bluuebunny/crossref_metadata_2025 huggingface dataset:
Components of variance involved in estimating soil water content and water content change using a neutron moisture meter
Authors: Sinclair DF , Williams J
Published: April 2005

In order to rationalize the allocation of resources in the estimation of soil water content using the neutron moisture meter, it is essential to have a thorough understanding of the sources and magnitudes of the variance components. An error analysis, taking into consideration current technology and methodology, identifies three components of total variance, attributable to: location error due to site heterogeneity with respect to soil water and random error associated with positioning the probe; calibration error; and instrument error. Data from three locations illustrate that the location variance is the major source of random error in the total variance of an individual estimate. For the total variance of the mean over a site containing n sample estimates, the large location component is reduced by a factor of n such that in many circumstances it will reduce to the same order as the calibration component which is independent of n. This is particularly true for field calibration. The instrument error and that error introduced by the use of count rate ratio are small and contribute in a very minor way to the total variance of the mean. The analysis reveals that the nature of the relationship between the magnitude of the location error and the calibration error is dependent on site heterogeneity, the value of n and the precision of the calibration equation.
Soil seals in tropical tall grass pastures of northern Australia
Authors: Mott J , Bridge BJ , Arndt W
Published: April 2005

Stable bare degraded areas exist in the lightly grazed perennial grass understorey existing in the eucalypt woodlands of northern Australia. Examination of these areas showed large differences in infiltration which led to increased runoff from the bare sites. However, there was little difference in soil composition between grass-covered and degraded sites apart from a higher organic carbon content in surface soil under grass. Micromorphological examination showed that soil without grass cover had lost its original open structure in the surface layers, developing a surface seal. The surface soil of the bare sealed area was shown to slake readily under quick wetting in contrast to soil surface under grass cover which did not slake. Heavy grazing of the grass understorey destroyed grass clumps within two wet seasons. Once the clumps were killed the soil surface quickly collapsed to form sealed areas, with the same properties as those occurring in ungrazed sites. The persistence of the bare sealed areas is attributed to seed removal during runoff, high temperatures and low moisture content in the sealed layer, as well as mechanical impedance preventing seedling emergence. As re-establishment of native grasses is difficult in this region, care must be taken in pastoral management to prevent the formation of degraded sites, which may take many years to re-vegetate.
The osmotic potential of soil water in plant/soil systems
Authors: Sands R , Reid CPP
Published: April 2005

Various techniques for measuring the osmotic potential of water in sand and loam at a range of soil water contents were examined. Results were inconsistent and variable when osmotic potential was derived by subtracting matric potential from total potential. Osmotic potential measurements on soil solution extruded at pressure through membranes were also unsatisfactory, probably due to salt sieving in the soil and/or at the membrane. Determining osmotic potential by linear dilution of an extract of 0.5 g g-1 soil solution can be criticized on several grounds, though the results presented for these soils seemed reasonable. The measurement of osmotic potential with in situ salinity sensors worked well in the loam but not in the sand. Measurements of the osmotic potential of displaced soil solutions were satisfactory for both soils. We concluded that the displacement technique was the most suitable for calibrating soil osmotic potential against soil water content, because it was simple, inexpensive in materials and time, and probably the least subject to error. The osmotic potential of soil dried by evaporation alone through a range of water contents was the same as that of soil dried by transpiration via lupins at two transpiration rates and via radiata pine. We concluded that the osmotic potential of the bulk soil in closed pots was independent of the activity of plants over the time scale of these experiments.
The prediction of water yield from a 5 ha experimental catchment, Krawarree, NSW
Authors: Aston AR , Dunin FX
Published: April 2005

A computer model called WATSIM was developed and used to predict the water yield of a 5 ha experimental catchment. The model is deterministic in describing the major hydrologic processes, has realistic input data requirements, and can treat the catchment as a series of cascaded hydrologic areas or as a single lumped entity. In both the cascaded and lumped modes of operation, the predicted monthly and annual yields agreed well with recorded data over a six year period, and accounted for approximately 98% of the monthly variation in yield.
Soils from Andesitic Tephra and their variability, Tongatapu, Kingdom of Tonga
Authors: Cowie JD
Published: April 2005

The taxonomic units proposed by Gibbs for the sequence of soils from andesitic tephra on Tongatapu have been redefined. The Lapaha series is defined as formed almost wholly from the older more weathered tephra, and the Vaini series as from moderately thick to thick younger tephra overlying the older tephra. Two new series are proposed-Fahefa series for soils from very thick deposits of the younger tephra, and Fatai series for soils with impeded drainage and evidence of gleying. Using the large number of profile observations that have been made on Tongatapu, percentage frequencies of the taxonomic units have been plotted for the mapping units shown on the original soil map of Gibbs, and on a revised map which is being prepared. These have shown that most of the mapping units are very variable and that some of them contain up to four taxonomic units. However, this present study has shown that predictions can be made for any one area on Tongatapu on the range of soils likely, the percentage frequency of occurrence of individual soils, and the dominant soil. Differences between most of the soils are due to variations in the thickness of the younger of the two contrasting tephras. The broad regional pattern of soils is related to the eastward thinning of the younger tephra. Superimposed on this regional pattern there is considerable variability related to local thinning and thickening of the younger tephra. This is partly related to present-day topography, which may have led to erosional redistribution of the younger tephra on sloping land and partly to some other factor unrelated to the present-day topography. This factor is probably related to irregularities in the underlying coral surface.
Water repellence of a heavy textured Western Australian surface soil
Authors: Mcghie DA , Posner AM
Published: April 2005

Water repellence is shown to be a property of the heavy (>20% clay) mallet hill soils found near Narrogin, W.A. The causes of the water repellence are examined, and the comminuted surface litter shown to be the major contributor. The water repellent soil could be made wettable by treatment with aqueous solvents, and water repellence could be restored by treating the wettable soil with non-polar solvents. A mechanism involving the coating of clay aggregates with hydrophobic litter to make the soil water repellent, and dispersion of the aggregates to make the soil wettable, is proposed. Spore-forming fungi do not cause water repellence and in some cases may reduce it. Water repellence is observed in artificial soil mixtures only when a litter component is present.
The effect of crop rotation on aggregation in a red-brown earth
Authors: Tisdall JM , Oades JM
Published: April 2005

Fifty years of crop rotations have decreased the stability of macroaggregates (> 250�m diameter) of Urrbrae fine sandy loam and simultaneously decreased the lengths of roots and hyphae and the percentage total organic matter in the soil. Regardless of the rotation, particles 50-250 �m diameter were very stable and were stabilized by organic matter. Practical implications of the results are discussed
A convective-dispersive-adsorptive flow model for solute transport in soils. I. Model description and some simulations
Authors: Murali V , Aylmore LAG
Published: April 2005

Solute transport predictions are usually based on mathematical (analytical and numerical) solutions of partial differential equations describing convective-dispersive-adsorptive flow and ion-soil interactions. In this paper computer simulations based on a numerical model of solute transport in soil columns have been used to illustrate the significance of flow dynamics and adsorption-desorption parameters in determining the shape and position of solute breakthrough curves. Approximating non-linear isotherms of the form S = KCM, where S is adsorption phase concentration, Cis solution phase concentration, and K and M are constants, by linear isotherms of the form S = KC + � where E is the intercept, to facilitate the use of analytical solutions. has been shown to result in significant errors when the retardation factor fails to account for the intercept � (when � is zero, the retardation factor equals 1 + �K/�, where � is the bulk density and � is water content). Using the dynamic form of Freundlich adsorption, the importance of non-linearity in the equilibrium isotherms is demonstrated. Computer simulations have also been used to demonstrate the extreme importance of intermittent flow, the simultaneous occurrence of adsorption dynamics, ionic fixation and hysteresis during instantaneous adsorption and desorption in determining the transport of solutes in soils.
The surface charge on manganese dioxides
Authors: McKenzie RM
Published: April 2005

Surface charge was measured on four synthetic manganese dioxides. Charge densities on two cryptomelanes followed closely the values predicted by a theoretical model. Charge densities on two birnessites were much higher, and did not fit the model.
Adsorption of pesticides by some Australian soils
Authors: Briggs GG
Published: April 2005

Adsorption of non-ionized organic chemicals from aqueous solution by 17 Australian soils was related to the organic matter content of the soils. The soil organic matter/water distribution (Kom) for each chemical was similar in all soils and could be predicted from the octanol/water distribution (Kow) of the chemical. The relationship between these two distributions, log Kom = 0.52log Kow, + 0.69, is similar to that reported for European and North American soils.
Comparative study of moisture release behaviour of soils, soil clays and pure clays
Authors: Datta B , Singh OP
Published: April 2005

The moisture release curves of a black cotton soil and a lateritic soil, their clay fractions and two pure clays (bentonite, kaolinite) containing mineral species similar to those in the clay fractions were studied in relation to clay mineral composition. While the dominant clay mineral did not solely govern the moisture characteristic curve of a soil, there was a strong similarity between the curves of a pure clay mineral and a soil clay dominated by that mineral. This similarity may be used to identify the dominant mineral constituent of an unknown soil clay.
Properties of clays and soils after acid treatment. II. Urrbrae fine sandy loam
Authors: Yeoh NS , Oades JM
Published: April 2005

Treatment of the soil with acids led to dissolution of aluminium which in the case of nitric acid remained in solution or as exchangeable aluminium. Thus the pH remained low, and the soils retained a positive charge for up to 40 weeks, resulting in flocculation of clay and some stabilization of aggregates with diameters >0.5mm. With phosphoric acid the dissolved aluminium was precipitated presumably as a complex phosphate which functioned as a cement within soil aggregates. The precipitation of the aluminium led to a more rapid rise in pH, compared with nitric acid treated soils. Negative charges in phosphoric acid treated soils were initially reduced, but within several weeks recovered to the same levels as in untreated soils; or even higher for a short period. The water-stable aggregation resulting particularly from the addition of phosphoric acid led to higher porosities and water-holding capacities, but lower bulk densities. The porous aggregates were mechanically weaker than those from untreated soils.
Changes in nitrogen and organic carbon of wheat growing soils after various periods of grazed lucerne, extended fallowing and continuous wheat
Authors: Holford ICR
Published: April 2005

Changes in total and mineral nitrogen and organic carbon were measured over a nine year period in two contrasting soils of northern New South Wales after various durations of grazed lucerne, extended fallowing and continuous wheat growing. At least 2 1/2 years of lucerne ley were required to raise the total soil nitrogen above the original level on both soil types. For each year of lucerne growth the average increase (above the control treatments) in total soil nitrogen (0-15 cm) was equivalent to about 140 kg nitrogen ha-1 in the black earth and about 110 kg nitrogen ha-1 in the red-brown earth. Significantly higher levels of soil nitrogen were maintained after the lucerne treatments throughout the 9 years of measurement on the black earth and for 5 years on the red-brown earth. Lucerne had a much larger effect on nitrogen than on organic carbon, which was significantly increased only in the black earth. There were very large increases in mineral nitrogen (0-15 cm) in the first year of measurement after lucerne. Levels remained greater than they were originally for the first 4 years, and they were greater for 7 years in the black earth and 4 years in the red-brown earth following lucerne than following continuous wheat or extended fallow. The decline in mineral nitrogen during wheat cropping after lucerne was greatly increased by excessive rainfall (574 mm or more) during the fallow. Leaching was greater in the red-brown earth than in the black earth, and this explained occasional differences in nitrogen uptake by wheat between the two soil types. Some evidence suggested that under moderately moist conditions nitrogen mineralization from lucerne-fixed nitrogen was greater in the red-brown earth than in the black earth but under drier conditions it was less.
Microanalytical evidence for short range clay coatings in weathered granodiorite
Authors: Koppi AJ
Published: April 2005

Thin sections of two soils formed in situ derived from granodiorite were examined by scanning electron microscope microprobe analyser to ascertain whether clay coatings in the weathered granodiorite are illuvial or whether they are a short range phenomenon. The clay in the clay coatings of the weathered rock was of markedly different composition from the clay in the soil above. It is concluded that clay was formed from the weathering minerals in the rock and deposited as short range clay coatings within the weathered rock.
Estimation of hydrodynamic dispersion in a fine sand using an approximate analytical solution
Authors: Watson KK , Jones MJ
Published: April 2005

The quasi-analytical approach to hydrodynamic dispersion during horizontal absorption under constant concentration conditions is discussed, and it is shown that the pore water velocity reaches a maximum at the � value where g(�) =0. The resulting small variations in pore water velocity that occur across the solute front and the relative constancy of water content in that region during absorption in a fine sand allow an approximate analytical solution for velocity-dependent hydrodynamic dispersion to be formulated. The equation is tested against computer-based numerical solutions for both horizontal absorption and vertical infiltration. The predictive quality of the approximate analytical solution is found to be very good for the systems examined.
Penetration of pea radicles into saturated soil cores related to organic matter amendments
Authors: Willoughby P , Willatt ST
Published: April 2005

The radicles of pea seedlings penetrated to different depths in saturated cores prepared from Goulburn Valley orchard soil according to the amount and type of organic matter added to the soil. Additions of ground straw and glucose restricted the penetration of the roots when grown for 4 days at constant temperature. Longer incubation times and higher incubation temperatures imposed on the cores before growing the seedlings further restricted the roots in the presence of added peat, straw or glucose. The restrictions to root penetration can be attributed to poor oxygen supply into the saturated soil matrix and to phytotoxins produced by the microbial decomposition of organic matter contained in the soil cores. The results suggest that structural units in an irrigated soil should not be larger than about 6 mm in diameter if roots are to fully exploit the soil volume.
A modification of Childs' field test for ferrous iron and ferric-organic complexes in soils.
Authors: Kennedy JA , Powell HKJ , White JM
Published: April 2005

A modification to Childs' field test for water-soluble and exchangeable ferrous iron in soils is described. To prevent redox decomposition of ferric-organic species, which is induced by the reagent �,�' -dipyridyl, a mixed NTA (nitrilotriacetic acid)-�,�-dipyridyl reagent at pH 7 is recommended.
The pedogenesis of desert loam soils in the Barrier Range, western New South Wales. I. Soil parent materials
Authors: Chartres C.J.
Published: April 2005

The particle-size distribution, silt (63-20 �m) mineralogy and micro-morphological properties of three desert loam soils developed over contrasting rock types are examined. The silt mineral assemblages in the soils contain more weatherable minerals and are more varied than those of the underlying rocks. Round to subround clayey pellets constitute the majority of the soil materials. Such pellets are probably aeolian in origin and are similar to clayey pellets originating in dried-out, saline lake beds elsewhere in southern Australia. The combination of aeolian silts and clays in the desert loam soils indicate that the soil parent materials are primarily transported aeolian deposits.
Soil morphology and distribution of iron and sulfur fractions in a coastal flood plain toposequence
Authors: Willett IR , Walker PH
Published: April 2005

A transect of soils across a toposequence on the coastal flood plain of the Shoalhaven River (N.S.W.) was described. The toposequence comprised a backswamp, toe of levee, and levee, and was underlain by a pyritic estuarine deposit. The development of an acid sulfate horizon along the toposequence was related to drainage as influenced by the topography. The backswamp profile had no acid sulfate horizon, whereas the soils of the toe of levee had well-developed acid sulfate horizons. The levee profiles had thin acid sulfate horizons. The distribution and form of the products of oxidation of the pyritic deposit were studied in profiles of each topographic unit by chemical fractionation of soil iron and sulfur. The levee soil showed marked redistribution of iron within its profile. Its acid sulfate horizon contained little jarosite, and its pH was higher than that found in the well-developed acid sulfate horizon of the toe of the levee soil. The latter horizon contained up to 24.3 m.e. sulfur/100 g as jarosite and had pH values near 3.9. The backswamp profile had little iron redistribution, and the estuarine sediment had been only partially oxidized. The distribution of various iron and sulfur fractions and soil pH, were discussed in relation to the oxidation of the pyritic sediment, migration of Fe2+, long term movements in the water table, hydrolysis of jarosite to free iron oxide under the influence of accreting alluvium, and periodic surface flooding.
Measuring saturated hydraulic conductivity and sorptivity using twin rings
Authors: Scotter DR , Clothier BE , Harper ER
Published: April 2005

A method of measuring, with minimal soil disturbance, the saturated hydraulic conductivity and sorptivity of field soil is presented and discussed. It involves measuring the steady-state infiltration of ponded water from two rings, of different radii, that have been lightly pressed into the soil surface. The method is based on Wooding's solution for steady infiltration from a shallow, circular pond. Criteria for selecting ring radii are discussed. Results for three field soils are found to give consistent values for the conductivity and sorptivity.
The influence of texture, structure and clay mineralogy on the soil moisture characteristic
Authors: Williams J , Prebble RE , Williams WT , Hignett CT
Published: April 2005

The relative importance of texture, structure, organic matter and clay mineralogy to the nature of the soil moisture characteristic is examined for an extensive group of Australian soils using numerical classification and diagnostic methods. The presence of pedality, particle size composition and grade of structure were the soil properties most consistently associated with differences between the groups of soils with similar moisture characteristics. By association, field texture was shown to be a useful property. Although the presence of pedality and grade of structure were important, the shape and size of ped had only weak associations with differences in the soil moisture retention. Montmorillonite, iron oxide, vermiculite and quartz were the minerals in the clay size fraction which appeared to be important if they were present. In contrast, the presence of illite did not show any strong associations with a particular position or form of the moisture characteristic. The soil moisture characteristic was successfully modelled as a power function. It appears that being able to group and classify the soil moisture characteristic and then to provide a description of these groups both in terms of soil properties and model parameters is a valuable means of developing simple predictive models for field soils. The error of our predictions for 44 horizons based on this simple approach appears to be only marginally larger than that encountered in conventional laboratory methods, and in view of soil heterogeneity it is argued that following further development these predictions may be adequate in many hydrological and agricultural applications.
Factors affecting the estimation of numbers of infective propagules of vesicular arbuscular mycorrhizal fungi by the most probable number method
Authors: Wilson JM , Trinick MJ
Published: April 2005

Factors affecting the estimation of the number of infective propagules of vesicular arbuscular mycorrhizal fungi by the most probable number (MPN) method were investigated. The value obtained was shown to be dependent on the conditions of the experiment. Both temperature and time of harvest changed the result because of their effects on the growth of both roots and propagules, and hence on their interception. Other factors which must be taken into account in order to optimize the MPN estimate are discussed. The number of infective propagules in a dried root/soil inoculum was shown to be affected by both the amount of infection in the pot culture from which it was formed and by its age.
Root distribution of Pinus radiata related to soil characteristics in five Tasmanian soils
Authors: Davis GR , Neilsen WA , Mcdavitt JG
Published: April 2005

Root distribution of Pinus radiata was studied on five diverse soils. Root concentration to 80 cm was most closely correlated with soil organic matter content. Considerable differences in the proportion of roots at different depths were found.
Soils of the cotter catchment area, A.C.T. : Distribution, chemical and physical properties
Authors: Talsma T
Published: April 2005

Studies on soil distribution and classification, together with their chemical and physical properties, were carried out in the Cotter Valley, a major water supply area for Canberra. Vegetative cover is mostly native eucalypt forest at high altitude and plantations of P. radiata at lower elevation; geology is diverse. Based on geologic diversity, five major soil associations were recognized, with significant differences in profile morphology, chemical and physical properties. Yellow earths occur on Silurian volcanic parent material; these soils are shallow and sandy, and calcium is the main exchangeable cation. They are moderately permeable but have low water retention. Gentler slopes on the same parent material are covered by red and yellow podzolic soils, with often dense A2 horizons. Exchangeable calcium is high in A horizons but in subsoils magnesium exceeds calcium. In the A2 and deeper horizons more than 30% of the exchangeable cations is aluminium. While red podzolics are reasonably permeable, yellow podzolics are not, and are likely to suffer surface waterlogging and are erosion prone. Profile water storage of these soils is good. Krasnozems and red earths are dominant soils on metamorphosed sediments. They are of clay loam to light clay texture and are largely base unsaturated, with aluminium the dominant exchangeable cation. These soils are permeable and have reasonable water retention, although krasnozems tend to be overdrained. The yellow podzolic soils on adamellite are coarse textured and have high bulk density. Calcium is the dominant exchangeable cation throughout the soil profile. These soils are reasonably permeable to 0.6 m depth, but water storage is low. The red and yellow earths found on granodiorite are not as dense as those on volcanic parent material, their clay content is higher, and soil profiles are deeper. About 30% of exchangeable cations is aluminium, and exchangeable potassium is rather high. These soils are moderately permeable and have reasonable water storage. All soils of the area are acid, with krasnozems and red earths being the most acid, and all have low CEC and thus low content of the metal cations. Their salt content is low, and exchangeable sodium and hydrogen are very low. The likely effects of forest management practices on these soils and on soilrelated catchment water quality aspects are discussed.
Numerical examination of a field classification of some red, yellow and grey earth profiles
Authors: Coventry RJ , Williams WT
Published: April 2005

Numerical methods have been used to examine an existing and accepted field classification of 48 profiles of red, yellow, and grey earths (mainly Alfisols) from central north Queensland. The three-dimensional soils data (sites by depths by descriptors, which may be mixed in type) were converted to a form which appeared to the computer as a two-dimensional set of profiles by attributes. The soils data were from independent depth intervals, and no assumptions were made about the inter-relationships among soil layers tvithin a profile; nor were the values of any of the soil attributes weighted. In order to consider shallow profiles on the same total depth basis as the deep profiles, the absence of a soil horizon or sampling interval at depth has been regarded as a positive attribute in the numerical classification. Comparison of the traditional field classification and a numerical classification of the same soils dataset showed that certain soil attributes played an important role in both classifications. The most striking difference between them was the relative importance of soil colour attributes, from which it might be argued that field pedologists have assigned to colour a weight out of proportion to its real importance in soil classification. However, this attribute carries additional information about the mineral constituents and hydrological regimes of the soils, and represents information known to, and used by, the field pedologist but not revealed to the computer. The essential subjectivity in the choice of attributes for soil classification is demonstrated.
Effect of climate on morphological features of soils from loess in the southern part of South Island, New Zealand
Authors: Bruce JG
Published: April 2005

Soils developed in thick loess deposits in subhumid and humid climatic zones in the southern part of the South Island, New Zealand, form a continuum in which the morphological features occur in sequential order. The sequence consists mainly of soils belonging to the Fragiochrept and Dystrochrept great groups. The climatic factor, particularly the moisture regime, is considered to be largely responsible for the differing morphological features. The principal morphological features are fragipans and stratigraphically equivalent horizons that are not 'fragic'; gammate colour patterns; and mottling and gleying above the fragipan. These features show an interrelationship that is explained by the progressive modification and destruction of the fragipan due to the impress of the moisture regime.
The nature of soil particles particularly those reacting with arsenate in a series of chemically treated samples
Authors: Fordham AW , Norrish K
Published: April 2005

Arsenate uptake by a surface sample of a lateritic podzol was controlled mainly by iron oxide particles in a very finely divided state of about 50 A in diameter. Despite their size, these particles had some crystalline characteristics - they had semi-regular appearance; had limited solubility in ammonium oxalate (in darkness) and in sodium pyrophosphate; and sometimes gave ring-type electron diffraction patterns identifiable as goethite. The particles contained a high degree of substitution of aluminium for iron. They associated with other soil components, for example, forming surface deposits upon larger kaolin flakes or else microaggregates with smaller ones. They reacted with soil organic matter, which caused marked inhibition of arsenate uptake. Titanium oxides competed with iron oxides for arsenate, and were able to dominate uptake when iron oxides were removed chemically. The behaviour of other components towards arsenate was described, together with their appearance, composition and stability during a series of successive chemical treatments. No iron-organic complexes nor poorly crystalline aluminosilicates appeared to be present. Some reputedly selective reagents extracted excess aluminium, most of it coming from chloritized vermiculite. Small kaolin particles were also dissolved and, in some cases,. this caused fresh precipitation of iron oxides from iron previously held within the clay lattice.
Copper and zinc species in the soil solution and the effects of soil pH
Authors: Jeffery JJ , Uren NC
Published: April 2005

A scheme to distinguish various species of trace metals in the soil solution has been used to study the forms of copper and zinc in the soil solution of a sandy loam that had been limed to give a range of soil pH values. The scheme is based on the lability of the metal species and involves the use of anodic stripping voltammetry, atomic absorption spectroscopy, and equilibration with Chelex-100 exchange resin. The solubility of zinc in this soil decreased markedly with increasing soil pH, with most of the zinc being present as free metal ions or as labile complexes. In contrast, copper species were largely moderately labile and non-labile and the solubility of copper varied only slightly with soil pH. The effects of enriching the soil with the metals and organic matter on the species present were also investigated.
Comparative study of the adsorption-desorption behaviour of copper(II), zinc(II), cobalt(II) and lead(II) at the goethite solution interface
Authors: Padmanabham M
Published: April 2005

The relative position of the adsorption curves for copper(II), zinc (II), cobalt(II) and lead(II) with respect to pH is shown to be related to the hydrolysability of the metal ion in solution. Thus the pH values at which the same molar amounts of these cations are adsorbed on the oxide surface are correlated with their respective first hydrolysis constants (pKt*) in solution. Such adsorption occurs well below the pKi* values, resulting in the release of one to two moles of protons per mole of cation specifically adsorbed. The relative effect of anions such as chloride and nitrate on the adsorption-desorption behaviour of zinc(II), cobalt(II) and lead(II) has also been investigated. Desorption trends for similar molar amounts of adsorbed cations, copper(II) zinc(II) and cobalt(II) are identical. The existence of two distinct types of adsorption sites on the oxide surface corresponding with the 'readily desorbed' and 'less readily desorbed' fractions of micronutrient cations such as copper, zinc or cobalt has been confirmed. The metal cation concentration and proton concentration play a dual role in determining the partition of heavy metal cations between the solution and surface phases. The position of the adsorption curve for lead(II) with respect to pH is close to that for copper(II), but desorption of copper(II) shows a considerable hysteresis, while lead(II) does not. Specifically adsorbed lead in the presence of either chloride or nitrate is reversible with respect to its concentration in solution with no hysteresis between adsorption and desorption isotherms. All the adsorbed lead is 'readily desorbable'.
The role of soil resistance in determining water uptake by plant root systems
Authors: Hulugalle NR , Willatt ST
Published: April 2005

Resistance to water flow in plant roots has been suggested as a significant factor limiting water uptake by plants. The results of previous experiments have been used to show that soil resistance may be more significant than has recently been suggested, particularly in soils of low hydraulic conductivity and where root density is low. As the technique used to determine soil resistance relies on hydraulic conductivity, the latter may be more appropriate as an indicator of water stress than soil water potential.
Movement of CaCl2 solutions in an unsaturated clay soil: the effect of solution concentration
Authors: Bond WJ , Gardiner BN , Smiles DE
Published: April 2005

The effect of solution salt concentration on the movement of calcium chloride during unsteady, unsaturated flow in a structurally stable, calcium-saturated, heavy clay soil is described. Solutions of CaCl, were supplied at a head of -10 mm of water to horizontal columns of soil containing solution with a different concentration of CaCl, at a low water content. The measured apparent solution concentrations near the inlet were less than the applied solution concentrations, and the identifiable salt front moved more rapidly than the 'piston-front' of the water. The magnitude of both effects was dependent on solution concentration. The observations are consistent with exclusion of anions from the diffuse double layer at the clay surface. The relationship between exclusion volume (or inaccessible water content) and solution concentration, obtained from the measurements, was affected by the interaction of double layers at low solution concentration and may also be affected by water content. An expression was derived which permits prediction of the position of the salt front from the properties of the initial and invading solutions.
Genesis and classification of a sequence of soils formed From aeolian parent materials in East Otago, New Zealand
Authors: Mcintosh PD
Published: April 2005

Eight soil types occurring between 60 and 480 m altitude on Waiora Research Farm, East Otago, New Zealand, are described. The soils are classified in the New Zealand Genetic and Soil Taxonomy classification systems respectively as yellow-grey earths (Fragiochrepts and Fra'giaquepts), yellow-brown earths and podzolized yellow-brown earths (Dystrochrepts), and a podzol (Placorthod). The soils form a development sequence related primarily to altitude, demonstrated chemically by greater leaching of the higher altitude soils and morphologically by the presence of a fragipan in the drier soils at lower altitude and an iron pan in the soils at higher altitude. Fragipans of yellow-grey earths at higher altitudes are modified by the effect of perched water. In the yellow-brown earths, podzolized yellow-brown earths and podzols firm subsoils with gammate colour patterns are found in some profiles and are regarded as relict features of fragipans formed under a previously drier climate. Planar fractures in lower B and upper C horizons, subparallel to the present soil surface, are attributed to breaks of loess deposition due to intermittent colder conditions. Relationships between soils are better demonstrated by the New Zealand Genetic Classification, because of lack of differentiae related to leaching or phosphorus sorption properties at subgroup or family level in the USDA classification.
The effect of gypsum on cation exchange in two red duplex soils
Authors: Greene RSB , Ford GW
Published: April 2005

Gypsum at rates of up to 15 t ha-1 was applied to the surface 10 cm of two red duplex soils in northern Victoria. At both sites, approximately five years after application, the following changes in soil properties were established: 1. Only when 15 t ha-1 of gypsum was applied was exchangeable sodium in the upper 25 cm significantly decreased. 2. Exchangeable magnesium was not decreased at depths greater than 15 cm. After five years only the 15 t ha-1 treatments still contained some undissolved gypsum in the A horizon. Of the gypsum that had dissolved, 53% had been involved in exchange. This represented an efficiency of exchange of 26-34%, based on the ratio of sodium replaced to calcium dissolved. At both sites over this five-year period, the mean solubility of gypsum from the 15 t ha-1 treatment was 120-130 mm of rainfall per t of gypsum.
Using bulk density to calculate soil water changes in soils with shrinkage cracks
Authors: Ross PJ
Published: April 2005

Apparent bulk �a measured between shrinkage cracks is used to assess vertical shrinkage on the assumption that soil cores shrink isotropically from a fully swollen reference bulk density pr. A fully swollen depth increment �X corresponds to an increment �x = (�t/�a)1/3 �X at any other water content, field bulk density (which includes cracks) is given by and the fractional area of shrinkage cracks is 1 - (�t/�a) 2/3. When gravimetric water contents are known, volumetric water contents can be calculated in terms of the fully swollen reference depth scale and changes in water contents of soil layers obtained. The procedure applies to any soil, from rigid through to one which undergoes normal shrinkage, provided the above assumption is satisfied. A BASIC program to perform the calculations is given.
The chemical composition and ionic strength of soil solutions from New Zealand topsoils
Authors: Edmeades DC , Wheeler DM , Clinton OE
Published: April 2005

In preliminary experiments a centrifuge method for extracting soil solutions was examined. Neither the time nor speed of centrifuging had any effect on the concentrations of cations in soil solution. The concentration of cations increased with decreasing soil moisture content, and NO3, Ca, Mg, and Na concentrations increased with increasing time of storage of freshly collected moist soils. It was concluded that to obtain soil solutions, which accurately reflect the soil solution composition and ionic strength (I) in situ, requires that soil samples are extracted immediately (<24 h) following sampling from the field. Prior equilibration of soil samples, to adjust soil moisture contents, is therefore not valid. The effect of time of sampling and soil type, and the effects of fertilizer and lime applications, on soil solution composition and ionic strength, were measured on freshly collected field moist topsoils. Concentrations of Ca, Mg, K, Na, NH, and NO, were lowest in the winter and highest in the summer. Consequently, there was a marked seasonal variation in ionic strength which ranged from 0.003 to 0.016 mol L-1 (mean, 0.005 s.d. 0.003) over time and soil type. Withholding fertilizer (P, K, S, Ca) for two years had only a minor effect on ionic composition and strength, and liming increased solution Ca, Mg and HCO3, but decreased Al, resulting in a twofold increase in ionic strength. These results suggest that the ionic strength of temperate grassland topsoils in New Zealand lie within the range 0.003-0.016 and are typically 0.005.
The reductive dissolution of phosphated ferrihydrite and strengite
Authors: Willett IR
Published: April 2005

The reduction of ferrihydrite, HFe5O8.4H2O, at three levels of phosphate saturation of its surface, and of strengite, FePO4.2H2O, was studied in flooded sand-straw mixtures. At equal redox levels, the overall effect of adding phosphate to ferrihydrite was to decrease its solubility, even when the solutions were supersaturated with respect to vivianite, Fe,(PO4),.8H2O. It was concluded that the addition of phosphate at levels less than the sorption capacity to reduced systems containing ferrihydrite will result in its sorption, and an increase in the stability of the oxide, rather than an increase in the dissolution of the oxide caused by vivianite formation. The reductive dissolution of strengite was congruent for the first 11 days of flooding, then phosphate accumulated in excess of Fe2+, probably because of vivianite precipitation. Strengite reduction occurred at levels of Eh and pH readily obtained in waterlogged soils. Strengite was always less soluble than phosphated ferrihydrite.
Influence of some environmental factors on indigenous earthworms in the northern jarrah forest of Western Australia
Authors: Abbott I
Published: April 2005

Indigenous species of earthworms (Family Megascolecidae) are widely distributed throughout the northern jarrah forest of Western Australia. They occur not at random, but in an aggregated pattern well described by a negative binomial. Earthworms are only active in the topsoil (to depth of 5.5 cm) when soil moisture (gravimetric) exceeds 4%. This occurs from May until November. The number of species occurring in jarrah forest at any place, and the frequency of occurrence, biomass and density of earthworms, vary with average annual rainfall. In the zone of highest rainfall six or seven species occur together, frequency of occurrence is 40-60%, and total biomass and total density do not exceed 8 g m-2 and 40 m-2 respectively, and generally average much less. In the lowest rainfall zone only one or two species occur in any one locality, with total density much less than 10 m-2. Multiple regression analyses between four earthworm variables and 20 site and soil characteristics were highly successful in that up to three predictor variables yielded coefficients of determination exceeding 0.70. The most useful predictor variables were rainfall zone, forest basal area, soil pH and proportion of silt and clay in the topsoil (to depth of 15 cm). Recurrent low intensity (spring) fires and a single moderate intensity fire (summer) have minor direct and indirect effects on earthworms. Logging also has scant effect on their frequency of occurrence. The land use most adverse to earthworms is the clearing of forest for mining of bauxite or gravel. The effect on earthworms of clearing of forest and subsequent reforestation with pines varies: in one case there was an adverse effect, whereas in two others there was no difference.
Estimates of soil solution ionic strength and the determination of pH in West Australian soils
Authors: Dolling PJ , Ritchie GSP
Published: April 2005

The average ionic strength of 20 West Australian soils was found to be 0.0048. The effects of three electrolytes (deionized water, CaCl2 and KNO3), three ionic strengths (0.03, 0.005 and soil ionic strength at field capacity, Is) and two soil liquid ratios (1:5 and 1:10) on the pH of 15 soils were investigated. pH measurements in solutions of ionic strength 0.005 differed the least from measurements made at Is. The differences that occurred in comparisons with distilled water or CaCl2 of ionic strength 0.03 (0.01 M) were much greater (20.4 pH units). An extractant with an ionic strength of 0.005 may provide a more realistic measure of pH in the field than distilled water or 0.01 M CaCl2 for West Australian soils.
Field relationships of ferricretes and weathered zones in southern South Australia: a contribution to 'laterite' studies in Australia
Authors: Milnes AR , Bourman RP , Northcote KH
Published: April 2005

Terrestrial landscapes have existed in parts of southern South Australia since the Carboniferous to Permian Gondwanaland glaciation. Widespread weathered zones and ferricrete horizons and crusts on present highland surfaces in the region have been ascribed by various workers to Mesozoic or early Tertiary weathering phases. A critical examination of field relationships, however, points instead to complex reworking and continuous weathering of relic landscapes since early Mesozoic times, leading to the intricate patterns of sediments and soils forming the present regolith. Ferricrete crusts sporadically distributed on the highland surfaces are interpreted dominantly as remnants of iron-impregnated sediments of ancient valleys or depressions. The great but variable thickness of kaolinized bedrock beneath the highland surfaces, regarded by other workers as the mottled and pallid zones of a 'laterite' profile, is the integrated product of leaching and weathering throughout the Mesozoic and Cainozoic and cannot be assigned to separate and distinct climatic events. The use of weathered landsurfaces and ferricretes as morphostratigraphic markers in such landscapes is questionable.
Estimation of salt storage in the deep lateritic soils of the darling plateau, Western Australia
Authors: Tsykin EN , Slessar GC
Published: April 2005

The salt content of soils in the principal bauxitic area of the Darling Plateau is broadly known from drilling. Soil salinities averaged over 15 km2 grid blocks bear a strong statistical relationship to a number of easily measured parameters, including distance from the Darling Scarp, mean annual rainfall and drainage density. We have used a nonlinear regression equation (r=0.96) to prepare maps showing soil salinity isopleths estimated with two levels of reliability. Similar regression equations have been used to estimate average soil salt contents over selected depth intervals. These regression equations and maps provide a useful means of estimating average soil salinities in areas where no drilling data are available.
The effect of soil strength on germination and emergence of wheat (Triticum aestivum L.). I. Low shear strength conditions
Authors: Collis-George N , Yoganathan P
Published: April 2005

Experimental studies of the germination and emergence of wheat as affected by soil shear strength are reported. A fine sand under saturated conditions was used as the seed bed and the shear strength of the seed bed was increased to 10 kPa (0.1 bar) by externally applied loads. From the results it is concluded that the initial soil shear strength in this range has little effect on germination. However, coleoptile growth and root elongation are markedly reduced in the range 0-2.2 kPa such that total emergence is reduced to 7% at 9.3 kPa in this fine sand. The results clearly show that coleoptile elongation is more affected than root elongation by the same mechanical stress. Roots are found to be thicker and coleoptile thinner under increasing soil shear strength conditions.