bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of soil bulk density on horizontal water infiltration
Authors: Sharda AK
Published: April 2005

Studies were conducted on soil columns of a silty clay loam packed at bulk densities of 1200, 1300 and 1400 kg/m3 to evaluate the influence of soil bulk density on water infiltration in the horizontal direction. Soil water diffusivity values were obtained by reversing the iterative procedure of Philip. A reduction to less than 25% in soil water diffusivity occurred near saturation with the increase in soil bulk density, but the influence of soil bulk density decreased with the decrease in relative water content. Lengths of infiltration, cumulative influx and infiltration rates also reduced markedly with the increase in soil bulk density from 1200 kg/m to 1400 kg/m3.
A study of the chemistry and hydraulic conductivity of mound materials and soils from different habitats of some Nigerian termites
Authors: Malaka SLO
Published: April 2005

Some aspects of the chemical characteristics of the crusts of the mounds of four Nigerian termites and physical properties of the crust of the mound of one were studied. It was found generally that the mound crust of Macrotermes bellicosus was poorer in chemical constituents than the surrounding soils. The reverse was the case in the mounds of Amitermes evuncifer Silverstri, Cubitermes sp., and Trinervitermes sp. The hydraulic conductivities of the crust of the mound of A. evuncifer was also determined.
A note on the bulk density of termite mounds
Authors: Malaka SLO
Published: April 2005

Termite genera such as Cubitermes, Trinervitermes and Macrotermes, are capable of compacting soils, and raising the bulk density too high for plants to colonize their mounds. In contrast, Amitermes has not been found to compact the mound texture, thus allowing the mounds to support plant growth.
Zinc chelate reactions in alkaline soils
Authors: Sinha MK , Dhillon SK , Dhillon KS
Published: April 2005

The changes in the distribution of competing metal ions during the reaction of Zn-EDTA (ethylenediamine tetraacetic acid), Zn-DTPA (diethylenetriamine pentaacetic acid) and Zn-FA (fulvic acid) with alkaline soils for periods ranging between 1 and 30 days were determined by monitoring the concentrations of complexed zinc, iron, manganese, copper, and calcium in the supernatant soil solution. The reactions of Zn-EDTA and &-FA were mainly influenced by pH of the soil suspension and the aqueous calcium concentration. The reaction of Zn-DTPA in these soils was also influenced by the release of labile iron, manganese, and copper from the solid matrix into the ambient solution. There was an initial fast decrease in the concentration of soluble zinc in the solution, followed by a slower rate of decrease. The initial fast reaction conformed to a first-order reaction kinetics. The implications of metal cation interaction during the reaction of zinc chelates with alkaline soils in the micronutrient nutrition of crops are indicated.
The nature of soil clays and the stability of microaggregates
Authors: Murti GSRK , Gurcharan Singh , Rengasamy P
Published: April 2005

The relative importance of the nature of clay fractions in the stability of microaggregates was investigated in the ferruginous soils, black soils and alluvial soils of India widely differing in their mineralogy. The influence of clay-iron oxide interaction was common in all these soils. However, the size range of stable aggregates depended on the dominant clay mineral, kaolinite influencing <50 �m aggregates and smectite in the formation of 250-1000 �m aggregates. The influence of cohesive forces between clay particles was more than the clay-iron oxide interaction in the smectitic soiIs.
Corrigenda - Ionic adsorption on variable charge mineral surfaces. Theoretical charge development and titration curves
Authors: Bowden JW , Posner AM , Quirk JP
Published: April 2005

A completely general theory is presented which can be used to describe both anion and cation adsorption on amphoteric oxide surfaces. It takes account of the fact that both the surfaces and adsorbing species are charged and that the surfaces change their charge when ionic adsorption takes place. The theory is applicable to both specific and non-specifically adsorbed ions. It is shown to account for the pH dependent charge curves of goethite, silica and two tropical soils.
The use of soil analysis for predicting the response to sulphur of pasture legumes in the Australian tropics
Authors: Probert ME , Jones RK
Published: April 2005

Sulphur extracted from soil with 0.05Ca(H2PO4)2 is shown to be useful for predicting responses to applied sulphur when establishing legumes into the native pastures of the Australian tropics. In many of the soils, levels of extractable sulphur are low (particularly in the surface horizon), and it is found that the use of a weighted profile mean gives improved predictions. A weighted profile mean of 4 ppm distinguished the responsive from the non-responsive sites. For some soils, extractable sulphur levels were much higher and increased with depth; these soils contained more than 15 ppm extractable sulphur in the surface horizon, and this criterion alone could be used to classify these soils as non-responsive. Species differences were not found. Using these criteria, 25 out of 27 observations would have been correctly predicted.
Within season variability of bicarbonate extractable phosphorus in wheat soils
Authors: Jessop RS , Palmer B , Mcclelland VF , Jardine R
Published: April 2005

Using a long-term experiment at Longerenong Agricultural College, Dooen, Vic., plots from a pasture-pasture-fallow-wheat rotation were sampled on a three-weekly basis for a year. Analysis of the samples by bicarbonate extraction for phosphorus indicated considerable short-term fluctuations in phosphorus which were only partially explained by environmental conditions. Bicarbonate extractable phosphorus was both lowest and less variable over time under a two-year pasture treatment than when under fallow.
An empirical model for drainage from soil under rain fed conditions
Authors: Aston AR , Dunin FX
Published: April 2005

An empirical relationship was derived for drainage from a podzolic sandy loam using a weighing lysimeter at Krawarree, N.S.W. The form of the equation was similar to those used to describe drainage following irrigation. The agreement between computed and measured soil moisture contents over a period of five years was good, and indicated the usefulness of such an approach to characterize drainage of soil water under natural field conditions.
Interaction of monomeric and polymeric species of metal ions with clay surfaces. I. Adsorption of iron(III) species
Authors: Rengasamy P , Oades JM
Published: April 2005

Uitrafiltration or dialysis against distilled water was used to separate polymerized ferric hydroxy cations from the monomeric cations in hydrolysed solutions of ferric nitrate. Separated poly[Fe(III)-OH] cations were polydispersed and the positive charge was inversely related to molecular size. The separated poly[Fe(III)-OH] cations were found to be stable and did not condense further during a period of 6 months. The association of iron(III) with the surfaces of sodium-kaolinite, sodium-bentonite and sodiumillite was studied using hydrolysed ferric nitrate solutions and separated poly[Fe(III)-OH] cations. As the OH/Fe ratio (and pH) of the ferric nitrate solutions increased, the critical coagulation concentration (CCC) and the maximum adsorption of iron(III) increased. The amount of iron adsorbed in the form of separated po1y[Fe(III)-OH] cations was small and was related to the positive charge per iron atom of the polycations. It is proposed that iron(III) in solutions containing only polycations and solutions containing a mixture of mono- and polycations reacted differently with clay surfaces. A reaction of polycations with the surface hydroxyls leading to chemisorption and irreversible flocculation of clays is proposed.
Interaction of monomeric and polymeric species of metal ions with clay surfaces. II. Changes in surface properties of clays after addition of iron(III)
Authors: Rengasamy P , Oades JM
Published: April 2005

The adsorption of poly [Fe(III)-OH] cation by claysurfaces led to flocculation of clay particles possibly by polymer bridging while the addition of iron(III) from hydrolysed ferric nitrate solutions resulted in flocculation and cementation by precipitated iron(III). Electrokinetically clays with adsorbed iron(III) behaved similarly to amorphous ferric hydroxides with positive mobilities below the point of zero charge (PZC). Polycations reversed the charge on the clay particles at maximum adsorption, which probably represents neutralization of charge due to surface hydroxyls. When hydrolysed ferric nitrate solutions were added to kaolinite and illite charge reversal occurred at pH values below 6. Adsorption of iron(III) resulted in a partial reduction of negative charge in clays. The reduction of negative charge in kaolinite and illite was close to the charge due to surface hydroxyls. The net charge estimated at all pH values corresponded with the electrophoretic mobility in all the iron(III) clay complexes except bentonite with adsorbed polycations.
Exchangeable calcium, magnesium and sodium and the dispersion of illites in water. I. Characterization of illites and exchange reactions
Authors: Chi CL , Emerson WW , Lewis DG
Published: April 2005

Three 'pure' illites were studied. Two, extracted from soils, were fine grained, and the other coarse, extracted from a shale. The average particle size of each clay was determined from electron micrographs and a specific surface area calculated. For the two soil illites any difference in the surface area deduced from water vapour sorption as compared with nitrogen sorption or by direct calculation, was consistent with the purity of the clay as determined by X-ray diffraction. For the shale, there was a large discrepancy, which is attributed to this illite having a greater surface density of charge. For the two soil illites, the exchange of calcium or magnesium for sodium, over the ESP range 0-12 and the calcium-magnesium exchange isotherms were determined. The exchange of sodium followed the same Gapon-type equation for both clays, and was independent of whether calcium or magnesium was the dominant cation. The calcium-magnesium isotherms were also symmetrical. No evidence was therefore found for calcium ions being more strongly held at exchange sites than magnesium ions. It was shown that in the solutions used to equilibrate the clays, which were 1 mM in divalent cations, diffuse double layers were not formed.
Sodium bicarbonate soil test values and the phosphate buffering capacity of soils
Authors: Helyar KR , Spencer K
Published: April 2005

Fifty-one field experiments dealing with responses of subterranean and white clover pastures to applied phosphate at a range of soil phosphorus levels, were carried out. The level of sodium bicarbonate extractable phosphorus above which little or no response to applied phosphate occurs (critical level), increased from 22 to 48 pg phosphorus/g soil with increases in soil phosphate buffering capacity (at solution [P] of 0.3 pg phosphorus/ml) from 1 to 20 ml/g x 10-1. On the few highly buffered soils occurring outside this range critical levels up to 60 �g phosphorus/g soil were indicated. A preliminary estimate is made of the way yield/soil test functions vary with changes in soil phosphate buffering capacity.
Zinc adsorption by goethite in the absence and presence of phosphate
Authors: Bolland MDA , Posner AM , Quirk JP
Published: April 2005

Zinc adsorption by goethite in the presence of 0.1M sodium chloride was found to occur at pH values well below the isoelectric point of the goethite when the surface was positive and the zinc in a cationic form. This confirms data already presented by Forbes et al. (1976). The presence of phosphate or zinc on the goethite surface was found to increase slightly the adsorption of zinc and phosphate respectively. Depending on the pH value, the total adsorption could be larger than for either ion in the absence of the other and the capacity of the surface for each of the ions. As suggested by Stanton and Burger, a surface complex may be formed.
Gadolinium in soils and its effect on the count rate of the neutron moisture meter
Authors: Nicolls KD , Hutton JT , Honeysett JL
Published: April 2005

Concentrations of gadolinium up to 36 ppm were found in some Tasmanian soils, particularly deep in the profile. The addition of 10 ppm gadolinium to a soil lowered the slope of the calibration line of a neutron moisture meter. Thus gadolinium needs to be added to the list of elements likely to occur in sufficient amount in soil to affect seriously the count rates of neutron moisture meters.
Halloysite in late pleistocene rhyolitic tephra beds near Opotiki, coastal Bay of Plenty, North Island, New Zealand
Authors: Kirkman JH , Pullar WA
Published: April 2005

Investigation of the clay mineralogy of 14 rhyolitic tephra beds with a suggested age of 125000 to 220000 years revealed that the squat cylindrical form of halloysite is the dominant crystalline mineral. This mineral has probably crystallized from allophane over a long time period, excess silica being precipitated as a weakly hydrated phase. The squat cylindrical crystals perhaps characterize halloysite formation in rhyolitic tephras.
The stability of soil aggregates as affected by organic materials, microbial activity and physical disruption
Authors: Tisdall JM , Cockroft B , Uren NC
Published: April 2005

On moist incubation the equivalent of 50 t ha-1 or more of ground, readily decomposable organic materials greatly increased the proportion of stable aggregates of Shepparton fine sandy loam within 1-4 weeks; the aggregates remained stable for up to 32 weeks if left undisturbed. Severe restriction of microbial activity in aggregates of Shepparton fine sandy loam by sterilization or dryness increased the effect of physical disruption associated with intermittent wetting and drying, and simulated cultivation. The results suggest that microorganisms in non-sterile moist soil can produce bonding substances which compensate partially for those bonds broken physically.
Humic substances in swamps of the Myall Lakes region, N.S.W
Authors: Alderdice DS , Craven BR , Creswick W , Johnson WD
Published: April 2005

Fulvic and humic acids have been extracted from swamp water and soil taken from the Myall Lakes area of New South Wales. Average molecular weights were estimated by gel permeation chromatography. Infrared spectra are presented.
Interaction of monomeric and polymeric species of metal ions with clay surfaces. III. Aluminium(III) and chromium(III)
Authors: Rengasamy P , Oades JM
Published: April 2005

Hydrolysis and polymerization in aluminium nitrate and chromic nitrate solutions with different metal/OH ratios were studied by gel filtration chromatography and ultrafiltration techniques. The characteristics of poly[Al(III)-OH] cations separated by ultrafiltration depended on the molecular weight which was controlled by the OH/Al ratio of the original solution. When the OH/Al ratio was <2.0, the polycations had molecular weight < 50 000, high positive charge and were stable. When the ratio was > 2.0 , the polycations had molecular weight > 100 000, low positive charge and rapidly condensed to gibbsite. Polymerization in chromic nitrate solutions was slow and the separated poly[Cr(III)-OH] cations had low molecular weight (<20000), high positive charge and were stable. The interaction of monomeric and polymeric species of aluminium(III) and chromium(III) with the surfaces of sodium-kaolinite, sodium-bentonite and sodium-illite was studied using hydrolysed nitrate solutions of aluminium and chromium, and separated polycations. The results obtained were consistent with the earlier observations of the iron(III) system, and the behaviour could be explained on the basis of positive charge and probable structure of polycations. The adsorption of aluminium(III) and chromium(III) on clay surfaces from hydrolysed metal ion solutions was related to OH/Al or OH/Cr ratios and pH. The adsorption of polycations was low and related to their positive charge. Maximum adsorption resulted in charge reversal on clays. Addition of the hydrolysed nitrate solutions to clays also caused charge reversal and reduction of negative charge. The adsorption from a mixture of monomers and polymers on bentonite surfaces reduced negative charge markedly due to interlayer formation, while the adsorption of separated polycations in low amounts neutralized the charge on surface hydroxyls and led to the flocculation of clays. The anomalous behaviour of the poly[Al(III)-OH] cations of molecular weight >100 000 could be explained if they consisted of planar sheets, formed from coalesced rings of aluminium octahedra, which crystallized into gibbsite.
Soil solution studies on weathered soils from tropical north Queensland
Authors: Gillman GP , Bell LC
Published: April 2005

Solutions obtained from six soils in tropical North Queensland after incubation at a moisture tension of 0.1 bar were analysed to obtain data on their ionic strengths. Soil extracts, at soil: solution ratios of 1:1, 1:2.5, 1:5, and 1:10 were also examined. Determinations on the aqueous phase included electrical conductivity, pH, ammonium, calcium, magnesium, potassium, sodium, bicarbonate, chloride, sulphate, and nitrate. Ionic concentrations of the soil solutions were found to be low when compared with many of the values reported in the literature. The upper limit for the ionic strength was about 0.005. Ionic strength was well correlated with the electrolytic conductivity of the soil solution itself, and also of the soil extracts. Relationships found between the soil solution and soil extracts in respect of total cation (and anion) content and also cation ratios, allow predictions about the soil solution to be made from soil extract data. Consideration of the ionic ratio of calcium to total cations in these soils suggests that the soils may have suboptimal levels of calcium for the growth of many plant species.
The oxidation of manganous ions under acid conditions by an acidophilous actinomycete from acid soil
Authors: Bromfield SM
Published: April 2005

A Stveptomyces sp. capable of oxidizing manganous ions in soil agar to manganese oxide over the pH range 5-6.5 was isolated from an acid (pH 5.0) soil. The organism failed to grow on organic media above pH 6.5 and had a pH optimum for growth of 5-5.5. On acid media its growth was restricted by manganous ions, and these were deposited as the oxide some distance from the colonies. It is suggested that the function of manganese oxidation is to protect the organism from inhibiting levels of manganous ions. The organism produced, under acid conditions (pH 5.0) in the presence or absence of added manganous ions, a water-soluble extracellular substance that could rapidly oxidize manganous ions to manganese oxide. These observations are discussed in relation to the manganese status of acid soils.
Soil variability within land systems and land units at Monarto, South Australia
Authors: Chittleborough DJ
Published: April 2005

The utility of a 1:100,000 scale land system survey near Monarto was assessed by using the profile data obtained from remapping part of the area, at 1:25,000 scale, to soil series and types by the free survey method. (i) The Land Systems: On a test for the completeness of the soil profile classes, it was found that no classes had been missed in the land system survey: all soils mapped in the free soil survey had been previously described in the land system report. The success of the survey in estimating the proportion of profile classes was 78 %, and the score for purity, the chance that any profile class can be correctly predicted from the map and report, was 37%. From these tests the survey was judged a success. (ii) The Land Units: The land systems were mapped into their component land units, and their quality or utility was assessed by measuring the variation of soil properties within each unit. While there was a statistically significant reduction in variability within the land units compared with that for the whole area unmapped, the amount of reduction was slight. The variability of individual properties, as indicated by coefficients of variation, varied widely. Least variable were B horizon texture, thickness and structure, and A horizon texture. The quality of the Monarto land system map would have been improved by the use of medium-scale colour aerial photos and a different field inspection method. It is advocated that the concept of the land unit be dropped.
A mossbauer and X-ray study of the corrosion products of mild steel plates buried in four New Zealand soils
Authors: Johnston JH , Metson JB , Childs CW , Penhale HR
Published: April 2005

57Fe Mossbauer spectroscopic and X-ray diffraction methods have been used to study the nature of the corrosion products of mild steel plates buried in four New Zealand soils of widely differing properties. This shows that superparamagnetic goethite (�-FeOOH) is the major corrosion product, with akagankite (�-FeOOH) and lepidocrocite (y-FeOOH) the next most abundant. Magnetite (Fe3O4) is also present in some samples.
Routine particle size analysis of soils using sodium hypochlorite and ultrasonic dispersion
Authors: Mikhail EH , Briner GP
Published: April 2005

A simple and rapid method for ultimate particle size analysis of soils has been developed which replaces the methods first introduced by Piper. The method relies on the removal of organic matter by sodium hypochlorite and a dispersion in an ultrasonic bath. This method has now been used nearly 2 years in our laboratories, and has resulted in a substantially greater throughput of samples with the same staffing component. The method is recommended for all service laboratories.
Water absorption by swelling seeds. II. Surface condensation boundary condition
Authors: Collis-George N , Melville MD
Published: April 2005

The previously developed model of water absorption by a swelling seed has been applied to imbibition and germination of wheat seed with the limiting supply condition of purely water vapour transport both with and without the presence of a porous medium. Experimental imbibition and germination data show that with vapour transport, the rate of imbibition and germination of wheat decreases with increasing distance from the supply source and that competition for water vapour occurs between seed. This competition effect was verified by values of the flow pathway shape factor for vapour transport to seed, measured in a three-dimensional electrical analogue. After accounting for heat production and losses with vapour absorption and using appropriate values of the flow pathway shape factors, the equilibrium seed absorption isotherms were used to derive surface condensation boundary conditions for several imbibition situations. These calculations suggest that in the absence of porous media a significant temperature rise of the seed retards the rate of imbibition. By comparison, with a close-packed porous medium around the seed, the large thermal conductivity of the medium should maintain nearly isothermal conditions. Using a finite difference approximation, the swelling seed model and condensation boundary conditions are analysed to give predicted imbibition data which can be compared with experimental data. These results show good agreement between predicted and experimental imbibition in the absence of a porous medium. For seed embedded in a porous medium, the predicted imbibition rate significantly exceeds the experimental rate, but no account could be taken for restriction of seed swelling by the porous medium. The results are discussed in terms of their relevance to the sowing of seed in 'dry' seed bed conditions.
Interpretation of electrical conductivity in a clay soil containing salts
Authors: Blackmore AV
Published: April 2005

The use of directly measured electrical conductivity of soil to provide an index of soil salinity is discussed. It is suggested that if an anion exclusion mechanism within the microfabric of a wet clay soil can lead to a non-uniform, but stable, range of salt concentrations, then the validity of such an index would be jeopardized. Experiments involved the monitoring of soil electrical conductivity during leaching and diffusion of salts from stable clay-soil aggregates packed in columns and cells. The equilibrium values of conductivity are inversely related to exchangeable cation valence, but are not affected by the type of anion involved. The soil conductivity was often much smaller than the value inferred from the amount of salts actually extracted from the columns or contained in the small isolated electrical conductivity cells. The results are consistent with the operation of a salt exclusion mechanism in the smaller pores of the soil fabric. With monovalent cations and relatively low electrolyte concentrations, the trapping of salts within the microfabric is maximized, while in contrast, with aluminium and aged hydrogen clays the exclusion effect is almost completely suppressed, in accord with double-layer theory. If salts are retained against concentration gradients within the fine structure units of the soil, current-transmitting regions between the units are of correspondingly high resistance, and this is reflected in a soil electrical conductivity value that is low relative to the amount of electrolyte between the electrodes. The observed soil conductivity may, however, bear a simple relationship to the salt fraction of the soil actually 'available' to plant roots.
Phosphate sorption by reduced and reoxidized rice soils
Authors: Willett IR , Higgins ML
Published: April 2005

Intact cores of two rice soils of south-eastern Australia were flooded for 146 days to simulate part of a rice-upland crop rotation. The phosphorus sorptivity, and acetate (pH 4.8) and oxalate (pH 3.0) extractable iron levels were monitored for 210 days, before, during and after flooding. The effects of additional organic matter (rice straw) and the growing of rice plants were examined. In non-flooded soils phosphorus sorptivity was mainly influenced by clay content; there were no relationships between extractable iron and phosphorus sorbed. On flooding there were large increases in acetate and oxalate extractable iron and phosphorus sorptivity. Additional organic matter initially increased the rates of formation of extractable iron, and phosphorus sorptivity increased accordingly. However, with prolonged waterlogging, levels of oxalate iron and phosphorus sorptivity reached values dependent on the free iron oxide content of the soils. The growth of rice plants had no significant effects on phosphorus sorptivity or extractable iron at any time of sampling. During oxidation of previously flooded soils, levels of phosphorus sorptivity and oxalate iron decreased rapidly, but did not return to levels occurring before reduction. The results are consistent with domination of phosphorus sorption processes by ferrous hydrous oxides during the flooded (reduced) phase and by poorly crystalline ferric hydrous oxides during the post-flooding reoxidation phase. Agronomic implications of the results are mentioned.
The influence of organic matter extracted from humified clover on the properties of amorphous aluminosilicates. I. Surface charge
Authors: Perrott KW
Published: April 2005

A series of synthetic amorphous aluminosilicates, hydrous oxides and allophanic soil clays were treated with aqueous extracts of humified clover. The resulting changes in surface charge due to organic treatment were determined by comparing the charge characteristics of these organic treated samples and samples treated with a synthetic mixture of the inorganic components of the humified clover extract. Organic treatment caused a change of net surface charge to more negative values. The change in surface charge varied with the mole ratio Al/(Al+Si) of the aluminosilicate, being largest at low values of Al/(Al+Si). Where the aluminosilicates contain positive charges these are reduced by the organic treatment. This is a major contributor to the alteration of net surface charge in the more aluminous samples. The effect of organic treatment on the charge characteristics of allophanic soil clays was similar to that for the synthetic aluminosilicates of intermediate composition. The inorganic treatments also caused an increase in negative charge, and this is attributed to the neutralization of positive charge by the adsorption of phosphate and the removal of charge-balancing aluminium-hydroxy material. The effect of the organic and inorganic treatments on the positive and negative charge components of amorphous aluminosilicates is discussed in terms of the degree of polymerization of chargebalancing hydroxy-aluminium as envisaged in current models of the structure of amorphous aluminosilicates.
A note on the effect of soil tillage on the frequency and vertical distribution of spores of vesicular-arbuscular endophytes
Authors: Smith TF
Published: April 2005

Spores of vesicular-arbuscular endophytes resembling Acaulospora laezis and Glomus monospovus were common in the surface layers of a soil under wheat and pasture, declining in numbers down the profile until rare at 500 mm. Tillage had no effect on total spore numbers, but directly drilled wheat had more spores in the surface 80 mm and fewer from 80 mm to 150 mm than conventionally tilled plots. This is thought to be a consequence of mechanical inversion of the soil during cultivation.
Radiocarbon measurements and soil micromorphology as guides to the formation of gilgai at Kaniva, Victoria
Authors: Blackburn G , Sleeman JR , Scharpenseel HW
Published: April 2005

Profiles from mound and depression at two apparently comparable gilgai sites provided samples for 82 radiocarbon measurements and other studies of profile variation, including micromorphology and swelling capacity. Comparable trends of apparent mean residence time (AMRT) of soil humus with depth were found for both profiles at Miram, with gradual increase to approximately 8500 years at 2 m. This contrasts with results for Lillimur, where the maximum AMRT for the mound profile is almost 6000 years but that for the depression profile is only 2000 years. Interpretation of the AMRT values is complicated by evidence of layering and the probability of a buried soil at each site. Downward movement of soil is shown by micromorphological features and by AMRT values taken in conjunction with evidence of layering. Evidence was sought on churning with a marked lateral component and on fossil gilgai, but without firm conclusions. It is probable that at both sites gilgai formation involved the upward movement of the mass of soils constituting the mound, at a time when it still retained relatively sandy top soil. Leaching of carbonate may have increased the microrelief.
Coupled infiltration and surface tunoff on a 5 Ha experimental catchment, Krawarree, N.S.W
Authors: Aston AR , Dunin FX
Published: April 2005

A simple two-stage infiltration model, originally developed for infiltration under constant intensity rainfall, was adapted to varying rainfall inputs and coupled with an overland flow routing procedure. The model was verified against selected rainfall events on a 5 ha experimental catchment with good agreement between simulated and measured catchment yields.
The effect of aggregate size on the infiltration behaviour of a slaking soil and its relevance to ponded irrigation
Authors: Collis-George N , Greene RSB
Published: April 2005

The depth and degree to which columns of aggregates of different sizes of a structurally unstable red-brown earth surface soil slaked when water was ponded on the surface were studied. The slaking affected the subsequent infiltration into the soil. Wetting front advance and cumulative infiltration data indicated that the depth of the zone of slaking increased as the aggregate size increased. However, the effectiveness of the slaked layer in reducing the infiltration rate depended not only on the depth of slaking, but also on the extent to which the different aggregates had slaked into microaggregates and to what extent the microaggregates filled the interaggregate pores, if any. Examination of vertical sections of the slaked surface region using an optical microscope provided independent confirmation of the phenomenon of slaking in the various aggregate sizes.
A laboratory and field study of border check irrigation
Authors: Collis-George N , Freebairn DM
Published: April 2005

Field and laboratory results of infiltration advance are presented. They are compared with results from equations that derive from the Lewis-Milne equation after substitution of infiltration relations based on independently determined parameters obtained from infiltration experiments. In the laboratory, change of slope, change of supply rate, prewetting of the surface, and restriction of vertical air escape were studied in various combinations for two homogeneous materials. Change of supply rate, q, affected the rate of advance, x, while change of slope and prewetting the surface had only second order effects with a change of q. Results are compared in terms of the ratio x/q. Agreement between theory and experimental results is good. The effect of restriction of air escape vertically ahead of the wetting front was marked, even though the measured increase in air pressure was small, and effectively reduced the parameters, sorptivity and hydraulic conductivity. An innovation is to introduce a further term-the 'instantaneous' crack-filling volume. This slightly modifies the equations used for homogeneous materials and provides very good descriptions of irrigation advance phenomena for a cracking grey clay, a duplex red-brown earth, and for laboratory simulated duplex profiles consisting of two thicknesses of coarse sand overlying fine sand. The movement of water into the layered sand systems showed that infiltration is not entirely vertical as equired by the Lewis-Milne equation. The implications of the experimental results and the use of infiltration-advance equations in studies of the irrigation of field soils are briefly discussed.
Compaction of sandy soils in Radiata pine forests. I. A penetrometer study
Authors: Sands R , Greacen EL , Gerard CJ
Published: April 2005

The mechanical strength of sandy soils under radiata pine plantations was measured with a penetrometer. Resistance to penetration was largely independent of water content in the range sampled, and was directly related to the bulk density of the soil. Soil strength at constant bulk density increased with depth owing to increase in overburden pressure and to a decrease in soil organic matter. Soil under native scrub was consistently less compact than that from adjacent radiata pine plantations on the same soil type. Soil from pasture was usually more compact in the surface 20 cm of soil than that from pine plantations, but was less compact at depth. Soil from second rotation plantations was more compact than soil on some first rotation sites, but on other sites no differences could be established. Radiata pine roots preferentially penetrated areas of lower soil strength. Root penetration was severely restricted above a critical penetration resistance of about 3000 kPa. Saturated soils were highly compacted even by light loads in a laboratory consolidometer compared to unsaturated soil. In the unsaturated condition compaction was greatest under heavy loads on soils at about 1% organic matter. Causes of the observed compaction in the field are discussed and remedial measures are suggested. Soil compaction reduced porosity but had little effect on water storage capacity. Increased organic matter at constant bulk density also reduced porosity, but greatly increased water storage capacity and unsaturated hydraulic conductivity. The importance of organic matter in maintaining a favourable structure in sandy soils and its relation to maintenance of site productivity is discussed.
The influence of placement geometry on the effectiveness of copper superphosphate
Authors: Gilkes RJ , Sadleir SB
Published: April 2005

In a glasshouse experiment wheat plants were grown for 45 days at various distances from granules of copper superphosphate. Only plants growing within 2 cm of the fertilizer granules were able to utilize the copper. This result is interpreted as indicating that close contact between plant roots and fertilizer is necessary for optimum copper utilization. Methods of fertilizer formulation and application should be designed to promote close contact.
A proposed method for the measurement of exchange properties of highly weathered soils
Authors: Gillman GP
Published: April 2005

The 'compulsive exchange' method of Bascomb has been modified to allow the determination of cation exchange capacity and anion exchange capacity of soils containing significant quantities of constant potential surfaces. The soil is equilibrated with unbuffered barium chloride solution at an ionic strength approximating that of the soil solution, so that the conditions under which determinations are made are similar to those found in the field. Barium on the exchange complex is then replaced by magnesium when the latter is added as magnesium sulfate, and this is accomplished without altering the solution ionic strength. If desired, exchangeable basic cations can be determined as an additional step in the procedure. Results obtained by the proposed method are compared with other commonly used procedures for determining cation exchange capacity and exchangeable basic cations.
Interaction of monomeric and polymeric species of metal ions with clay surfaces. IV. Mixed system of aluminium(III) and iron(III)
Authors: Rengasamy P , Oades JM
Published: April 2005

Polymerization of aluminium(III) and iron(III), in mixed solutions of the nitrates, by dialysis against distilled water resulted in polycations having higher Fe/(Fe+Al) mole ratios than those of the starting solutions. A maximum of 25 mole per cent aluminium(III) entered probably into the structure of the po1y[Fe(III)-OH] cation. Ferric aquo-ions polymerized quickly and slower polymerization of aluminium(III) led to the exclusion of the monomeric aluminium(III) during hydrolysis. A more complete polymerization of both aluminium(III) and iron(III) in mixed solutions was initiated by adding sodium hydroxide up to a OH/(Fe+Al) mole ratio of 2.5 and then removing the monomers by dialysis. The resultant polycations had Fe/(Fe+Al) mole ratios close to the original solutions. The pH values and positive charge of these products were higher than any obtained with either pure aluminiurn(III) or iron(III) systems, suggesting that these are copolycations of aluminium(III) and iron(III) rather than a mixture of separate aluminium(III) and iron(III) species. The infrared spectra of these copolycations were different from the pure end members, viz. po1y[Fe(III)-OH] and poly[Al(III)-OH] cations prepared under similar conditions, confirming that they were copolymers rather than a physical mixture of individual polymers. The copolycations coagulated by adding an indifferent electrolyte, sodium nitrate, were amorphous to X-rays. Electron micrographs showed that the morphology of particles in these solutions of copolycations became regular hexagons as the aluminium(III) content increased. The pure aluminium(III) sample showed regular hexagonal particles. In general the particle size decreased with increasing aluminium(III) content. The results obtained for critical coagulation concentration and maximum adsorption for sodium-kaolinite were consistent with the earlier reports for pure aluminium(III) or iron(III) system. Both were related to the positive charge on the copolycations. Maximum adsorption of copolycations on sodium-kaolinite caused charge reversal. The pzc of the copolycation treated kaolinites were between 6.40 and 8.65, the PZC increasing with a1uminium(III) content. The significance of the possible existence of copolycations of aluminium(III) and iron(III) in soil systems is discussed.
Isotope studies on the comparative efficiency of nitrogenous sources
Authors: Dev G , Rennie DA
Published: April 2005

In a growth chamber experiment with 15N-labelled potassium nitrate, ammonium sulphate and urea at 75 and 150 kg nitrogen/ha and ammonium nitrate at 150 kg nitrogen/ha, nitrogen application produced significant responses of dry matter yield and total nitrogen uptake by shoot and root of barley in chernozemic dark brown Elstow silt loam and deep black Hoey clay soil. Total nitrogen removal per pot and isotope-derived criteria, viz. percentage nitrogen derived from fertilizer, 'A' value and percentage fertilizer nitrogen utilization, indicated that potassium nitrate was the most efficient and urea the least. At 75 kg nitrogen/ha, the recovery of fertilizer nitrogen in shoot and root was 47, 42 and 34% in Elstow silt loam and 65, 54 and 50% in Hoey clay with potassium nitrate ammonium sulphate and urea respectively. At 150 ppm nitrogen, these values were 62, 46 and 45 % in Elstow silt loam and 75,51 and 53 % in Hoey clay and that of ammonium nitrogen from ammonium nitrate, 17 and 43 % in the two soils respectively. The percentage excess of 15N in soil total nitrogen after the harvest of barley showed that urea was tied up more in the soil, causing lower efficiency for crop recovery. The contribution of root portion for different parameters in such evaluation studies needed equal consideration. The availability of fertilizer nitrogen for crop utilization was more in Hoey clay than in Elstow silt loam. Immobilization and losses of fertilizer nitrogen were greater in Elstow silt loam.
Interactions between soil type and tillage level in a dryland situation
Authors: Hamblin AP , Tennant D
Published: April 2005

Soil physical conditions were measured under conventional, minimum and zero soil disturbance cropping systems. Seedbed differences were small in soils cropped after stubble, but significantly different on light sandy soils cropped after pasture. Soil resistance to penetrometer was significantly higher at 10 cm with direct drilling. Soil porosity, and properties dependent upon it, varied more with tillage level on loamy sand than on clay loam soil. Root distributions and associated soil interactions were measured by means of soil cores. Root growth rate varied with soil texture and with tillage level. Soil water contents were at matric potentials well above - 1.5 MPa at 6 weeks, but root depth in the finer-textured soil was only half that of the loamy sand. Root extension rate was restricted by soil strength rather than water shortage in the early part of the growing period. Direct tillage with a triple disk drill reduced root extension rate at both sites in the early phase. Evidence of a compaction pan on the loamy sand is presented.
The movement of titration curves in the presence of specific adsorption
Authors: Pyman MAF , Bowden JW , Posner AM
Published: April 2005

The crossover point of potentiometric titration curves is usually identified with the point of zero charge. It is shown both theoretically and experimentally that in the presence of specific adsorption the crossover point and the point of zero charge do not necessarily coincide. When a specifically adsorbing anion is present in small and constant amounts in varying concentrations of indifferent electrolyte, the crossover point decreases relative to the pristine point of zero charge. When the specifically adsorbing anion is the only anion of the electrolyte, the crossover point increases relative to the pristine point of zero charge.
Selection and use of representative sites in a large neutron moisture meter network
Authors: Johns GG
Published: April 2005

The assessment of the representivity of individual sites in a large neutron moisture meter (NMM) network, and the errors incurred by selecting subsets of various sizes, and using different methods to estimate the full set value from the subsets, is described. Soil water data collected over 13 months from the NMM network (240 sites, divided into eight strata) were analysed to determine the relationship between individual sites and their stratum means. Relationships were assessed using the following four methods: (1) root mean square of the discrepancy; (2) linear regression; (3) quadratic regression; (4) power curve regression. Sites best related to their stratum means were then included in various size subsets, and estimates based on these subsets were compared with the respective full stratum means using 24 months' data. The best estimates of stratum means were obtained by using quadratic regressions and c. eight sites per subset. Using this method, the root mean square discrepancy between estimates of profile water content and observed full stratum means averaged 2.1 mm when the total profile was estimated directly and 2.5 mm when the profile water content was computed as the sum of individual estimates for four arbitrary horizons within the profile. Daily readings of one group of selected subsets indicated the potential of frequent NMM readings at key sites to indicate short-term changes in the soil water content of an area. The performance of the selected subsets has been monitored for a further 12 months as an independent check on their representivity. The root mean square discrepancy of estimates during that period was 2.7 mm. Subsequently only the selected eight sites in each stratum of the field study are being read on a routine basis.
Adsorption of nitrate, chloride and sulfate by some highly weathered soils from south-wast Queensland
Authors: Black AS , Waring SA
Published: April 2005

Soil was collected from a number of sites and depths to 300 cm within four great soil groups (krasnozem, red earth, xanthozem, podzolic). Nitrate, chloride and sulfate adsorption were determined at the soil pH. Various soil properties likely to influence the magnitude of adsorption were determined, and their relative importance to adsorption was assessed using stepwise multiple regression. The subsoils of all four soil groups adsorbed nitrate ranging up to 0.47 mmoles/100 g from 0.005 M potassium nitrate solution. The mean adsorption for soil groups decreased in the order krasnozem, xanthozem, red earth and podzolic. Chloride and sulfate adsorption was largely equivalent to that of nitrate. The variations in adsorption between and within great soil groups could be attributed to changes in organic matter, smectite minerals, hydroxy aluminium, surface area and pH.