bluuebunny/crossref_metadata_2025 huggingface dataset:
The measurement of the variation with depth of the hydraulic conductivity of saturated soil monoliths
Authors: YOUNGS E.G.
Published: July 2006

Hydraulic conductivity profiles of saturated composite porous columns were obtained in two ways: first, from measurements of the hydraulic potential profiles with uniform vertical flow; and second, by making use of a potential theorem concerning the flow between sources and sinks, from measurements of the hydraulic potential difference between the ponded surface and the base when the flow was intercepted in turn by successive drains located at intervals down the column. Both techniques gave the same results. The hydraulic conductivity profile of a structurally unstable column changed significantly with time, suggesting that such measurements might be used to monitor soil structural changes and root development in lysimeter studies.
Trimethylsilylation of commonly occurring primary and secondary minerals in soils
Authors: SMITH B. F. L. , PATERSON E. , MITCHELL B. D.
Published: July 2006

Soil is formed through the weathering of minerals—mainly silicates—and the manner in which these materials weather is related to some extent to the arrangement of silica units within their structures. This has been termed the degree of polymerizafion of the silica and can be quantitatively assessed by preparing organic (trimethylsilyl) derivatives which can be separated and identified. This procedure has been applied to a number of primary and secondary (including clay and highly disordered) minerals occurring in soils and has indicated that: (a) of the primary minerals, the ferro‐magnesian are the most susceptible to acid attack; (b) inorganic gels, particularly those high in alumina, are reactive; and (c) crystalline clay minerals, especially kaolinite and illite, are relatively stable.
Composition and development of some soils on glauconitic Cretaceous (Upper Greensand) rocks in southern England
Authors: LOVELAND P. J. , FINDLAY D. C.
Published: July 2006

Three soils developed in glauconitic parent materials and differing in water regime have been examined. Particle size distribution and mineralogical data show them to be free of additions of extraneous material and major lithological discontinuities. The principal soil‐forming processes have been physical disaggregation of glauconite grains, translocation of clay, removal of Fe II from the glauconite structure due to charge imbalance following loss of structural K, and oxidation of this Fe II to form hydrous Fe oxides. A randomly interstratified illit‐mectite has also formed by weathering of the glauconite. The evidence of void argillan formation at considerable depth in the coarser textured soils is difficult to reconcile with conventional ideas regarding the formation of such features. The glauconite in these soil parent materials has an unusually low Fe II content, which confers considerable stability on the glauconite surface. As a consequence, the glauconite in these soils is relatively resistant to weathering.
Soil water behaviour in response to changes in soil structure
Authors: HAMBLIN A. P.
Published: July 2006

Surface horizons of two Australian alfisols which had been cropped for 3 years to wheat by zero, minimum and ploughed tillage were compared for differences in structure. Total porosities and pore size distributions differed between treatments, but values for water and air permeability, sorptivity, diffusivity and evaporation rate were not necessarily ranked in the same order. The stability of soil structure was usefully described by the ratio of water to air permeability (kw/ka), which indicated the relatively fragile nature of the ploughed structures, despite their initially greater proportion of coarse porosity. Time of sampling after seeding also influenced hydraulic properties which were found to vary significantly over a 10‐week period. Variations in vertical distribution of organic matter between tillage treatments is postulated as influencing the differences in structural stability.
Suppression of decomposition of 14C‐labelled plant roots in the presence of living roots of maize and perennial ryegrass
Authors: REID J. B. , GOSS M. J.
Published: July 2006

The rates of decomposition of barley roots labelled with 14C were investigated in soil planted with maize or perennial ryegrass and in fallow controls. Evolution of 14CO2 was significantly less from the planted soils than from fallow controls.

Roots of maize and ryegrass appeared to compete substantially with soil microbes for 14C‐labelled materials. Simple competitive effects were, however, insufficient to explain all of the observed effects of root growth on soil organic matter decomposition.

There was no indication that the detrimental effects of maize roots on aggregate stability could be associated with increased degradation of native soil organic materials; the broader significance of the results is also discussed.
Soil physical conditions on reclaimed colliery spoil heaps
Authors: RIMMER D. L.
Published: July 2006

Soil physical conditions are inherently poor and lead to summer droughtiness and winter waterlogging on many spoil heaps. The high stone content makes soil physical measurement difficult. The development of appropriate field and laboratory methods, which allow the calculation of sample composition, bulk density, total porosity, air‐ and water‐filled porosities and available water capacity are described.

A survey of 12 reclaimed colliery spoil heaps of varying age showed that, apart from an increase in organic matter in the surface layer (0–5 cm) with increasing age of site, there were no consistent trends with age and this is attributed to initial between‐site variability. General trends with depth down the profile to 30 cm were obtained by combining the data from all 12 sites. With increasing depth the bulk density increased and the porosity decreased. A higher porosity in the 0–5 cm layer was associated with (i) lower stone content (>2 mm) due to weathering and (ii) organic matter accumulation. In the subsurface layers (>5 cm) the stone content was essentially constant and the decreasing porosity with depth is explained as being due to settling. Overall there was a strong negative correlation between porosity of samples and stone content, which in turn was determined by the weatherability of the material.
Changes in soil aggregate water stability induced by wetting and drying cycles in non‐saturated soil
Authors: UTOMO W. H. , DEXTER A. R.
Published: July 2006

Wetting and drying of remoulded soil resulted in water stable aggregation. The greatest proportions of water stable aggregates arose from wetting and drying in the −1 to −100 kPa range of matric water potential. The effect occurred with sterile and non‐sterile soil. but the proportion of water stable aggregates was less with sterile soil.

The application of wetting and drying cycles in the laboratory to non‐tilled soil resulted in a steady decrease in the proportion of water stable aggregates. With tilled soil, the proportion of water stable aggregates first increased to a maximum and then decreased steadily with further wetting and drying cycles. However. with sterilized, tilled soil, only a steady decrease in the proportion of water stable aggregates was observed.

Natural water content fluctuations in the field after tillage gave an increase in water stability to a maximum after a few days followed by a steady decrease. The similarity of this result to that obtained in the laboratory for tilled. non‐sterilized soil indicates that micro‐organisms were probably contributing to the observed short‐term changes in the water stability of aggregates in the field.
A comparative study of three methods of water removal prior to resin impregnation of two soils
Authors: MURPHY C. P.
Published: July 2006

The water in replicate samples from sub‐surface horizons of a clayey and a fine‐silty soil was removed either by oven‐drying, freeze‐drying or by acetone‐replacement prior to resin impregnation. Pore space photograms (pores >60 μm diam.) from thin sections were analysed on a Quantimet 720 image analysing computer following each drying technique. During oven‐ and freeze‐drying the clayey soil contracted considerably and subsequently satisfactory impregnation of these samples was either difficult or impossible. This macro‐shrinkage caused a decrease in number and lengths of most planar pores and a decrease in size and number of all intra‐aggregate pores. The loss in pore space and continuity obviously affected resin impregnation. The clayey samples in which water was replaced by acetone, and all samples of the silty soil, however pretreated, showed no measurable macro‐shrinkage and all impregnated well. Oven‐drying the silty soil appears to increase the porosity, causing an increase in size of all pores. A mechanism for this apparent enlargement is proposed. It is evident that acetone‐replacement of the soil water prior to resin impregnation is the best of the three methods used here and should be seriously considered when image analysis is to be carried out on resin‐impregnated blocks from soils of similar or related textures.
Pyrite and siderite oxidation in swamp sediments
Authors: POSTMA DIEKE
Published: July 2006

Differences in the processes of pyrite and siderite oxidation, in reclaimed swamp sediments of the Skjernå delta (Denmark), are described from sediment chemistry, mineralogy and pore water chemistry.

Pyrite oxidation leads to extreme soil acidification, with pH dropping to about 2, the release of large amounts of weathering products to the pore water, and the precipitation ofiron oxides, jarosite and gypsum.

Siderite oxidation results only in moderate soil acidification where the pH does not drop below 3.5, while part of the acidification is due to the oxidation of small amounts of sulphur compounds together with siderite. The release of weathering products to the pore water is limited and only iron oxide is precipitated.

Calculations indicate that equilibrium with amorphous FeOOH, gypsum and amorphous Al(OH)3 sets an upper limit to the Fe3+, SO4 and Al concentrations in the pore water.
Gas diffusion through soil crumbs: the effects of wetting and swelling
Authors: CURRIE J. A.
Published: July 2006

Gas diffusion coefficients for hydrogen through air in packings of 1–2 mm crumbs from a clay loam (both under grass and under arable) and from a sandy loam were measured over a range of water contents as the soils were wetted. Diffusion coefficients decreased with increasing water content (decreasing air content) in three stages: in the first, to specific water contents of 0.08–0.10 gg1, decreases were small indicating the filling of pores less effective for diffusion; in the second, to crumb saturation, decreases were greater, and in the third, to complete saturation, decreases were greatest. Two of these stages are related to swelling: in the first, any slight swelling is contained within the crumb and there is loss to the gas of crumb pores only; in the second, the crumbs swell and there is simultaneous loss of crumb pore space and, more important, inter‐crumb space; in the third, swelling is complete, so, as in nonswelling soil, there is loss of inter‐crumb space only. Pore size and pore shape in the three soils, and pore distribution (intra‐crumb structure) in the grassland clay loam, may also affect diffusion but to a lesser extent: these influences are discussed. On subsequent drying there was little evidence of hysteresis in diffusion with water content, and only a slight indication in the arable clay loam of decreases due to structural degradation during the measurements.
A field study of effects of contrasting methods of cultivation on soil nitrate content during autumn, winter and spring
Authors: DOWDELL R. J. , CREES R. , CANNELL R. Q.
Published: July 2006

The nitrate content of three heavy clay soils (Evesham, Denchworth and Lawford series) was examined after direct drilling or ploughing, and of another clay soil (Denchworth series) with or without mole drainage and after tine cultivation. Autumn‐sown crops were grown at all these sites during the years 1973–80. Except in 1974–75, the nitrate concentration of the soil solution sampled from direct‐drilled plots was less than from the ploughed plots, particularly in late autumn and early winter. By January the plots which had been ploughed contained 12–65 kg N ha−1 more mineral nitrogen than direct‐drilled plots, but differences between cultivation treatments disappeared rapidly and had gone by early March. After tine cultivation, the nitrate content of the soil profile was not affected by the contrasting drainage status of the plots with or without mole drainage. These results support the view that although denitrification can be greater in direct‐drilled soil, the larger nitrate concentrations present in ploughed soil result from the soil disturbance exposing less accessible substrates to mineralization by microbes. By this means, considerable amounts of mineral nitrogen are made available at the beginning of the winter, during the establishment of autumn‐sown crops.
Water and oxygen regimes of four soil types at Newcastleton Forest, south Scotland
Authors: PYATT D. G. , SMITH K. A.
Published: July 2006

The water and oxygen status of four upland soils under Sitka spruce plantations was studied for 2 years. In a brown earth, waterlogging only occurred ephemerally in the subsoil and oxgen concentrations were generally high. In contrast, waterlogged and near‐anaerobic conditions persisted for much of the year in stagnogley and stagnohumic gley soils. In a peaty stagnopodzol moist conditions occurred above and below the thin ironpan, but while high oxygen concentrations generally persisted in the subsoil, low concentrations were common in the soil above. In the brown earth, healthy roots of Sitka spruce were present at a depth of 85 cm, but in the gley soils rooting was mainly limited to 25 cm and many roots were dead. In the peaty stagnopodzol, roots penetrated the ironpan and grew in the subsoil to 75 cm depth.
Fulvic acids: structure and metal binding. I. A random molecular model
Authors: MURRAY K. , LINDER P. W.
Published: July 2006

We have investigated a model of fulvic acid based on randomized positioning of functional groups and aromatic rings which can be used to deduce the types of metal chelating sites and provide statistical estimates of their concentrations. A FORTRAN program ‘RANDOM’ has been written which generates random molecules of fulvic acid. For each molecule generated the program also searches for and counts 14 types of binding site and calculates average concentrations over one thousand such molecules. A formula relating percentage aromatic carbon to the molar hydrogen/carbon ratio is also derived. The results show that the predominant bidentate sites are likely to be phthalate‐ and salicylate‐type sites with a significant proportion of aromatic carboxyl and phenolic hydroxyl not participating in chelating sites.
Diffusion coefficients of nitrate, chloride, sulphate and water in cracked and uncracked Chalk
Authors: HILL D.
Published: July 2006

The rates of diffusion of chloride, sulphate and water, labelled respectively with 36Cl, 35S and 3H, and unlabelled nitrate, were measured in small cylindrical Chalk monoliths. Using a simple mathematical model, diffusion coefficients were calculated to provide a basis for comparing the movement of these substances through Chalk rock in the absence of hydrostatic pressure gradients. The diffusion coefficients of chloride and nitrate were similar, with a range of values (0.52–3.23 × 10−6 cm2 s−1) and (0.53–3.20 × 10−6 cm2 s−1) respectively. These were slightly less than for tritiated water (0.60–3.51 × 10−6 cm2 s−1), while the coefficient for sulphate was about half that of the others (0.28–1.47 × 10−6 cm2 s−1). The coefficients indicate the absence of any interaction with the Chalk surfaces.
Gel permeation chromatography studies on the speciation of lead in solutions of heavily polluted soils
Authors: GREGSON SUSANK. , ALLOWAY B. J.
Published: July 2006

Samples of solutions from soils contaminated with lead as a result of three different processes: natural weathering and dispersion from an ore body, mining and smelting, and sewage sludge‐amendment to land, were fractionated on Sephadex gels. Solutions from the sludge‐amended soil, dried sludge and calcareous mine soils were found to contain a proportion of lead eluted at the exclusion limit of the gel, accompanied by a peak in U.V. absorbance, implying the occurrence of a high molecular weight organo‐lead complex. This fraction was proportionally highest in the solution from the dried sludge sample; however, low molecular weight organic peaks were also accompanied by elution of Pb in all samples except that from the low pH, naturally contaminated site. Association of Pb with organic matter was observed to be greater in samples of soil solution with a higher initial pH and this may be related to increased stability constants for Pb‐organo complexes at higher pH.
Highly weathered soils in the east coast hinterland of Southern Africa with thick, humus‐rich A1 horizons
Authors: MACVICAR C. N. , FITZPATRICK R. W. , SOBCZYK M. E.
Published: July 2006

Strongly weathered red and yellow soils with thick (490–900 mm) humic Al horizons (Haplohumox and Palchumults) derived from sandstones and basic igneous rocks, and occurring near the east coast of Southern Africa, are described and discussed in terms of their distribution, morphology, texture, mineralogy, chemistry, genesis and classification. The high organic matter content (2–5%C) of the Al contributes significantly to a high pH‐dependent negative charge, probably to poorer crystallinity of goethite and kaolinite and to the transformation of haematite to goethite. Varying proportions of kaolinite and gibbsite reflect different soil ages within these old landscapes. The yellow colour of aluminous goethite, the main pedogenic iron oxide, is masked in the Al by organic matter and in red B2 horizons by haematite. Temperature may have influenced the broad pattern of occurrence of red and yellow B2 horizons. These soils need not, as previously suggested, have developed from the weathering products of an ancient laterite. Neither Soil Taxonomy nor the South African soil classification system accommodates the soils entirely satisfactorily and possible improvements to the latter are discussed.
A lysimeter study of the fate of fertilizer nitrogen in spring barley crops grown on a shallow soil overlying Chalk: denitrification losses and the nitrogen balance
Authors: DOWDELL R. J. , WEBSTER C. P.
Published: July 2006

Four successive spring barley crops were grown in monoliths of a shallow soil overlying Chalk, contained in lysimeters. After harvest of the fourth crop, 25% of the nitrogen‐15 labelled fertilizer applied 4 years earlier was found remaining in the roots and soil. Of this, 73% was present in the upper 30cm of the profile. From the amounts of fertilizer derived nitrogen that remained at the beginning of each cropping season we estimate that 5–6% of the residual nitrogen‐15 turned over each year, representing a net release of 20% of the labelled nitrogen contained in the microbial biomass. Mineralization of the total biomass at the same fractional rate would release 120 kg N ha−1 a−1. This estimate is supported by the difference between input and outputs of total nitrogen during the experiment of 76–94 kg N ha−1 a−1 in fertilized lysimeters and 129kg N ha−1 a−1 in unfertilized control lysimeters. The total recovery of the applied labelled nitrogen was 81–87%. The nitrogen not accounted for was taken to be lost by denitrification of nitrate to dinitrogen, as no nitrous oxide emissions were detected during the experiment. Laboratory studies in aerobic and anaerobic conditions in presence of acetylene confirmed that 10–20% of the applied nitrogen‐15 could have been transformed to dinitrogen.
Modelling the effects of pH on phosphate sorption by soils
Authors: BARROW N. J.
Published: July 2006

Samples of six soils were incubated at 60°C for 24 h with several levels of either calcium carbonate or hydrochloric acid. Phosphate sorption was then measured on sub‐samples of the treated soils over 24 h at 25°C. In one set of measurements on all soils, 0.01 M calcium chloride was used as the background electrolyte. In another set, on two soils, 0.01 M sodium chloride was used. An interpolation method was used to give points on the three‐dimensional surface relating the final pH of the suspensions to sorption of phosphate at specified solution concentrations of phosphate.

The effects of pH on phosphate sorption differed between soils. For unfertilized soils, increases in pH up to about pH 5.5 decreased sorption. Further increases in pH decreased sorption further in one soil and increased it in three others. For fertilized soils, measured sorption increased with pH. When sodium chloride was used instead of calcium chloride, there was a more marked trend for sorption to decrease as pH increased.

Differences between the soils were ascribed to differences in two soil properties. One was the rate at which the electrostatic potential in the plane of adsorption decreased as pH increased. Only small differences in the rate of change of potential were needed to reproduce the observed differences between soils. The electrostatic potential would decrease more quickly in solutions of a sodium salt than in solutions of a calcium salt and this explains the observed differences between these media. The other soil property that affected observed sorption was the release of phosphate from the soil. The amount released was largest at low pH. Consequently, for fertilized soils, measured sorption increased with pH.
Proto‐imogolite and the process of podzol formation: a critical note
Authors: BUURMAN P. , VAN REEUWIJK L. P.
Published: July 2006

The 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

The 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

A 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

Clay 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

This 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

Two 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

In 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

Stability 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

The 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

Duplicate, 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

The 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

Measurements 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

A 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

Samples 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

The 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

The 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

The 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

Darrah 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

The 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.
Micromorphological and analytical studies of the fine matrix of an Australian humus iron podzol
Authors: MILNES A. R. , FARMER V. C.
Published: July 2006

Detailed micromorphological observations and associated electron probe microanalyses are used to examine the proposition that kaolinite and gibbsite in the B horizon of a humus iron podzol could arise by transformation of allophanic deposits. The B horizon of this podzol is highly complex. In the upper B horizon, this complexity is due to alternating episodes of the influx of organic matter and the deposition of allophanic material; evidence for the separate deposition of allophane and organic matter is presented. Material within the B horizon that has gibbsiporphyric fabric appears to have arisen by crystallization of gibbsite from aluminium‐rich gels deposited before the main influx of allophanic material; there is no convincing evidence that allophanic material has transformed to kaolinite or gibbsite.
Effect of timing of simulated rainfall on ammonia volatilization from urea, applied to soil of varyingmoisture content
Authors: BLACK A. S. , SHERLOCK R. R. , SMITH N. P.
Published: July 2006

Ammonia volatilization from granular urea applied at 10gNm−2 to pasture was investigated using an enclosure method. Misting 0, 4 or 16 mm of water on to the soil at field capacity within 3 h of urea application resulted in total NH3 losses of 2.81, 0.92 and 0.18 g N m−2 respectively. Further delaying the watering reduced this effect until at 48 h, volatilization was lowered from 3.33 to only 3.09gNm−2 with 16mm of water. Hydrolysis and NH3 loss were rapid. Similar trends occurred at a lower initial soil moisture content.

On air‐dry soil (0.06 g H2O/g soil), hydrolysis was slow (73 ± 14% of the urea remained after 30 days) and volatilization, while gradual, accounted for 33% of applied urea‐N after 30 days. Addition of 16 mm of water 48 and 96 h after urea application was followed by a period of rapid hydrolysis and volatilization, resulting in a total loss of 2.59 and 2.40gNm−2 respectively. Repeated addition of 2mm of water produced bursts of hydrolysis and NH3 loss until completion of hydrolysis when additional water had no effect. A total loss after 30 days of 3.94 g N m−2 occurred in this 2 mm treatment.
Size and charge characteristics of kaolinitic soils in SE Queensland
Authors: KOPPI A. J. , SKJEMSTAD J. O. , PAGE D. W. , COCKAYNE D. J. H.
Published: July 2006

Some kaolinitic soils derived from basaltic material contain 2:1 minerals as a discrete phase and/or interstratified with kaolin as determined by X‐ray diffraction (XRD) and by chemical analysis of DCB‐treated clays, while others show little or no evidence of 2:1 minerals. Mineral impurities were not detected by electron diffraction in the latter group. There is good agreement between the interpretation of XRD traces and the SiO2/Al2O3 ratio given by chemical analysis. Some kaolin is seen by electron microscopy to be of very small particle size, and two distinct morphological types have been recognized. High surface area measurements are consistent with fine particular size. These profiles contain kaolin with higher than normal CEC and permanent negative charges which cannot be accounted for by the presence of 2:1 clay minerals alone and which are attributed to a degree of isomorphous substitution. This substitution and/or mineral impurities may have limited kaolin crystal growth during neoformation.