bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterizing soil aeration with a platinum microelectrode. I. Response in relation to field moisture conditions and electrode diameter
Authors: McIntyre DS
Published: April 2005

Measurements with a platinum microelectrode under field conditions in a range of irrigated soils have been analysed in terms of applicability of the method for the field measurement of soil aeration. In well-drained soils the moisture content fell below the range in which the electrode operates satisfactorily within 2 days of heavy watering, but in poorly drained soils the electrode remained operative for up to 6 days. Field measurements were made with an electrode of 1.22 mm diameter, so diffusion theory was applied to convert the values to those for a 0.50 mm diameter electrode, a size more frequently used. Measurements were then made under controlled conditions in saturated and unsaturated media to confirm the theoretical determinations.
Determination of withdrawal of water from soil by crop roots as a function of depth and time
Authors: Rose CW , Stern WR
Published: April 2005

Theory is presented to permit the calculation of water withdrawal by plant roots at any depth in soil as a function of time, without neglect of water movement in the soil. Such neglect may be a source of error in using other approaches to this problem. The method proposed requires a knowledge of the moisture and hydraulic conductivity characteristics of the soil as a function of depth. When this theory was applied to data from an irrigated cotton crop, it was shown that the maximum rate of water withdrawal by roots was between the soil surface and 25 cm, and that rates were relatively low below 30 cm. The withdrawal pattern is discussed in relation to potential evaporation and the water status of the crop.
Changes in some physical properties of the surface of an impoverished red-brown eath under pasture
Authors: Clarke AL , Greenland DJ , Quirk JP
Published: April 2005

The effects of growing monospecific swards of two grasses and a clover for 3 years on some physical properties of a loamy fine sand have been examined. Increases in the stability of aggregates in water (aggregation (2 mm)) occurred mainly in the surface 2 in. They were greatest under Wimmera ryegrass and least under subterranean clover. Over the 3 year period aggregation (2 mm) in the 0-3 in. layer generally increased linearly with herbage yield. Infiltration capacity was related similarly to yield of herbage in preceding years. Mulching caused insignificant aggregation changes. With increasing stability, aggregates became less dense, fractured more readily, and wet more rapidly. Despite marked increases in aggregate stability the soil reached only an 'immature' stage of structure development.
The swelling in water of complexes of montmorillonite with polyvinyl alcohol
Authors: Theng BKG , Greenland DJ , Quirk JP
Published: April 2005

The swelling in water of complexes of sodium and calcium montmorillonite with polyvinyl alcohol has been studied. The polymer reduced the swelling of the clay. The extent of reduction was dependent on the properties of the polymer, the conditions in which the adsorption of the polymer took place, and the previous history of the clay. The swelling of the montmorillonite-polyvinyl alcohol complex at low hydrostatic suctions did not fall below 50% of that of the parent clay, whilst sorption of water from the vapour phase was only reduced by about 15%. These results indicate that the polymer is adsorbed around clay crystals or domains, within which swelling can still occur, although adsorption of water between domains is restricted.
Studies on soil polysaccharides. II. The composition and properties in soils under pasture and under a fallow-wheat rotation
Authors: Swincer GD , Oades JM , Greenland DJ
Published: April 2005

After the removal of light fraction from soils under old pasture and under continuous fallow-wheat rotation, carbohydrates were extracted using IN HC1 followed by 0.5N NaOH and finally an acidic acetylation procedure, or by a single extraction with 0.2N NaOH only. The sequential extraction procedure removed 70-80 % of the carbohydrate from the soil under both agronomic systems. 0.2N NaOH removed a larger proportion of the carbohydrates from soil under fallow-wheat rotation (43-52%) than from soil under old pasture (35-38%). The composition of the carbohydrates in a given extract from the soil under pasture or fallow-wheat was similar. This similarity extended even to the neutral sugar composition of fractions obtained by gel filtration of the purified extracts. Generally, low molecular weight materials were rich in amino acids and compounds such as glucose, ribose, and glycerol. Polymers of molecular weight 4000-100,000 contained relatively high proportions of uronic acids and amino acids. Least amino acids were present in materials of molecular weight greater than 100,000 which contained appreciable quantities of deoxyhexoses (up to 20% of the total neutral sugars) indicative of their microbial origin. Against this background of similarity, certain differences between the carbohydrates from soils under pasture and fallow-wheat rotation were apparent. 1N HCl extracts contained more high molecular weight material from the old pasture soils than from the cultivated soil. The composition of these extracts indicated that they comprised the easily extractable recently synthesized microbial polysaccharides. The proportion of such polymers was lower in the cropped soil. A higher proportion of materials of small size was present in soils under a wheat crop. Maximum amounts of these compounds were present during periods of maximum plant and microbial activity. Extracts from soils under fallow-wheat rotation contained a higher proportion of uronic and amino acids and less ribose, arabinose, and deoxysugars than the extracts from soils under pasture. Based on relative deoxysugar contents it was calculated that the pasture soil contains about four times as much microbial polysaccharide as the soil under fallow-wheat.
The isotopically exchangeable form of native and applied cobalt in soils
Authors: Tiller KG , Honeysett JL , Hallsworth EG
Published: April 2005

The experimental conditions and precision of alternative methods of measuring isotopically exchangeable cobalt (Coi.e) were investigated. The values of Coi.e varied from 0.16 to 5.4 p.p.m. for 25 soils and were highly correlated with the sum of cobalt extracted by ammonium acetate and subsequently by quinol, and the relationships between these forms are discussed. The amounts of cobalt sorbed in the presence of calcium chloride by different soils varied markedly between and within soil groups. The bonding energy of specific sorption of cobalt did not vary significantly between soils after the first sites were filled. Cobalt sorption capacity for all soils studied was highly correlated with cobalt content and surface area and to a lesser extent with manganese and clay content and pH, but not with organic matter. When soils of high montmorillonite content were excluded, highly significant correlations were obtained only with manganese and cobalt contents and surface area. The initial slope of isotherms of isotopically exchangeable cobalt 60Co(soi1)/60Co (solution) and Coi.e may provide measures of the intensity and capacity factors, respectively, of cobalt availability to plants.
Solid-state reduction at a platinum microelectrode in relation to measurement of oxygen flux in soil
Authors: Black JDF , West DW
Published: April 2005

In acidic soils (pH < 5.5) saturated with water the polarogram measured with a platinum microelectrode between applied potentials - 0.1 to - 0.9 V (versus a saturated calomel electrode) corresponds to an oxygen reduction polarogram from - 0.1 to - 0.4 V but deviates markedly at more negative potentials. As the pH of the soil decreases the extent of the deviation increases, but at pH values as low as 3.5 there is no material effect on the current reading at - 0.4 V. Evidence is presented which suggests that interference to the oxygen reduction polarogram occurs over and above the liquid phase effect by solid-state reduction of at least carboxyl groups within the soil. It is recommended that the maximum negative potential to be applied to a platinum microelectrode to measure oxygen flux in a saturated soil should be -0.4 V (v. S.C.E.).
Sorption and precipitation of iron of Kaolinite. II. Sorption isotherms and their interpretation in terms of Iron(III) ionic equilibria
Authors: Fordham AW
Published: April 2005

The sorption of iron(III) by kaolinite was studied in different media as a function of iron concentration, pH, and time, with such low concentrations of total iron that precipitation was excluded over most of the pH range examined. The reaction continued at a measurable rate for several weeks but a state of quasi-equilibrium, independent of the medium and of clay : solution ratio, was achieved in about 1 week. The amount of iron sorbed from the most acidic solutions was relatively low but increased markedly with increasing pH. Total iron concentrations measured in equilibrium with the clay were resolved by computer into concentrations of the component ionic species, which were then plotted against the total amount of iron sorbed. Unique relationships were found within specified pH ranges. From pH2O to 2.7, the amount of iron sorbed was correlated with the concentration of the species FeOH2+ and, from about pH 2.7 to 3.6, with the concentration of Fe(OH)2+. Specific sorption of these species by the clay is discussed. At higher pH values and prior to the precipitation of iron, other factors contributed to the sorption of iron. A reaction of monomeric iron species from solution with iron already sorbed by the clay is proposed, leading to the formation of polymers on the clay surface. Under suitable conditions of iron concentration and pH, precipitation of ferric hydroxide, probably a later stage of the polymerization process, occurred on the clay surface, in accordance with a well-defined solubility product relationship.
Inhibition and simulation of proteolytic enzyme activities by soil humic acids
Authors: Ladd JN , Butler JHA
Published: April 2005

The effects of neutralized solutions of soil humic acids on the activities of a range of proteolytic enzymes and of tyrosinase have been measured. Humic acids inhibit carboxypeptidase A, chymotrypsin A, pronase, and trypsin activities, stimulate papain, ficin, subtilopeptidase A, and thermolysin activities, and had no effect on phaseolain and tyrosinase activities. Stimulation of papain and ficin activities is not due to formation of metal ion-humic acid complexes. Inhibition of trypsin activity and stimulation of papain activity increased with increasing molecular weight of the humic acid. However, humic acid fractions of varying molecular weights had similar effects on the magnitude of inhibition of pronase and carboxypeptidase A activities. Polycondensates derived from p-benzoquinone and catechol influenced enzyme activity in the same way as humic acids, although the order of their relative effectiveness changed with different enzymes. Polyacrylate preparations were the most effective inhibitors of trypsin activity but had no effect on papain and ficin activities.
In situ measurement of sorptivity
Authors: Talsma T
Published: April 2005

Measurements of sorptivity are reported for a number of field soils. The main method, used in situ, is simple and consists of timing initial vertical flow of water into an undisturbed soil profile. This method relies on the assumption that, during the measurement time of 1-2 min, the first term of the infiltration equation i = St1/2 + At + Bt3/2 . . . dominates flow. In other methods horizontal inflow was timed into undisturbed soil blocks, and capillary rise was observed in undisturbed field cores. Sorptivity was quite variable on each site, with standard deviations of the same order as those found for hydraulic conductivity. For most soils the three methods estimated sorptivity differently, the field method giving the largest values. These differences were largely due to the effect of water depth over the soil on sorptivity. Head dependence of sorptivity, verified experimentally and with delta function theory, was particularly strong in soils of composite structure, where infiltration is dominated by structural cracks and root channels. These soils also have relatively large values of the ratio of hydraulic conductivity to sorptivity. Large ratios of hydraulic conductivity to sorptivity and strong head dependence of sorptivity may cause significant errors in calculating sorptivity in the field method. However, these errors are compensating, and analysis of the data indicates that over-estimation of sorptivity in such soils is at the most 5%. For subsoils and soils of single grain structure these errors were negligible. Average sorptivity values of some of these soils have given good quantitative agreement between theory and field data on two-dimensional flow.
Weathering and soil development on a sequence of river terraces
Authors: Brewer R , Walker PH
Published: April 2005

Five soil profiles on alluvial terraces in the Macleay River Valley, N.S.W., have been studied to determine changes in soil development with increasing age. The criteria used were mainly macromorphology, micromorphology (basic fabric, evidence of weathering of lithorelicts and biotite, and depth functions of illuviated clay), depth functions of grain-size distributions, and clay mineralogy. The evidence suggests that the four youngest soil profiles represent successive stages of profile development by weathering for the most part and, to a lesser extent, formation of an horizon of illuviated clay; data for the oldest soil indicate a different history of profile development.
Changes in chemical fractions of nitrogen during incubation of soils with histories of large organic matter increase under pasture
Authors: Moore AW , Russell JS
Published: April 2005

A lateritic podzolic soil and a solodized solonetz soil, with histories of organic matter increase under tropical and temperate pastures respectively, were incubated over a period of a year with a weekly wetting and drying cycle. Decreases in organic matter (7 and 11%), total nitrogen (12 and 10%), and non-distillable acid-soluble nitrogen (30 and 25%) occurred, but there were no significant changes in residual nitrogen. Although there were marked increases in mineral nitrogen at the beginning of the incubation in both soils, nitrification was relatively poor in both soils. In a short-term (4 weeks) incubation of a lateritic podzolic soil and a grey clay soil the addition of labelled nitrogen followed by fractionation allowed nitrogen transformations to be examined precisely. Although differences in total nitrogen (labelled + unlabelled) with time were not statistically significant (P = 0.05) in the sandy soil (lateritic podzolic) a loss (28%) of total labelled nitrogen did occur. Parallel with this was an increasing incorporation of labelled nitrogen in all three organic fractions and a disappearance of ammonium nitrogen without the appearance of an equivalent amount of nitrate nitrogen. On the other hand, in the clay soil there was no loss of total labelled nitrogen with time and little incorporation of labelled nitrogen in the organic fractions after the first week. There was little change in the pool of labelled mineral nitrogen between the first and fourth weeks, but virtually complete and quantitative conversion from ammonium nitrogen to nitrate nitrogen. Some of the results point to varying biological lability of chemical fractions of soil nitrogen. These fractions are unlikely to be of much use as indices for sensitive measurement of nitrogen changes in the field, however, possibly because of the continuing accretion and losses which occur in the field.
Sorption and precipitation of iron on kaolinite. III. The solubility of iron(III) hydroxides precipated in the presence of kaolinite
Authors: Fordham AW
Published: April 2005

Iron(111) hydroxides were precipitated upon kaolinite suspended in acidic solutions of either 0.15M NaCl or 0.15M NaClO4. The progress of the reaction was followed for up to 15 weeks by periodic measurements of pH values and total iron(111) concentrations in solution. Total iron(m) concentrations varied from 1 0 - 3 ~ to 2 x 10-7 and pH values from 2.2 to 4.4. In NaCl media, steady state conditions were reached within 4-5 weeks. Allowing for the various iron(III) ionic species present in the solution phase, the solubility product *K++S2 (= [Fe(OH)+2]/aH+) was found to be 4.9 x 10-3 (S.D. = 0.7 x 10-3 log*K++S2 = - 2.31; log Kso = - 38.9). Although the initial precipitates were amorphous, the presence of �-FeOOH in aged suspensions was detected by X-ray analysis, in agreement with electron microscope observations. In NaClO4 media, the solubility of precipitates decreased rapidly during the first 3 weeks and relatively slowly thereafter. Although equilibrium was obviously not established within 5 weeks and possibly not within 15 weeks, values of solubility products, constant over the whole pH range, were derived from results at both reaction times. For suspensions aged for 5 weeks, *K++S2 was 4.85 x 10-3 (S.D. = 0.75 x 10-3 ; logKso = -38.9), whilst for those at 15 weeks, *K++S2 was 2.45 x 10-3 (S.D. = 0.3 x 10-3; log Kso = -39.2). X-ray and infra-red analyses and electron microscope examination indicated the presence of lepidocrocite in the aged products. There was no evidence that either the type or the solubility of products formed on aging was influenced by the presence of kaolinite, although the clay accelerated the rate of crystal growth.
The effects of fluctuations in soil moisture content on the availability of recently applied phosphate
Authors: Simpson JR , Williams CH
Published: April 2005

Incubation for short periods at a high moisture content reduced the subsequent plant uptake of phosphorus from recently applied monocalcium phosphate in several soils. The effects on phosphorus uptake were reflected in the amounts of phosphate extracted by 0.5M sodium bicarbonate and by 0.01M calcium chloride. Phosphate availability decreased with increasing moisture content up to saturation. At saturation, availability decreased with increasing incubation period up to 4 days, but was not reversed by several weeks of subsequent incubation at 100 cm tension. The effect of waterlogging usually was greater on the air-dried soil than on soil which had undergone moist pre-incubation. The results suggest that the decrease in phosphate availability was closely associated with the reduction of iron during the anaerobic phase and its subsequent oxidation. Preincubation at 100 cm tension progressively decreased the amount of iron released, and phosphate subsequently immobilized. This appeared to be caused by oxidation of organic substrate during the aerobic phase, thus delaying the onset of anaerobiosis during waterlogging. Phosphate applied to the surface was affected by waterlogging in a similar way to phosphate mixed into the soil.
A double layer theory for mixed ion systems as applied to the moisture content of clays under restraint
Authors: Collis-George N , Bozeman JM
Published: April 2005

A double layer equation (after Gouy) for heterovalent ionic systems is applied to the thickness of the water films associated with the ionic double layer of clay particles. The equation is tested against a Ca/Na/Cl montmorillonite described by Smiles and Rosenthal (1968) in terms of moisture content versus pressure restraint. The equation reduces to simpler exact formulae for the case of unconstrained clays and gives useful approximations for the situations of small interactions and of large interactions which cover most situations to be encountered in soil systems. The restrictions of the application of the double layer model to swelling clay systems are considered.
Some aspects of the genesis of an alpine humus soil
Authors: Brewer R , Haldane AD
Published: April 2005

An alpine humus soil profile has been examined in the field, in thin section and by X-ray diffraction. The presence of a stone line and the sudden change in characteristics across the stone line, including particle size distribution, degree of exfoliation of the micas, major mineral composition, and clay mineralogy suggest that this is a polygenetic profile consisting of two soil stratigraphic units. There has been little pedological reorganization within either unit, soil formation consisting essentially of in situ weathering, removal of soluble constituents, and accumulation of organic matter, with some biological activity, in the upper unit. It is shown that gibbsite derived from weathering of feldspar is a major component of the clay fraction, especially in the lower unit. The clay mineralogy is considered in relation to proposed mineral weathering sequences and weathering in a yellow podzolic soil.
A dual source gamma ray traversing mechanism suitable for the non-destructive simultaneous measurement of bulk density and water content in columns of swelling soil
Authors: Bridge BJ , Collis-George N
Published: April 2005

A traversing mechanism is described in which 100 mCi sources of americum-241 and caesium-137 are alternately brought into line with a sodium iodide (thallium) scintillation counter connected to a single-channel pulse height analyser equipped with two preset base lines. The equipment is capable of scanning a 10 cm diameter soil column equipped with sensors to a height of 200 cm, and facilities are provided for automatic indexing at preset intervals to an accuracy of 0.01 cm. Non-linear counting losses in the spectrometer system are described, and were found to be dependent on the window setting of the pulse height analyser. With the window setting adjusted to cover the apparent spread of the gamma peak, counting losses were negligible. Mass absorption coefficients of various materials were obtained using a compartmented box. Measured mass absorption coefficients of water, silica sand, and a chernozemic soil were 0.201, 0.247, and 0.303 cm2 g-1 respectively for americum-241, and 0.0826, 0.0746, and 0.0728 respectively for caesium-137. The precision of the apparatus was demonstrated by determining the moisture characteristic and bulk density characteristic of 0.5-1.0 mm aggregates of Narrabri soil during absorption and desorption. Gamma ray attenuation measurements and direct volumetric measurements were comparable. The standard deviations in the gamma ray measurements were found to be 0.03 g cm-3 for bulk density and 0.04 cm3 cm-3 for water content. Most of this inaccuracy arose from lack of precision in the americum-241 mass attenuation coefficient for the soil. By contrast, changes in moisture content and bulk density, at any level, of 0.004 cm3 cm-3 and 0.004 g cm-3 respectively, were statistically very significant.
An experimental study of vertical infiltration into a structurally unstable swelling soil, with particular reference to the infiltration throttle
Authors: Bridge BJ , Collis-George N
Published: April 2005

The infiltration phenomena associated with a structurally unstable swelling soil are compared with those of a two-layer stable system of a fine sand layer over coarse sand, the fine sand simulating a slaked layer at the soil surface. Water content and bulk density are measured using dual source gamma ray attenuation, pore water pressures by means of individual tensiometer-transducer systems, and soil temperatures by means of individual thermistor-bridge systems. Analysis of the sand column using well-established principles shows that after the wetting front has passed the texture boundary, infiltration is controlled by Kmax of the fine sand layer and the negative moisture potential in the coarse sand at the texture boundary. After the wetting front penetrates the column, the moisture potential at the texture boundary becomes steady and is unaffected by the development of a capillary fringe and outflow at the base of the column. The negative moisture potentials at the texture boundary give rise to potential gradients up to 6.0 in the simulated slaked layer, and an infiltration rate several times that of Kmax. The low flow rates caused by the fine sand layer give rise to an unstable wetting front in the coarse sand and severe 'fingering' occurs. In the swelling soil column, with aggregates of the same size as the coarse sand, the infiltration throttle occurs immediately below the visibly slaked layer and not at the ground surface. Potential gradients through the throttle reach a maximum of 5.9 similar to that in the layered sand column, but the infiltration behaviour of swelling soil differs from the latter in other respects. Infiltration into the former does not occur under isothermal conditions, a 'hot front' 3�C above ambient occurring 2-3 mm ahead of the wetting front, and infiltration does not reach a constant rate because of changes in the hydraulic properties of the throttle with time. Moisture profiles in the swelling soil column during infiltration show the various zones described by Bodman and Colman (1944) for non-swelling soils. An enlarged apparent transition zone extend to 12 cm below the soil surface. Other properties such as density, moisture content, and total potential suggest that much of this apparent transition zone is really part of a transmission zone made up of layers of soil which have different properties because of swelling.
Soil stabilization by polyvinyl alcohol and its effects on the growth of wheat
Authors: Stefanson RC
Published: April 2005

A factorial experiment was carried out in the glasshouse using six levels of polyvinyl alcohol (PVA) and five levels of nitrogen fertilizer. Each pot contained 3 kg of the Urrbrae fine sandy loam taken from an area of low fertility. When no PVA was added, only 35% of the wheat seeds emerged, while at the lowest application rate of PVA (0.05% W/W for 0-2 cm layer of soil) the emergence rate was 90%. PVA did not affect plant growth or the uptake of nitrogen. Contrary to previous experience, the acceptance of simulated rain was not increased with the application of PVA, but soil losses were not significantly reduced.
An evaluation of two techniques for the removal of ultraviolet-absorbing contaminants from clays
Authors: Simpson GH , Hughes JD
Published: April 2005

Elution of clays with buffer solutions was compared with the more destructive technique of peroxide oxidation to remove ultraviolet-absorbing contaminants from kaolinite and montmorillonite. Repetitive elution of kaolinite at pH 7.0 and of montmorillonite at pH 8.4 removed significant amounts, but the level of contamination after this treatment was still unacceptably high. Oxidation with hydrogen peroxide was considerably more effective, but X-ray diffraction data on the oxidized clays provided evidence of the breakdown of aggregates in the 2-5 �m size range. It was concluded that the contaminants were organic and that oxidation removed bonding groups from clay domains.
Water absorption by swelling seeds. I. Constant surface boundary condition
Authors: Collis-George N , Melville MD
Published: April 2005

Recent analyses of water absorption by seeds have used a non-swelling model with constant diffusivity and constant surface concentration boundary condition. A physically realistic modification of such analyses is developed, where the spherical seed has the properties of normal swelling, moisture content dependent diffusively, and a moisture characteristic which is described by the double layer theory relevant to colloids under mechanical restraint. Analysis of this model by a finite difference approximation produces a relationship between linearized moisture content and dimensionless time which is appropriate to all spherical swelling materials. A good match was obtained between this relationship and experimental absorption data for wheat seed. The relationship given graphically in dimensionless form is applicable to any swelling system, e.g. soil aggregates, which satisfy normal swelling and constrained double layer boundary conditions. The analysis gave values for the diffusivity of the seed similar to, but larger than, those calculated from non-swelling models. These are much smaller than most values of diffusivity of soils in the available water range. The magnitude of the maximum rate at which a seed can absorb water relative to that which the soil can supply, predicts that for seeds embedded in most soils, the constant surface concentration boundary condition used by most authors is inappropriate. In terms of the swelling behaviour of most soils, the swelling model, unlike the non-swelling model, predicts that imbibing seed embedded in soil will be subject to a mechanical constraint.
Internal surface area and porosity of kaolinitic glaebules
Authors: Sills ID
Published: April 2005

Specific surface areas, cation exchange capacities and pore size distributions have been determined on sieved fractions of a sandy loam from Merredin, W.A., certain horizons of which contain significant proportions of kaolinitic glaebules. The sand-sized glaebules are resistant to breakdown by normal dispersion techniques, and so remain in the sand fraction during particle size analysis. However, certain of their physicochemical characteristics are consistent with those of soil colloids. For instance, the 250-500 �m fraction of the 155-190 cm horizon has a specific surface area of 16.3 m2/g, an average pore size of some 6 nm plate separation and a surface charge density of 3.8 x 104 esu/cm2. In soils containing significant proportions of such glaebules, the physicochemical properties will differ markedly from those inferred from particle size analysis.
Soil stratigraphy in a deeply weathered shield landscape in south-western Australia
Authors: Finkl CW , Churchward HM
Published: April 2005

Soil stratigraphy on an erosionally modified deeply weathered shield landscape in south-western Australia is described. in situ development of deep profiles of weathering are indicated by preservation of weathered rock fabrics and intact quartz veins. The independence of sedimentary layers is shown by reference to lateral trends within layers, by the relationship of these trends to associated layers, and by certain distribution patterns of mineral grains and reverse weathering patterns between layers. The succession of soil-stratigraphic layers described is used as a basis to interpret profile morphology and aspects of landform development. Striking features of soil morphology and soil pattern can be related to soil stratigraphy and hence to landform history rather than to pedogenic processes. In particular, texture contrast profiles relate to superposition of a shallow slope sediment on clayey saprolite. Red and yellow earths relate to deep phases of this sediment or to erosional exposure of elements of the profiles of deep weathering.
The effect of bulk density on neutron meter calibration
Authors: Greacen EL , Schrale G
Published: April 2005

The effect of dry bulk density on neutron transport in soil is discussed in relation to the calibration of the neutron moisture meter. Olgaard's model based on three group diffusion theory predicts count rate with acceptable accuracy in soils with an absorption cross section less than 0.004 cm2 g-l. For soils with a high absorption cross section, which are common in Australia, the model fails to predict the plane of the calibration line. The theoretical model predicts that, at constant total water content (available plus constitutional water), the count rate increases with increasing bulk density; for all soils for values of total water content less than 0.5 a correction factor based on this prediction significantly reduces scatter in the experimental calibration points; at water contents higher than this, clay soils are intractable, and it has not been possible to assess the density effect. An alternative, more simple procedure of correcting for the effect of bulk density on count rate is proposed; the method is based on the assumption that count rate at constant total water content is proportional to the square root of bulk density.
Subplasticity in Australian soils. III. Particle size properties of soil materials of varying plasticity
Authors: Walker PH , Hutka J
Published: April 2005

Soil materials from the Riverina, N.S.W., ranging from superplastic to highly subplastic on field criteria, were disaggregated by various mechanical and chemical methods. Of these methods, an ultrasonic probe proved to be the most successful in disaggregating subplastic soils. The behaviour of soils under this treatment was consistent with their field plasticity rating. Chemical treatments such as hydrochloric acid for carbonate enriched soils and sodium dithionite for the removal of iron oxide were unsuccessful in disaggregating subplastic soils. Detailed particle-size analyses showed that superplastic and normal plastic soils were readily disaggregated with gentle methods, and only minor changes occurred in their particle-size distributions with prolonged ultrasonic treatment. In particular, the fine clay fractions of these soils were readily released. Soils with subplastic properties showed an increasing stability of silt-size aggregates with increasing subplasticity and a corresponding difficulty in the release of fine clay. It was concluded that subplasticity in these soils is closely associated with the presence of a fine clay fraction, a high proportion of which is very strongly bonded into silt-size aggregates.
The geographic variation of salt precipitated over Western Australia
Authors: Hingston FJ , Gailitis V
Published: April 2005

The amounts of Na+, Mg2 +, K+, Ca2 +, C1-, SO42-, HCO3- and dust precipitated in rainfall and as dry fallout into continuously open collection funnels are reported for 59 centres throughout Western Australia. Ionic accessions for 1973 were in the following ranges; Na+, 2-98 kg ha-1; Mg2+, 0.3-15 kg ha-1; Ca2+, 0.8-35 kg ha-1; K+, 0.3-14 kg ha-1; SO42-, 2-57 kg ha-1; C1-, 2-180 kg ha-1; HCO3-, 1-105 kg ha-1. Chloride deposition at the coast is approximately an order of magnitude greater in the south-west of the state than in the north. In each region the amount of chloride precipitated exhibited the usual decrease with distance inland. There were regional differences in rainwater salt composition. Excess of ions over the amounts attributed to oceanic aerosols are explained by the locations of sampling centres relative to other source areas. Perth, the largest city, had the highest excess sulphur and above average values were obtained at the larger mining and country centres. Industry and domestic fires are the probable sources of this sulphur. Excesses of all ions from terrestrial sources were indicated at many inland centres, and were greatest in the zone of salt lakes and occluded drainage in the south-west.
Relative significance of electrolyte and cation exchange effects when gypsum Is applied to a sodic clay soil
Authors: Loveday J
Published: April 2005

The hydraulic conductivity of disturbed samples of a sodic clay taken from a field experiment at Benerembah, in the Riverina of New South Wales, was increased markedly by the addition of gypsum (at 12.5 t ha-1). This initial response is considered to result mainly from an electrolyte effect rather than from cation exchange. After three seasons of irrigation of cotton, essentially all the gypsum had dissolved and the response had declined very considerably. Residual cation exchange accounted for an increase of about 10% in exchangeable calcium, and a decrease of 20 % and 5 % in exchangeable sodium and magnesium contents respectively, in the top 30-40 cm. The exchange involved 40-50% of the calcium applied and represented, in terms of exchangeable sodium lost, a replacement efficiency of some 20-30%. Below 60 cm the situation was reversed with an apparent loss of exchangeable calcium and an increase in exchangeable sodium. Leaching of soluble calcium, magnesium and sodium chlorides, somewhat greater than that in normally tilled soil, occurred especially from between 40 and 120 cm in the gypsum treated-deep tilled soil. Soluble sulphate, on the other hand, was retained in the profile above 130 cm, in amounts about equal to that applied as gypsum. The soluble chlorides accumulated below 130 cm, including apparently the unaccounted applied calcium and exchangeable calcium lost from depths below 60 cm. Deep tillage alone enhanced leaching of soluble calcium and sodium in the upper 80 cm to a similar degree to that when combined with gypsum treatment.
On the validity of the theory of flow in saturated swelling materials
Authors: Smiles DE
Published: April 2005

Recently there has been concern that the reorientation of particles during transient flow of water in a saturated swelling material might result in the hydraulic conductivity and capillary potential not being well-defined functions of the water content. If this were the case, the conventional theory of one-dimensional liquid flow in these materials would be invalid. This paper shows that the hydraulic-conductivity/water-content relationship calculated using physically based approximate theory applied to outflow data obtained from red mud, is single-valued and independent of initial water content. Furthermore, the relationship permits recalculation, using a correct iterative procedure, of the data from which it was derived. It is concluded that the data provide no evidence to reject the theory, and that particle reorientation, if it occurs, is parametrized by the water content.
Improved method of analysing difficult soil extracts by flame atomic absorption spectrometry - Applicable to measurement of copper in ammonium oxalate extracts
Authors: Simmons WJ , Plues-Foster LA
Published: April 2005

The advantages of a simple procedure, using very small volumes of solution (200 �l), in overcoming the difficulties associated with the aspiration of soil extracts containing either high salt concentrations or salts of low solubility, is illustrated by its application to the measurement of copper in ammonium oxalate extracts. Details of the simple precautions necessary to obtain optimum performance with the method are given. Relative standard deviations ranging from 12 to 3 % were obtained for soils containing 0.31-1.94 �g copper/g. Good agreement with the results obtained by a more time-consuming method, as well as satisfactory recoveries and the absence of the effect of dilution of the extract on the result, indicate the good accuracy of the proposed procedure.
Measurement of aggregate size
Authors: Coughlan KJ , Fox WE
Published: April 2005

A technique was developed, based on the addition of quartz of different sizes to a mechanically dispersed soil clay, to determine the size of the largest aggregates (agglomerates) stable to both wetting and drying. The technique was based on the assumption that quartz particles larger than the agglomerate cannot be incorporated within it, and thus will act as foci for failure upon wetting and drying. The agglomerate size determined using this technique, approximately 0.2 mm, was in good agreement with estimates from measurements of water stability, dry aggregate stability and aggregate bulk density on pure clay samples. Neither mechanical dispersion nor the addition of quartz appeared to alter the size of the clay agglomerate; aggregates larger than 0.5 mm are apparently formed by amalgamation of agglomerates, and subsequent fragmentation, on drying.
A note on the shrinkage behaviour of a clay paste under various loads
Authors: Talsma T
Published: April 2005

Experimental shrinkage lines, obtained by simple measurements of vertical shrinkage and moisture loss, are shown for a swelling clay paste. Sample loading substantially lowered the void ratio at any given moisture content, although all shrinkage lines remained approximately parallel to each other. Ranges of 'zero', 'residual', and 'normal' shrinkage were readily identified for the loaded samples, but were less distinct for the unloaded samples.
Salinization of non-irrigated soils and associated streams: a review
Authors: Peck AJ
Published: April 2005

Saline seepage has reduced agricultural production and increased solute and sediment loads in streams and rivers in Australia and North America. The problem has developed where soils which contain substantial quantities of soluble salts have been developed for cultivation within the last 50-100 years. Salts may accumulate in surface soils by evaporation of saline surface water from poorly drained areas, or by seepage and capillary flow from unconfined or leaky confined aquifers. For some part of the year, water at atmospheric pressure is usually found within a few metres of the surface of a saline seep. In exceptional combinations of soils and weather, salts accumulate in the plant root zone because there is no net movement of water beyond this depth. The key to reclamation of a saline seep is appropriate management of water: either surface or subsurface drainage, or encouraging maximum use of water by plants, particularly in recharge areas. Another strategy is to plant salt-tolerant vegetation on the seep and await the result of natural leaching processes, but these are often very slow. Several reclamation techniques have been investigated, but they have found little application up to the present time.
The use of environmental chloride and tritium to estimate total recharge to an unconfined aquifer
Authors: Allison GB , Hughes MW
Published: April 2005

A portion of the Gambier Plain underlain by an unconfined aquifer with readily definable hydrologic boundaries has been divided into a number of areas within which soil types have similar hydrologic properties. Mean annual recharge has been estimated for each area using both the tritium concentration and the chloride concentration of water within the soil profile. Good agreement was obtained between the two methods with local recharge varying between 50 and 250 mm year-1. Total mean annual recharge for the area has been estimated to be 2.4 � 0.3 x 108 m3 year-1, and this compares favourably with an estimated discharge of 2.5 � 0.3 x 108 m3 year-1.
An investigation of recharge to the Namoi Valley aquifers using environmental isotopes
Authors: Calf GE
Published: April 2005

Environmental tritium and radiocarbon were used to study aspects of groundwater origin, transport and mixing in the complex aquifer system underlying the Namoi Valley, N.S.W. A substantial proportion of the water in the upper aquifer (depth less than 25 m) percolated underground in the post-nuclear period (after 1955). The observed relationship between �13C value and distance is evidence for riverwater recharge in the upper aquifer. There is evidence that water in the middle aquifer system (depth 50-75 m) percolated underground about 600 years ago. Finally, it is suggested that water from the Great Artesian Basin leaks into the deeper water of the lower aquifer system.
Note on the role of a shallow aquifer in dryland salinity
Authors: Peck AJ
Published: April 2005

The depth of a saline water table which may affect salinity of non-irrigated surface soil is estimated by extrapolation of the criterion used in irrigation agriculture.
Binary packing theory and the physical properties of aggregates
Authors: Coughlan KJ , Loch RJ , Fox WE
Published: April 2005

The objective of this study was to examine variations in the physical properties of non-compacted soil-sand aggregates in terms of binary packing theory. Two soils were used, a swelling black earth and a krasnozem with low swelling capacity, and aggregates with varying clay percentage were prepared by dispersing the soil, mixing with 100-50 �m sand, and wetting and drying. At lower clay percentages, void ratio with increasing clay was greater than that predicted from theory. This was attributed to clay entering between sand junctions and increasing porosity by expanding the coarse matrix. From water retention and swelling data, the transition from coarse to fine matrix occurs in both soils at about 40 % clay. In the fine particle matrix, variation of void ratio in the krasnozem aggregates was as expected from theory. In the black earth, no significant variation in void ratio occurs at clay percentages > 40%. This was attributed to porosity created around the sand particles owing to differential swelling and shrinkage. Results obtained by other workers are explained in terms of binary packing theory and the concepts developed in this paper.
Changes in soil phosphorus and pH in a red earth soil during build-up and residual phases of a wheat clover ley farming system
Authors: Batten GD , Blair GJ , Lill WJ
Published: April 2005

In a red earth soil at Wagga eight soil phosphorus pools, and pH, were measured. Positive linear relationships were found between the amount of fertilizer phosphorus applied prior to the start of the experiment (1972) and the inorganic (Pi) pools. Despite a range in total phosphorus of 130 ppm the plots had similar organic (Po) pools. Mehlich phosphorus (0.05 N hydrochloric acid + 0.025N sulphuric acid) and its major component, aluminium phosphorus, increased more rapidly with each unit of fertilizer phosphorus than other Pi pools. During 1972-1974 the soil carried grazed clover pasture but no phosphate fertilizer was applied. There were linear declines in soil total phosphorus, aluminium phosphorus and Mehlich phosphorus pools. The rates of decline were higher on plots which had higher phosphorus levels at the beginning of the residual phase. The Mehlich phosphorus pool declined by 1.8 to 9.3 ppm. 'Available' phosphorus (Bray and Kurtz 1) declined at a similar rate, but 'available' phosphorus (Colwell) declined more rapidly. Po increased at a mean rate of 5.4 ppm year-1. This was similar to the estimated return of Po in plant and faecal material on low phosphorus plots, but only about 30% of the return of Po and high phosphorus plots, indicating that a substantial quantity of Po can be mineralized in a pasture ecosystem. Some movement of phosphorus to the subsoil was noted during and immediately following phosphate application. Soil pH declined by 0.1-0.2 units during the residual phase.
Corrigenda - The nature and possible origins of soluble salts in deeply weathered landscapes of eastern Australia
Authors: Gunn RH , Richardson DP
Published: April 2005

Extensive areas of salt-affected soils in eastern Australia occur on the exposed lower zones of lateritic profiles or in derived materials. Analyses of 96 samples of mottled and pallid zones collected in this study show that they generally contain appreciable soluble salts, predominantly sodium chloride, particularly where they developed in argillaceous sedimentary rocks which underlie about two-thirds of the area, and in some granitic rocks. Analyses of 96 samples of unweathered rocks indicate that some contain moderate to appreciable quantities of sodium and chloride, and it is suggested that these and other soluble ions accumulated in the lower zones as a result of deep weathering in the Mid-Tertiary. Atmospheric accessions of sea salts in rain or dry fallout at present rates account partly for the occurrence of salt-affected soil landscapes in some coastal areas but are unlikely sources of salts far inland. Soils formed in situ on weathered basalt, argillaceous sedimentary and granitic rocks which have been exposed at the surface since the Late Tertiary are not salt-affected, because climatic, topographic and hydrologic conditions are different from those of the Mid-Tertiary and only small volumes of rock are involved.