bluuebunny/crossref_metadata_2025_split huggingface dataset:
The over‐estimation of clay and the under‐estimation of pores in soil thin sections
Authors: MURPHY C. P. , KEMP R. A. 
Published: July 2006

SUMMARYThe amounts of clay visible in four thin sections from paleosol horizons (clay contents 9–32%) were measured by point counting. These sections were used as references for visual estimates, without point counting, of the amounts of clay in 14 further sections. The measurements and estimates were recorded on pore‐free and gravel‐free bases so they could be related to gravimetric analyses. Amounts of clay measured and estimated by area in these thin sections were between 1.6 and 3.1 times those determined gravimetrically.The reasons for these differences are discussed. Firstly, clay in soil thin sections contains much pore space beyond the resolution of the optical microscope and has an apparent density dependent on the amount of submicroscopic pore space. An edge effect also causes over‐estimation of clay in soil thin sections and under‐estimation of visible pore space. Components (clay, mineral grains, pores) are usually sloped at their borders with each other within the standard 25–30 μm (three‐dimensional) thin sections. Clay, for instance, may overcap a pore at its border, hiding some pore space. The need for true two‐dimensional images of soil pore patterns in image analysis is indicated.A nomogram has been constructed, using apparent density, to allow estimation of clay in thin sections of soils with any clay content. Coarse/fine ratios can be determined more accurately and estimates of clay can also be recalculated to provide illuvial to total clay ratios that are more meaningful. It is recommended that the micromorphological identification criterion for the argillic horizon be reassessed and that 4% illuvial to total clay in a soil thin section be adopted as the diagnostic cut‐off.
The wetting and drying of a grazed and ungrazed clay soil
Authors: REID I. , PARKINSON R. J. 
Published: July 2006

SUMMARYA 4 year field experiment clearly demonstrates the role played by desiccation cracks in the redistribution of rainfall during the autumn re‐wetting of a Windsor Series clay soil. Where topsoil structure is damaged by the trampling of grazing animals, cracks are well developed and a portion of rain water is diverted down them, by‐passing the topsoil. Redistribution takes place from two centres, the bottom of the cracks and the surface. But where structure is unaffected by trampling, the soil accommodates seasonal shrinkage without cracking and redistribution is by diffusion from the surface only. Summer evaporation is shown to be linearly related to Penman's potential evapotranspiration over a wide range of soil moisture deficits, and simple constants are provided to correct ET to obtain EA. The M.A.F.F. method of estimating evapotranspiration is shown to be too conservative and fails to identify the October maximum soil moisture deficit common in this soil.
Determination of the nitrogen composition of colliery spoil
Authors: PALMER J. P. , MORGAN A. L. , WILLIAMS P. J. 
Published: July 2006

SUMMARYFreshly exposed unameliorated spoil and vegetated spoil were analysed for their nitrogen constituents using methods devised for soils. The main components found were non‐exchangeable ammonium (25%), hydrolysable nitrogen (33%) and unidentified non‐hydrolysable nitrogen (62%). Summation of these exceeded 100% because hydrolysis with 6 M HCI extracted much of the non‐exchangeable ammonium. Ammonium in the hydrolysate accounted for over 90% of hydrolysable nitrogen in freshly exposed unameliorated spoil and 70% of hydrolysable nitrogen in vegetated spoil. Correction for this ammonium in the hydrolysate allowed estimates of ‘recent organic’ nitrogen accumulation to be made. These estimates were significantly correlated with spoil mineralizable nitrogen levels. The nature of the nitrogen constituents of colliery spoil and the use of ‘recent organic’ nitrogen estimates in assessing site fertility are discussed.
Thermoluminescence dating of soils developed in Late Devensian loess at Pegwell Bay, Kent
Authors: WINTLE A. G. , CATT J. A. 
Published: July 2006

SUMMARYThermoluminescence (TL) measurements on the present organic surface soil and two buried soils in loess and colluvium derived from loess at Pegwell Bay, Kent, suggest that the signal is almost completely zeroed during soil development, mainly by optical bleaching. The technique may therefore be used to date buried soils developed in loess and possibly other terrestrial sediments. Decalcification, gleying and other soil‐forming processes may also affect the TL signal of the soil parent material, and seem to be the main reasons why the Btg horizons of the Early Holocene buried soil at Pegwell Bay give more recent TL dates than the parent calcareous loess.
Experimental simulation of the results of clay translocation in the B horizons of soils; the formation of intrapedal cutans
Authors: AKAMIGBO F.O.R. , DALRYMPLE J. B. 
Published: July 2006

SUMMARYA series of laboratory experiments designed to simulate the formation of intrapedal cutans was carried out through repetitive leachings of undisturbed blocks of soils (6 × 3 × 4 cm3) by suspensions (0.3% concentration) of clay‐sized particles from two commonly occurring Bt horizons in southern England. After leaching, thin sections were cut and point‐counted, thus enabling the visual recognition, replication and potential quantification of newly formed intrapedal pore and grain cutans. They all exhibit morphological, physical and optical properties diagnostic of illuviation cutans, and can be differentiated from inherited cutans on these and on spatial grounds. A general relationship between numbers of newly formed cutans and increasing leaching cycles was observed, and experimental support obtained from these soils for the significance of the complex, three‐dimensional spatial pattern of tubular pores in the translocation of clay‐sized materials and the formation of these argillic, Bt horizons. This study highlights both the value and difficulties of designing laboratory‐based, soil/water/gravity studies in pedology.
Transport and deposition of dilute colloidal suspensions in soils
Authors: VINTEN A. J. A. , NYE P. H. 
Published: July 2006

SUMMARYTransport and deposition of suspended particles occur during many soil processes. The mechanisms of removal of particles from suspension during saturated flow are described, and a simple equation of depth filtration is used to test experimental data. A method for labelling dilute clay suspensions with 14C‐paraquat is developed. Particles are removed from flowing suspension even when they are dispersed. The depth filtration equation holds only under these conditions, though the mechanisms of removal of particles from suspension by the soil are unclear. A surprisingly large reduction in flow rate accompanies passage of dilute clay suspensions through soil columns.
Losses of nitrogen by denitrification from a grassland soil fertilized with cattle slurry and calcium nitrate
Authors: EGGINTON GWEN M. , SMITH K. A. 
Published: July 2006

SUMMARYLosses of N by denitrification from an imperfectly drained grassland soil were measured by the acetylene‐inhibition technique over a 1‐yr period, during which applications of up to 200 kg ha −1 of N as cattle slurry or calcium nitrate were made. The quantities of N lost from nitrate‐treated soil were much greater than from slurry‐treated areas, and ranged up to 21% of the N applied. The losses occurred predominantly over brief periods following fertilizer application in the spring. Ratios of N released as N2 to that released as N2O increased as denitrification rates increased. The highest ratio recorded, 24, may have been a conservative estimate because inhibition of N2O reduction may not have been complete on all occasions. Increased respiration was observed in the soil profile as a result of adding C2H2. This effect should be taken into account in interpreting experiments using the C2H2‐inhibition technique.
Structure of a silty soil in relation to management
Authors: DOUGLAS J. T. , JARVIS M. G. , HOWSE K. R. , GOSS M. J. 
Published: July 2006

SUMMARYIn the United Kingdom silty soils have been classified as unsuitable for direct drilling since these soils may produce seed‐beds that are inadequate for satisfactory crop emergence. This judgement was based on problems encountered in the first 2–3 yr of direct drilling as well as on an appreciation of soil physical properties. Longer‐term experimentation (10 yr) has indicated that, subsequent to that initial period, soil conditions after zero‐tillage are not a major limitation to growth of autumn‐sown cereals. This eventual parity between simplified and conventional tillage can be attributed largely to improvement in the surface of direct‐drilled land. In the tenth experimental year this layer comprised more strongly developed aggregates, of greater stability, than those from the annually ploughed soil. Porosity and soil strength measurements did not indicate that root growth would be severely restricted below this depth. When this soil was wet in winter it was weak and relatively unstable and so it would most likely be unsuitable for sequential direct drilling of spring‐sown crops.At the same site soil that had been continuously under grass throughout the same 10 yr period developed better structure than that in the arable area, in part because of a greater earthworm population and an increased organic matter accumulation. In any subsequent change to arable usage this improved structure would best be conserved by avoiding soil inversion and using direct drilling or some other simplified method of cultivation.
Drop‐cone penetration in situ and on minimally disturbed soil cores
Authors: CAMPBELL D. J. , HUNTER R. 
Published: July 2006

SUMMARYDrop‐cone penetration was measured both in situ and on minimally disturbed cores at a selection of soil matric potentials for four soils. The drop‐cone penetration/water content relation was linear in situ and, if results for very low water contents were excluded, for the cores. The slope of the line for the field data was much greater than for the core data and this raises doubts about the value of other than in situ measurements of soil strength for predicting field behaviour. Vane shear strength is negatively correlated with in situ drop‐cone penetration. The drop‐cone test is a useful strength test for small volumes of soil, but care must be taken in selecting the mass of the cone as this affects the volume of soil which will influence the test results.
A statistical study of seven curves for describing the sorption of phosphate by soil
Authors: RATKOWSKY D. A. 
Published: July 2006

summarySeven mathematical models, which have been advanced for describing phosphate sorption by soils, are studied here with respect to their statistical behaviour in estimation. These seven non‐linear regression models include the Langmuir equation and two extensions of it, the Freundlich equation and two extensions of it, and Gunary's equation. Measures of non‐linear behaviour, such as the Bates & Watts (1980) curvature measure of intrinsic non‐linearity and the Lowry & Morton (1983) asymmetry measure of non‐linearity, were calculated for each model in combination with each of six data sets. It was found that the Freundlich equation and the extension of it proposed by Sibbesen behaved best, with Gunary's equation also having acceptable statistical properties, whereas the Langmuir equation and its extensions behaved worse, exhibiting properties which indicate that the estimators of their parameters would be severely biased and non‐normal in distribution. It is believed that similar conclusions may apply to other processes involving surface adsorption.
Nitrogen in particle size fractions of soils incubated for five years with 15N‐ammonium and 14C‐hemicellulose
Authors: CHRISTENSEN B. T. , SØRENSEN L. H. 
Published: July 2006

SUMMARYFour soils with a range of clay and silt contents were incubated for 5 a with 15N‐labelled (NH4)SO4 and 14C‐labelled hemicellulose and then fractionated according to particle size by ultrasonic dispersion and sedimentation. The distribution of labelled and native N between clay, silt and sand fractions was determined and elated to previous results on the C distributions.Between 29% and 48% of the added N was found in organic form. The 15N atom percentage excess decreased in the order: clay > whole soil > silt > sand. For both clay and silt, the enrichment factor for labelled and native N decreased with increasing fraction weight. Clay enrichment was higher for labelled than for native N, the converse being true for silt. The distribution of whole soil labelled organic N was: clay 77–91%, silt 4–11%, and sand <0.5%. Corresponding values for native N were 69–74%, 16–22%, and 1–2%, respectively.All soils had higher proportions of labelled than of native N in the clay, the converse was true for the silt. The C/N ratio of the native silt organic matter was higher and that of clay organic matter lower than whole soil C/N ratios. Differences between the C/N ratio distributions of native and labelled organic matter were small.The relative distribution of labelled N and C was very similar confirming that the turnover of C and N in soil organic matter is closely interrelated.
Reclamation of colliery spoil: the effect of amendments and grass species on grass yield and soil development
Authors: RIMMER D. L. , GILDON A. 
Published: July 2006

SUMMARYResults are presented of a field trial in which various methods for the reclamation of coarse colliery waste were tested. The site was divided into three blocks and each block received a different level of deep cultivation; however, these treatments appeared to have no long‐term significant effect on grass yield. Within each cultivation block a number of treatments were superimposed. These included: amendments of soil and organic materials, deep placement of P fertilizer, and the use of different grass seed mixtures. Grass yield was measured annually for 6 years. At the end of that period soil samples were taken for analysis and tests were conducted in the field to measure the effects of treatments on the developing soil conditions. There was a general decline in grass yields during the course of the experiment. However, the rate of decline varied with the different treatments, being lower on amended spoil (i.e. treated with soil or organic materials) and on treatments sown with a seeds mixture containing S143 cocksfoot (Dactylis glomerata). Differences in the soil conditions resulting from the use of amendments were detected; in particular, the soil‐amended plots had higher pH and exchangeable Ca and greater penetrability.
Mobile iron, aluminium and carbon in sandy coastal podzols of Fraser Island, Australia: a quantitative analysis
Authors: LITTLE I. P. 
Published: July 2006

SUMMARYIn this paper podzols of free‐draining sands in south‐eastern Queensland are examined. The 14 profiles represent a chronosequence from young incipient podzols, to ancient ‘giant podzols’ of Pleistocene age, with a spodic horizon at a depth of 8–10 m.Carbon, Fe and Al were determined in pyrophosphate, and Fe, Al and Si in oxalate extracts. The resulting profile distributions were modelled by three expressions, fitted for each attribute, which accounted for surface accumulation, B horizon development and a phase (B/C horizon) of constant composition with depth.The parameters may be used to characterize soil profiles. They show that there is a tendency for the accumulation of carbon in the B horizon to be reflected by Fe and particularly A1 accumulation, which supports the proposition that carbon is directly associated with the transport of A1 and Fe.A feature of many of these soils is a deeply weathered surface with little tendency for commensurate development of an illuvial horizon. Rates of removal of Fe and Al from the A horizon were obtained by comparison of the depths of leaching with age estimates based on geomorphology, and they indicate a non‐linear rate of increase in the thickness of the A horizon.
On the fractal dimensions of some transient soil properties
Authors: ARMSTRONG A. C. 
Published: July 2006

SUMMARYSpatial variation of soil properties can be studied by use of the concept of fractals, and the overall roughness of a surface characterized by its fractal dimension. Soil surface strength was recorded by both cone penetrometer and field shear vane, along a series of transects, at 10 cm spacings. In the natural state, such data gave fractal dimensions very close to 2, implying an almost totally random data set, and only the deliberate action of cultivations introduced an order of persistence. Microtopography, measured by a profile meter at 1 cm intervals, had fractal dimensions of 1.7 on two separate sites. Problems are identified specifically in the choice of a suitable model for fitting the semi‐variogram, and in the collection of an efficient data set.
Contributions by fungi and bacteria to aggregate stability of cultivated soils
Authors: MOLOPE M. B. , GRIEVE I. C. , PAGE E. R. 
Published: July 2006

SUMMARYStability changes during ageing (sterile) or incubation (non‐sterile) of both natural field aggregates and remoulded aggregates from five soils were studied for periods up to 30 days. Growth of fungal hyphae, estimated by ergosterol measurement, corresponded to temporary stability increases in both types of aggregates during the first 15 days. Thereafter, fungal hyphae disappeared and were replaced by actinomycetes and bacteria. Increased stability due to entanglement by hyphae was comparable to that due to thixotropy in remoulded aggregates. Bacterial growth accompanied the fall in stability associated with fungal decline, but had little direct effect in stabilizing soil aggregates. Destruction of polysaccharides by periodate oxidation greatly diminished aggregate stability. The role of bacterial polysaccharides in soil aggregate stability is discussed.
Torus‐shaped pedological features associated with soil microorganisms
Authors: SULLIVAN L. A. , KOPPI A. J. 
Published: July 2006

SUMMARYTorus‐shaped features 1–7 urn in diameter were found on the smooth surfaces of the structural units of a Red Podzolic Soil (Udic Haplustalf) B horizon and on the smooth surfaces within the columnar structures of a Solodized Solonetz (Typic Natrustalf)‐SEM & EDS were used to characterize these features, and to determine their probable pedogenesis. The size range was bimodal in the Red Podzolic B horizon, being either ∼5 μm or ∼2.0 um. In the Solodized Solonetz all tori were ∼ 1.5 μm in diameter. The larger tori consisted of fine‐clay coated collapsed fungal spores, whilst the smaller tori were fine‐clay coated collapsed bacteria‐sized cells.
Composition and properties of poorly ordered minerals in Welsh soils. I. Composition
Authors: ADAMS W. A. , KARIM M. I. , GAFOOR S. N. 
Published: July 2006

SUMMARYEleven horizons of acidic soils in mid‐Wales developed from Lower Palaeozoic sedimentary rocks were examined. Selective extraction of Al and Si provided evidence against the occurrence of significant quantities of poorly ordered Al‐silicates. Fe0 was weakly correlated with Al0, but very closely correlated with Al0 minus Al extracted by cold 5% Na2CO3, implying that poorly ordered Al occurs in part as a substituent in Fe oxide and in part in a form unassociated with Fe oxide. Support for this was obtained by analysis of oxide fractions concentrated from aqueous suspensions by sequential ultracentrifugation and through the examination of synthetic Al‐substituted Fe oxides. Fe oxide containing Al substituted at an almost constant level was the dominant constituent of the poorly ordered fraction in four of the five Bs horizons examined. The occurrence of Al in this form is an important mechanism by which Al is retained in aerobic but highly acidic Bs horizons.
Interpretation and presentation of cone resistance data in tillage and traffic studies
Authors: O'SULLIVAN M. F. , DICKSON J. W. , CAMPBELL D. J. 
Published: July 2006

SUMMARYRecommendations are made regarding the analysis and presentation of cone resistance data. Methods for eliminating extreme readings due to stones are compared and the effects of stones on variability and treatment comparisons are discussed. Results showed very high variability between positions, even at 100 mm separation. Measurements separated by more than 1 m were independent of each other except where trends in other soil properties influenced cone resistance. The assessment of compaction under wheels is described for cone resistance measurements made under the rut centre‐line. Parameters are derived from measurements made on two‐dimensional, vertical grids to quantify the depth, extent and intensity of compaction and loosening. The usefulness of penetrometers in tillage and traffic studies is discussed.
Gaseous diffusion through peat
Authors: KING J. A. , SMITH K. A. 
Published: July 2006

SUMMARYRelative gas diffusivity (D/D0) was measured in peat cores equilibrated to set moisture tensions between zero and ‐ l0 kPa, using the radioactive gas 85Kr. A relationship between relative diffusivity and the air filled porosity was obtained, which showed lower values of D/D0 at air‐filled porosities above about 0.13m3m−3, and higher values at porosities below about 0.10m3m−3 than some of those found in the literature for mineral soils. The likely effects of shrinkage behaviour on drying in the field, on the relationship between D/D0 and air‐filled porosity, are discussed.
Estimating hydraulic conductivity values from ring infiltrometer measurements
Authors: YOUNGS E.G. 
Published: July 2006

SUMMARYInfiltration from ring infiltrometers of different radii was measured into four soil materials contained in laboratory tanks. The infiltration per unit area was larger the smaller the ring size, coming to a steady state at an earlier time. Scaling based on similar media theory was applied to the results using a microscopic characteristic length defined in terms of the hydraulic conductivity of the saturated soil and a macroscopic characteristic length taken as the radius of the ring. The relationships between scaled cumulative infiltration and scaled time merged into a single relationship at small scaled times for all soil materials and for all sizes of ring, but were different for the different soils and for the various ring radii at large scaled times. The relationship at small times was used as a type curve to interpret in situ measurements with ring infiltrometers on three field soils in terms of the hydraulic conductivity of the saturated soil. These estimates of hydraulic conductivity pertained to the small volume of soil near the surface which was wetted during the measurement. Large variations in hydraulic conductivity values were found from experiments with small sized rings, but little variation was found for large sized rings. The technique provides a simple method of investigating soil structural changes near the surface.