of null‐point concentration were both calcium and sodium nitrate. The effect of the temperature at which null‐point concentration was measured was also investigated. After incubation with zinc nitrate, desorption of zinc, and sorption of further zinc, were measured.Null‐point concentration of zinc decreased with increasing period of incubation, with the rate of decrease greatest at high temperatures of incubation. The effects of both temperature and time were closely described by a model which postulated an initial rapid adsorption of ZnOH+ ions onto heterogenous charged surfaces, followed by a diffusive penetration. Increasing the temperature of incubation increased the rate of diffusive penetration and led to low solution concentrations. In contrast, increasing the temperature at which null‐points were measured increased the concentration of ZnOH+ ions. This was shown to be consistent with a change in position of the equilibrium of the initial, rapid, adsorption reaction.Curves for desorption of zinc were continuous with curves for sorption of further zinc, but neither desorption nor further sorption coincided with the position of the curves relating retention of previously added zinc to concentration. This result was consistent with the model and occurred because desorption must reverse diffusive penetration. However, the model under‐predicted the magnitude of both desorption and sorption of further zinc. Desorption in calcium solutions was greater than in sodium solutions, even when the solution concentration of zinc approached zero. This was consistent with exchange diffusion of calcium ions for some of the penetrated zinc.
Studies on aggregate stability. 11. The effect of humic substances on the stability of re‐formed soil aggregates
Authors: CHANEY K. , SWIFT R. S. 
Published: July 2006

SUMMARYThe effects of both physical addition and adsorption of humic substances on the aggregation of soils were studied. To investigate the effect of adsorbed humic materials onto soils it was necessary to develop an effective adsorption procedure. Mono‐ionic soils (either sodium‐ or calcium‐saturated) were used to ensure that adsorption had occurred and to enable the results to be properly interpreted. Physical addition of humic acid followed by incubation with glucose produced aggregates with low stability values. When humic acid was adsorbed onto the soil minerals and incubated, significant increases in aggregate stability were observed which persisted with time. The stability of the re‐formed aggregates was even greater when the samples were incubated with glucose.This work has shown that humic substances were capable of stabilization of aggregates under difficult conditions where extracellular polysaccharides were ineffective, and that the stabilization had long term persistance. It is suggested that humic substances are particularly involved in the formation of micro‐aggregates.
A comparison of the thermocouple psychrometer and the pressure plate methods for determination of soil water characteristic curves
Authors: MADSEN H. B. , JENSEN C. R. , BOYSEN T. 
Published: July 2006

SUMMARYThe thermocouple psychrometer method and the pressure plate apparatus method werecompared for determining the energy status of soil water, and it has been shown that the resulting soil water characteristic curves might differ significantly. Ψt determined by the psychrometer method was always higher than Ψm, determined with the pressure plate method. Thus, the soil water characteristic curve determined with the pressure plate method may not represent the true condition of soil water, and the actual matric potential may be considerably higher than that assumed from the applied chamber pressure. This suggests the need for careful examination of the pressure plate method for determining the soil water characteristic curve.
Influence of pool substitution on the interpretation of fertilizer experiments with 15N
Authors: HART P. B. S. , RAYNER J. H. , JENKINSON D. S. 
Published: July 2006

SUMMARYThe uptake of labelled and unlabelled N by wheat was measured in pot and field experiments with 15N‐labelled fertilizer. Soils from two sites on the same series were used in the pot experiment; one had been bare‐fallowed for 22 years and contained 1.6% organic C, the other had been under grass for many years and contained 3.8% organic C. Fertilizer N increased the uptake of unlabelled soil N in both soils, i.e. there was a positive ‘added nitrogen interaction’ (ANI). There was no ANI in the field experiment. A simulation model is used to show how positive ANIs can arise as a result of ‘pool substitution’—labelled inorganic fertilizer N standing proxy for unlabelled inorganic soil N that would otherwise have been immobilized. In the low‐organic fallow soil, pool substitution accounted for the whole of the observed ANI and fertilizer N did not enhance either gross or net mineralization of soil N. Pool substitution also operated in the high organic grassland soil, but here net mineralization of soil N increased with increasing additions of fertilizer, giving rise to a ‘real’ ANI in addition to the larger ‘apparent’ ANI caused by pool substitution. This increase in net mineralization is probably caused by a decrease in immobilization of N as fertilizer N additions increase, not by an increase in gross mineralization of soil N. For pool substitution to operate, fertilizer N and soil inorganic N must occupy the same pool. This occurred in the pot experiment but not in the field experiment, where fertilizer and soil inorganic N remained separate and there was no ANI. When pool substitution occurs, fertilizer use efficiency is predictably lower as measured by the isotopic method than as measured by the conventional non‐isotopic procedure.
Simultaneous nitrification and diffusion in soil
Authors: DARRAH P. R. , WHITE R. E. , NYE P. H. 
Published: July 2006

SUMMARYDarrah et al. (1985b, 1986) presented a model that predicted the distribution of ammonium and nitrate in a column of soil, following the addition of ammonium chloride as a band of fertilizer to one end of the column. Ammonification and nitrification, the inhibition of nitrification by high levels of fertilizer addition and the simultaneous diffusion of ammonium and nitrate were modelled. By simplifying algorithms concerned with the calculation of the concentration of ammonium in solution and the diffusion of solutes in the column, up to eight‐fold savings in the time required to run the model could be made without significantly affecting the accuracy of the predictions. This simplified version was used to test the effect of a ±25% change in the values of the main input parameters. The distribution of ammonium was mainly influenced by parameters affecting the diffusive flux of solutes and the concentration of ammonium in the soil solution; that of nitrate was influenced by parameters affecting the growth, activity and inhibition of the nitrifiers. In general, the model was most sensitive to changes in the maximum specific growth rate of the nitrifiers, while almost no effect was observed when the affinity constant for ammonium oxidation was varied. Given the present state of knowledge of the range of parameter values in different soils, it is necessary to measure all the input parameters tested, with the possible exception of the diffusional impedance factor, in order to obtain accurate predictions from the model.
An analysis of crack pattern in clay soil: its density and orientation
Authors: SCOTT G. J. T. , WEBSTER R. , NORTCLIFF S. 
Published: July 2006

SUMMARYThe structure of much clay soil is angular blocky, and the pore space consists of a three‐dimensional network of narrow, approximately planar cracks. This paper presents a means of describing such a network in terms of its density and orientation.Undisturbed samples are impregnated with resin containing a fluorescent dye. Plane sections of known azimuth and elevation are cut through them and photographed under ultra‐violet light. The photographs are projected onto a screen and the spacings between successive cracks along linear probes are measured in several directions. The sets of distances obtained are then analysed.The method was applied to subsoil of the Windsor series. The distribution of inter‐crack distances appeared to be exponential but with a dearth of distances less than about 1 mm. The crack pattern was judged to be the outcome of a Poisson process, but one in which some of the very narrow wedges of soil had collapsed. The crack network was perceptibly anisotropic, and was modelled as two superimposed patterns, one isotropic and the other a set of approximately parallel cracks. The orientation of the parallel component was estimated from the sections. The cracks were found to be aligned parallel to the contour of the land and to dip into the hill slope at angles ranging from about 25° to 75° to the horizontal. The intensities in the soil of the two components were estimated as 0.18 mm−1 for the isotropic component and 0.2 mm−1 normal to the parallel component, equivalent to 0.1 mm−1 for a random direction.