bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron microprobe and electron microscope studies of soil clay particles
Authors: .Fordham AW , Norrish K
Published: April 2005

Several soils were examined in detail by electron microscope and microprobe to assess the nature of clay size particles and microaggregates. Morphology, analytical composition, identity and association between particles were determined. Of the mineral oxides, pellets of goethite and hematite about 1 �m in size were most distinctive. They were found in all the soils examined except one. They contained both aluminium and silicon, sometimes in fairly constant proportions, but the presence of adhering fine material made it difficult to assess the extent to which these elements were part of the iron oxide structure. Discrete gibbsite particles of micron size were rarely encountered, although some soils contained appreciable quantities of it in much smaller form. At least a few rutile or anatase particles were found in all soils, while they were common in some. They also were usually contaminated by surface deposits, in contrast to ilmenite and quartz grains which were always relatively clean and were often isolated from other particles. The ratios of ironltitanium in ilmenites were well defined but different from soil to soil. Uncontaminated clay mineral particles were rare. Most had substantial deposits of fine-grained material upon their surfaces, much of it < 200 A in diameter. The most easily detected components of these surface deposits were goethite and hematite, and often they were dominant. Finely divided clay minerals were usually present as well, together in some soils with gibbsite and occasionally with titanium oxides. In one soil where coarser (1 �m) host particles were not readily available to carry it, the fine-grained material formed microaggregates consisting of kaolin, gibbsite and hematite, all of comparable size. Soils containing both kaolin and illite were composed mainly of compact microaggregates of the two clay minerals, which had the appearance of single particles. These results demonstrate the close association frequently existing between micron and submicron soil particles and between submicron particles themselves. The structural units of soil particles were often much smaller than generally supposed.
Arsenate-73 uptake by components of several acidic soils and Its Implications for phosphate retention
Authors: Fordham AW , Norrish K
Published: April 2005

The arsenate (and phosphate) sorbing properties of the various components in the clay fractions of several acidic soils were assessed by autoradiography using radioactive arsenate-73. Arsenate uptake from solution was recognized by localization of silver grains upon soil particles dispersed on electron microscope grids. The composition and identity of these particles was then established by electron microprobe analysis. In most of the soils examined, arsenate was retained mainly by iron oxides, and to a much lesser extent, by titanium oxides. Both minerals were active either as micron-size pellets or as very fine particles, the latter occurring in surface deposits upon clay minerals and other particles or in microaggregates composed wholly of finely divided material. Gibbsite occurred predominantly in finely divided form and, on a unit mass basis, was much less effective in taking up arsenate than iron or titanium oxides. However, in one soil where it was present in large amounts (50-65%), it was able to account for 20-25% of total arsenate uptake. When free of surface deposits of finely divided oxides, other components of the clay fractions examined were comparatively inert towards arsenate. These components included kaolinite, illite, vermiculite, muscovite, potassium-felspar, ilmenite and quartz.
Effect of soil types and rootstocks on root distribution, chemical composition of leaves and yield of valencia oranges
Authors: Mikhail EH , El-Zeftawi BM
Published: April 2005

Effects of three soil types and three rootstocks on the performance of Valencia orange trees as measured by root distribution, leaf composition and yield were studied. The majority of roots were concentrated in the top 60 cm of soil. Trees on Murray sand had twice as many roots as on Barmera sand 'shallow phase', or as on Moorook sandy loam below 90 cm. Chlorophyll and iron levels were lowest in new 3-month-old leaves and increased with age. Levels of zinc, manganese, magnesium, calcium and chloride showed similar trends. Trees on Moorook sandy loam were not chlorotic in spite of the low chlorophyll in their leaves and the lowest production.
A modification to Schoonover's method of gypsum requirement determination of soil
Authors: Chauhan RPS , Chauhan CPS
Published: April 2005

During laboratory studies it was noted that water-soluble carbonate plus bicarbonate interferes with the determination of gypsum requirement (GR) by Schoonover's method and has significant correlation with the latter (r = 0.89). The interference of carbonate and bicarbonate can be eliminated through their precipitation as magnesium carbonate. A modified method to this effect is suggested hereby, and values of GR determined by this method are quite close (r = 0.99) to those of exchangeable sodium and give a fair approximation to it.
Size characteristics of soils and sediments with special reference to clay fractions
Authors: Walker PH , Hutka J
Published: April 2005

Soils and sediments from south-eastern Australia were examined to determine whether texture B horizons had distinctive and unique particle-size characteristics. Most texture B horizons had higher contents of fine clay (<0.2 �m) than coarse clay (0.2-2 �m), whereas coarse clay was the dominant clay-size fraction in A and C horizons. Sequences of soils in alluvium showed a systematic increase in particle-size differentiation with increasing stratigraphic age and corresponding increases in the proportion of fine clay in their B horizons. Pedologically unmodified, clay-rich sediments generally had lower contents of fine clay and higher contents of silt than B horizons. However, sediments of a lake floor and samples of argillans had clay-size fractions similar to B horizons. The distribution of fine clay in soils, determined here by centrifugal sedimentation, was poorly related to illuviated clay determined microscopically. Detailed particle-size data showed that texture B horizons were more enriched than adjacent horizons by a fraction with upper size limits between 0.25 and 0.5 �m. The greater the profile texture contrast, the more pronounced this enrichment became. The enriched clay-size fractions of these B horizons had the particle-size characteristics of log normal distributions. Within the clay-size range of texture B horizons, the fraction < 0.5 �m was the most directly related to surface area measurements made on dry soil samples. Sediments of a lake floor and samples of argillans had similar clay-size characteristics to soil B horizons. It was concluded that particle-size differentiation in these soils was related mainly to pedogenetic processes within the profile. However, the particle-size characteristics of texture B horizons are not unique. Criteria other than those based on particle-size analysis are therefore required to determine the relative importance of translocation and weathering.
Sources of bias in the field calibration of a neutron meter
Authors: Greacen EL , Hignett CT
Published: April 2005

Field calibrations of a neutron moisture meter and a gamma density meter were made on the individual layers of a duplex soil consisting of a metre depth of sand overlying a deep cracking clay. Two sources of bias were encountered in the case of the clay layer: (1) differences in bulk density and composition between sites caused a bias of 20% in the calibration coefficient resulting in an underestimate of change in water content, and (2) non-representivity of the access tubes, due to failure to sample cracks, caused an additional negative bias of up to 30%. The first of these inaccuracies can be avoided by using a better design for the calibration experiment and by correcting neutron count rate for soil density. The second bias due to poor crack sampling can be corrected for on the assumption that only three-dimensional swelling occurs on a field-wide basis.
Evaluation of porous cup soil-water extractors: Physical factors
Authors: Talsma T , Hallam PM , Mansell RS
Published: April 2005

The performance and characteristics of small, porous cup, soil-water extractors, installed in a soil with known water-transmission properties, are described. Cup conductivities decreased sharply during an 8 week period and, in the absence of other flux limiting factors, would limit water entry in the permeable topsoil but not in the slowly permeable subsoil. Measured cup water uptake however was much less than that predicted from either cup conductivity or soil water transmission properties. This is attributed to flow impedance near the cup walls. Under these conditions flow distribution in a soil with extractor cups would be much closer to that of an unextracted soil than is predicted from soil water flow theory.
Stabilization of soil aggregates by the root systems of ryegrass
Authors: Tisdall JM , Oades JM
Published: April 2005

The root system of ryegrass was more efficient than that of white clover in stabilizing aggregates of Lemnos loam because ryegrass supported a larger population of vesicular-arbuscular mycorrhizal hyphae in the soil. Electron micrographs show that the hyphae were covered with a layer of amorphous material, probably polysaccharide, to which clay particles appear firmly attached.
Soil water in a fragiaqualf
Authors: Scotter DR , Clothier BE , Corker RB
Published: April 2005

The profiles of density and soil water retentivity for a Fragiaqualf, the Tokomaru silt loam, were found to correspond with the morphological features, with a bulk density of up to 1670 kg m-3 and a negligible volume of macropores in the C horizon fragipan. The saturated hydraulic conductivity at undrained sites was as low as 0.1 mm day-1 in the B horizon, although there is evidence that at mole-tile drained sites the effective permeability is much higher. Water movement is non-uniform in the subsoil, apparently due to preferential flow between the large polygonal structure units. Comparison of neutron probe profiles and laboratory soil water retentivity data demonstrated the difficulties in using the latter to estimate the available-water holding capacity of the soil. The main problem was the lack of a clearly defined rooting depth. This was probably due to non-uniform water extraction from the subsoil by pasture roots, because of their preferential distribution between rather than within the large structure units. This made it impossible to correlate the 'permanent wilting point' with a particular soil matric potential.
Calcined Christmas Island C-grade rock phosphate fertilizers: Mineralogical properties, reversion and assessment by chemical extraction
Authors: Gilkes RJ , Palmer B
Published: April 2005

Calcination of Christmas Island C-grade ore at temperatures up to 1050�C produces phosphorus fertilizers that differ greatly in effectiveness as determined by citrate extraction and plant growth. Maximum effectiveness is obtained by calcination at temperatures between 500� and 650�C, and is best predicted by extractions of between 1 and 3 h duration in neutral ammonium citrate. Alkaline ammonium citrate and citric acid are poorer indicators of phosphorus availability. The mineralogical and chemical properties of the calcines may be used to explain variations in amounts of citrate soluble phosphorus for different temperatures of calcination. Incubation of moist 500�C calcined C-grade ore induces recrystallization (i.e. reversion) of some crandallite, resulting in a decrease in the solubility of phosphorus in neutral ammonium citrate and its availability to plants.
The age of a red earth profile in central north Queensland
Authors: Coventry RJ
Published: April 2005

The red earths of the Charters Towers-Torrens Creek area of north Queensland are generally found in those parts of the landscape that have not been subjected to extensive erosion. Previous workers in the region have used indirect methods to suggest a Tertiary age for such soils. Direct evidence of a late Tertiary age for a red earth profile, formed in high level alluvium of the Burdekin River, has been derived from isotopic dates from an overlying basalt flow. Dates of 2.3-2.4 million years show that the buried red earth profile developed before or during the late Tertiary.
The 'most probable number' method for enumerating infective propagules of vesicular arbuscular mycorrhizal fungi in soil
Authors: Porter WM
Published: April 2005

Estimates of the number of infective propagules of vesicular-arbuscular (VA) endophytes in two soils were obtained using a most probable number (MPN) method. These estimates were compared with counts of the number of spores in the same soils obtained using a conventional wet sieving method. In one soil, there was good agreement between the number of coarse endophyte propagules, estimated by the MPN technique, and the number of germinable spores extracted using the wet sieving technique. However, a large population of fine endophyte propagules (more than 230 per 50 g soil) could only be enumerated using the MPN technique. In the second soil, fewer coarse endophyte propagules were found using the wet sieving technique than when using the MPN technique. The MPN technique appears to give a more realistic estimate of the number of infective propagules of VA endophytes in field soils than the conventional method.
An objective method for fitting models of ion adsorption on variable charge surfaces
Authors: Barrow NJ , Bowden JW , Posner AM , Quirk JP
Published: April 2005

Models for the change in electrostatic charge and for the adsorption of anions and of cations by variable charge surfaces involve sets of simultaneous equations. A method for solving these equations was developed and incorporated in a computer program. This was linked to an optimization program so that values of the parameters of the models could be selected objectively. The program was used to test and to compare the fit of various models to observations on the charging behaviour of goethite in solutions of sodium chloride, sodium sulfate, and calcium chloride. A good description of the observed behaviour was obtained, provided that terms to describe specific adsorption of the electrolyte ions were included. Models in which the specifically adsorbed electrolyte ions were assigned to a separate plane did not improve the description of charge over simpler models, but gave more realistic values for electrostatic potentials.
Describing the adsorption of phosphate, citrate and selenite on a variable-charge mineral surface
Authors: Bowden JW , Nagarajah S , Barrow NJ , Posner AM , Quirk JP
Published: April 2005

The effects were measured of varying the pH and the concentration of adsorbing ion on adsorption of phosphate, citrate and selenite by goethite and on the charge conveyed to the surface. The ability of the model of Bowden et al. to describe these effects was investigated. The observed effects were closely described by the model, provided it was modified to permit the adsorbed ions to reside in a plane between the surface and the diffuse layer. The model requires that individual ionic species be considered. For phosphate and selenite, the divalent ion appeared to be the only ion adsorbed whereas for citrate it was the trivalent ion. The model also requires that adsorption depends on the electrostatic potential in the plane of adsorption. This potential decreases with increasing pH. Thus the effects of pH on adsorption were explained by changes in this potential, together with changes in the proportion of the ionic species present. Because adsorption made the surface more negative, it also decreased the electrostatic potential in the plane of adsorption. This made further adsorption more difficult, and as a result, adsorption at a constant pH did not follow the Langmuir equation. The model showed that the increase in negative charge as a result of adsorption was partly balanced by an uptake of protons by the surface. This was most marked at near-neutral pH and as a result the net charge per adsorbed ion was least.
Growth of subterranean clover when subirrigated from water tables at different depths
Authors: Stewart RL , Turner AK , Wilson JH
Published: April 2005

Subterranean clover plants were grown in a glasshouse with sub-irrigation from water tables maintained at depths of 0.30 m, 0.60 m, and 0.90 m. The depth of water table had little effect on the weights of the above-ground parts; there was a non-significant trend towards greater weights with deeper water tables. However, there were striking effects of treatment on root growth. Active root extension occurred while soil moisture content of the soil was between about 25 and 15%. With the deeper water tables, the zones of active root growth moved downwards as the soils dried out, i.e. out of the zones where, through increasing plant intake of water, demand exceeded supply from the water table. By the third harvest (about flowering time of the clover plants) the greatest root density with all treatments was between 0.20 m and 0.30 m above the water table. For the soil type used, this was apparently the height above the water table at which plant intake and upward movement of water from the water table were in equilibrium.
Hydraulic conductivity of deeply weathered materials in the Darling Range, Western Australia
Authors: Peck AJ , Yendle PA , Batini FE
Published: April 2005

The hydraulic conductivity (K) of unconsolidated, deeply weathered material was measured by the slug test method In 214 boreholes distributed over five distinct areas in the Darling Range of Western Australia. Most of the measurements were made in the zone 0-3 m above hard rock. Theory of the method was extended to include a layer of material with lower K about the slotted pipe. The frequency distribution of K in each area was well fitted by the log-normal function. Parameters of the linear regression of logK against the inverse Gaussian function of cumulative frequency differed significantly (P<0.001) between areas. In one area of 134 ha, measurements were made in 54 boreholes located on a grid. There was a very poor correlation between values of K at the smallest separation of grid points (100 m), which suggests that there is an essentially random spatial variation of K measured by this method in this study area. Assuming log-normal frequency distributions and random spatial distributions, bulk conductivities were estimated for each area. On the basis of these investigations, it is concluded that the bulk hydraulic conductivity of the weathered material in the Darling Range is slow to moderately slow, and relatively uniform on the broad scale.
Hydraulic conductivity measurement of forest catchments
Authors: Talsma T , Hallam PM
Published: April 2005

Measurements of hydraulic conductivity, K, on four forest catchments that show substantial differences in hydrological behaviour are reported. Field descriptions of principal profile forms and extended profile forms were used as criteria for determining catchment uniformity. Simple and rapid measurement methods for K were necessary. These are described, and one, the well permeameter method, has been further evaluated. Results of many measurements indicated that K distribution was very nearly log-normal for all catchment components and depth intervals studied. Strong variability with respect to K was apparent within each 'uniform' component; however, most of this variability was already present within very small areas. Subdivision of catchments using principal profile forms explained differences in mean K of an order of magnitude, extended principal profile form descriptions were useful to distinguish smaller, but significant, differences in mean K. The usefulness of these catchment conductivity data, for inter-catchment comparison, and for explaining storm-hydrograph shapes of individual catchments, is indicated.
Compaction of forest soils. A review
Authors: Greacen EL , Sands R
Published: April 2005

The problem of soil compaction in forestry differs from that in agriculture because of differences in the nature of the crop, in particular the weight and size of the plant members and the length of time that they persist. The roots compact the soil as they increase in size, but they also transmit the weight of the tree and forces generated by the wind onto the soil. There are important differences in management practices; in forestry modern harvesting machines apply heavy loads and, for reasons of cost, tend to be kept in operation throughout the year. As a consequence the structure of the soil suffers some damage, often manifested as compaction. Compaction arising from such sources may reduce the growth of the current trees or trees subsequently planted on the site. But it is difficult to predict the extent of such reduction, if any, because of the complex of interactions involved. Important factors concerned, namely, the soil water regime and the organic matter content, are emphasized. A conceptual model is proposed as a predictive tool. The mechanics of soil compaction, the effects of compaction on the physical properties of the soil, and techniques for the prevention and amelioration of compaction of forest soils, are discussed.
Chloride displacement by water in layered soil columns
Authors: Ghuman BS , Prihar SS
Published: April 2005

The displacement of a surface slug of chloride as affected by rates of water application (v) and redistribution time in two-layered combinations of loamy sand, sandy loam, and silt loam soils was studied in 10 cm I.D., 95 cm long plexiglass columns. The salt moved deeper with a given amount of water in coarse-over-fine than in the fine-over-coarse sequence of layering. This is attributed to the low water retention of the coarse top layer and more complete and rapid redistribution of water due to greater suction in the lower fine layer. The chloride peak, after redistribution, coincided with the wetting front in the coarse-over-fine, but lagged behind it in fine-over-coarse profiles. However, the solute front coincided with the wetting front in all cases. Immediately following infiltration, salt was displaced deeper with v = 0.1 cm h-1 than with 1.0 cm h-1 (or ponding) in all combinations. But when infiltration plus redistribution times were matched for the two rates, v = 1.0 cm h-1 (or ponding) was more efficient than v = 0.1 cm h-1 in a coarse-over-fine profile, except in loamy sand-over-silt loam. In fine-over-coarse profiles both rates displaced the solute to comparable depths. The findings have implications in reducing leaching losses of nutrients.
Hydroxyl interaction with an alkaline clay soil during column leaching
Authors: Blackmore AV
Published: April 2005

A study was made of the diffusion of hydroxide ions, added as leachant, from the inter-aggregate pores of a red-brown earth subsoil into the microporous fabric of the aggregates themselves, and then out again when the columns were leached with water. Electrical conductivity and pH were monitored within the column, in the leachate, and in extracts of the soil. The effects of flow rate, aggregate size, neutral salt content, change of cation, and the state and concentration of the hydroxide were considered. In systems having calcium as the dominant cation, the hydroxyls were able to freely enter the fabric and to react with edges of clay particles. In systems with sodium dominant both of these processes were actively inhibited. Strong anion exclusion, arising in the double layers at clay surfaces, operates in sodium but not in calcium systems. Leaching with water, which by hydrolysis reverses the edge adsorption of hydroxyl, revealed a low reservoir of hydroxide ions in sodium systems but a large one, resulting in strong buffering at high pH, in calcium. It is contended that other anions, although less mobile and less reactive than hydroxyl, will also respond to double layers in their approach and their entry to clay soil fabric. Consequently, any ionic solutes, introduced in the leaching stream or produced by root processes, will sometimes be impeded in penetrating soil fabric, just as such solutes are impeded in leaving it.
Calcium-Magnesium exchange equilibria in a range of New Zealand soils
Authors: Edmeades DC
Published: April 2005

Calcium-magnesium exchange equilibria were studied in several New Zealand topsoils. All soils showed a preference for calcium which increased with increasing proportion of magnesium in the equilibrium solution (XMg) Soils containing allophane had greater (P <0.05) selectivity preference for calcium than the 'non-allophanic' soils and had significantly (P <0.05) higher contents of organic carbon and Tamm's aluminium.
Comparison of the variability in a soil taxonomic unit with that of the associated soil mapping unit
Authors: Adams JA , Wilde RH
Published: April 2005

The variation in morphological and chemical properties within the Westmere silt loam mapping unit mapped at the soil type level in the Wanganui district of New Zealand is compared with the variation in the same properties in the Westmere silt loam taxonomic unit. Nearly half of the measured morphological properties are similarly distributed in both the taxonomic and mapping unit, while approximately equal proportions of the remaining properties show either leptokurtic (more peaked) distributions or platykurtic (broader) distribution in the taxonomic unit. Chemical properties generally show slightly less variance (as shown by cv values) in the taxonomic unit. Considered overall, a similar degree of variation exists in both the taxonomic and mapping units. This can be explained by the main inclusions within the Westmere silt loam mapping unit being characterized by a range of morphological and chemical properties similar to the Westmere silt loam taxonomic unit and with a similar (or possible lesser) degree of variability.
The contribution of the mallet hill surface to runoff and erosion in the Narrogin region of Western Australia
Authors: Mcghie DA
Published: April 2005

Severe erosion in the Great Southern area of Western Australia has long been associated with the land class known locally as the 'mallet hill'. This association was confirmed by means of an aerial photograph survey of a representative part of the area. Use of a recycling rainfall simulator showed the mallet hill land class to yield far higher runoff than any of four adjacent upper landscape surfaces. Several factors were thought to contribute to the higher runoff from the mallet hill surface. Among these were steeper slopes, a heavier texture and water repellence of the surface soil which varied from severe in the virgin and freshly cleared state to slight or non existent in soils, which had been cleared for many years. No assessment of the relative contributions of the various factors was made, although it appeared likely that water repellence would be more important in the early years after clearing. Removal of the topsoil by sheet erosion would increase the importance of the low hydraulic conductivity of the heavy-textured subsoil in causing runoff.
The occurrence of earthworms in the wheat belt of Western Australia in relation to land use and rainfall
Authors: Abbott I , Parker CA
Published: April 2005

The distribution of earthworms in a large portion of the wheat-belt of Western Australia was documented in August 1979. Four species were found, three of which are introduced. Two of these (Allolobophora trapezoides Duges, Microscolex dubius (Fletcher)) were widespread. The occurrence of earthworms was related to land use: the percentage of gardens, pasture, cultivated and uncleared sites examined which had earthworms present was 100, 54, 18 and 23% respectively. There was no relation between the proportion of pasture sites occupied by earthworms and rainfall zone. Food supply, and not rainfall, appears to be the major determinant of distribution of earthworms in the wheat-belt. Both Allolobophora trapezoides and Microscolex dubius jointly occur in more garden samples than pasture samples; in pasture one or the other species tends to occur alone. Four laboratory experiments were conducted. In two, earthworms (Allolobophova trapezoides, Eisenia foetida) lost weight over 8 weeks when kept in virgin and cultivated wheat-belt soils with adequate moisture, suggesting that the nutrient status of such soils is too poor for earthworms. In the other two experiments, in which adequate food was supplied in a confined space, earthworms did not persist for 8 weeks where soil water was only 10% or 20% of pore space. Most survived in soil where moisture was 30-100 % of pore space, indicating that these earthworms can tolerate a broad range of soil moisture regimes.
The availability of soil and fertilizer phosphorus to wheat and rape at different water regimes
Authors: Strong WM , Barry G
Published: April 2005

The uptake of native phosphorus and band-applied fertilizer phosphorus was studied for wheat (Triticum vulgare L. Oxley) and rape (Brassica napus L. Dwarf Essex) at two water regimes in a pot experiment. Soils were cracking clays known to differ in phosphorus availability. Both crops responded to fertilizer on Cecilvale (low available phosphorus), but not on Waco soil (high available phosphorus), and wheat also responded on Mywybilla soil (intermediate phosphorus). Fertilizer uptake was in the order: Cecilvale > Mywybilla > Waco for wheat and Cecilvale > Waco for rape. Crops recovered generally twice as much native phosphorus from each soil with the wet than with the dry regime. There was no effect of water regime on uptake of fertilizer phosphorus by wheat on any soil. Water regime did not increase fertilizer uptake by rape from Waco soil, although it did increase uptake on Cecilvale soil. Favourable fertilizer response under arid conditions appears to be due to a reduction in accessibility of native soil phosphorus due to the stunted root system, but no reduction in the availability of fertilizer phosphorus.
Seasonal levels of available nutrients under grassed down, Cultivated and zero tilled orchard soil management practices
Authors: Haynes RJ , Goh KM
Published: April 2005

The effects of zero-tillage, clean cultivation or the maintenance of a sward on the seasonal levels of available nutrients in a silt loam were examined during the third season of an orchard soil management trial. Total nitrogen and sulfur and oxidizable carbon were highest in the surface soil of grassed plots, intermediate in untilled plots and lowest in cultivated plots. The seasonal pattern in levels of nitrate nitrogen and sulfate sulfur showed similar trends in both the surface soil down the profile. Levels of both nitrate nitrogen and sulfate sulfur in the top 5 cm of soil remained high for a longer period into autumn under zero-tillage than under cultivation. During the summer and autumn period, concentrations of nitrate nitrogen in the surface soil from non-grassed treatments were notably higher than those from grassed plots. There was an accumulation of sodium bicarbonate extractable phosphorus and total phosphorus in the surface soil of untilled plots and a phosphorus fractionation indicated the accumulation of phosphorus in the aluminium and iron phosphate fractions. To a lesser extent exchangeable phosphate also accumulated at the surface of the untilled soil. Levels of exchangeable calcium and magnesium in the surface soil under the grassed treatment were markedly higher than those from the non-grassed treatments, indicating less leaching of cations in the former treatment. The possible relevance of the results is discussed in terms of orchard nutrition and maintenance of soil fertility.
Describing the effects of electrolyte on adsorption of phosphate by a variable charge surface
Authors: Barrow NJ , Bowden JW , Posner AM , Quirk JP
Published: April 2005

The effects were measured of varying the concentration of sodium chloride and of calcium chloride on adsorption of phosphate by goethite. The ability of the model of Bowden et al, to describe these effects was investigated. At low pH, increasing the concentration of either salt decreased adsorption. As the pH was increased, a point was reached at which there was no effect of salt on adsorption. Beyond that point, increasing the concentration of salt increased adsorption. For calcium chloride, adsorption was greater than for sodium chloride of equal ionic strength, but observations were limited to below pH 6 because octo-calcium phosphate precipitated at higher pH. The effects were closely described by the model. They were ascribed to differences in the distribution of electrolyte ions near the surface, with the result that the electrostatic potential in the plane of adsorption was changed. The direction of the effect differs on either side of the point of zero charge of the phosphated surface. The greater adsorption in calcium chloride was ascribed partly to the greater valency of the cation, and partly to a specific affinity of calcium ions for the surface.
Critical soil test values for predicting the phosphorus and sulphur status of subhumid temperature pastures
Authors: Spencer K , Glendinning JS
Published: April 2005

Field experiments in which five levels of phosphorus application were combined factorially with five levels of sulfur application were carried out on a range of improved pastures on the Southern Tablelands and South-West Slopes of New South Wales. Dry matter responses by the pastures in the winter-spring period were correlated with soil test values obtained early in the growing season. When a best-fit curve of the Mitscherlich form was fitted to the relative yield-bicarbonate extractable phosphorus relationship, critical values for the surface 7.5 cm of soil varied between 25 and 35 ppm phosphorus, depending on the method of choosing the optimum yield. The parallel relation with phosphate-extractable sulfur was so ill defined that no critical value could be identified. Deeper sampling was of no advantage with either nutrient.
A soil toposequence on bunya phyllite in Brisbane
Authors: Koppi AJ
Published: April 2005

A common toposequence on Bunya Phyllite in south-east Queensland was studied in detail at a representative site. Four sample profiles on the slope are described, and some physical and chemical properties are given. The clay minerals, derived from the weathering of the quartz-sericite-chlorite phyllite, comprise dioctahedral mica, dioctahedral vermiculite, an interstratification of these minerals, and kaolin. Properties are related to the slope; and the clay-rich horizon of the middle and lower slopes is considered to be formed mostly by in situ weathering. The classification of the genetic unit given by the slope and parent material is discussed.
Soil and plant resistance effects on transpirational and leaf water responses by groundnut to soil water potential
Authors: Samui RP , Kar S
Published: April 2005

The phasic and diurnal leaf water potential (�L) and transpirational responses to soil water potential by groundnut (Arachis hypogea L.) were investigated under controlled soil water conditions in a glasshouse. Three different soil water potentials (�s) in the tensiometric ranges were maintained in a lateritic sandy loam soil (Oxisol) during the seedling (S1), branching (S2) and peg formation (S3) stages of groundnut. Measured values of �s, �L rooting density, soil capillary conductivity and transpiration rate were used to calculate the soil and plant resistances to water uptake by the plant. The soil and plant resistances to water uptake by the groundnut plant increased appreciably as the soil water potential decreased from -0.11 to -0.70 bar. Plant resistance (Rp) was two to three orders of magnitude higher than soil resistance (Rs). Rs decreased with growth of the plant, whereas Rp increased, especially at -0.7 bar �s, Decreases in transpiration at �s lower than -0.33 bar were closely associated with the increases in the plant and soil resistances, and with lower leaf water potentials.
Critical depth to saline groundwater in non-irrigated situations
Authors: Nulsen RA
Published: April 2005

The salinity of soil sampled from profiles exposed by a backhoe did not relate well with the vegetative cover growing on the soil, yet there was a good relationship between cover and depth to the saline water table. Results demonstrated that the depth to a saline water table can be used as an indicator of the possible productive potential of a soil.
The texture profile forms of New Zealand soils
Authors: Cutler EJB
Published: April 2005

The concept of Primary Profile Forms as developed by Northcote has been applied to New Zealand soils. It has been found that four additional Primary Profile Forms are widespread in New Zealand. The term Texture Profile Form is proposed, because it is more informative and is more likely to be accepted outside Australia than Primary Profile Form. The criteria for identification of these in the field are outlined. Explanations are given for the origin of the proposed Texture Profile Forms of New Zealand.
Spatial variability in the water balance of an experimental catchment
Authors: Dunin FX , Aston AR
Published: April 2005

Data from a 5 ha catchment were used to assess systematic spatial variability in the soil water content. The importance of incorporating this variability into hydrologic models was evaluated. The catchment was subdivided into three zones on the basis of slope and topographic position to reflect variations in the gain, loss and transfer of soil water. Temporal patterns of soil moisture behaviour of these zones were shown to be statistically different using a detailed network of sampling sites by the neutron moisture meter. This subdivision was justified because computed values of catchment vapour loss which incorporated the variable influence of soil water were better than point measurements using a lysimeter for the catchment scale. The respective performances of two variants of a process model, lumped and cascaded, were compared with measured catchment discharge. Both methods were comparable during wet periods for monthly yields of runoff. For dry periods and for weekly time scales, the cascaded variant was superior to the lumped version of the process model.
Surface runoff experiments on the eastern Darling Downs
Authors: Freebairn DM , Boughton WC
Published: April 2005

Rainfall and runoff were measured from 1976 to 1980 on four 1 ha catchments at Greenmount, about 25 km south of Toowoomba, to study the effects of crop and residue management practices. For the first 2 years, three cropping strategies were carried out - summer cropping, winter cropping, and double cropping. In the following 2 years, four summer fallow conditions and a summer crop were used in the experiment. On average, about 4% of rainfall became runoff, and this was highly variable from storm to storm and among the surface treatments. U.S. Department of Agriculture curve numbers were calculated for each occurrence of runoff and grouped according to stubble management practice. For low, medium and high antecedent moisture, curve numbers averaged 70, 82 and 95 where stubble was burnt, compared with 55, 65 and 75 where stubble was incorporated or mulched. Time of concentration of the catchments was found to be in the order of 10-15 min from studies of unit hydrographs and rational method runoff coefficients. Runoff coefficients varied with amount of surface cover and rainfall intensity, and were in the same range of values found elsewhere in Australia. A multiple linear regression was derived to relate runoff coefficient to surface cover and rainfall intensity. The highest observed runoff rates from the experiment were used to check estimates of design flood flows from the procedures in the Queensland Soil Conservation Handbook and in 'Australian Rainfall and Runoff. The estimates from these design manuals compared very well with the recorded data.
Properties of soils and clays after acid treatment. I. Clay minerals
Authors: Yeoh NS , Oades JM
Published: April 2005

Phosphoric acid was more efficient than nitric acid of the same molarity in dissolution of clays in a closed system. Phosphoric acid released considerably more aluminium from kaolinite than did nitric acid. Acid attack released equimolar quantities of aluminium and silicon from kaolinite, but with illite and bentonite the tetrahedral silica layer was preferentially dissolved compared with the octahedral layer. When the reaction products from acidification with phosphoric acid were precipitated in the presence of the clays, they were shown to exist as an aluminium phosphate containing 2 moles of aluminium to each mole of phosphorus and probably amorphous silica. The material existed as small (0.025 �m diameter) particles with a negative charge approaching 20Cg-1. The new materials increased the surface area of a kaolinite consisting of large particles, but decreased the surface area of an illite and montmorillonite. The material was responsible for aggregating all three clays. The results indicate that phosphoric acid treatment of soils should decrease water dispersible clay and improve aggregation of soils by supplying intersititial cements of aluminium phosphate and silica.
Factors affecting the retention of phosphorus applied as superphosphate to the sandy soils in south-eastern South Australia
Authors: Lewis DC , Clarke AL , Hall WB
Published: April 2005

The retention of phosphorus applied as superphosphate was measured in 31 multi-rate experiments on siliceous sands in the south-east of South Australia. The amount of phosphorus retained in the top 30 cm of soil and recovered in harvested pasture 5 months after application ranged from 0 to 100% and averaged 57% for an average dressing of 32 kg phosphorus ha-1. Of the eight soil parameters measured, 'active' iron, 'active' aluminium, organic carbon and phosphorus sorption were most closely correlated with phosphorus retention. Combinations of these variables accounted for far more of the variation than did single factors. 'Active' iron and organic carbon accounted for 53.6% of the variation. The inclusion of quadratic 'active' iron and aluminium terms improved the fit with 63.9% of the variation accounted for. Rainfall during the experiments varied from 168 to 484 mm but had no effect on retention. Some agronomic implications of the leaching losses are discussed. It is considered that a measure of 'active' iron and organic carbon could be used as indicators of leaching and could assist in determining phosphorus recommendations in the region.
Field tests for ferrous iron and ferric-organic complexes (on exchange sites or in water-soluble forms) in soils
Authors: Childs CW
Published: April 2005

A 1 M solution of ammonium acetate containing �, �-dipyridyl indicator is recommended for use in field tests for exchangeable and water-soluble ferrous iron in soils. In using the test, a soil sample may be added to a vial containing the solution, or the solution can be sprayed on to a freshly exposed soil face. A field test for ferric-organic complexes in soils, using the same vials, is proposed. This is based on the photochemical nature of the reduction of ferric to ferrous iron in the presence of oxidizable organic ligands. Two subsamples of soil are added to separate vials, and light is excluded from one. After 5-15 min, a positive test for ferrous iron in the vial exposed to light, and a negative test in the other, indicates the presence of ferric-organic complexes.
Estimation of the amounts of allophane and other materials in the clay fraction of an Egmont loam profile and other volcanic ash soils, New Zealand
Authors: Russell M , Parfitt RL , Claridge GGC
Published: April 2005

The allophane content of the clay fraction of six samples taken at different depths in an Egmont loam profile and samples from three other volcanic ash soils has been determined by acid-oxalate dissolution and infrared spectroscopy and the results from the two methods were in good agreement. The tephra that accumulated during 3500-10000 years B.P. (30-80 cm depth) in the Egmont profile had the highest allophane content (about 70% of the clay fraction). The allophane was identified as the proto-imogolite form of allophane. The allophane content of the clay fraction of the top 10 cm of the profile was lower than that of the underlying horizons, and the clay fraction also contained significant amounts of glass, laminar opaline silica, imogolite, and halloysite. A sample from the lower unit of the profile (below 80 cm), derived from tephric loess, contained about 50% allophane in the clay fraction, together with halloysite, gibbsite, chlorite and quartz. Halloysite was recognized in all the samples from infrared absorption bands at 470, 1035 and 1100 cm-1. These bands were enhanced and the other halloysite bands were observed after allophane was removed by selective dissolution in acid-oxalate. Chlorite appeared to be a common minor component of the clay fractions and probably has an aeolian origin.
The undrainable water in sand
Authors: Tschapek M , Boggio L , Wasowski C , Torres Sanchez RM
Published: April 2005

It has long been known to soil science that after water-saturated sand has been allowed to drain freely, a small percentage of fluid (2-3%) is still to be found in the sand. This undrainable water, localized on the surface of particles and at the contact points between particles under a negative capillary pressure, is studied here as a function of its surface tension and the apparent specific surface of sand. The influence of the surface tension of water on the amount of undrainable water in quartz sand suggests that most of the fluid is retained by capillary forces which are presumably localized near the points of contact between particles. However, the influence of the apparent specific surface of sand on the amount of undrainable water suggests that some of the fluid forms a layer c. 0.5 �m thick on the rugose surface of the sand particles.
Influence of pH on copper and zinc uptake by soil clays
Authors: Maguire M , Slavek J , Vimpany I , Higginson FR , Pickering WF
Published: April 2005

Nine soil clays were isolated from a wide range of soil horizons in New South Wales, and after minerological characterization, the adsorptive behaviour of the NH4+ form of the organic-free material was examined. The amount of copper and zinc sorbed increased with pH and, prior to precipitation of hydroxy species material, differences in pH-dependent capacity were discernible, reflecting differences in clay composition. Uptake at a fixed pH (5) did not always vary with concentration in accordance with Langmuir isotherms. Calculated parameters for amenable systems were similar to those observed by other workers, but capacities at a fixed pH proved to be less informative than pH dependence curves. The implications of the data for availability of the metal ions in the environment have been considered.
Buried soil cracks in alluvium near Braidwood, NSW
Authors: Chartres CJ , Costin AB
Published: April 2005

Buried soil cracks developed within sandy alluvium are described from the Upper Shoalhaven Valley south-west of Braidwood. The cracks, 10-40 mm wide and filled with an indurated sandy matrix, are about 1 m apart, up to 1.75 m deep, and arranged in a polygonal pattern. Determinations are made of the field and laboratory characteristics of the materials in which the cracks are developed and of the in-fill matrix, and these characteristics are related to possible mechanisms of formation. One possible group of mechanisms is seasonal frost-induced cracking associated with periodic filling in of the cracks by wind- or water-borne debris, then partial truncation of the materials followed by burial under alluvium. The cracks are unlikely to be more than c. 21 000 years old, and may be younger.