bluuebunny/crossref_metadata_2025 huggingface dataset:
Movement of peak solute concentration position by leaching in a non-sorbing soil
Authors: Rose CW , Hogarth WL , Dayananda PWA
Published: April 2005

A simple mathematical model based on mass conservation is derived and tested which allows prediction of the displacement of the solute peak concentration position in soil from a knowledge of water inputs and losses. Comparison of the model with two different sets of field leaching data for chloride and nitrate indicates that its predictions are accurate within c. 10% provided two major assumptions in the theory are satisfied. These are: (i) that there is no significant soil-solute interaction or chemical transformation; (ii) that drainage through the soil profile to field capacity takes place. Making these assumptions and also neglecting dispersion, an alternative derivation is given to that in the literature showing that the velocity of the position (depth �) of the concentration peak is equal to the pore water velocity at �. This equality is integrated, showing that the finite displacement �� in a is equal to the equivalent ponded depth of water which has been displaced beyond the previous position of a divided by the volumetric water content at field capacity. The effect of dispersion on prediction of peak concentration position was investigated analytically. Neglect of dispersion in the model leads to an overestimation of peak displacement, this error being c. 10% in an illustrative example, decreasing in magnitude as dispersivity increases. It is concluded that the simple theory presented may be of special utility in guiding nitrate management in situations of high potential leaching loss. In situations where predictions of the model are inaccurate because assumption (i) is not satisfied, consequent management decisions are conservative rather than dangerous in the sense of inducing an irretrievable situation.
Analysis of salinity profiles in lateritic soils of south-western Australia
Authors: Watson JD
Published: April 2005

Salinity profiles in deeply weathered lateritic soils of south-western Australia frequently exhibit very high concentrations in the unsaturated zone above a less saline water table. A one-dimensional steady-state model using the simultaneous mass balance equations for water and solute is used to predict salt profiles which are compared with those observed. The model assumes input of salt in rainfall and water uptake by plants. Model parameters imply magnitudes of transpiration, water flux rates and possible mechanisms for water movement to the saturated zone. Some salt profiles cannot be accounted for with the steady-state model. In some cases there appears to be an injection of low salinity water at depth which could occur by movement through preferred pathways from the soil surface. In other cases the probable explanation is that the profiles are accumulating salts under the present hydrologic regime.
Shrinkage characteristics of soil clods from a grey clay under intensive cultivation
Authors: Chan KY
Published: April 2005

Structural degradation in a grey clay under intensive cropping was investigated by studying the shrinkage characteristics of soil clods collected from the field. Soil clods with different cropping histories differed in the amount of structural shrinkage relative to normal shrinkage. Soil clods (c. 50 cm3) from the irrigated site were found to have a smaller degree of structural shrinkage than those from the dryland wheat site, resulting in higher bulk density and lower air-filled porosity. The 'degraded' soil clods remained almost saturated with water over the available moisture range.
An electromagnetic induction technique for reconnaissance surveys of soil salinity hazards
Authors: Williams BG , Baker GC
Published: April 2005

An assessment has been made of an electromagnetic induction (EM) technique for reconnaissance surveys of soil salinity. The instrument used provides values of apparent electrical conductivity to depths ranging from 7.5 to 60 m. A comparison of EM values with actual profile salinities at 19 sites of widely differing geological and geomorphic origin showed that approximately 65% of the variance of EM values is explained in terms of salinity alone. An area of 10000 km2 in the mid-Lachlan River Valley of New South Wales was surveyed with a grid spacing of approximately 5 km at a rate of 30-40 sites per day. This permitted the definition of areas of high subsoil apparent conductivity and hence, by inference, of high soil salinity. The EM technique was demonstrated to have a potential for providing a significant contribution to land use planning at both a regional and local scale, by defining areas of possible salinity hazard.
Root distribution and water uptake by irrigated soybeans on a duplex soil
Authors: Willatt ST , Olsson KA
Published: April 2005

Water uptake by plants is described in relation to the root system configuration for an irrigated soybean crop on a duplex soil in northern Victoria. Measurements are described for three irrigation cycles as the crop grew to maximum ground cover and advanced physiological development. Few roots penetrated below 0.7 m, and the total root length beneath unit area of ground surface was lower than soybean root systems measured elsewhere. Water uptake patterns reflected this as uptake took place mainly from the depth interval 0.15-0.5 m. 'Crop water use' decreased below maximum values, even though water was placed in the profile at potentials higher than c. -90 kPa. In this situation, it is suggested that low root numbers at depth and low hydraulic conductivity in the subsoil were limiting water uptake. Practical consequences for irrigation management of soybeans are discussed.
Dispersion of calcium clay
Authors: Rengasamy P
Published: April 2005

The dispersion of samples of calcium-saturated soil clay, calcium illite, and calcium bentonite was compared with the dispersion of sodium clays. Each clay was first freed of electrolytes, one sample of each being dialysed with water and a second washed with ethanol. All samples were then dried at 105�C. The dialysed calcium clays did not disperse in water even after a week, but dispersed spontaneously when immersed in water immediately after they had been remoulded. The calcium clays that had been washed in ethanol dispersed spontaneously in water to the same extent as dialysed sodium clays. After the samples were equilibrated at a fixed relative humidity, the water uptake in ethanol-washed calcium clays was twice that of corresponding dialysed calcium clays but similar to the dialysed sodium clays. A mechanism of hydrogen bonding in dry calcium clay is proposed which includes exchangeable calcium, water molecules, and the exposed oxygens of the clay layers. The replacement of water molecules in the bond by ethanol weakens the bond and leads to swelling and dispersion of the clay.
The influence of organic matter extracted from humified clover on the properties of amorphous aluminosilicates. III. Potassium-magnesium exchange selectivity
Authors: Perrott KW
Published: April 2005

Potassium-magnesium cation exchange selectivity measurements were made on a series of synthetic and amorphous aluminosilicates, allophanic soil clays and hydrous alumina after treatment with aqueous extracts of humified clover. The results were compared with those obtained from similar measurements on samples treated with only the inorganic components of the humified clover extract. For the soil clays and the aluminosilicates of intermediate composition organic treatment increased the preference for Mg2+. With the siliceous aluminosilicates, however, the effect of organic treatment on Mg2+ preference at acid pH values was limited because of specific interaction of K+ with these samples. This occurred despite the large increase in surface negative charge which would be expected to favour the divalent cation. In the case of the siliceous aluminosilicates organic treatment was found to decrease the preference for Mg2+ at neutral and alkaline pH values. This is attributed to the removal of aluminium-hydroxy material providing sites for the specific adsorption of Mg2+. While hydrous alumina specifically adsorbs Mg2+ at neutral and alkaline pH values, it does not adsorb K+. However, the organic matter adsorbed by hydrous alumina during organic treatment provides sites for the electrostatic adsorption of K+ as well as Mg2+.
Measurement and simulation of evaporation from a red earth. II. Simulation using different evaporation functions
Authors: Johns GG
Published: April 2005

The performance of several alternative evaporation functions for simulating water loss from a bare red earth was assessed by including them in a computer model which was used to simulate evaporation both from red earth monoliths in a glasshouse, and from a study site in the field. The coefficients in the different evaporation functions were also optimized to minimize the root mean square discrepancy (RMSD) between simulated and observed soil water contents. RMSD values for the alternative evaporation functions before optimization of coefficients ranged from 3.2 to 7.0 mm for the glasshouse data and from 4.0 to 6.6 mm for the field data. Optimization reduced these values 3.0 to 6.4 mm (glasshouse) and 3.9 to 6.1 mm (field). The sensitivity of the model to errors in hydraulic conductivity estimates was assessed. Overestimating hydraulic conductivity by 2 and 10 times increased predicted cumulative evaporation by 8 and 28% respectively. Underestimating conductivity by the same factors produced similar reductions in predicted cumulative evaporation. The model was used to test the effect of basing the simulation of field evaporation on different thicknesses of surface compartment, for two alternative evaporation functions. Optimum thicknesses of surface compartment were 20 and 30 cm, and increasing these thicknesses to 60 cm resulted in only c. 20% increase in RMSD. This effect was considerably less than the increase caused by using inferior alternate types of evaporation function.
Leaching patterns in soil under pasture and crop
Authors: Kanchanasut P , Scotter DR
Published: April 2005

The distribution of surface-applied bromide, after leaching with 50 mm of ponded water, was measured in soil profiles under long-term pasture and under an oat crop. Also measured was the bromide distribution under pasture after leaching with natural rainfall. The method of water application, the vegetative cover, and the soil structure interacted to produce quite different leaching patterns. However, in all experiments the highest bromide concentrations after leaching were in the top 20 mm of soil. It is suggested that the vegetation, by inducing preferential flow pathways, retarded the leaching of bromide from the soil near the surface. Also rainfall on pasture apparently was subject to interception and stem-flow, which caused less effective leaching from the topsoil than would have occurred under fallow. Rainfall did, however, leach more efficiently than ponded water, probably as it induced largely unsaturated flow. But, even after 182 mm of rain in excess of evapotranspiration, 10% of the applied bromide was still recoverable from the top 50 mm of soil under pasture. Different soil structures under cropping and pasture affected the leaching patterns with ponded water. A compacted layer at 100-140 mm depth in the cropped soil apparently throttled infiltration, resulting in unsaturated flow, and hence more uniform miscible displacement below than above it. In all cases the bromide concentration at any soil depth was highly variable, with replicates tending toward a log-normal rather than normal frequency distribution.
Characterization of soil structure and stability using modulus of rupture - exchangeable sodium percentage relationships
Authors: Aylmore LAG , Sills ID
Published: April 2005

Measurements of the modulus of rupture (MOR) and in particular of the way in which it changes for a given soil with change in exchangeable sodium percentage (ESP) from zero to 20, have been used to characterize the structural stability of a range of soils from the Western Australian wheat-belt. For convenience soils were categorized as hard-setting or non-hard-setting by an arbitrary choice of an MOR value of the natural soil of 60 kPa as the lower limit of the hard-setting behaviour. The most striking differences between the two soil categories are the higher soil strength at zero ESP (baseline MOR) and rapid increase in MOR with increasing ESP (sodium sensitivity) generally characteristic of the hard-setting soils compared with the non-hard-setting soils. The MOR values quantitatively evaluate the tendency of the soils to slake on wetting, and the sensitivity of the MOR to increasing ESP (as a result of increasing double layer swelling forces) illustrates the extent and permanency of the stabilizing bonds in the soil matrix. The presence of exchangeable magnesium on the exchange sites has been shown to increase the MOR values compared with those for exchangeable calcium at all ESP values in line with previous evidence of the deleterious effects of this cation on soil structure. Although more detailed studies are required, the value of this approach is illustrated by its apparent ability to differentiate clearly between the effects of different management techniques (e.g. continuous cultivation as against continuous cropping), and even between short term effects arising within 1/1 rotations. The results from the 'paired' sites where soils, similar in most respects and having undergone identical management, exhibit significant differences in sodium sensitivity of their MOR, suggest that the strength and longevity of structural bonds may be related to the nature of the exchangeable cations present (in particular, whether sodium or calcium dominate) at the time of incorporation of organic matter in the soil.
The comparative significance and utility of the Freundlich and Langmuir parameters for characterizing sorption and plant availability of phosphate in soils
Authors: Holford ICR
Published: April 2005

In studies using 62 Australian and English soils, the two parameters of the Freundlich sorption equation were compared with phosphate sorption capacity, calculated from the Langmuir 'two-surface' equation, and sorptivity and affinity indices calculated from the simple Langmuir equation applied to an isotherm concentration range of 0-5�g phosphorus/ml. The Freundlich extensive parameter was most highly correlated with sorptivity, and to a decreasing extent with sorption capacity and affinity. It appears to be fundamentally a sorptivity index which reflects the sorption capacity more than the affinity component of sorption, although greatly underestimating sorption capacity. The reciprocal of the Freundlich exponent proved to be an affinity parameter and was most useful in this role on soils of similar sorption capacity. However, conflicting results on different groups of soils showed that this parameter was less distinctive in its role than the others. Studies on two different groups of soils showed that the sorptivity and affinity parameters from the Langmuir equation accounted for more of the variance in plant uptake of labile phosphate than the Freundlich parameters.
Estimation of historical groundwater recharge rate.
Authors: Allison GB , Forth JR
Published: April 2005

Chloride concentrations of groundwater samples have been used to show that present-day recharge to an unconfined aquifer is approximately 2.5 times that which occurred prior to European settlement.
Effects of lime on the growth and nodulation of four grain legumes.
Authors: Jessop RS , Mahoney J
Published: April 2005

Using an acid sand with differing proportions of added ground limestone, a range of soil pH levels was achieved from 5.4 to 9.2. Four winter grain legumes (field peas, faba beans, lupins and chickpeas) were grown for 8 weeks before being sampled for nodulation, dry matter and nitrogen production. Chickpeas appeared the least affected by the range of soil pH values and calcium levels in terms of root and shoot growth; all the legumes produced the greatest number of root nodules at pH 7 or 8. Top dry weight production in lupins was maximized at pH 6, and declined rapidly above pH 7; field peas, chickpeas and faba beans all showed maximum above-ground dry weights between pH 7 and 8.
Interaction of chlorides with soils — a factor in salt retention by saline soils
Authors: Tucker BM
Published: April 2005

The soluble chloride salts in soils may be divided into two parts, one which is freely soluble even at low moisture contents and may be extracted by a suitable anhydrous solvent, and a second which becomes soluble only when ample moisture is present. The chloride retained in the less soluble form may be estimated by the difference between the chloride extracted from a dry soil sample by an anhydrous mixture of 90% ethanol and 10% ethylene glycol and that extracted by an aqueous solvent, 17% glycerol with 83% water. This technique could be used to identify weakly and strongly salt-retentive soils, and to follow changes in salt retention caused by various types of land use.
The pedogenesis of desert loam soils in the Barrier Range, western New South Wales. Ii. Weathering and soil formation
Authors: Chartres CJ
Published: April 2005

Micromorphological, clay mineralogical and chemical data are used to demonstrate the complex, polygenetic nature of soils developed in a mixture of aeolian deposits and in-situ weathered material. At least three separate layers can be recognized in the soils, though some pedological reorganization of these has occurred. The lowest layer consists of weathered rock, aeolian deposits, gypsum and calcium carbonate, and may be, in part, the truncated remnant of an older soil. The middle layer is predominantly composed of aeolian clayey pellets and silts. The upper layer is a slope-wash deposit. The majority of soluble salts, carbonates and sulfates in the soils appear to have been transported into the soils by wind. Pedogenetic processes after the last phase of aeolian deposition have been restricted to the redistribution of some of the more soluble salts and iron oxides, and the modification of soil structure and fabric.
Field rainfall simulator studies on two clay soils of the Darling Downs, Queensland. I. The effect of plot length and tillage orientation on erosion processes and runoff and erosion rates
Authors: Loch RJ , Donnollan TE
Published: April 2005

Runoff and sediment concentrations were measured under simulated rainfall for a range of plot lengths, tilled either across or up and down the slope, on two soils, both of 4% slope. Sediment was moved by either rain-flow transport (the combined action of drop impact and shallow overland flow), or rilling, in which overland flow alone was the main agent of detachment and transport. Rain-flow transport occurred on all plots, while rilling developed only at plot discharges greater than 0.3-0.7 L s-1. For both processes, sediment was dominantly bed-load, and on both soils the concentration of bed-load carried by rills was approximately 4.8 times that carried by rain-flow. From this and other evidence it was concluded that sediment concentrations were controlled by transport capacity rather than the supply of detached sediment. For both rainflow and rill transport, sediment concentrations were constant over a range of plot discharges. It is suggested that rainflow concentrations were controlled largely by rainfall intensity, which was constant. Rills were observed to widen rather than deepen with increasing discharge, which would minimize changes in rill transport capacity. Tillage across slope delayed runoff and reduced total runoff and soil loss. Tillage orientation affected the plot discharges needed for rill initiation, but did not affect the sediment concentrations transported by either of the two main sediment transport processes that were observed.
Improvement in soil structure resulting from sown pastures on degraded areas in the dry savanna woodlands of northern Australia
Authors: Bridge BJ , Mott JJ , Winter WH , Hartigan RJ
Published: April 2005

The structure of the surface soil under pastures sown on a former Themada australis native grassland and on degraded areas in the red earths of northern Australia was examined micromorphologically. Heavily grazed pastures containing the legumes Stylosanthes hamata cv. Verano and Alysicarpus vaginalis had more macropore space in the surface soil than arlightly grazed native grassland, while pastures containing S. humilis (Townsville stylo) had as little macropore space as degraded areas. Macropore space in a S. hamata pasture increased between the third and fourth wet seasons after establishment. Where macropore space was high, infiltration measurements showed that sorptivities were as high as those in the native grassland. Where macropore space was low, sorptivities were as low as those in degraded areas. However, all sown pastures showed low hydraulic conductivities equivalent to those in the degraded areas, and this was attributed to trampling during the wet season under the higher stocking rates involved. The improvement and maintenance of soil structure in the S. hamata and A. vaginalis pastures, together with their high sorptivities, indicates that they are stable in the long term.
The formation of degraded areas in the dry savanna woodlands of northern Australia
Authors: Bridge NK , Mott JJ , Hartigan RJ
Published: April 2005

The perennial tall grass understory of a eucalypt woodland on a commonly occurring red earth (Northcote Principal Profile Form Gn2.11) in northern Australia was burnt during the dry season and subjected to weekly clipping during the following two wet seasons to simulate overgrazing. Clipping killed many plants during the first wet season and almost all of them during the second. Infiltration measurements showed that sorptivity and hydraulic conductivity were greatly reduced after the first wet season following burning only, and micromorphological examination showed surface sealing and structural collapse. There was recovery of sorptivity after the second wet season, but not of hydraulic conductivity, and this was accompanied by an increase in the macropore space of the upper 5 mm of surface soil. With burning plus clipping, structural rearrangement formed a vesicular porous layer during the second wet season and infiltration rates remained low. Since no organic carbon was lost from the surface soil following burning only, the structural collapse was attributed to raindrop impact rather than loss of structural bonds in the oil. In the burn+clip treatment, organic carbon was lost only during the second wet season when most of the grass tussocks had died. Respiration measurements showed that there was little difference in biological activity between the burnt and unburnt grassland during the first wet season and that an estimated 600 g m-2 year-1 of carbon was respired. Overgrazing pastures on these soils results in complete degradation within two set seasons and the formation of bare areas with surface seals.
Rainfall runoff in soil erosion with simulated rainfall, overland flow and cover
Authors: Singer MJ , Walker PH
Published: April 2005

The 20-100 mm portion of a yellow podzolic soil (Albaqualf) from the Ginninderra Experiment Station (A.C.T.) was used in a rainfall simulator and flume facility to elucidate the interactions between raindrop impact, overland water flow and straw cover as they affect soil erosion. A replicated factorial design compared soil loss in splash and runoff from 50 and 100 mm h-1 rainfall, the equivalent of 100 mm h-1 overland flow, and 50 and 100 mm h-1 rainfall plus the equivalent of 100 mm h-' overland flow, all at 0, 40 and 80% straw cover on a 9% slope. As rainfall intensity increased, soil loss in splash and runoff increased. Within cover levels, the effect of added overland flow was to decrease splash but to increase total soil loss. This is due to an interaction between raindrops and runoff which produces a powerful detaching and transporting mechanism within the flow known as rain-flow transportation. Airsplash is reduced, in part, because of the changes in splash characteristics which accompany changes in depths of runoff water. Rain-flow transportation accounted for at least 64% of soil transport in the experiment and airsplash accounted for no more than 25% of soil transport The effects of rainfall, overland flow and cover treatments, rather than being additive, were found to correlate with a natural log transform of the soil loss data.
Mineralization of soil organic nitrogen under waterlogged conditions in relation to other properties of tropical rice soils
Authors: Sahrawat KL
Published: April 2005

The mineralizable nitrogen pool in wetland rice soils plays a dominant role in the nitrogen nutrition of rice even in fertilized paddies. There is a lack of information on how different soil properties affect ammonification of organic nitrogen in wetland rice soils. Surface samples of 39 diverse Philippine soils representing a wide range of pH, organic matter and texture were studied to determine the relationships between ammonification of organic nitrogen and soil properties. Simple correlation analysis showed that ammonium production was correlated highly significantly with total nitrogen (r = 0.94**), organic carbon (r = 0.91**) and C/N ratio (r = -0.46**), but it was not significantly correlated with cation exchange capacity, clay or pH. Multiple regression analayses showed that organic matter (organic carbon and total nitrogen) accounted for most of the variation in mineralizable nitrogen. These results suggest that organic carbon content is a good index of mineralizable nitrogen in tropical wetland rice soils.
Nutrient concentrations in runoff from pasture in Westernport, Victoria
Authors: Greenhill NB , Peverill KI , Douglas LA
Published: April 2005

Concentrations of nitrogen and phosphorus forms, calcium, sulfur and potassium in runoff from previously fertilized plots were explained on the basis of differences in slope, previous fertilizer history, and land management at three runoff sites. Data are also given for concentrations of nitrogen and phosphorus forms, calcium, sulfur and potassium in runoff that occurred after superphosphate was applied. High concentrations of phosphorus forms, calcium and sulfur occurred in runoff from a storm 24 h after fertilizer application. At other times, concentrations of all measured parameters were low, and similar to those reported elsewhere.
Physical characteristics of sands amended with fly ash
Authors: Campbell DJ , Fox WE , Aitken RL , Bell LC
Published: April 2005

Fly ash from a coal-fired power station was incorporated with each of a 'fine' (0.2-0.5 mm) and 'coarse' (1.4-2.0 mm) sand fraction to give mixtures containing 0, 10, 20, 30, 40, 50, 75 and 100% fly ash by weight. The addition of 10% by weight of ash increased the available water capacity by factors of 7.2 (1.0-7.2% by weight) and 13.5 (0.4-5.4% by weight) for the 'fine' and 'coarse' sands respectively. Subsequent additional 10% increments of ash increased the capacity by smaller amounts. The saturated hydraulic conductivity of the sands decreased markedly with ash addition. The changes in available water capacity and hydraulic conductivity were associated with an increase in capillary pores at the expense of non-capillary pores. Addition of fly ash to both sand fractions resulted in a bilinear relationship between void ratio (volume voids/volume solids) and fly ash percentage in the mixes which was closely related to that theoretically predicted for binary mixtures. The measured void ratios of the mixes exhibited minimum values at 36% and 20% ash by volume for the 'fine' and 'coarse' sand mixes respectively, which compared with the theoretical void ratios for these mixes of 27% and 23% respectively.
Poorly soluble, iron-aluminium phosphates in ammonium phosphate fertilizers: Their nature and availability to plants
Authors: Gilkes RJ , Mangano P
Published: April 2005

Both monoammonium and diammonium phosphate fertilizers contain various (Ca,Mg)(NH4)- (Fe,Al)(PO4)(F,OH)H2O compounds that are insoluble in water and comprise 4.9-9.9% of the total phosphorus content of the fertilizers. The compounds have been isolated and characterized by chemical, X-ray powder diffraction, ix., and thermogravimetric techniques. The compounds are only 35-60% as effective as monocalcium phosphate (MCP) in supplying phosphorus to wheat grown under glasshouse conditions. The residual effectiveness of the compounds for a second crop of wheat was generally lower (10-20% relative to freshly applied MCP) than the residual value of MCP (20 %).
Observations on the determination of the availability of potassium for rhodes grass grown in open-cut mine overburden
Authors: Elliott GL
Published: April 2005

A potassium availability index, the value of the free energy of exchange of calcium and potassium, was determined when Rhodes grass growing in mine overburden and in topsoil exhibited visual potassium deficiency symptoms. The value was found to be -4060 � 100 cal equiv.-1. There was no significant difference in this value between the overburdens and topsoil studied. The potassium characteristics of the growth media changed form during the growth of the Rhodes grass.
Seasonal variation in infectivity of vesicular-arbuscular mycorrhizal fungi in relation to plant response to applied phosphorus
Authors: Bolan NS , Abbott LK
Published: April 2005

The effect of applied phosphorus on the growth of subterranean clover was studied in a virgin forest soil sample collected in summer and again in spring. The soil sample was used soon after it was collected. The shape of the response curve for plant growth differed greatly in the two experiments. This may be related to the presence of vesicular-arbuscular mycorrhizal infection in plants grown in the soil sample collected in summer and its absence in the soil sample collected in spring.
Adsorption-desorption behaviour of copper(II) at the goethite-solution interface
Authors: Padmanabham M
Published: April 2005

Adsorption-desorption studies using copper(II) as the adsorbate and synthetic crystalline iron oxide, goethite (�-FeO.OH), as the adsorbent have been carried out on the acid side of the pH of isoelectric point (7.5) in the presence of a large excess of indifferent electrolyte. Specific adsorption of copper(II) on goethite is accompanied by the release of one to two moles of protons per mole of cation adsorbed. Desorption experiments have revealed two types of adsorption sites for copper(II) on the oxide surface, one of low bonding energy and the other of high bonding energy, corresponding with the 'readily desorbed' and 'less readily desorbed' fractions of copper(II) respectively. It is suggested that the two kinds of bonding are associated with the cation being coordinated to one and two surface-OH moieties respectively. The apparent hysteresis between adsorption and desorption isotherms is attributed to the existence of two types of adsorption sites of differing binding constants corresponding with the 'readily desorbed' and 'less readily desorbed' fractions of the cation respectively. The gradual interchange of some 'readily desorbed' copper(II) into a category that is not readily desorbed after an initial 'time-lag' between adsorption and desorption is attributed to a possible time-dependent reaction involving isomorphous substitution of lattice Fe3+ by Cu2+ of comparable ionic size. Some aspects of the relevance of present work to soil-plant system are indicated.
The chemical assessment of the boron status of soils
Authors: Cartwright B , Tiller KG , Zarcinas BA , Spouncer LR
Published: April 2005

Extraction of soils by shaking for 1 h at 20� with 0.01 M CaCl2, + 0.05 M mannitol was found to be a more convenient soil test for plant-available boron than the standard hot water soluble (HWS) method, and to be as good in predicting the response in boron uptake by plants. Wheat plants were grown in a pot experiment involving 18 different surface soils having a range of HWS-boron concentrations of 0.22-2.52�g g-1. Two treatments applied were with and without the addition of 1�g g-1 H3BO3 to the soils. The relative boron uptake by the plants in response to the treatment was correlated with extractable boron in the untreated soils, as measured by the HWS method and six alternative extractants. Boron determined in the low availability range using a CaCl2- mannitol extractant was significantly related to the HWS boron, although less boron was extracted. At potentially toxic concentrations the mannitol method extracted more boron than the HWS method. Optimization of the mannitol procedure is described, and the advantages of the extractant are discussed. The clear, colourless extract obtained was suitable for analysis by inductively coupled plasma spectrometry and by spectrophotometry.
Mapping soil erosion and accumulation with the fallout isotope caesium-137
Authors: Longmore ME , O'Leary BM , Rose CW , Chandica AL
Published: April 2005

The fallout isotope 137Cs has been used to trace the redistribution of soil in a cultivated paddock, in an upland catchment on the Darling Downs. The areal concentrations (mCi km-2) have been used to construct a caesiographic map which illustrates the areas of 137Cs depletion and build-up and the major areas of soil erosion and deposition, respectively, in the paddock. These areas have been graded on the basis of apparent relative intensity of erosion or deposition. Therefore, this method allows retrospective, quantitative estimates to be made of the extent and degree of soil redistribution within the last 3 decades. In addition the 137Cs results will be used to test mathematical models of erosion/deposition processes.
Salinity of atmospheric precipitation in the Murray-Darling drainage division, Australia
Authors: Blackburn G , Mcleod S
Published: April 2005

Rain and dry deposition were sampled together for 28-day periods throughout 1974-75 at 27 stations, all but three being in the Murray-Darling Drainage Division (1.06 x 106 km2). Samples were analysed for calcium, magnesium, potassium, sodium, chloride and sulfate. Similar procedures continued during 1975-77 for six stations used previously and a new one. Rainfall records and the mean ionic concentrations, including estimates of HCO3 + NO3, indicate that the mean aggregate concentration for eight ions in 1974-75 ranges from 3 to 35 mgL-1 for 24 stations in the drainage division and from 14 to 23 mgL-1 for three stations near the South Australian coast. Higher concentrations in the drainage division refer principally to stations in a semi-arid district and are associated with relative abundance of calcium and HCO3 derived from the calcareous soils there. Terrestrial and oceanic sources of the ions are considered. Oceanic input of chloride is estimated using mean annual concentrations to give a maximum value and concentrations for the most rainy periods to give a minimum value. These estimates are compared with discharge of chloride by the Murray and Darling Rivers, with the conclusion that in 1974-75 the oceanic input of chloride to the Darling catchment was mostly retained there, but amounts equal to the accessions to the Murray catchment were probably all flushed out. Details are given in an appendix of NO3 concentrations determined by others at two stations in frequent samples of rain.
The use of computer assisted tomography to determine spatial distribution of soil water content
Authors: Hainsworth JM , Aylmore LAG
Published: April 2005

To date no experimental technique has been capable of directly and repetitively measuring spatial distributions of soil water content in a non-destructive manner. The potential of computer assisted tomography (CAT) to overcome this problem has been examined in this paper. The results obtained from a commercially-produced X-ray CAT scanner and a conventional gamma scanner suggest that CAT scanning can be used to determine spatial changes in soil water content with adequate resolution for soil-plant studies. The technique can clearly be used to resolve spatial changes in soil water content with time. Application of the technique to water uptake by a single plant root shows that CAT scanning presents an extremely exciting possibility for studies of soil-plant water relations.
The effect of kinetic energy of excess rainfall on soil loss from non-vegetated plots
Authors: Kinnell PIA
Published: April 2005

Data obtained from three 0.01 ha runoff and soil-loss plots, established with a bare fallow treatment on a yellow podzolic (Albaqualf) soil and slope gradient of 4.2%, were analysed in terms of the kinetic energy of raindrops and the efficiency of the use of that energy in generating soil loss. The results indicate that the difference between rainfall intensity and the average infiltration (acceptance) rate of the soil during an event can be used to estimate variations in the efficiency of use of rainfall energy in generating sheet erosion.
The adsorption of molybdenum on oxide surfaces
Authors: McKenzie RM
Published: April 2005

Adsorption of molybdenum was measured on 12 oxides with zero points of charge (ZPC) ranging from pH 2 to 7.6. Adsorption envelopes calculated using the Bowden adsorption model agreed well with the experimental results for goethite. Oxides with low ZPC, however, showed adsorption maxima well below the predicted value of pH 3.3. It was postulated that a positively charged polycationic form of molybdenum was adsorbed at low pH by oxides with low ZPC.
Comparative study of phosphorus and potassium levels of basaltic soils associated with scrub and forest communities on the Darling Downs
Authors: Ahern CR , MacNish SE
Published: April 2005

Morphologically similar scrub and forest basalt soils were investigated for differences in soil phosphorus and potassium levels. Surface samples (0-10 cm) from 181 scrub and 111 forest sites were analysed for five soil tests: 0.05 M H2SO4-extractable phosphorus, 0.5 M NaHCO3- extractable phosphorus, 0.05 M HCl-extractable potassium, total phosphorus and total potassium by X-ray fluorescence. Highly significant differences (P <0.001) between scrub and forest soils were found for each soil test when all sites were assessed in terms of regional differences based on vegetation. These differences were then investigated further for each of the three common Great Soil Groups - black earths, euchrozems and lithosols - and then for six individual soil series common to both the scrub and forest areas. An unexplained geographic trend in phosphorus values previously reported (1972) in the same area could be accounted for by this difference between scrub and forest soils. Similar differences in soil phosphorus and potassium for scrub and forest soils on other parent materials are also discussed. It was clearly shown that the scrub means were always greater than the forest means for all five soil tests for all soils combined, each Great Soil Group and each soil series, and that there is a strong association between vegetation distribution and these soil differences.
The place of 'genesis' in the classification of soils
Authors: Beckmann GG
Published: April 2005

The purpose of classification is to indicate relationships and differences between objects and to establish groups at various levels of generalization; i.e. to produce simplified models based on experience. In soils the object to be classified is often the soil profile, which may be considered to be analogous to the hand specimen in geology and to the individual organism in biology. For purposes of discussion a profile is considered to be a vertical column, up to 20 cm square, and extending to c. 2 m from the surface, to rock or to some distinct soil layer underlying the profile, across which physical, chemical and mineralogical variations are small. There is no conceptual continuum of soil profiles, even though there is a physical continuum across the surface of the earth. Rather there are a number of common forms each of which may be represented by a 'central concept' with intergrades between them. Such a central concept can be recognized at each level of a hierarchy. Soils are natural objects with a complex structure and history, as are organisms, rock specimens and even landforms. They should be considered in the same way as the other natural objects when a classification is being constructed. Their 'history', as conceived at present, should be involved in classification, even though major emphasis is placed on physical, chemical and mineralogical properties. To illustrate these ideas, the Australian Great Soil Groups are re-examined and suggestions are made about possible subgroups.
Analysis of breakthrough curves: effect of mobile and immobile pore volumes
Authors: Pandey RS , Gupta SK
Published: April 2005

A new technique of evaluating readily displaceable liquid has been outlined. The use of this technique has been illustrated for several breakthrough curves, highlighting the deviations in earlier estimates of pore volumes which are either positive or negative. The implication of these deviations has been discussed. The effect of this change in pore volume on Peclet number is presented. The prediction made with the new set of parameters is illustrated and compared with the observed data resulting in an overall improvement in predictions.
The relationship between aggregation and other soil properties in cracking clay soils
Authors: Coughlan KJ , Loch RJ
Published: April 2005

This paper explores the processes responsible for clay dispersion, and the formation of large dry aggregates, in cracking clay soils. It also isolates the soil factors causing variations in dry aggregate size using regression analysis. Twelve cracking clay soil samples were selected on visual differences in dry aggregate size distribution following seedbed preparation, and a range of soil structural and chemical properties were measured. The per cent dry aggregates > 5 mm was found to increase with resistance to mechanical abrasion, stability to wet sieving after capillary wetting, and dispersion ratio, indicating that large dry aggregates are formed as a result of binding by dispersed clay. Both raindrop impact and puddling by cultivation may be involved in dispersion. There was a strong relationship between dry aggregate size in the 0-10 cm layer and salt content in the subsurface (60-90 cm) layer. Coarse surface aggregation is explained in terms of limited profile hydraulic conductivity. For the soils studied, the properties of the surface layer appear to be responsible, at least in part, for the limitation in profile hydraulic conductivity. Dry aggregate size in the 0-10 cm layer was not simply correlated with any of the chemical properties of that layer. However, equations containing two (ESP and CEC per gram of clay) or three (ESP, per cent clay and CEC) independent variables were derived to explain variations in dry aggregate size, both for the 12 soils studied and for a wider range of Queensland cracking clay soils.
Using variable charge characteristics to understand the exchangeable cation status of oxic soils
Authors: Gillman GP
Published: April 2005

The model of Uehara and Gillman was used to estimate the amounts of permanent surface charge, and variable surface charge at soil pH, in two soils from the high rainfall region of coastal Queensland. For each soil series, samples from virgin rain-forest were compared with soil collected from nearby sugarcane fields. One soil contained relatively large amounts of permanent negative charge (up to 3 m.e. per 100g), and hence was moderately supplied with exchangeable cations, while the other soil was dominated by variable charge components and at soil pH contained sufficient positive charge to reduce exchangeable cations to near zero values, despite the presence of about 1 m.e. per 100 g of permanent negative charge. In the latter the position of soil pH with respect to the point of zero charge is of utmost importance for the development of cation exchange capacity. The effect of adsorbed sulfate on positive charge measurement, and valency of the ion used for negative charge measurement, are briefly discussed.
Effects of zero tillage and stubble retention on some properties of a cracking clay
Authors: Loch RJ , Coughlan KJ
Published: April 2005

Soil chemical and physical properties of a black cracking clay were measured after five years under a zero tillage and stubble retention trial. Stubble retention slightly increased the organic carbon content of the 0-10 cm layer, and the dispersion ratio of the 0-4 cm layer. Stubble retention increased dry aggregate size in the 0-4 cm layer of the zero tilled treatments, apparently due to a reduction in the rate of drying of the surface after rain. Changes in the distribution of cations in the surface soil developed in the absence of tillage, with lower exchangeable sodium percentage (ESP) and higher exchangeable potassium percentage in the 0-4 cm layer under zero tillage. The reduction in ESP in the 0-4 cm layer under zero tillage also reduced dispersion ratios. The ratio CEC : % clay for the 0-4 cm layer was reduced by zero tillage. Chloride profiles gave evidence for increased deep infiltration under zero tillage. This is attributed to the presence of cracks that were not closed by tillage.
Preliminary investigation of clay soils' behaviour under furrow irrigated cotton
Authors: Mcgarry D , Chan KY
Published: April 2005

Six experimental sites were selected, in the Namoi Valley, N.S.W., all on self-mulching cracking clay soil, to provide a variety of both management practice and length of time under cotton. Within each of the sites randomly located plots were positioned to cover both wheel-track and non-wheel-track areas. The design allowed assessment of both during-season effects caused by tractor wheels and between-site effects. Neither soil physical status (as measured by soil water extraction, air permeability and recovery of air-filled pores) nor yield was influenced by during-season tractor passes. However, non-wheel areas had significantly taller plants and more green cotton bolls per plant than wheel-influenced areas. Pronounced differences between sites in both soil physical status and cotton growth and yield were measured. For those sites in their first year of cotton there was greater soil water extraction, greater air permeability and more rapid recovery of air-filled porosity. They also produced up to 30% more yield in comparison with sites growing cotton for 8-17 years. At no site did any evidence arise to show 'ploughpan' or 'hardpan' formation.
Moisture measurement in a swelling clay soil using neutron moisture meters
Authors: Jayawardane NS , Meyer WS , Barrs HD
Published: April 2005

Neutron meters were calibrated for moisture determination in a layered swelling soil, showing changes in both swelling characteristics and texture with depth. The bulk density-moisture content relationship of each layer determined from small soil cores agreed with those predicted from in-situ swelling measurements taken during a previous study. The precision of calibration of two neutron meters was markedly improved by correcting for textural and bulk density changes with depth. The regressions of total moisture content on corrected neutron ratios were similar for the two moisture meters and comparable to those obtained for similar soils in previous studies, provided that the same calibration techniques were used. For moisture determination in the field, separate calibration equations of volumetric moisture content against neutron ratios were required to account for the individual bulk density-moisture content relationship of each soil layer. The calibration equation for the surface layer had a markedly lower calibration coefficient and a much higher intercept constant than for the subsoil. Measured changes in soil moisture following irrigation using the above calibration equations of the neutron moisture meter agreed closely with values predicted by water balance within a large soil core in a lysimeter.