bluuebunny/crossref_metadata_2025 huggingface dataset:
A convective-dispersive-adsorptive flow model for solute transport in soils. II. Evaluation of single and two-component adsorption models for phosphate movement in soils
Authors: Aylmore LAG , Murali V
Published: April 2005

Comparisons have been made between experimental breakthrough curves for phosphate ions in soil columns and computer simulations of solute transport based on a number of different adsorption models. These include single component linear and non-linear, instantaneous and dynamic adsorption models; as well as the model incorporating a combination of instantaneous and time-dependent components suggested in Part I. While certain portions of the complete breakthrough curves for phosphate could be reasonably approximated using simple one-component models, these generally failed badly to describe the shape and position of the experimental data over the complete range of the breakthrough curve. This was even more evident when both adsorption and desorption phases were considered. On the other hand, the model described in Part I combining instantaneous linear and a simultaneous time-dependent (dynamic) Freundlich-type adsorption components provided a good simulation of the experimental data over the full range of the breakthrough curves for both adsorption and desorption phases. Of particular significance is the ability of the model to handle successive experimental breakthrough curves with different amounts of residual adsorption. A method for 'normalizing' the solute transport equations to facilitate computer simulations is presented.
Describing the adsorption of copper, zinc and lead on a variable charge mineral surface
Authors: Barrow NJ , Bowden JW , Posner AM , Quirk JP
Published: April 2005

The ability of a model to describe quantitatively the adsorption of copper, lead and zinc on goethite was tested. The model was able to describe both the increase in adsorption of metals with increasing pH and the release of protons that accompanied adsorption. For copper and zinc, MeOH+ were the adsorbing species. Part of the increase in adsorption with increasing pH arose because these ions increase in concentration with pH. For lead, Pb2+ ions appeared to be adsorbed, and in this case the increase in adsorption with pH was entirely due to the decreased charge on the surface and thus decreased repulsion. For all three metals, the MeCl+ ions also appeared to be adsorbed, and this explained higher adsorption from chloride solution than from nitrate solutions. The observed release of protons accompanying adsorption was matched by moving the plane of adsorption of metal ions relative to that of the H+ and OH- ions. When the two planes were close, the proton release was almost equivalent to the charge on the metal ions; as the distance increased, proton release decreased.
A comparison of the Langmuir, Freundlich and Temkin equations to describe phosphate adsorption properties of soils
Authors: Mead JA
Published: April 2005

Four adsorption equations were fitted to phosphate isotherm data for 38 soils from northern New South Wales. The two-surface Langmuir equation provided the best fit to the data. The Freundlich equation, however, was almost as effective, provided that an estimate of native adsorbed phosphate was included. It required fewer adsorption points because the transformed data produced a straight line. A regression constant, a, from the Freundlich equation although underestimating adsorption capacity, calculated from the Langmuir II equation, was highly correlated with this parameter (r = 0.984) and a buffering index (r = 0.986), calculated from the Langmuir I equation. The other Freundlich regression constant, n, was significantly correlated (P <1%) with the intensive parameters of adsorption from the one- and two-surface Langmuir equations. Since only two adsorption points are required for fitting the Freundlich equation and the parameters are easier to derive, it is suggested that this equation may be more suitable for commercial soil-testing laboratories than the Langmuir one- and two-surface equations for routine determination of phosphate adsorption characteristics of soils.
The influence of soil nitrogen status and previous crop on nitrogen fixation (acetylene reduction) in Barrel Medic, Medicago truncatula Gaertn
Authors: Alston AM , Graham RD
Published: April 2005

Barrel medic (Medicago truncatula Gaertn.) was grown in a glasshouse in pots containing solonized brown soils with total nitrogen contents ranging from 1.2 to 2.7 g kg-1. The dry weight and nitrogen content of the plants were determined on three occasions, and the acetylene reduction technique was used to estimate the rate of nitrogen fixation. All soils had been subjected to rotations of cereal and annual pasture, but half were sampled following pasture, while the others were collected after cereal. Both groups of soils had similar ranges of total nitrogen content, but the pasture soils contained higher concentrations of mineral nitrogen at the time of sowing the experiment and produced more mineral nitrogen on incubation. Correlations among these three indices of nitrogen status were exceedingly low for such a collection of similar soils, and only mineral plus mineralizable nitrogen correlated reasonably well with nitrogen uptake by wheat plants grown on the soils for 9 weeks. Medic on the pasture soils generally had higher dry weights and contained more nitrogen than plants on soils which were cropped with cereal, but rates of acetylene reduction were lower. These differences, which diminished as the season progressed, were closely related to the mineral nitrogen but not the total nitrogen content of the soils. Thus, the rate of accretion of nitrogen in the soils from nitrogen fixation, as estimated in this study, was independent of the existing soil total nitrogen content but was decreased by soil mineral nitrogen when the latter was high. The results have implications for the maintenance of the nitrogen status of soils under cereal-pasture rotations.
A note on the methods for determining soil water diffusivity
Authors: Acharya HS
Published: April 2005

In experimental methods for determination of soil water diffusivity using the water distribution from horizontal infiltration into a soil column, hand smoothing of the experimentally obtained distribution introduces uncertainties in the calculations. A method of calculation involving techniques of quadratic programming has been used to minimize the possible errors caused by inhomogeneous packing of the horizontal soil columns. Examples are given to illustrate the method of calculations.
Swelling of a clay soil profile under ponding
Authors: McIntyre DS , Watson CL , Loveday J
Published: April 2005

The total vertical swelling under long-term ponding, of two apparently identical soil profiles, into one of which gypsum had been incorporated, is described. The effect of gypsum per se was minor, and reduced swelling only near the surface. Its indirect effect was to allow more water entry, which in turn increased the swelling of deeper soil. Total and incremental swelling to a depth of 2.10 m, and water absorption, are analysed in terms of models of swelling and shrinking. Except for the interval 0.25-0.55 m in the untreated profile, swelling was not normal, the water absorbed being somewhat greater than themeasured swelling. It is concluded that, particularly in the profile with gypsum, macropores contained an appreciable amount of water which did not contribute to swelling; others have called this structural water, and the macropores, structural pores. The likely types of macropore, as described in micromorphology, are indicated.
Field studies of water and salt movement in an irrigated swelling clay soil. I. Infiltration during ponding
Authors: McIntyre DS , Loveday J , Watson CL
Published: April 2005

Infiltration and deep percolation were measured during ponding of a saline sodic cracking clay soil, commonly used for rice production in the Riverina of New South Wales. Because gypsum may be used to ameliorate this soil for row cropping, the effect of incorporating gypsum into the plough layer was determined. Without gypsum, 292mm water infiltrated in 379 days of ponding, wetting the profile to approximately 2.1 m. In contrast when gypsum was incorporated in the plough layer, 605 mm of water infiltrated in 145 days, and water had penetrated beyond 4.5 m in 57 days. In the latter case, sufficient water percolated below 2.0m to raise the groundwater level by as much as 10m. The infiltration rate for the unameliorated soil was similar to values determined by others; for the ameliorated soil, infiltration behaviour was more like that of non-sodic self-mulching grey or brown clays, and raises questions regarding the amount of deep percolation when rice is grown on such soils.
Field studies of water and salt movement in an irrigated swelling clay soil. II. Profile hydrology during ponding
Authors: McIntyre DS , Loveday J , Watson CL
Published: April 2005

Two plots on a saline sodic cracking clay soil, to one of which gypsum was applied at 10 t/ha, were instrumented to 4.5 m from a pit, in order to observe wetting patterns during extended inundation. On the gypsum-treated plot the wetting front was diffuse. Water content increased simultaneously within quite large depth intervals, and two distinct wetting phases were detected to a depth of 2.7 m. The change in water potential with time showed the same pattern. Once steady-state flow had been reached, tensiometer-pressure potentials were positive except between 0.55 and 1.50 m. In contrast, the untreated soil exhibited a better defined wetting front which moved slowly down the profile. Only in the upper 0.55 m were two distinct wetting phases discernible; tensiometer-pressure potentials were generally lower than for the gypsum-treated soil, and remained negative throughout the ponding period except at 0.25 m. This behaviour, and the estimated values of hydraulic conductivity, suggest that, in the ameliorated soil, water penetrated and moved through the profile mainly in macropores associated with structure, and that, in the unameliorated soil, such flow was largely prevented by a region of low hydraulic conductivity between 0.25 and 0.55 m.
Field studies of water and salt movement in an irrigated swelling clay soil. III. Salt movement during ponding
Authors: McIntyre DS , Loveday J , Watson CL
Published: April 2005

The effect of gypsum, incorporated into the plough layer of a saline, sodic, clay profile, on the leaching of salt, was determined from both in situ measurements, and from chloride determinations using samples taken before and after ponding. Observed differences in leaching patterns are attributed to water in the treated profile moving through interpedal macropores as well as through micropores within the peds (or matrix), but only through micropores in the untreated profile. The efficiency of the two mechanisms is discussed.
Hydrous iron oxide minerals with short range order deposited in a spring/stream system, Tongariro National Park, New Zealand
Authors: Childs CW , Downes CJ , Wells N
Published: April 2005

An iron-rich deposit occurs on the bed of the Waiuku Stream and one of its tributaries, on Mt Ruapehu, New Zealand. The upper limit of the deposit is a spring which vents in the bed of the tributary. Isotope ratios, 18O/16O, D/H, and 13C/12C, indicate that the spring water is largely meteoric in origin, from a catchment at higher altitude, and that the dissolved carbon dioxide has a volcanic source. Dissolved solids appear to be derived from acid attack on andesite. Ferrous iron (30 g m-3) in the spring water is oxidized on reaching the surface, at a rate which can be accounted for abiotically, forming the ochrous deposit. The major components of the deposit are Fe (40-50%), Si (5-10%), H2O(+) (11-13%), and H2O(-) (14-23%), and surface areas of samples lie in the range 120-240 m2 g-I. Electron micrographs show globular aggregates of indistinct, approximately spherical, particles with diameters about 5-10 nm. This information, together with X-ray diffractograms, i.r. and differential thermal analysis patterns indicate that the deposit is a hydrous iron oxide (more correctly, oxyhydroxide) with short range order. Most of the samples have characteristics close to those of material presently known as protoferrihydrite, though one is closer to ferrihydrite. The deposit readily adsorbs silica and phosphate from the stream water.
Phosphorus availability in soils subjected to short periods of flooding and drying
Authors: Willett IR
Published: April 2005

The effects of flooding and drying on the availability of original soil phosphorus, phosphorus added before flooding and phosphorus added after drying were studied. In four soils high in organic carbon and reducible iron, 2 or more days of flooding (at 25�C) caused the immobilization of phosphorus added after drying. Four or more days of flooding caused immobilization of original soil phosphorus. Phosphorus applied before the flooding period was immobilized to a greater degree than phosphorus applied after drying in a soil rich in organic carbon and reducible iron. In a soil low in these, phosphorus applied before flooding was immobilized, but phosphorus applied after drying was not. Changes in soil extractable iron and phosphorus, and in phosphorus sorption index, caused by flooding and drying, were consistent with immobilization of phosphorus added after flooding by a surface reaction, and the immobilization of phosphorus present during flooding by occlusion of phosphorus with iron(III) hydrous oxide, or by formation of iron(III) phosphate.
Loss-on-ignition and the carbon contents of Australian soils
Authors: Spain AV , Probert ME , Isbell RF , John RD
Published: April 2005

Regression relationships between high temperature loss-on-ignition and organic carbon values are presented for data from a range of Australian soils. Inclusion of the clay content markedly improves the proportion of variance explained by the regressions. It is shown that soils differ in their regressions of organic carbon on loss-on-ignition. Loss-on-ignition is concluded to be a useful index of soil organic matter status closely related to organic carbon levels.
Measurement and simulation of evaporation from a red earth. I. Measurement in a glasshouse using a neutron moisture meter
Authors: Johns GG
Published: April 2005

The evaporation of water from, and redistribution of water within, intact monoliths (23.6 cm diameter, 60 cm depth) of red earth were studied in a glasshouse under a wide range of evaporative conditions. A neutron moisture meter was appropriately calibrated and used to document changes in the distribution of soil water. This is a novel use for such equipment. Strongly curved and generally different calibrations were required for each depth. Prolonged exposure to highly evaporative environments resulted in the removal from the profile of 90% of water available at matric potentials of between -0.01 and -1.5 MPa within 3 months. Bare soil evaporation was not controlled solely by soil hydraulic parameters as the profile dried, but was influenced by evaporative demand throughout the drying cycle. Only two stages of evaporation were discerned. The first stage, when evaporation from the soil surface was similar to free water evaporation, was virtually non-existent under highly evaporative conditions. The second stage was characterized by a continuous exponential decrease in evaporation. By the end of the drying cycles, evaporation was still decreasing exponentially, with a half-life averaging 34 days. Empirical predictive relationships for the dependence of evaporation on soil water parameters in the surface 10 cm, and evaporativity, were established. These relationships are tested in the following paper.
A torsional shear box for determining the shear strength of agricultural soils
Authors: Lloyd JE , Collis-George N
Published: April 2005

A hand-held torsional shear box, suitable for direct measurements of the in situ soil strength (�o) under field conditions and for laboratory determinations of shear strength parameters, is described. A field procedure is given, and the errors in the method are discussed. Under field conditions, it is simple to operate and requires a single measurement to determine �o. Field studies indicate that it is suitable for a wide range of soil conditions which occur in agricultural soils. Results are presented, which show that both moisture status and structure influence the value of �o, as well as the nature of the failure plane. Agricultural soils have a number of characteristics which make it difficult to design methods for determining soil strength parameters or to interpret empirical estimates of soil strength. Chief amongst these are: (1) marked changes in most soil physical properties with depth; (2) a polymodal distribution of pore sizes. Because the measurement is on a surface which is nearly horizontal and is of an area to allow for all forms of failure, the described torsional shear box largely overcomes these problems, and provides a value of �o which is physically interpretable and relevant to studies concerned with soil failure.
Nitrate movement in sandy soil under varying water and fertilizer management
Authors: Gupta SK , Chaudhary TN , Pandey RN
Published: April 2005

The field evaluation and prediction of nitrate-nitrogen movement are given for varying rates of irrigation and urea application to wheat growing on a sandy soil. Nitrate leaching increased and depth to peak concentration moved deeper with heavier irrigation. Larger splits of nitrogen in combination with light irrigation reduced the leaching loss, permitting greater utilization of nitrogen by plants. Under heavier irrigation, the amount of residual nitrogen increased with the number of nitrogen splits. A simple analytical solution has been presented for predicting the movement of surface applied solutes. The solution can be used for predicting nitrate leaching losses. The applicability of the expression in determining depth to peak concentration is established under a variety of situations.
Macropores and hydraulic conductivity in a swelling soil.
Authors: McIntyre DS , Sleeman JR
Published: April 2005

The volume of macropores filled with water in a near-saturated swelling clay soil has been measured and related to the hydraulic conductivity. To measure the macropore volume, it has been assumed that only water absorbed by the soil matrix (or peds) contributes to swelling, that this swelling is 'normal', and hence the volume of water held in macropores (termed 'structural' or interpedal water) does not contribute to swelling. This volume of water is thus estimated from the difference between water absorption by the soil and the normal swelling, provided that previous drying had not reached the shrinkage limit. The hydraulic conductivity was measured and found to be exponentially related to the volume of structural water, at least for a degree of saturation greater than 0.90. The relative proportions of the three types of macropore - planes, channels and vughs - were evaluated from thin sections. The profile depth interval for which hydraulic conductivity was found to be greatest, coincides with the depth at which channels and interconnected vughs show maxima.
Capillary rise from saline groundwater in clay soil cores
Authors: McIntyre DS
Published: April 2005

The rate of salinization by capillary rise from a saline water table in wet clay soil cores, 0.60, 0.75 and 0.90 m long, and 0.25 m in diameter, is described. Tensiometer-pressure potential and electrical conductivity were measured as a function of time at vertical spacings of 0.15 m. Initially a relatively rapid rise of saline water occurred to a height of 0.30 m above the water table, but subsequent movement was very slow. Although the potential evaporation rate was only 1.0 mm/day, drying of the surface occurred quickly, and proceeded down the cores, reducing the upward moisture flux to a very low value. The salinization hazard of such a soil is low, but the possibility of application of the measurement to more permeable soils, in which salinization may be more likely, is discussed.
Effect of dispersible clay on the physical properties of the B horizon of a red-brown earth
Authors: Shanmuganathan RT , Oades JM
Published: April 2005

Three methods were compared for the determination of dispersible clay in the absence of chemical treatments. Treatment of the B horizon of a red-brown earth with a range of amounts (0-0.24% iron) of iron poly[Fe(III)-OH] cations of nominal molecular weight 10 000 to 50 000 allowed production of a range of dispersible clay contents from 0 to 70%. The samples of clay B horizon with decreasing contents of dispersible clay showed decreasing electrophoretic mobilities with zero mobility when the content of dispersible clay was zero. In such samples the clay particles were present in aggregates 50-250 mu m diameter according to sedimentation techniques. The amounts of dispersible clay present appeared to control various physical and mechanical properties of the soil such as swelling, porosity and water retention capacity, hydraulic conductivity, friability and modulus of rupture. It is suggested that the content of dispersible clay may be a useful quantitative characteristic of soils as it controls many other properties.
Effect of the method of dispersion on the yield of clay and fine clay
Authors: Chittleborough DJ
Published: April 2005

Because the relative proportion of fine (< 0.2 �m) and coarse clay (2-0.2 �m) is considered an important pedogenetic and taxonomic criterion, the effect on yield of these fractions by different methods of dispersion was investigated for a sandy loam and a clay from the Urrbrae loam. Both soils showed a continued increase in fine clay with time of shaking even after 14 h. This may be a subplasticity effect or due to attrition of coarse clay. Electron micrographs showed that incrustations on coarse clay particles may be a source of fine clay. The amount of total clay from the sandy loam soil continued to rise after 14 h of shaking, but yield from the clay soil was constant after 100 s. Of the chemical treatments only sodium hydroxide had a significant effect. This treatment lead to a marked decrease in the proportion of fine clay. The amount of total and fine clay was unaffected by the 1iquid:solid ratio in the dispersing medium.
Developments in the approach to soil studies in Australia
Authors: Butler BE
Published: April 2005

The author reviews the basic features of soil studies in Australia from 1927 through to the present time. From the beginning the Russian soil system of the late nineteenth century was adopted and expounded. This system adopts the morphological profile as the basic soil entity. This profile is a dynamic system in equilibrium with its environment and with its associated chemical, physical and agronomic attributes. Its association with many attributes makes morphology an ideal basis for soil classification and for soil mapping; however, the adopted procedures for sampling, and for the analyses of attributes, and for the association of attributes within class populations, are so cursory as to make these claims quite indefensible. Neither can it be claimed that because the soil classes are 'natural' that these are less in need of comprehensive sampling and analyses. The need at present is for the development of a new approach based on efficient sampling and analyses of associations within classes
Aluminium substitution in goethites in soils from alluvium, Gippsland, Victoria
Authors: Little IP , Gilkes RJ
Published: April 2005

The nature of the iron oxides associated with a chronosequence of soils on silty sediments in Gippsland was investigated. The soils range from 5 000 to approximately 763 000 years in age. Iron is present in the unaltered sediments, as represented by the younger soils, mainly as hematite. As the soils develop, this is replaced by goethite, which becomes more aluminous with increasing age. Thus there is continuing pedogenic development throughout the time scale investigated. In the A and B horizons of the older soils, small, coarse-sand sized hematite or maghemite concretions develop in the clay B horizons, and remain as a constituent of the light-textured A horizons as these develop through loss of the clay component of the soil by eluviation and lateral transport.
Field rainfall simulator studies on two clay soils of the Darling Downs, Queensland. II. Aggregate Breakdpwn, sediment properties and soil erodibility
Authors: Loch RJ , Donnollan TE
Published: April 2005

Size distributions of the solids in runoff water were measured for two clay soils subjected to simulated rain under a range of plot lengths and two tillage orientations. Selective transport did not appear to have affected the sediment size distributions. Therefore, these could be used as a measure of soil structure and aggregate breakdown by rainfall and runoff. There was little dispersed clay, most of the sediment remaining aggregated. For each soil, sediment size distributions were bimodal, peaks in sediment size being related to orders of aggregation in each soil. Concentrations of dispersed clay provide evidence that stresses on aggregates moved by rain impact on flowing water were greater than on those moved in rills by flowing water alone. Consistent with this, sediment size distributions showed much less breakdown to sizes <0.125 mm in rills. Suspended load (sediment < 20 �m) showed little temporal fluctuation, and little or no decrease with time, suggesting that for these soils, aggregate disruption by raindrops and overland flow provides a continuous source of suspendable material. Bed-load was more variable and saltating and contact load appeared to be complementary to some extent. Large differences between the two soils in measured sediment concentrations could not be explained by slight differences in sediment size. However, large differences between the soils in the water content and density of saturated aggregates were found. Transport equations for bed-load sediment suggest that the measured difference in aggregate density is sufficient to explain the difference between the soils in rates of sediment transport.
Black and white waters and their possible relationship to the podzolization process
Authors: Reeve R , Fergus IF
Published: April 2005

Highly coloured, organic-stained water (black water) occurs as springs, seeps and perched lakes in the Cooloola area of south-eastern Queensland (latitude 26� S.). Springs of clear, colourless water (white water) sometimes occur in close proximity to the black water. Field evidence suggests that black waters move laterally along semipermeable B horizons of humus podzols, whereas white waters are part of a much larger storage system in which the water has been decolorized by contact with the C horizons. Thus it appears that black waters are the active eluviating agent and white waters are the residual liquid phase of the podzolization process. Chemical analyses of black and white waters, and the results of a laboratory leaching experiment, support this view. Possible mechanisms and some implications for the genesis of podzol B horizons are discussed.
Effects of sample handling on some chemical properties of soils from high rainfall coastal north Queensland
Authors: Gillman GP , Murtha GG
Published: April 2005

The effects of drying, storing in an air-dry condition, and collecting samples at different times of the year, on cation exchange properties and phosphate sorption characteristics have been examined for two soils from coastal north Queensland. The properties measured are independent of sampling time, but both air-drying and storage reduced the capacity of these soils to sorb phosphorus.
Further examination of the use of the equivalent salt solutions method for predicting hydraulic conductivity of soils for different salt solutions
Authors: Jayawardane NS
Published: April 2005

Hydraulic conductivities of Pachappa and Waukena soils for different salt solutions, predicted by the equivalent salt solution methods, showed satisfactory agreement with measured values. The values of equivalent salt solutions for these soils were calculated from macroscopic swelling values of extracted clays. The equivalent salt solution method and the simplified domain model method of McNeal predicted equally accurately, the changes in hydraulic conductivities of Pachappa soil in salt solutions with sodium absorption ratio values from 15 to 100.
Reactions of copper with soil affecting its availability to plants. II. Effect of soil pH, soil sterilization and organic matter on the availability of applied copper
Authors: Brennan RF , Robson AD , Gartrell JW
Published: April 2005

Incubation of copper with warm, moist soils reduced its effectiveness for uptake by wheat plants when compared to copper freshly applied. On two soils (Gingin, Dongara), the relative effectiveness of incubated compared to freshly applied copper was lower at higher pH. On the third soil (Lancelin) relative effectiveness was unaffected by changing soil pH from 6.7 to 7.8. Soil sterilization before incubation increased the effectiveness of incubated copper compared with that freshly applied on two soil types (Lancelin, Dongara), while on the other soil (Newdegate) soil sterilization did not affect relative effectiveness. The addition of cereal straw decreased the effectiveness of copper both freshly applied and when incubated with the soil. The effect of cereal straw was more marked where the copper was incubated with the soil, suggesting that organic matter is strongly involved in reducing the effectiveness of incubated copper compared with that freshly applied. The same reactions which reduce the availability of freshly applied copper appear to continue to decrease the availability of copper throughout incubation.
Polyphase moisture transfer as influenced by potential and thermal gradients in a vertisol
Authors: Magar SS , Kar S
Published: April 2005

Water content changes and soil water flux profiles as influenced by temperature gradients at soil depth intervals for 60 days in a packed laboratory column containing a vertisol were measured and compared with predicted values. The rate of increase of isothermal vapour diffusivity with decrease in water was faster than for thermal vapour diffusivity at relatively low moisture content (<0.30 cm3 cm-3), and the observed thermal vapour diffusivity values in dry soil (0.24 cm3cm-3) were about 10 times greater than those in wet soil. The measured high water flux (0.42 cm day-') was concomitant with the increased liquid diffusivity. Water flux decreased sharply at all depths initially, but after about 24 days it decreased gradually with time. The curve of cumulative evaporation versus square root of time in days exhibited a linear relationship up to 13th day.
Pedological significance of the gravels in some red and grey earths of central north Queensland
Authors: Coventry RJ , Taylor RM , Fitzpatrick RW
Published: April 2005

Red, yellow and grey earths consist largely of quartz, kaolin, and iron oxides and hydroxides, but little is known of the pedological processes that have resulted in their formation. Iron oxides and hydroxides, however, vary markedly according to their soil environments and can be used to study pedogenetic pathways in soil profiles. A detailed mineralogical examination has been made of two soils representing the red and grey end-members of the red-yellow-grey earth soil continuum in the semiarid tropical Torrens Creek area, 200-300 km southwest of Townsville, in central north Queensland. The profiles selected (a Plinthustalf and Haplargid of Soil Taxonomy) have high contents of ferruginous gravels in the solum, and are underlain by mottled, weathered sandstone. Four corresponding layers were sampled from each soil profile. Washed gravels from these samples were sieved into four size classes, and were sorted by hand into morphological groups, and into magnetic and nonmagnetic fractions. Subsamples of the resultant groups of gravels (>2 mm), of the fine earth ( < 2 mm), and of the whole soil, were analysed by X-ray diffraction. Quartz, kaolin, goethite and hematite were found in various proportions in the 205 analysed samples, but maghemite was restricted to the magnetic materials; few other minerals were detected. The mineralogical composition of each morphological group of gravels was found to be independent of the particle-size of the materials in the group. The iron oxide mineralogy of the soils suggests that the red, yellow and grey earths developed under different soil water regimes: free drainage and high organic matter oxidation rates in the red earths yielded hematite, with its strong red-pigmenting capacity, and goethite; profile saturation for relatively short periods of time has resulted in the formation of goethite, characteristic of the yellow earths and of the ferruginous gravels of the grey earths; and saturation of the grey earth profiles for lengthy periods has led to the loss of iron from the soil, which has then assumed the grey colour of the minerals (quartz and kaolin) comprising its matrix. These mineralogical interpretations are supported by field observations of contrasting hydrological regimes in the soils.
Movement of solids in air and water by raindrop impact. effects of drop-size and water-depth variations
Authors: Moss AJ , Green P
Published: April 2005

Transportation of 200 pm sand grains by impacting raindrops in both air and water was experimentally investigated through the water depth range 0-75 mm, employing four drop sizes. Airsplash movement, greatest for large drops impacting bare sand, fell rapidly with decreasing dropsize and increasing water depth. Shallow surface water inhibited airsplash strongly, yields falling by large factors through the depth range 0-2 mm. Hence, airsplashing of solids, even if randomly directed from any one point, must produce net migration from bare to water-covered surfaces. Drops over about 1.5 mm in diameter disrupt on impacting water at terminal velocity, generating disturbances which can, if water is shallow, suspend soil particles. Smaller drops evidently penetrate water surfaces without disruption, disturbing soil particles more directly and efficiently. If target water flows, even very slowly on low slopes, net downstream particle migration (rain-flow transportation) results. Rain-flow transportation rates rose from zero at zero depth to near-maximum values at 2 mm. Actual maxima were reached at depths of 2-3 drop diameters, transport rates declining rapidly with further depth increases. The combination of airsplash and rain-flow transportation extends transportation to areas where overland flow is either absent or too weak, acting alone, to move solids significantly.
Chemical and charge characteristics of kaolinitic soils of south-east Queensland
Authors: Skjemstad JO , Koppi AJ
Published: April 2005

Cation exchange capacity at field pH and net negative charge at pH 8.5 of 39 kaolinitic soils were studied in relation to surface area and other soil characteristics. All soils exhibited an anion exchange capacity at field pH, but this was very low compared with cation exchange capacity. Little evidence could be found for the presence of amorphous aluminium or silica, or short-range order alumino-silicates on the basis of acid oxalate-extraction, in contrast to Tiron extraction. All samples had significant permanent negative charge as deduced using the method of Gillman and Uehara, in addition to pHdependent charge. The former was strongly related to the exchangeable divalent cations, and this may explain the great variation in base saturation observed. Most of the charge in these soils is derived from the small poorly crystalline kaolins, although at high pH oxalate-extractable iron contributes significantly to the negative charge. Based on the results for those soils containing less than 5% iron oxide, surface area determined by ethylene glycol is linearly related to the net negative charge at pH 8.5. The average surface charge density on the soils containing <5% hematite and goethite measured at this pH value is 0.9 nm2/charge. Hematite and goethite show much lower negative charge densities and effectively dilute the active surface.
Modification of soil physical properties by addition of calcium compounds
Authors: Shanmuganathan RT , Oades JM
Published: April 2005

In a soil to which gypsum, calcium carbonate or cement was added, the content of dispersible clay was related to both exchangeable sodium percentage (ESP) and electrical conductivity (EC). The electrolyte concentration in the soil which could be maintained by addition of calcium carbonate was such that an ESP of >3 was required to maintain clay coagulation. Small amounts of gypsum (0.2% w/w) coagulated most of the clay by lowering the ESP and raising the electrolyte concentration. However, the clay gradually dispersed as the soil was subjected to wetting and drying cycles and the electrolyte concentration was decreased. The most efficient use of gypsum would appear to be as small annual additions. The addition of cement resulted in the stabilization of particles 250-2000 �m diameter, i.e. cementation as opposed to coagulation. Both processes resulted in changes to various physical properties and mechanical properties of the soil. It is suggested that both coagulation and cementation in a soil may be achieved by the addition of gypsum and cement or lime, with significant improvements of soil structure. In soils with gypsum added the germination and total yield of dry matter of wheat were improved significantly, but the opposite trend was recorded for soils treated with cement.
Influence of sorbed phosphate on the stability of ferric hydrous oxide under controlled pH and Eh conditions
Authors: Willett IR , Cunningham RB
Published: April 2005

The reduction of ferric hydrous oxide at three levels of phosphate saturation of its surface was studied in a chemical system at various controlled combinations of pH and Eh. Hydrogen in the presence of a catalyst was used as the reductant. Without added phosphate the reduction of the oxide, as measured by the release of Fe2+ into solution, occurred at pH levels between 4.0 and 7.0. The Eh, value at which reduction started ranged from 0.2 V at pH 4.0 to -0.1 V at pH 7.0. The addition of phosphate markedly inhibited reduction of the oxide. At each pH, the Eh required to cause reduction was lower after the addition of phosphate to the surface of the oxide than when no phosphate was added. With added phosphate, no reduction occurred at pH 7.0, even at Eh -0.3 V. The release of phosphate from the surface of the oxide was significant only at pH 4.0 and below Eh -0.2 V. It was shown that pH had a greater effect on the distribution of phosphate between the solution and the oxide than Eh. The significance of the results to the behaviour of phosphate in waterlogged soils is discussed.
Effects of lime on phosphate sorption characteristics, and exchangeable and soluble phosphate in fifteen acid soils
Authors: Holford ICR
Published: April 2005

Fifteen acid soils (pH <5.2 in 0.02 M KCl) from eight Great Soil Groups were used to examine the effects of lime on exchangeable and soluble phosphate in relation to changes in soil phosphate sorptivity, affinity and sorption capacity. Soils varied widely in their reactions to liming, which raised the pH to as high as 7.0 in a sandy solodized soil but only to 4.85 in a yellow earth. Liming to a pH of about 4.8 decreased sorptivity and sorption capacity in four soils whose initial pH was <4.5. Higher sorptivity in these unlimed soils was attributed to precipitation by soluble aluminium. Liming to pH values of about 4.8 to 5.8 minimized soluble aluminium, but increased sorption and greatly increased sorptivity and affinity in most soils. As the pH rose above 5.8 sorptivity and affinity decreased, while sorption capacity remained constant or increased. The results suggested that in most soils sorption was dominated by adsorption, but in a sandy solodized soil liming appeared to change the dominant sorption process from precipitation to adsorption. Soluble phosphate was increased by liming in most soils, but these increases were often inconsistent, with small or negative increases in exchangeable and extractable phosphate and large increases in sorptivity. These results suggest that phosphate solubility in some acid soils is controlled more by the dissolution of iron and aluminium phosphates than by the desorption of exchangeable phosphate.
An overview of silicification in Cainozoic landscapes of arid central and southern Australia
Authors: Milnes AR , Twidale CR
Published: April 2005

Silica diagenesis in the near-surface zones of subdued Tertiary drainage basins in the arid interior of central and southern Australia produced a mosaic of silcretes now exposed as relic duricrust on mesas that are significantly higher than the contemporary base-level of erosion. The silcretes comprise a variety of silica-cemented sediments and possibly soils that exhibit a range of textures and chemical compositions. Acid-weathering conditions in pedogenic environments near the margins of the Tertiary drainage basins are likely to have provided soluble silica for soil waters and groundwater moving slowly through the regolith into depositional zones in the lower reaches of the basins. The silica cement in silcretes ranges from ordered forms of opal to quartz overgrowths, and the existence of incomplete transformations between structural states and between textural forms suggests heterogeneous precipitation and recrystallization in response to local fluctuations in properties such as pH and moisture regime. High concentrations of titanium were precipitated from solution in bedrock fractures as well as in sediments in the piedmont of the ancient drainage basins, but as yet there is no unequivocal explanation for its occurrence. Apart from zircon, enrichment of zirconium and aluminium in areas of high titanium concentration is evident from electron probe microanalyses and X-ray scanning images, but the mineral phase or phases responsible for this distribution are unidentified.
Iron oxide minerals in soils of the Ha'apai group, Kingdom of Tonga
Authors: Childs CW , Wilson AD
Published: April 2005

The iron oxide mineralogy of three soils from the Ha'apai Group (c. latitude 19�50�S., longitude 174�30' W.), Kingdom of Tonga, has been investigated. The Group consists mainly of an archipelago of low coral atolls. Soils are formed in the andesitic tephra which overlie the coral. Accessions of marine salts are high and give rise to high soil pH values (>7) and high concentrations of exchangeable cations. The soils are dark reddish brown to reddish brown in colour, with limited colour differentiation with soil depth, and they are not hqdromorphic. The results of study of whole soils and size fractions by chemical extraction, X-ray diffraction, differential thermal analysis, Moessbauer spectroscopy, and by measurement of variation of magnetic attraction following heating to various temperatures, lead to the following conclusions: iron oxide minerals comprise 7-12% by weight of the soils; the predominant clay size iron oxide is very poorly crystalline aluminium-substituted lepidocrocite (�-Fe 0.8Al 0.2,OOH); ferrihydrite is probably also present in the clay fraction; lepidocrocite and ferrihydrite together account for 50-60% of the total iron in the soils studied; magnetite, probably partially oxidized towards maghemite, is present, particularly in sand and silt fractions, and accounts for about 10% of the total iron in the soils. The remainder of the total iron occurs in unweathered minerals in the silt and sand fractions and in the structure of halloysite in the clay fraction. The common soil iron oxides, goethite and hematite, have not been detected. Although the occurrence of lepidocrocite is usually linked with hydromorphic soil conditions, this report, along with others, suggest that it is also found under non-hydromorphic conditions.
Structural units in humic acids from south-eastern Queensland soils as determined by 13nmr spectroscopy
Authors: Skjemstad JO , Frost RL , Barron PF
Published: April 2005

Solution 13C Fourier transform nuclear magnetic resonance (FTNMR) spectra of six humic acids extracted from a range of soil types and a solid state, cross polarization/magic angle spinning (CP/ MAS) 13C NMR spectrum of a lignin are reported. Quantifying specific regions of the spectra reveals the presence of alkyl, carbohydrate, aromatic and carboxyl carbons. Alkyl carbon is in general the major contributor to these spectra, averaging 38% of the total carbon. Long-chain units comprise a significant proportion of this group, although highly branched systems are also in evidence in two samples. Carbohydrate carbon is a major contributor in two samples, representing 27% and 28% of the total carbon nuclei measured. Aromatic carbon content shows the greatest variability, ranging from 10 to 45%. Humic acids from soils developed under rainforest show the lowest aromaticity, and it is suggested that aromatic structures are not integral building blocks of terrestrial humic acids. Little evidence was found for the presence of hydroxy- and methoxy-substituted aromatic carbons even in humic acids high in aromaticity.
Accumulation of copper, lead and arsenic in some Australian orchard soils
Authors: Merry RH , Tiller KG , Alston AM
Published: April 2005

A survey was made of copper, lead and arsenic in 98 surface soils from orchards in South Australia and Tasmania and the distribution of these elements in six representative soil profiles was studied. Copper, lead and arsenic have accumulated in the soils due to the use of sprays. Concentrations were found which were 25-35 times greater than background values. Investigation of the profiles indicated that copper and lead have been strongly retained in the upper parts of the profiles, but arsenic can be lost. Possible mechanisms for loss of arsenic are discussed. Copper and lead extracted by DTPA and EDTA were highly correlated with 'total' concentrations determined on aqua regia digests. No relationships were evident between the concentrations of copper, lead and arsenic in former orchard soils and the concentrations in ryegrass and white clover.
Decomposition of plant material in Australian soils. I. The effect of quantity added on decomposition and on residual microbial biomass
Authors: Ladd JN , Jackson RB , Amato M , Butler JHA
Published: April 2005

14C and 15N-labelled legume (Medicago littoralis) material was added in amounts ranging from 23.0 to 92.1 kg nitrogen ha-1 to a calcareous, sandy-loam topsoil and allowed to decompose under field conditions for up to four years. Characteristic curves for decomposition were obtained; residual organic 14C accounted for about 65% and 18% of input after four weeks and four years respectively. About one-half of the 15N in the added plant material remained in organic residues after four years. However, the amounts of residual organic 14C and 15N were only approximately proportional to the amounts originally added. The proportions of plant material 14C and 15N mineralized calculated from recovery data differed significantly with the amount of substrate added; the greater the amount of plant material added, the more extensive its decomposition. Carbonate in soil became labelled during plant residue decomposition. Levels of carbonate 14C were low, however, and were directly related to the total residual 14C levels, whether in soils sampled four weeks or four years after substrate addition. Carbonate 14C accounted for only 1.1% of total residual 14C. Biomass 14C and 15N in soil decreased significantly with time within a 2-4 year decomposition period, the percentage decrease being greater than for 14C and 15N in the corresponding non-biomass organic pool. Further, the proportions of substrate 14C and 15N retained as biomass 14C and 15N in soils decreased significantly with increasing amounts of added substrate. From a consideration of the turnover of biomass C and N during plant residue decomposition in soils, we concluded that stabilization of extracellular substrates and metabolites alone does not account for the greater percentage retention of organic residues when lower amounts of substrate are added, but that factors leading to the accumulation of higher proportions of substrate carbon and nitrogen in microbial biomass are important.