bluuebunny/crossref_metadata_2025 huggingface dataset:
The relative contribution of plant residues and fertilizer to the phosphorus nutrition of wheat in a pasture cereal system
Authors: Mclaughlin MJ , Alston AM
Published: April 2005

Wheat plants (Triticum aestivum cv. Warigal) here grown in a solonised brown soil (Calcixerollic xerochrept) which had been previously cropped to medic (Medicago trunculata cv. Paraggio). The 33P-labelled medic residues and 32P-labelled monocalcium phosphate were added to the soil in factorial combination. Amounts of 31P, 32P and 33P in the wheat plants and in the soil microbial biomass were determined. Addition of residues depressed wheat dry weight, 31P and 32P uptake, while simultaneously increasing amounts of 31P and 32P incorporated into the microbial biomass. Addition of fertiliser had no effect on the proportion of plant P taken up from the residues, but significantly increased the proportion of microbial P derived from this source. The 31P held in the microbial biomass was significantly increased by both residue and fertiliser P addition, with the former having the larger effect. Of the total P applied to the soil, medic residues contributed approximately one-quarter of that supplied by the fertiliser. Of the total P in the wheat plant, medic residues supplied approximately one-fifth of that supplied by the fertiliser.
Erosive effects of the large water drops (gravity drops) that fall from plants
Authors: Moss AJ , Green TW
Published: April 2005

A large proportion of rainfall, intercepted by plants, is released again as large 'gravity drops', averaging about 5 mm in diameter. Almost all raindrops are considerably finer, and less erosive, than these large drops, and such conversions can thus result in increased drop erosivity. Because all are large, fall height provides the major control of gravity-drop erosivity. Experimental studies demonstrated that erosivity rose rapidly over the first 2 m of free fall, and it was found that only drops released from less than 0.3 m above the soil surface had small-to-negligible erosivity. Conversion of some 15-20% of a fine, artificial rain to gravity drops by a small tree branch, held only 0.8 m, above a shallow water flow, more than tripled the transport rate of medium sand.
Thermal properties of swelling clay soils
Authors: Ross PJ , Bridge BJ
Published: April 2005

The thermal properties of swelling clay soils do not appear to have been previously studied, even though they should be different from those of non-swelling soils because of changes in pore size and structure with water content. We measured the thermal diffusivity of small discs cut from cores of a highly swelling black earth (Pellustert) using the pulse method, common in materials science but not previously applied to soils. Thermal conductivity was calculated from thermal diffusivity and heat capacity per unit volume. The behaviour of these thermal properties was indeed different from those reported for nonswelling soils. The conductivity and diffusivity at low water contents were several times higher, increased much less with water content, and eventually decreased when the soil became saturated and swelled. The heat capacity per unit volume increased more slowly with water content because of the swelling. Over the agriculturally important suction range from 10 kPa to 1.5 MPa (0.1 to 15 bar), the conductivity decreased with increasing water content, a behaviour opposite to that of non-swelling soils. The behaviour could be predicted by three theoretical models, each with two parameters estimated from the data. The first parameter, the conductivity of soil solids, was common to all models, and estimated values ranged from 2.2 to 2.6 Wm-' K-l. The model of de Vries, commonly used in soil science, was applied with the soil solids matrix as the continuous medium and fitted the data particularly well. The second parameter in this model was a shape factor for small pores. Its estimated value corresponded with spheroidal pores with a diameter-to-height ratio of 16, which is reasonable in a swelling clay soil. The de Vries model was used to calculate the conductivity of bulk soil in the vertical direction, assuming that 20% of soil shrinkage appeared as isolated, randomly distributed cracks between aggregates. The conductivity was substantially less than that of the aggregates at lower water contents, but differed little for wetter soil at suctions below 1.5 MPa. In contrast, calculated values of conductivity were much lower when the de Vries model was applied with air as the continuous medium to a cultivated soil structure such as might be found in a seedbed.
The nature of swelling in soils
Authors: Jayawardane NS , Greacen EL
Published: April 2005

While existing swelling models adequately describe the swelling in extensively-swelling soils, their applicability to moderately-swelling soils has not been previously tested. The swelling of different layers of a transitional red-brown earth measured in situ using swelling gauges could not be described using existing swelling models. Values of �, defined as the ratio of change in bulk volume of the soil to change in gravimetric moisture content, were less than 0.33 over the whole of the measured moisture range in all layers of this soil, except the 0.25-0.55 m depth. This indicates that the extent of swelling was less than the normal, three-dimensional swelling described by existing models. Modifications to these existing models are proposed to describe the swelling in soils with moderate swelling characteristics. The compressibility factor (�), defined as the ratio of the change in void ratio to the change in moisture ratio, measures the same soil property as the values. Values of � determined in previous field studies and on soil cores of several clay soils are also less than the 0.33 specified for normal swelling, in keeping with the expectations of the modified swelling model. However, the need for further field testing of this model for moderately-swelling soils is emphasized. The limitations of existing methods for determining swelling characteristics of soils using core samples are discussed and several alternative procedures for in situ measurements are suggested.
Wood ash stone near Sydney, NSW - a carbonate pedologial feature in an acidic soil
Authors: Humphreys GS , Hunt PA , Buchanan R
Published: April 2005

Wood-ash stone, composed mainly of calcite (XRD, XRF, EMS and petrological determination), has been found within the remains of a large, standing and mostly burnt tree (Angophora costata) near Sydney, N.S.W. This may be the first recorded occurrence of wood-ash stone in Australia and outside North America. Slow burning of standing trees is proposed as a mechanism for producing carbonate features in nutrient poor and acidic soil parent materials such as the quartzose Hawkesbury Sandstone.
The influence of dolerite dykes on saline seeps in southwestern Australia
Authors: Engel R , Mcfarlane DJ , Street G
Published: April 2005

Geophysical surveys, soil and geological mapping and hydrologic studies have been used to show an association between dolerite dykes and the occurrence of saline seeps on two catchments in southwestern Australia. The role of the dykes in the location of the saline seeps is explained and the potential contribution of routine geophysical surveys to salinity studies is highlighted. Magnetic surveys and soil and geological mapping identified dolerite dykes crossing the main drainage line of each catchment. Soil resistivity and conductivity surveys showed that these dykes are associated with saline soils. Seismic refraction surveys over these dykes indicate deeper weathering profiles. Groundwater pressures and hydraulic conductivities measured in bores across one of the weathered dykes showed that the clay saprolite formed above the dolerite is less permeable than the surrounding weathered granite. The lower permeability is probably due to the finer texture of the saprolite and/or a lower frequency of preferred flow pathways. The clay formed above the dolerite acts as a linear hydraulic barrier to lateral groundwater flow and results in the discharge of saline groundwaters into surface soils.
Effects of extraction technique on concentrations of soluble salts in soil saturation extracts
Authors: Dowling AJ , Howitt CJ
Published: April 2005

Solution yield and saturation extract salinity for a range of south-east Queensland soils are described in relation to solution extraction by leaching, over a range of extraction times, and by centrifuging. Yield, pH, [Ca] and [HCO3] were affected by extraction technique. In leached extracts, compared with centrifuged extracts, solution pH was more variable and [HCO3] and [Ca] were higher. Leaching overnight consistently produced solution yields in excess of 20 g 100g-1 added water to saturation. Variations in these attributes reflect differences between the two extraction techniques which can be explained in terms of variable levels of CO2 in the solution collection assembly with air entry during extraction. Centrifuging minimised air entry and, hence, the gadliquid ratio in the extractor. The CO2 mediated changes are thus less for centrifuged than leached extracts. Centrifuging, as an extraction technique, therefore, has more relevance than leaching if specific mineralogic controls on solution composition are being determined.
Observed and predicted trends from a sandy loam soil under constant and staggered evaporativity
Authors: Jalota SK , Prihar SS
Published: April 2005

This study was undertaken to check whether the evaporation loss computed from isothermal flow equation supported the previous observations of the authors concerning the sensitivity of evaporation rate in the falling rate stage to evaporativity (E0), with evaporation under higher E0 lagging behind that under a lower E0. Evaporation, computed from the successive moisture profiles predicted numerically from water content gradients and D(�) and K(�) relations, agreed closely with the observed values under the constant, as well as staggered E0 irrespective of redistribution time before commencement of evaporation. Thus, the study has theoretically established that, depending upon the soil and E0�s involved, cumulative evaporation under lower E0 can exceed that under higher E0. The evaporation rate during the falling rate stage is not only governed by transmission properties of the soil alone but also is influenced by E0.
Evaluation of selected extractants for boron in some Queensland soils
Authors: Aitken RL , Jeffrey AJ , Compton BL
Published: April 2005

Glasshouse and laboratory studies were undertaken to evaluate a range of extractants for determining the boron status of a suite of predominantly acidic soils. In addition to hot water (commonly used as an extractant for soil boron), hot 0.01 M CaCl2,, 0.05 M mannitol/0.01 M CaCl2, 0.05 M mannitol (buffered at pH 7.9, 1 M NH4OAc, 5% (v/v) glycerol and 0.01 M tartaric acid were assessed as extractants since these reagents can complex boron. Sunflower (Helianthus annuus cv. Hysun 31) was grown with three levels of applied boron (0, 0.5 and 1.0 kg B ha-1) in each of 20 soils. Relative dry matter yield, tissue boron concentration, boron uptake and relative boron uptake of control plants (0 kg B ha- l) were determined. Both hot water and hot 0.01 M CaCl2 extractable boron were related to each of these plant parameters, whereas boron extracted by the other procedures was not. Levels of boron extracted with mannitol and glycerol were very low in comparison to those displaced from the soil by the refluxing procedures. The inability of mannitol to extract boron from these soils is discussed in relation to the chemistry of mannitol-boron complexes, and it is suggested that mannitol would not be an effective extractant for boron in acid soils. Soil solution extracts (obtained after equilibration at 10 kPa matric suction) had concentrations < 0.1 �g B ml-l. Because of the low concentrations and narrow range across the 20 soils, soil solution boron was not related to plant growth parameters obtained from the glasshouse study.
The association of maghemite and corundum in Darling Range laterites, Western Australia
Authors: Anand RR , Gilkes RJ
Published: April 2005

Maghemite in Darling Range lateritic duricrust ranges from 2 to 10% in abundance, contains less than 5 mole % Al and occurs as aggregates of very small ~ 150 A subrounded platy crystals. Corundum is also present, ranging from 1 to 3.5% in abundance, and it contains less than 3 mole % Fe and occurs as rounded (~250 A) crystals. The maghemite and corundum contents are positively correlated (P < 0.01), which may indicate a common origin due to dehydroxylation of Fe and Al oxyhydroxides in bush fires.
The influence of the addition of goethite to soil on the dissolution of North Carolina phosphate rock
Authors: Kanabo IAK , Gilkes RJ
Published: April 2005

This laboratory experiment investigated changes in the dissolution of North Carolina phosphate rock and NaHCO3-soluble P arising from the addition of goethite (�-FeOOH) to soil. Increasing goethite in the soil increased the amount of phosphate rock (PR) dissolution as measured by the increase in exchangeable Ca (�Ca) values. Increased dissolution was, however, associated with decreased NaHCO3- soluble P due to P retention by goethite. The proportion of P dissolved from PR that was soluble in 0.5 M NaHCO3 solution decreased with contact period and with increased goethite. The increase in exchangeable Ca (�Ca) was a better indicator of the extent of PR dissolution in goethite-containing soils than NaHCO3-soluble P.
Effects of different dispersion and fine fraction determination methods on the results of routine particle size analysis
Authors: Thorburn PJ , Shaw RJ
Published: April 2005

Particle-size analysis (PSA) methods to be used in routine situations need to be rapid, require no prior information about the sample and give precise results over a wide range of soil textures. Effects of three physical dispersion and two fine-fraction determination methods on PSA results were investigated over a wide range of soil textures to find the most appropriate technique for routine PSA. Interactions between physical dispersion and fine-fraction determination methods were also investigated. The reciprocating shaker produced significantly lower silt and fine sand and higher coarse sand (and clay, although not significant) values than either drink mixer or end-over-end shaker dispersions. This result was interpreted as the reciprocating shaker giving the most effective dispersion, with aggregated clay being dispersed to primary particles while coarse sand was not fragmented to fine sand or silt. The end-over-end shaker did not reliably disperse a heavy clay soil, and so cannot be recommended for routine use where similar soils may be encountered. When considered over all soils and dispersion methods, hydrometer clay and clay + silt values were higher than pipette values. These results were due to the effective depth of the hydrometer being greater, on average, than the depth of the pipette. However, there were interactions between dispersion and fine-fraction determination methods for the clay and clay +silt classes. Hydrometer values were greater than pipette values with drink mixer and end-over-end shaker dispersion, but were similar with reciprocating shaker dispersion. For the clay fraction, inferior dispersion given by the drink mixer and end-over-end shaker resulted in a significant mass of particles between the sampling depths of the pipette and hydrometer, causing the higher hydrometer values. For the clay +silt fraction, both drink mixer and end-over-end dispersion methods fragmented sands to a size which was recorded by the hydrometer but not the pipette. These interactions highlighted the requirement for effective dispersion where clay and silt are determined by the hydrometer, and may explain some of the conflicting observations of the precision of the hydrometer compared with the pipette. Reciprocating shaker physical dispersion combined with the hydrometer fine-fraction determination method was found the most appropriate PSA method combination for use in a routine situation.
Estimation of parameters for the Philip two-term infiltration equation applied to field soil experiments
Authors: Bristow KL , Savage MJ
Published: April 2005

Two methods based on least squares analysis used to estimate coefficients in the Philip two-term infiltration equation are compared. The one method maintains the infiltration equation in its original form, while the other involves a mathematical transformation which introduces self-correlation and yields different estimates of the coefficients. Data from field infiltration experiments are used to illustrate these differences, and the need to distinguish between fitting data to empirical models and deriving system parameters from analysis of physically based models is emphasized.
Adsorption and desorption of boron by goethite
Authors: Bloesch PM , Bell LC , Hughes JD
Published: April 2005

The effects of varying pH, concentration of boron, and competing anions on the adsorption of boron were examined. Boron adsorption initially increased with pH, peaked at approximately pH 8, and then declined. The presence of phosphate reduced adsorption over the pH range 5.2-10.6; the effect of sulfate was less than that of phosphate and ceased at about pH 7. The presence of mannitol caused virtually no difference in boron adsorption up to about pH 6, but reduced adsorption at higher values. The model by Bowden and coworkers was successful in describing both the charge characteristics of goethite in the absence of boron adsorption and the effects of pH and boron concentration on adsorption of the element. The best fit of the model was achieved when B(OH)4-, B3O3(OH)4-, B4O5(OH):- and B5O6(OH)4- were considered as the adsorbing species, although B(OH)4- and B4O5(OH)24- were predicted to be the major adsorbing ions. Boron adsorption was found to be reversible with respect to both concentration and pH. Elevated temperature increased the amount of desorption at both pH 6 and 8. The effect of mannitol on boron desorption mirrored the effect of the compound on adsorption of the element; there was no effect up to pH 6, but at higher pH values desorption was increased. The significance of the desorption data for soil testing for boron is discussed.
Binding of cadmium by montmorillonite humic acid mixtures - Miscible displacement experiments
Authors: Campbell GD , Galicia HF , Schindler PW
Published: April 2005

By means of the miscible-displacement approach, investigations have been carried out on cadmium adsorption-desorption by mixtures of freeze-dried montmorillonite and freshly precipitated humic acid. Low Cd surface loadings were employed and acidic (pH 4.5-5) solution conditions were maintained during both adsorption and desorption cycles. Compared with montmorillonite, Cd adsorption by humic acid was much greater so that clay-humic mixtures containing only a few per cent w/w humic acid removed appreciably more Cd from solution than that by clay alone. However, this greater Cd uptake by humic acid was offset by the susceptibility of bound Cd to desorb once the supply of Cd in the column ihput solutions was removed. Thus, both montmorillonite and undissolved humic acid had a limited ability to fix Cd, a result which may have some implication to mechanisms of Cd binding by natural clay-humic mixtures in acidic soil environments. The miscible-displacement approach appears to be well suited to examining solute interactions with poorly soluble, high molecular weight soil humic materials.
A comparison between plant response and chemical measurements of the dissolution of reactive phosphate rock in soils of different pH and phosphorus retention
Authors: Kanabo IAK , Gilkes RJ
Published: April 2005

Chemical measurements of the dissolution of reactive North Carolina phosphate rock (PR) in a lateritic podzolic soil adjusted to different pH values or amended to different P retention capacities were compared with plant response data. Soil pH adjustment consisted of incubating soil mixed with dilute HCl or solid SrCO3. The P retention capacity was adjusted by adding different amounts of synthetic goethite. Clover was grown as a test crop under glasshouse conditions on soils treated with no P and 800 �g Pg-1 soil as PR. The dissolution of PR, measured as the increase in soil exchangeable Ca (�Ca) at harvest time, increased by 46% for a decrease in soil pH from 5.78 to 4.55. Both dry weight and P content of clover tops showed no response to the greater PR dissolution at low soil pH, although twice as much P was bicarbonate-soluble at pH 4 55 compared with pH 5.78. This increase in bicarbonate-soluble P was only partly due to the greater dissolution of PR. Increasing the goethite content of the soil by 9% resulted in a 107% increase in PR dissolution but induced a 54% decrease in the bicarbonate-soluble P level compared with the control soil and consequently reduced both dry weight yield and P content of clover tops by 19% and 34% respectively.
Long term trends in fertility of soils under continuous cultivation and cereal cropping in southern Queensland .VII. Dynamics of nitrogen mineralization potentials and microbial biomass
Authors: Dalal RC , Mayer RJ
Published: April 2005

The dynamics of nitrogen mineralization potential (N0) and mineralization rate constant (k) were studied in six major soils which had been used for cereal cropping for up to 20-70 years. In the top 0.1 m layer of virgin soils, N0 varied from 110 � 22 mg kg-1 soil (Riverview) to 217 � 55 mg kg-1 soil (Langlands-Logie), representing about 13% and 11%, respectively, of total N in these soils. Upon cultivation and cropping, N0 declined by 1 7 � 0.5 mg kg-1 yr-1 (Riverview) to 4.8 � 2.0 mg kg -1 yr -1 (Billa Billa). This represented < 20% of total N lost annually from the top layer (0-0.1 m depth) of these soils. The k values varied less than the N0 values, both within and among soils, and were also less affected by cultivation than N0. The mineralizable N in cultivated soil during cropping for periods up to 70 years can be estimated from N0 and k values, taking No as 5% of total N for soils of <40% clay and 15% of total N for soils of >40% clay and k as 0.066 week-1 at 40�C (0.027 week-1 and 0.054 week-1 at 25�C and 35�C, respectively). Organic C and N contained in the 'stabilized' microbial biomass (determined after 30 weeks' pre-incubation) accounted for 1.7-38% of total organic C and 2.0-5.1% of total N in the six soils studied. The microbial biomass C and N declined with cultivation in most soils, biomass N representing 10-23% of the total annual loss of N0. The microbial biomass, urease activity and total N, in addition to a number of other soil properties [e.g. light-fraction (<2 Mg m-3) C, sand-size C, CEC and ESP], were significantly correlated with N0 and k, thus indicating the existence of a myriad of environments for the activity, association and stability of microbial biomass and potentially mineralizable N in soil.
Microflora of soil and wheat rhizosphere in a field following fumigation
Authors: Sivasithamparam K , MacNish GC , Fang CS , Parker CA
Published: April 2005

Light sand and heavier sandy loam wheat-growing soils at Wongan Hills, W.A. were fumigated (2: 1 mixture of chloropicrin and methyl bromide) to study its effect on the soil microflora. In fumigated soil, numbers of bacteria and fungi, after an initial reduction, remained high and low, respectively, in comparison to untreated soil, throughout the period of study. In the fumigated soil Trichoderma species rapidly recolonized the soil, becoming the dominant fungus by 15 days and remaining so to the end of the experiment (145 days after fumigation). There was no difference in the total numbers of bacteria, actinomycetes or fungi in the rhizosphere of wheat grown in fumigated and non-fumigated soils. The numbers of some fungal species were lower in the rhizosphere of wheat grown in the fumigated soil, these included Aspergillus glaucus, A. fumigatus, Beauveria bassiana, Cladosporium cladosporoides, Embellisia tumida, Fusarium oxysporum, Penicillium patulum, P. tardum, Phialophora mutabilis and Trichoderma saturnisporurn. The only fungi found to be significantly higher in the rhizosphere of plants in fumigated soil were F. merismoides, T. koningii and T. viride.
Characterizing water use by irrigated wheat at Griffith, New South Wales
Authors: Meyer WS , Dunin FX , Smith RCG , Shell GSG , White NS
Published: April 2005

Wheat is being grown increasingly in the irrigated areas of south-east Australia. Its profitability depends on high yields, which in turn, are highly dependent on accurate water management. This combination, together with the increasing need for greater water use efficiency to minimize accessions to rising water-tables, calls for effective irrigation scheduling. To achieve this, accurate estimates of crop water use and upward fluxes of water into the root zone from shallow water-tables are required. A weighing lysimeter, installed in 1984, measured hourly evaporation (Ea) from a wheat crop which enabled the accuracy of water use estimates to be assessed. Daily potential evaporation (Ep) was calculated from a combination equation previously calibrated over lucerne, while previously developed crop coefficients for wheat were used to convert Ep to estimated Ea. Daily Ea was the major component in a water balance model for irrigated wheat. The model was quite efficient (r2 = 0.911, but with a bias of -8.8%, which indicated that Ea values were generally underestimated. The underestimate was due primarily to the wind function used in the calculation of Ep, and alternative functions for both daily and hourly calculations were derived. The 1984 lysimeter data also showed that change in soil water content was accurately measured with the field-calibrated neutron probe. Comparisons of measured and estimated water use from field experiments in 1981 and 1982 indicated that upward flux from a water-table between 1 a5 and 2.1 m below the soil surface may be up to 30% of daily Ea. This upward flux will need to be taken into account if irrigation scheduling is to promote efficient use of irrigation water.
The relationship of gully sidewall shape to sediment production
Authors: Crouch RJ
Published: April 2005

Reports of gully side erosion describe a range of side forms. The lack of information on the relative significance of the various forms in terms of sediment production hinders the identification of the major sediment sources within gullies. Observations of gully sides in a catchment in central New South Wales showed a range of side forms being eroded at significantly different rates. Side classification and measurement by survey and erosion pins showed that vertical sides, subject to undercutting, had the highest erosion rate (75 mm yr-l) followed by vertical fluted walls (37 mm yr-l). These different rates are critical in predicting present and future rates of erosion and identifying sediment sources within gully systems.
Modified runoff curve numbers for bare crust forming sandy soils
Authors: Sharma KD
Published: April 2005

Runoff curve numbers (CN) for bare crust-forming sandy soils in the Indian Arid Zone were derived from rainfall and runoff data recorded over a period of 7 years from 1975 to 1981. Contrary to the Soil Conservation Service (SCS) handbook value of 77, the actual optimized CN for 0.5% and 5-10% slopes were found to be 87 and 91, respectively, indicating a greater volume of generated runoff from these soils than estimated by the SCS method. The handbook CN value underpredicted runoff by 47-68% for storms >100 mm and 163-400% for storms <25 mm. A significant correlation (r = 0.898, n = 227) was found between the observed and predicted values using a modified CN based on the measurements.
Comparison of three soil tests for phosphate on lateritic soil fertilized with superphosphate, crandallite rock phosphates and apatite rock phosphates
Authors: Bolland MDA , Allen DG
Published: April 2005

Different amounts of superphosphate, crandallite-millisite rock phosphate (three different samples of C-ore from Christmas Island), 500�C calcined C-ore (three different samples of Calciphos) and apatite rock phosphate (two different samples from the Duchess deposit, Queensland) were applied once only in May 1977 on lateritic soil in Western Australia. Samples of the top 10 cm of soil were collected in the summer (January-February) of 1979 and 1980 for measurement of extractable soil phosphate by the Colwell, Olsen and Bray soil tests, and the data were compared with dry matter production of subterranean clover pasture in the following spring (August). For each fertilizer in each year, the Olsen and Brayl soil test values (as dependent variables) were closely correlated with the Colwell soil test values (independent variable), and the Bray 1 soil test (dependent variable) was closely correlated with the Olsen soil test (independent variable). For the relationship between yield and soil test values, separate calibrations were required in most cases for each fertilizer and each soil test, and these calibrations showed large differences in two successive years. None of the soil tests was significantly better for predicting clover yields for the different fertilizers applied two and three years previously.
Effects of flooding and subsequent drying on consolidation of beds of aggregates of a gray clay from Narrabri, NSW
Authors: Chan KY
Published: April 2005

Changes in porosity of beds of aggragates of a grey clay, from Narrabri, NSW, on drying after flooding were studied in a laboratory experiment. For both surface soil (0-0.2m) and subsoil (0.8-1.0m) as a result of quick wetting, air-filled porosities sufficiently low (<0.1m3m-3) to be adversely affecting plant growth were recorded in the aggregate beds for much of the plant-available moisture range. Resultsindicated that, for the subsoil, the structural shrinkage phase was completely absent. Normal shrinkage prevailed and air-filled prosity remained at<0.1m3m-3 until the commencement of the residual shrinkage phase, which occurred at moisture content drier than the permanent wilting point (-1.5kj kg-1). Calcium chloride (0.01M) did not have an effect on the surface soil but significantly increased air-filled porosity of the subsoil by creating a structural shrinkage phase and hence reduced the extent of normal shrinkage (consolidation), Relevance of these laboratory results to field situations under furrow irrigation was discussed.
The effect of Aeolian accessions on soil development on granitic-rocks in south eastern Australia. I. Soil morphology and particle-size distributions
Authors: Walker PH , Chartres CJ , Hutka J
Published: April 2005

Four Alfisols in south-eastern Australia were studied to determine their genesis with special reference to textural profile development and aeolian accession. Sampling sites were located in erosional terrain developed from granitic rocks of similar composition and in hillcrest positions to reduce the chance that colluvial deposition had affected pedogenesis. The sampling transect was placed in such a way that differences in regional aeolian accession could be reflected in soil properties. The chemical and physical characteristics of these soils indicated that strong leaching had been important in their genesis. Detailed particle-size data confirmed that the coarsest fractions in all profiles were derived from weathered granite. The A horizons tended to have a single size mode in the sand range and very little clay-size material. The B horizons tended to be bimodal with the greatest amount of clay in the 0.12-0.06 �m size class and a mode in the sand range close to that of the A horizons. The appearance of a peak in the 62-31 �m size class, which is progressively stronger in the western sites, probably relates to a fine aeolian accession which has penetrated the B and C horizons. The amount of clay contributed by aeolian accession to textural B horizons is unknown. At erosional sites in south-eastern Australia, where the probability of colluvial and fluvial sedimentary layering is minimal, aeolian accession of fine fractions has complicated the interpretation of pedogenesis.
The effect of Aeolian accessions on soil development on granitic-rocks in south eastern Australia. II. Oxygen-isotope, mineralogical and geochemical evidence for Aeolian deposition
Authors: Chartres CJ , Chivas AR , Walker PH
Published: April 2005

Oxygen-isotope abundance in quartz grains, total chemical analyses and clay mineral data are used to identify aeolian deposits in four soil profiles developed on granitic rocks. Results indicate that quartz fractions derived from I-type granitic rocks have �18O values less than 10.7%, whereas fine sand-sized (50-31 �m) quartz separates from the same soils have �18O values of > 11.6�. Similar, but less marked, differences were observed in a soil on an S-type granitic rock, suggesting that addition of aeolian material to all the soils investigated has been an important process of soil formation. X-ray diffraction data indicate the presence of decreasing proportions of clay mica h the soils with increasing distance from probable sources of aeolianites in the Riverine Plain, raising the possibility that clay mica, along with other clay minerals and clay-size quartz, may have been also deposited by wind in the soils. Titanium/zirconium elemental ratios are less useful indicators of aeolian accession because of complications arising from the weathering of biotite in the underlying granitic rocks. Probable losses of yttrium from the soils also appear to result from weathering of materials derived from the granitic rocks, although some data indicate that zirconium/yttrium ratios for the 50-2 �m fractions may also be indicative of aeolian accession.
The effect of Aeolian accessions on soil development on granitic-rocks in south eastern Australia. III. Micromorphological and geochemical evidence of weathering and soil development
Authors: Chartres CJ , Walker PH
Published: April 2005

Micromorphological, mineralogical and chemical data show that clay illuviatidn, clay decomposition and strong weathering of biotite and feldspars to clay mineral$ have all been significant processes of soil development in three red podzolic soils and one red earth. Decomposition of biotite and illuviation of swelling clays into fissures in the saprolite and C horizons appear to have aided the physical fragmentation of the granitic parent materials. Disruption of illuvial features by faunal activity and shrink-swell processes in the upper B horizons accentuate apparent illuvial clay maxima in the B3 and C horizons. Low clay contents in the A horizons of the red podzolic soils examined result from ehviation and clay decomposition, whereas the higher fine sand contents of these horizons result, in part, from the deposition of aeolian transported materials. Substantial aeolian deposition at another site has led to the development of a red earth. The deposition of greater amounts of aeolian material to the soils to the west of Canberra has led to the development of complex, polycyolic soil profiles in comparison to the profiles investigated towards the coast.
Measurement of soil aggregate settling velocities. 1. A modified bottom withdrawal tube method
Authors: Lovell CJ , Rose CW
Published: April 2005

Sediment eroded by water consists largely of soil aggregates. The settling velocity of such aggregates and primary soil particles is of fundamental importance to the processes of sediment transport and deposition in water. A modified bottom withdrawal tube method is presented for the direct measurement of the settling velocity distribution of soil aggregates or particles of different sizes that settle together in a polydisperse suspension. The modified method overcomes experimental error and analytical deficiencies present in the initial method and is suitable for measuring settling velocities up to 0.5 m s-1. The method employs the bottom withdrawal principle; new exact theory is presented for interpretation of sedimentation data thus measured. By complementing the pipette or hydrometer methods which measure settling velocities less than 10-3 ms-1, this modified method allows analysis of the entire range of settling velocities encountered in natural sediment. Settling velocity distributions measured for a variety of sediment types are illustrated.
Measurement of soil aggregate settling velocities .II. Sensitivity to sample moisture content and implications for studies of structural stability
Authors: Lovell CJ , Rose CW
Published: April 2005

The importance to settling velocity of initial sample moisture content of non-immersed sediment is presented for a well-aggregated, cracking clay soil (a Vertisol). Eroded sediment was analysed immediately following deposition and after drying to various moisture contents. Settling velocity distributions were measured using the modified bottom withdrawal tube method. Initial aggregate settling velocities are not retained if sediment is allowed to dry to pore water suctions greater than 1.5 MPa prior to analysis, which involves immersion. Coarse aggregate velocities are reduced, a result attributed to slaking, while fine aggregate velocities are increased, a result attributed to binding of dispersed clay during drying with reduced re-dispersion upon immersion. Exposure of air-dry sediment to a saturated atmosphere for varying lengths of time can improve agreement with initial levels of aggregation, but the improvement varies between different samples of this Vertisol. The settling velocity distribution of a sediment is shown to be an indicator of aggregate stability to wetting. Combination of a useful pretreatment of air-dry sediment, which affords improved reproducibility, with the recognized low technique variability given by settling tubes, is demonstrated to be a useful method for comparative studies of structural stability.
Application of computer assisted tomography (CAT) to gamma attenuation measurement of soil water content
Authors: Hainsworth JM , Aylmore LAG
Published: April 2005

This paper demonstrates the successful application of computer assisted tomography (CAT) to �-ray attenuation measurements and the modification of a conventional gamma scanning system to enable changes in the spatial distribution of soil water content to be accurately monitored in soil columns. The relatively inexpensive gamma system has been shown to provide a resolution comparable to that obtainable with commercially available but extremely expensive X-ray CAT scanning systems. However, longer counting times are required with gamma radiation, thus limiting the usefulness of the technique for some soil water studies. A comparison of the efficiency of several source-detection combinations illustrates their relative advantages and disadvantages.
Flow behavior of allophane and ferrihydrite under shearing forces
Authors: Wells N , Childs CW
Published: April 2005

Allophane and ferrihydrite, two minerals of short-range order, impart major physical and chemical character to soils derived from weathered volcanic ashes. Undisturbed samples of both minerals, having low dry bulk densities, ~0.3 t m-3, and high natural water contents, ~250% w/w, have been sheared between cone and plate in a rotary-type viscometer. During rotor acceleration, both developed maxima of shear stress that did not re-establish on deceleration. A sudden loss of strength indicated sensitivity to shearing forces. By sieving lumps of aliophane and ferrihydrite, pastes were readily produced which were adjusted to a range of moisture contents and sheared. These pastes developed maxima of sensitivity at ~170% H2O w/w. Below 100% H2O w/w a state of friability, with make and break of particle adhesion, replaced that of laminar flow. Ferrihydrite, in both crumb and paste form, had lower sensitivity than allophane. Pastes of both materials became less sensitive on resting, but their initial strength had not recovered after 2 months. These properties of sensitivity to shear and lack of strength in their disturbed state have implications in soil engineering for trafficability and stability of earthworks.
Phosphorus leaching in sandy soils .II. Laboratory studies of the long-term effects of the phosphorus source
Authors: Weaver DM , Ritchie GSP , Anderson GC
Published: April 2005

Long-term phosphorus (P) losses and gains in sandy soils continuously fertilized with either ordinary superphosphate or coastal superphosphate (a granulated mixture of superphosphate, rock phosphate and elemental sulfur) or previously fertilized with superphosphate were investigated under leaching conditions in columns in the laboratory. The soils were subjected to 10 consecutive cycles designed to simulate the mediterranean weather conditions in the Harvey region of the Coastal Plain of Western Australia. Each cycle consisted of a wet phase during which the equivalent of 850 mm of rainfall was leached through the soil and a drier phase during which the soil was incubated in the presence of moisture equivalent to summer rainfall (150 mm). Dissolved inorganic P in the leachate was used as a measure of P loss. A sequential fractionation procedure (a resin extraction followed by 0.5 M sodium bicarbonate, 0.1 M sodium hydroxide and 0.1 M sulfuric acid extractions) and total inorganic and organic P were used to measure changes in P levels in the soils. Phosphorus losses from the previously fertilized soils decreased logarithmically with increasing number of cycles. Total inorganic P and resin-extractable P were able to explain >94% of the variation in P losses. Addition of either fertilizer increased the amount of P leached from the soil and 10-40% more P was leached by adding superphosphate rather than coastal superphosphate. The percentage of the cumulative P lost by leaching decreased with increasing application rate of both fertilizers when expressed as a percentage of the cumulative water plus citrate-soluble P added. Addition of either fertilizer increased the amount of acid-extractable P, but coastal superphosphate had a much greater effect than superphosphate. Leaching losses of P were influenced by fertilizer solubility in the short term (< 1 year). In the long term, however, the water plus citrate-insoluble P in the fertilizers also contributed to P losses by leaching.
Hydrological effects of land use change on small catchments at the Narayen research station, Queensland
Authors: Prebble RE , Stirk GB
Published: April 2005

The hydrological effect of a change in land use, where trees were killed and improved pasture was established, was examined in an open grassy woodland on duplex soil derived from granite. Two pairs of small catchments at the Narayen Research Station, Queensland, were instrumented to measure rainfall, runoff, soil water and meteorological variables. The treated catchments stored up to 26 mm more soil water in the 0-1 m depth than those in their original condition. Evapotranspiration over a period, calculated from rainfall, runoff and soil water storage change, was similar for both treated and untreated catchments. This result was attributed to compensating factors following death of the trees which removed interception of rain and solar radiation, caused an increase in wind velocity at ground level, and allowed enhanced grass growth in the areas previously under tree canopies. A water balance model did not provide a satisfactory calibration for the detection of runoff changes resulting from the treatment. The ratios of the annual runoff from catchment pairs, although variable, did not show drastic changes as a result of treatment. So, provided a good grass cover was maintained, it seems unlikely that the treatment would greatly alter runoff. The chloride balance in the undisturbed woodland under the present climate suggests that any changes due to treatment are unlikely, but indicates that in these soils soluble ions are readily lost from the system.
Use of neutron and gamma radiation meters to estimate bulk density and correct for bias of sampling for water content in a swelling clay soil
Authors: Hodgson AS
Published: April 2005

Two radiation methods were used to estimate the bulk density of a three-dimensionally swelling grey clay soil used for furrow irrigation at Narrabri, N.S.W. Firstly, gamma ray scattering was calibrated with measurements of wet bulk density derived from undisturbed soil cores. Secondly, a high correlation between neutron counts and gravimetric water content in this soil provided a basis for predicting bulk density corrected for bias in sampling of shrinkage cracks by using a published theoretical model of three-dimensional soil shrinkage. Gamma ray backscattering was poorly correlated with wet bulk density (�w), possibly because dry bulk density and water content are negatively correlated in swelling soil, which restricted �w to a relatively narrow range of values. This technique is therefore not recommended for use in this soil. High correlation (0 82 < r < 0.98, all P < 0.001) between neutron counts and bulk density corrected for three-dimensional shrinkage was found at all soil depths between 0.1 and 1.5 m. A precision of k0.01 Mg m-3 required from three to six samples per mean, depending on soil depth. The mean relative difference between predictions of bulk density from neutron counts compared with independent estimates by the core method was <4.1% at depths below 0.3 m. The recommended procedure is therefore to predict bulk density from neutron counts in order to correct for sampling bias and bulk density effects associated with the neutron attenuation method. The method eliminates the need for additional sampling for bulk density in conjunction with the neutron moisture meter in soils that shrink and swell three-dimensionally. However, the method is not appropriate for detecting differences in bulk density between soils with different structure unless the constants used in the model and the shrinkage behaviour are known for each soil. The latter requirements would usually preclude the technique for this purpose. At low water contents near the permanent wilting point for cotton, neutron escape through shrinkage cracks did not cause problems at depths below 0.3 m. The neutron method should therefore be appropriate for use at depths below 0.3 m in dryland hydrological studies in this soil.
Influence of management on the composition of organic matter in a red-brown earth as shown by 13C nuclear magnetic resonance
Authors: Oades JM , Waters AG , Vassallo AM , Wilson MA , Jones GP
Published: April 2005

Samples were obtained from the same red-brown earth: (a) in an undisturbed state, (b) after 60 years of an exploitive wheat-fallow rotation and (c) after 40 years under a fertilized mixed grass-legume pasture. Organic materials were concentrated in various fractions which enabled comparative chemical composition of the organic materials in the three soils by 13C CPMAS n.m.r. spectroscopy. Despite more than twofold differences in the organic carbon content of the soils, the chemistry of the organic matter in the soils was similar, particularly organic matter associated with clay fractions. Most of the differences detected were associated with plant debris in particles > 20 �m which contained most of the aromatic carbon. The results indicate a rapid disappearance of phenolic-carbon which originates in lignins. The composition of sodium hydroxide extracts reflects quite well the composition of the organic matter in the soil. It is concluded that in a particular soil type, changes in amounts and nature of added photosynthate do not change the composition of the organic matter which is controlled by the microbial biomass and interactions of the biomass and its decomposition products with the soil matrix. Implications of this conclusion for the turnover of organic carbon in soil and stability of soil structure are discussed.