bluuebunny/crossref_metadata_2025 huggingface dataset:
A method to prevent edge-flow in undisturbed soil cores and lysimeters
Authors: Cameron KC , Harrison DF , Smith NP , Mclay CDA
Published: April 2005

This study shows that edge-flow of water and solutes between soil samples and lysimeter or permeameter casings can result in significant errors in the measurement of hydraulic conductivity and leaching rates. A new lysimeter design and technique are described which prevent edge-flow from occurring. Liquefied petrolatum is injected into an annular gap between the soil and the lysimeter casing producing a watertight seal. Water and solute movement in the sealed lysimeter is therefore confined within the soil monolith and no edge-flow occurs. Hydraulic conductivity and solute leaching rates are significantly lower in sealed lysimeters compared with unsealed ones.
Surface charge characteristics and clay mineralogy of some variable charge soils in Papua New Guinea
Authors: Bleeker P , Sageman R
Published: April 2005

Clay mineralogy and charge characteristics of two lowland volcanic ash soils (Andepts or Andisols) and two strongly weathered soils (Oxisols) have been studied. The clay mineralogy of the Oxisols is strongly related to the composition of the parent material, one profile on ultrabasic rocks being dominated by goethite and the other, developed on basaltic rocks, having kaolinite as the major clay mineral. In contrast, the clay minerals of the soils developed on volcanic ash deposits are dominated by hydroxy Al-interlayered vermiculite which, in one soil, is most likely formed as an alteration product of biotite. In the other profile, however, in the absence of mica, the vermiculite may have formed as an alteration product of feldspars. Charge characteristics for each of the four profiles studied show a characteristic set of curves related to organic matter content, clay mineralogy and exchangeable aluminium at low pH. The results clearly show that organic manuring within the root zone and/or rejuvenation of silica-rich ash showers can be very beneficial in retaining the chemical fertility levels of soils that contain both variable and permanent charge colloids.
Effects of decalcification on the phosphate sorption characteristics of eight calcareous soils
Authors: Holford ICR , Chater M , Mattingly GEG
Published: April 2005

Phosphate sorption isotherms and parameter values were determined on eight calcareous soils which were carefully decalcified using a procedure which minimized changes in cation saturation. Calcite content of the original soils varied from 0.8 to 24 2% and calcite surface areas from 4 . 0 to 8.5 m2 g-1. Sorption parameters were derived from the Langmuir 'two-surface' equation. Decalcification increased phosphate sorption at low residual P concentrations (<0.8 mg L-1) but decreased it at higher concentrations. The higher P sorption was associated with an increase in affinity because the calculated sorption capacities of high-affinity surfaces were not increased. These sorption capacities were well correlated with iron oxide contents of the soils, so the increase in phosphate affinity of these surfaces was consistent with the decrease in pH (0.5 to 1.5 units) of the decalcified soils. The lower P sorption at higher concentrations was associated with a substantial decrease in sorption capacity of the postulated low-affinity surfaces. These latter decreases were quantitatively correlated with the calcite surface areas of the original soils. These and other changes in phosphate sorption characteristics support the utility of the Langmuir 'two-surface' equation in providing information, compatible with what would be expected from more complex mechanistic models, and which exceeds what one would expect from other simpler models such as the Freundlich equation. They also support an hypothesis that an important component of low-affinity surfaces of these calcareous soils is calcite on which organic anions are co-adsorbed.
Comparison of different models for describing gypsum dissolution kinetics in different aqueous salt solutions
Authors: Singh H , Bajwa MS
Published: April 2005

Gypsum dissolution as a function of time was measured in solutions having a sodium adsorption ratio (SAR) of 7.5, 14 and 27 (mmol(+) kg-1)1/2 and an electrical conductivity (EC) of 1 5 and 3.1 dS m-1. The amount of gypsum dissolved increased with increases in the SAR and EC values of the different equilibrating solutions. The rate of gypsum dissolution was higher initially but declined with increasing time of equilibration. Of the total amount of gypsum dissolved in 40 h, about 60-70% dissolution occurred during the first 5 min. Comparisons of coefficients of determination (r2) and standard errors of estimate indicated that, in addition to the most widely used linear form of the first-order model, other models such as the power function, empirical (modified from first-order) and the Elovich equation, can also be used to describe the kinetics of gypsum dissolution in aqueous solutions varying in SAR and EC.
The effect of rate of water addition on the response of wheat roots to added nitrogen in a leaching environment
Authors: Diggle AJ , Bowden JW
Published: April 2005

Wheat was grown under a range of leaching regimes in columns of a loamy sand soil to which nitrogen had been added as calcium nitrate. Rates of water addition up to depths of 4.5 cm per week were found to have little effect on the amount of nitrogen taken up at 6 weeks after seeding, but higher rates of water addition progressively reduced uptake. Distributions of root length in the soil profiles varied markedly with leaching intensity, and were found to be related to the distributions of mineral nitrogen that had existed in the soil as the roots were growing.
Influence of chemical properties on nitrogen mineralization and nitrification in podzolized sands. Implications for forest management
Authors: Carlyle JC , Lowther JR , Smethurst PJ , Nambiar EKS
Published: April 2005

The relationship between selected chemical properties and nitrogen mineralization and nitrification was examined in soils collected from 39 sites of varying history. All sites were on podzolized sands; such soils represent more than 95% of the P. radiata growing area in south-east of South Australia/western Victoria. Given their uniformity in texture and similarity in pedogenesis, the organic matter concentrations of the sampled soils were highly variable (loss-on-ignition 0.8-10.2%). Total nitrogen was highly correlated with loss-on-ignition (r2 = 0.95, P<0.001). Nitrogen mineralization was correlated neither with total nitrogen nor loss-on-ignitition (i.e. P > 0.05), but was correlated with organic phosphorus (r2 = 0 70, P < 0.001), suggesting a major effect of phosphorus on nitrogen mineralization in these soils. On the basis of nitrate production during a 56-day aerobic incubation of disturbed soil, 18 soils were classed as strongly nitrifying (having a high potential to nitrify) and 18 as weakly nitrifying (having a low potential to nitrify). This separation reflected differences in other soil properties, with discriminant analysis giving a 91.7% correct classification into the two groups using only pH and Bray (II) extractable phosphorus for discrimination. Strongly and weakly nitrifying groups could also be discriminated on the basis of their value/chroma rating (after ignition), with a 94.4% probability of correct classification. Within each classification, nitrogen mineralization was correlated with total nitrogen (r2 =0.59 and 0.65, P< 0.001, for strongly and weakly nitrifying soils, respectively) but with a different relationship in each case. The significance of this difference in nitrogen dynamics is discussed in relation to site-specific forest management practices.
Calculating pH from EC and SAR values in salinity models and SAR from soil and bore water pH and EC data.
Authors: Robbins CW , Meyer WS
Published: April 2005

Currently used soil salinity models do not contain a mechanism for including exchangeable sodium effects on soil pH. A method is needed that allows pH calculation from the sodium adsorption ratio (SAR) or exchangeable sodium percentage (ESP) and electrical conductivity (EC) data. This study developed a simple method for calculating saturated soil paste and aqueous solution pH from SAR (or ESP) and EC data and compared the results with measured values from a number of soils and subsurface waters. The equation pH =A+{B*(SAR)1/2/(1+C*EC)} estimated soil pH from EC and SAR or ESP values. When rewritten as: SAR or ESP={(pH-A)(1 + C*EC)/B)2, the SAR or ESP was estimated from pH and EC data. By using shallow bore (well) water and soil extract data from the Murray Basin, values were determined for the scalar terms A, B and C. These values differed among subsurface water and soil types, however, the range of each scalar was reasonably small. It was found that a range of at least 2.5 pH units in the calibration data was necessary to obtain reliable regression between predicted and measured pH and SAR or ESP values. When these conditions were met, the predicted results were satisfactory. These relationships provide a method for pH calculation in soil salinity models which takes into account soil EC and sodium effects. They also provide a rapid field method to estimate SAR or ESP from easily obtainable EC and pH data. Further research is needed to define the factors that determine the values of A, B and C.
Diffuse reflectance infrared fourier transform (DRIFT) spectroscopy in soil studies
Authors: Nguyen TT , Janik LJ , Raupach M
Published: April 2005

The diffuse reflectance spectroscopic technique provides a convenient means of obtaining mid-infrared spectra of soils, as an alternative to the pressed halide disc method. Advantages and drawbacks of the DRIFT technique are discussed and compared with those for the KBr pressed disc method for a range of Australian soils. Useful sample concentrations for DRIFT spectra range from 1-100%, i.e. much higher than for typical pressed halide discs. This high sample concentration leads to an apparent enhancement of relatively weak band intensities, providing increased information content for soil characterization. Some neat soils and soil minerals, however, show severe distortion of strongly absorbing bands at high sample concentrations, generally at frequencies below 1100 cm-1. This results in some bands having an 'inverted' appearance. Bands due to organic components are clearly visible in the range 3100-2800 cm-l. Mineral components of soils often show a group of broad, weak-medium intensity bands in the 2600-1650 cm-1 region due to overtone and combination vibrations. These bands, enhanced in DRIFT spectra, are useful for characterization purposes. For example, bands in the region near 2600-2500 cm-1 are diagnostic features for the identification of calcite and dolomite, while those in the region 2000-1650 cm-1 are characteristic of quartz and kaolinite.
An analysis of variability in the activity of nitrifiers in a soil under pasture .I. Spatially dependent variability and optimum sampling strategy
Authors: Bramley RGV , White RE
Published: April 2005

Variability in the activity of nitrifying organisms in a Tokomaru silt loam (Typic Fragiaqualf) under a ryegrass-white clover pasture was measured using a short-term nitrification assay (SNA). Spatial dependence of the variability in SNA value and associated soil properties was examined for an area of 625 m2 using geostatistical analysis. The values of SNA, soil nitrate (NO3-N), and exchangeable ammonium (Ex-NH4+) were all highly variable and conformed to lognormal distributions. The range of spatial dependence in the variability of SNA, NO3-N, and the pH of the SNA incubation media, which was assumed to approximate the field soil pH, was 3.3, 12.0 and 13.8 m respectively. EX-NH4+ showed no spatial dependence. SNA, NO3-N and incubation pH varied isotropically within the sampling area, but soil moisture content was strongly anisotropic. These results are discussed in relation to the most efficient sampling strategy for estimation of the mean field NO3- concentration. It was concluded that sufficient small localized clusters of samples should be taken to give a low standard error of the mean, with each cluster separated by at least 12 m. In the case of the Tokomaru silt loam, 12 clusters, each comprising bulked subsamples, would be required for estimation of the mean field nitrate concentration with 95% probability of �, the sample mean, being within � 5% of �, the true mean. This represents a large sampling effort.
An analysis of variability in the activity of nitrifiers in a soil under pasture .II. Some problems in the geostatistical analysis of biological soil properties
Authors: Bramley RGV , White RE
Published: April 2005

An investigation of spatially dependent variability in the activity of soil nitrifiers indicated a number of shortcomings in the application of geostatistical methods to the analysis of spatial variation in biological soil properties which inherently have high variability. The relationship between the sill variance (Co+C) and sample variance (s2)), problems in the identification of anisotropic variation, and the effect of the scale of sampling on s2 are considered in relation to the sampling design used for collection of sample data. It is concluded that for minimum complication, sampling designs should be symmetrical in at least four principal directions, and that some sampling sites should be positioned at points between the nodes of the grid to ensure as wide a spread as possible in the distances between pairs of observations.
Movement of solutes associated with intermittent soil-water flow .II. Nitrogen and cations
Authors: Tillman RW , Scotter DR
Published: April 2005

The movement of applied potassium and nitrogen through columns of repacked silt loam was examined in the laboratory. The nutrients were applied as 5 mm of a dilute solution of potassium bromide and urea, left for 3 or 10 days, and then leached further down into the soil. Twelve days after the start of the experiment, the columns were sectioned to allow the distribution of applied and resident nutrients to be assessed. Most of the urea nitrogen was transformed to nitrate over the 12 days. The timing of water application relative to nitrification was important in determining the amount of nitrogen leached. The soil solution anion concentration determined the amount of cation leaching. Although potassium was the cation added, calcium and magnesium were the dominant cations accompanying the nitrate downwards.A mechanistic model was constructed, driven by the water movement, and with the solute dispersion, diffusion and adsorption parameters derived from the literature. It assumed the Gapon relationship for cation exchange, and that hydrogen ion production reduced the effective cation exchange capacity. This model was able to simulate closely the experimental data.
Effect of slope length, aspect and phosphogypsum on runoff and erosion from steep slopes
Authors: Agassi M , Ben-Hur M
Published: April 2005

The efficiency of phsophogypsum as an amendment for controlling erosion on embankments was studied on a Typic Rhodoxeralf soil, with 48% slope and 10 and 1.5 m long plots, with western and northern aspects and a westerly dominant wind during rainstorms. Phosphogypsum reduced the runoff by 23%, and the erosion was 2-3 times less than on the control slope. The embarkment's aspect has no effect on the amounts of rainfall and runoff, but the erosion from the long plots with a western aspect compared with the long plots with a northern aspect was 1.4 and 2.5 times higher in the control and phosphogypsum treatments, respectively. The length of the plots has no effect on the runoff, however, soil loss was 6.4 times higher in the longer plots. High correlations were found between the amount of erosion and the erosivity index or the runoff amount.
Structural component of the swelling pressure of calcium clays
Authors: Quirk JP , Pashley RM
Published: April 2005

The presence of a major repulsive ion-induced structural force or disjoining pressure between Ca-clay particles is demonstrated. This arises from the perturbation of the normal structure for water to distances of about 50 A. This force operates in slit-shaped pores between clay particles and is opposed principally by attractive ion-ion correlation forces in regions of clay particle overlap.
Calcium chloride extractable cadmium as an estimate of cadmium uptake by subterranean clover
Authors: Whitten MG , Ritchie GSP
Published: April 2005

Cadmium (Cd) may accumulate in soils which have been regularly fertilized with phosphate fertilizers which contain Cd originating in rock phosphate. Soil was taken from three sites in the wheatbelt of Western Australia which were estimated to have received different amounts of phosphate fertilizer over the past decade. The pH was adjusted with dilute HCl or CaCO3. No Cd was added experimentally. The concentration of Cd in the whole tops of Trifolium subterraneum cv Mt Barker grown in a glasshouse pot experiment increased from 0-2-0.8 �g g-1 dry wt at pH 6 -6-6.9 (1:50-01 M CaCl2) to 2-4 �g g-1 at pH 4.1-4.2. The highest concentration of Cd in the plant tops at any particular pH occurred on the soil which had the highest concentration of P in the CaCl2 extract. There was a linear relationship between the concentration of Cd in the whole tops of sub-clover and the concentration of Cd in the CaCl2 extracts which was independent of site. The concentration of Cd in the CaCl2 extracts was a function of pH and concentration of P in the CaCl2 extract.
Effects of incubation time and filtration technique on soil solution composition with particular reference to inorganic and organically complexed Al
Authors: Menzies NW , Bell LC , Edwards DG
Published: April 2005

Soil solutions were extracted from surface and subsoil samples of highly weathered soils in the field moist state and from air-dry samples which had been re-wet and incubated at 28�C for 1 to 64 days. Soil solutions were analysed following filtration through 0.22 pm and 0-025 �m pore-diameter hembranes. Selected samples were also incubated following sterilization by gamma irradiation (50 kGy) to investigate the effects of microorganisims on soil solution C dynamics. Ultra-filtration did not affect the concentration of the major cations or anions but significantly reduced Al, Fe, Mn, Si and organic C concentration in some surface soil solutions extracted from field-moist samples and from re-wet air-dry samples after short incubation periods. The organically-complexed Al concentration in soil solution was significantly increased by air-drying and re-wetting soil; the organic Al concentration decreased with increased time of incubation to levels comparable with that present in field-moist samples. Inorganic monomeric Al reached a stable concentration, comparable with that in field moist samples, when air-dry soils were re-wet and incubated for 1 day. While gamma irradiation effectively sterilized the soil and stabilized the concentration of Al and organic C in solution, the magnitude of the changes in soil solution composition observed as a result of irradiation diminish the value of this finding.
Relationships between zinc and phosphate adsorption on montmorillonite and an iron oxyhydroxide
Authors: Madrid L , Diaz-Barrientos E , Contreras MC
Published: April 2005

A comparison is made between the behaviour of lepidocrocite and Ca-saturated montmorillonite in the adsorption of zinc and phosphate. It is shown that both adsorbents are sensitive to pH changes, so that the amounts of Zn adsorbed increase as pH increases in P-free systems, although the pH-dependence is much stronger in the case of the oxide. There seem to be two kinds of sites present on the clay surface, with one site showing higher preference for Zn over Ca. The number of high-preference sites for Zn increases as pH increases, and it is suggested that they are located on edge, variable charge regions. The amount of phosphate adsorbed by montmorillonite is nearly constant for pH values above 5, and the position of the plateau is independent of whether Zn is present in the system or not. This result contrasts with the known behaviour of oxides, and can be explained by assuming that P is adsorbed as H2PO4 H2PO-4 on surfaces with an electric potential of about -90 mV, which agrees with values of the electric surface potential calculated for montmorillonite in the literature. Adsorption of Zn or phosphate by the oxide is enhanced by the presence of the other adsorbate; however, when the adsorbent is montmorillonite, the amounts adsorbed are insensitive to the presence of the other adsorbate. It is suggested that, for the levels of Zn coverage studied here, adsorption of Zn and phosphate occurs on different kinds of sites on the clay mineral, while there seems to be a close relationship between the adsorbing sites for both adsorbates on the oxide.
Field studies on effect of soil conditioners and mulch on runoff lrom kaolinitic and illitic soils
Authors: Stern R , Laker MC , Vandermerwe AJ
Published: April 2005

Runoff plots (1 - 5 m2) were constructed at three sites where crusting, runoff and erosion are severe problems. The effect of surface application of phosphogypsum (PG), polyacrylamide (PAM) and mulch cover on runoff during natural rainstorms were studied. Runoff percentage from control (bare) plots in some rainstorms exceeded 90% of the rainfall. The annual runoff from control plots ranged between 33 and 73% of the annual rain. Mulch was highly beneficial in reducing runoff, indicating that seal formation restricted water penetration rather than hydraulic properties of the profile. PG reduced runoff to 0.15-0.82 of the untreated plots. The efficiency of PG in reducing runoff was inversely correlated with rainstorm intensity. The beneficial effect of PC in reducing runoff lasted throughout the rainy season. Its beneficial effect terminated during the consecutive season in the Irene site when the cumulative rain depth exceeded 700 mm. PAM treatment reduced annual runoff by two to three fold in comparison with the control treatment. The effect of PAM on diminishing runoff in the rainfall simulator studies was more pronounced than in the field conditions.
Corrigenda - The effects of minimum cultivation after three years on some physical and chemical properties of a red-brown earth at Forbes, NSW.
Authors: Cavanagh PP , Koppi AJ , Mcbratney AB
Published: April 2005

Reducing cultivation may improve many soil physical and chemical properties of a red-brown earth. A trial was set up in 1986 on a red-brown earth near Forbes, N.S.W., comparing direct-drilling and conventional-cultivation crop establishment techniques. The surface soil (0-100 mm) was sampled at the end of the third year and assessed for macropore structure, infiltration characteristics, bulk density, pH, electrolytic conductivity, organic carbon and total nitrogen content. Cultivation degraded some desirable soil physical properties as indicated by data obtained from image analysis and infiltration. Bulk density did not mirror differences in macroporosity. Organic carbon, total nitrogen and electrolytic conductivity levels were higher in direct-drilled soil in comparison to conventionally tilled soil. It ib concluded that the improvement of soil chemical and physical properties afforded by a reduction in tillage would lead to an increase in soil water infiltration rate and storage.
Rain impact soil crust. II. Some effects of surface slope, drop size and soil variation
Authors: Moss AJ
Published: April 2005

Formation and non-formation of the rain-impact soil crust were studied experimentally over ranges of surface-slope, drop-size and soil variation. In these contexts, the formative process was found to be very versatile. However, stable particles, of a size just movable on the soil surfaces by raindrops, appear to play a special role in preventing crust development. Becoming juxtaposed on the surface, these particles form clusters which allow hydraulic penetration of water from impacting drops, through their large pores. This maintains loose packing in the near-surface zone as opposed to the compaction associated with crust formation where only small surface pores exist. A method of soil modification, involving increasing the proportion of durable, barely rain-movable particles in soils, is suggested as a means of combating crusting on a long-term basis.
Rain impact soil crust. III. Effects of continuous and flawed crusts on infiltration, and the ability of plant covers to maintain crustal flaws
Authors: Moss AJ , Watson CL
Published: April 2005

Experiments on unsteady infiltration, through rain-impact soil crusts on an albaqualf, employed 70 mm diameter cylinders surrounded by airsplash-exchange areas. Significant throttling effects resulted. Circular, fabricated flaws of varying diameter caused strong bypassing of the crust by infiltrating water. As the percentage of total area flawed rose from 1% to 10%, infiltration rates rose from near those of fully-crusted values to those of uncrusted values, further areal increases bringing little change. This result suggested three-dimensional water movement beneath flaws. Sheltering by plant covers produced flaws in the rain-impact soil crust. However, sheltered areas often acted as traps for incoming, finely comminuted, airsplash debris which, once deposited, could also throttle infiltration. Moreover, the compacted layer, the main throttling agent of the rain-impact soil crust, often extended laterally into sheltered areas. Wheat-straw stems, less than a drop diameter apart, were effective flaw preservers, even under heavy airsplash, inhibiting formation of the compacted layer and stimulating removal of airsplash deposits. Grass covers, dense enough to intercept all raindrops, were also highly effective against infiltration throttling because intercepted raindrops were converted, via the double-edge effect, into non-erosive, fine, impact droplets which could not disturb the soil.
Atrazine persistence and toxicity in two irrigated soils of Australia
Authors: Bowmer KH
Published: April 2005

The persistence of atrazine in two contrasting irrigated soils from the Riverine Plain of south-eastern Australia was measured in the laboratory at three constant temperatures. Particularly at lower temperatures atrazine was more persistent, by an order of magnitude, than reported for soils overseas; but in two successive field experiments, encompassing both surface and incorporated applications of atrazine in the heavier soil, residues measured after about 7 months were within the range expected from the literature. The measured residues were 2-6 times smaller than predicted using a simulation model, probably reflecting volatilization and other losses which are not included in the model, but which are expected to be substantial at the extremely high soil surface temperatures observed in the field. Comparative measurements of aged residues in the heavy clay soil showed higher results from chemical analysis of acetonitrile-water soil extracts than by in situ glasshouse bioassay using oats and turnips, demonstrating that only one third of the extractable residue was available to crops. Comparison of soil-based and hydroponic assay using soybeans showed that this soil reduced the effective atrazine concentration in solution by at least 16-fold, but sensitive crops could still be damaged when grown in rotation after tolerant crops, or if irrigated with contaminated water.
An evaluation of the intrinsic sorptivity water repellency index on a range of New Zealand soils
Authors: Wallis MG , Scotter DR , Horne DJ
Published: April 2005

Undisturbed cores were removed from the surface of 14 New Zealand soils with a wide range of textures. The sorptivity to ethanol and water was measured with a 'sorptivity tube' to determine the repellency index (Rl) of each soil. Texture and gravimetric water content were measured, and the water drop penetration time (WDPT) and molarity of ethanol droplet (MED) tests for water repellency were conducted on the soils. The RI measured all soils water repellent (RI> 1.95) at field moisture conditions, and was more sensitive than the WDPT or MED tests. The RI was used to demonstrate that water repellency reduced short-time water infiltration of all soils by approximately an order of magnitude. Actual and 'potential' infiltration was then compared with rainfall and irrigation intensities. This illustrated the hydrological significance of the phenomenon, even in soils which appeared to wet normally (low WDPT). In all soils the curves of cumulative infiltration versus the square root of time for both water and ethanol stayed linear long enough for sorptivity evaluation. However, at longer times the slope of the curve tended to increase for water sorption in the more repellent soils, but decreased consistently for ethanol.
Estimation of infiltration and deep drainage in a furrow-irrigated sodic duplex soil
Authors: Dowling AJ , Thorburn PJ , Ross PJ , Elliot PJ
Published: April 2005

Infiltration and deep drainage fluxes are difficult to measure directly in slowly permeable soils under furrow-irrigated upland crops such as maize (Zea mays L). This paper combines a solute mass balance model and a furrow irrigation advance model to provide an estimate of these fluxes, indirectly from simpler measurements. The models were applied to a newly cleared sodic duplex soil from the Burdekin River Irrigation Area, north Queensland, where no field measures of infiltration and deep drainage were available. The study site was sown to consecutive furrow-irrigated crops after clearing. In applying these models, measures of soil and irrigation water chloride, irrigation water applied, furrow geometry and irrigation advance were required. Estimated infiltration and deep drainage decreased with distance down the furrow from 1044 and 98 mm year-1 at 50 m to 966 and 0 mm year-1 at 260 m. In an area that received an application of gypsum (20 t ha-1) prior to planting the second crop, values ranged from 1617 and 200 mm year-1 at 50 m to 1370 and 70 mm year-1 at 260 m. Infiltration did not satisfy the estimated soil water deficit unless gypsum was applied. Where gypsum was applied, infiltration exceeded the soil water deficit and deep drainage increased. Evapo-transpiration rate and maize yield also increased. If correct, these results have local and regional implications for irrigation design and management.
Daily temperature extremes as an indicator of high temperature stress
Authors: Bristow KL , Abrecht DG
Published: April 2005

Theory outlining a general relationship between stress experienced by an organism exposed to supra-optimal temperatures and daily temperature extremes is discussed. It is shown that useful nomograms relating Tmax, Tmin, Tcritical, and high temperature stress can be developed and that these nomograms are not particularly sensitive to changes in daylength (caused by changes in time of year or latitude). Sensitivity of high temperature stress to changes in Tmin is also considerably less than that to changes in Tmax, suggesting that in situations where Tmin, does not vary greatly, Tmax alone can be used as an indicator of high temperature stress. Application of these concepts is illustrated by analyses of high temperature stress in pre-emergent maize seedlings. Results show that Tmax alone can account for more than 90% of the variation in the reduction of shoot length due to the occurrence of supra-optimal temperatures.
The role of iron in the weathering of a climosequence of soils derived from schist
Authors: Aldridge LP , Churchman GJ
Published: April 2005

Mossbauer spectra were obtained of the whole soil and clay fractions and some of the sand fractions, as well as some rock samples that were taken from eight soils forming a climosequence on schist in South Island, New Zealand. They show that the main changes in iron across the sequence involve the oxidation of ferrous ions in muscovite mica and its initial weathering products to ferric ions in these minerals and also in oxyhydroxides. The extremes of weathering in the sequence led to the mobilization of iron from primary minerals in soils at the surface of profiles into oxyhydroxides that were deposited lower down in these profiles. While these changes in iron have occurred alongside the loss of K+ from the interlayers of the micas to form expanded phases, there is not a close parallel between the changes on oxidation and those from the initial loss of interlayer potassium.
Effect of organic matter and allophane on adsorption of polyethylene glycols onto some soils
Authors: Ishida T
Published: April 2005

Polyethylene glycols were adsorbed onto some soils that had been previously leached with hot water to remove water-soluble organic substances and then either oven-dried or kept moist. The amount of glycol adsorbed onto the dried soils decreased as organic matter content increased. The amount adsorbed onto the moist soils showed a different trend. The parameters for an adsorption equilibrium model based on statistical thermodynamic considerations, namely the equilibrium constant, Ka, and the total volume of the adsorbed phase, w1(0), were estimated in order to interpret this adsorption behaviour. The change in Ka (indicating the change in nature of the soil surface due to drying) significantly depended on allophane content, while the value of w1(0) (representing the amount of surface exposed) was more affected by organic matter content. In addition, the relationship of w1(0) to the liquid limit confirms the validity of w1(0) in modelling soil-water systems.
Cationic interferences on zinc adsorption
Authors: Krishnasamy R , Krishnamoorthy KK
Published: April 2005

The effects of bivalent cations such as Mg2+, MN2+, FE2+ and Cu2+ on zinc adsorption in 16 surface soil samples (0-25 cm depth), representing major soil series of Tamil Nadu (India), and of the soil orders Vertisol and lnceptisol were studied. The study revealed that the interference of the four bivalent cations on zinc adsorption was in the order Cu2+ > Mn2+ > Me2 + > Mg2+. The effects of these ions on zinc adsorption could be explained on the basis of chemical properties such as magnetic moment value, kinetic classification, crystal field stabilization energy (CFSE) and kinetics of substitution. The variations in soil properties, particularly soil texture, also influenced zinc adsorption in these soils.
Valley reforestation to lower saline groundwater tables - Results from Stene Farm, Western-Australia
Authors: Schofield NJ , Bari MA
Published: April 2005

Dense planting of selected trees in salt-affected valley floors and non-saline adjacent slopes has been evaluated as one strategy for controlling rising saline groundwater under agriculture. Of the 127 ha experimental catchment, 44% had been cleared of native forest in the 1950s. Valley reforestation covering 35% of the cleared area took place in 1979, by which time a groundwater of 5300 mg L-1 TSS had risen to within 0.5 m of the soil surface. The eucalypt reforestation was successful in lowering the groundwater table by 1.5 m by 1989, whilst groundwater levels under nearby pasture had risen by 1.8 m. The groundwater salinity beneath reforestation decreased by 30% over the study period, allaying fears of a detrimental groundwater salinity increase brought about by transpirative concentration. Measures such as replanting failed areas, implementing agricultural recharge control or selecting higher water using tree species would improve the performance of the valley reforestation strategy.
Groundwater recharge from rainfall and irrigation in the campaspe river basin
Authors: Chiew FHS , Mcmahon TA
Published: April 2005

Reliable estimates of groundwater recharge are required for effective evaluation of management options for salinity control and high water-tables in the Riverine Plain of south-eastern Australia. This paper provides a brief description of the integrated surface and groundwater modelling approach used to estimate regional recharge rates and presents the recharge rates estimated for the Campaspe River Basin. The integrated model is a powerful management tool as it can predict the relationship between rainfall, irrigation, recharge and rises in the water-table levels. The model predicted that approximately 15% of irrigation water recharges the shallow aquifer. Approximately 6% of rainfall contributes to recharge in the irrigated areas while 4 to 5% of rainfall becomes recharge in the dryland areas. Rainfall makes a greater contribution in the irrigation areas compared to the dryland areas because irrigation predisposes the soil to recharge from rainfall. The water-table levels in the irrigation areas are currently rising at approximately 0.14 m yr-1. This rate of rise will increase faster than the increase in irrigation applications.
Soil erosion processes. I. The relative importance of rainfall detachment and dunoff entrainment
Authors: Proffitt APB , Rose CW
Published: April 2005

Experiments carried out in a simulated-rainfall tilting-flume facility are reported in which sediment concentrations (c) in runoff water resulting from overland flow only, or from a combination of rainfall and overland flow, were measured under controlled conditions using a series of slopes (0.1, 05, 1, 3 and 5%). The mixture of rainfall (of rate 100 mm h-1) and runon of water at the top of the flume were arranged to provide a constant volumetric flux (1.0x10-3 m3 m-l s-1) at exit from the 5.8 m long flume. Two contrasting soil types were studied: a cracking clay (black earth or vertisol), and a slightly dispersive sandy clay loam (solonchak or aridisol). Two major processes which can contribute to soil erosion under rainfall are rainfall detachment and runoff entrainment. For both soil types, c was generally highest for the steepest slope and decreased with slope. For constant rainfall and/or runoff conditions, c generally decreased with time until an equilibrium concentration was reached. At this equilibrium, the relative importance of rainfall detachment and entrainment in terms of soil loss was dependent on soil type and streampower which incorporates effects of slope and water flux. For streampowers <0.1 W m-2 for the black earth, and <0.3 W m-2 for the solonchak, the greatest contribution to c was by rainfall detachment, whilst at greater streampowers entrainment was the dominant contributor to c. At any streampower, the contribution by rainfall detachment was greater for the weakly structured solonchak than for the well aggregated black earth. At lower strearnpowers, the interaction between erosion processes was found to give higher c than the sum of both sediment concentrations resulting from the separately occurring processes. At streampowers greater than approximately 0.5 W m-2, rainfall reduced eroded sediment concentration by suppressing rill development. The findings in this study suggest that both runoff entrainment and rainfall detachment can contribute to sediment concentration from 'interrill' areas.
Soil erosion processes.II. Settling velocity characteristics of eroded sediment
Authors: Proffitt APB , Rose CW
Published: April 2005

Settling velocity characteristics of sediment eroded by overland flow only, or from a combination of rainfall (100 mm h-l) and runon were measured under controlled conditions in a simulated rainfall tilting-flume facility. Two contrasting soil types were studied: a cracking clay (black earth or vertisol), and a slightly dispersive sandy clay loam (solonchak or aridisol). For a constant volumetric flux (1.0x10-1 m3 m-1 s-1) at exit from the 5.8m long flume and a slope of 0.5%, sheet erosion prevailed, whilst for the same flux at a steeper slope of 5%, rill erosion prevailed. Settling velocity characteristics of eroded sediment were found to be dependent on erosion process, flow hydraulics, soil type, and time in the erosion event. For both soil types, there was a progressive change in settling velocity characteristics with time, this change being less pronounced for sediment eroded dominantly by rill flow as opposed to sheet flow. Temporal changes in settling velocity characteristics were attributed to the development of a deposited layer of coarser, faster settling sediment on the soil surface. The net outcome of rill erosion was less size-selectivity compared with sheet erosion, as determined by the measured settling velocity characteristics of eroded sediment. This outcome was associated with the greater erosive power of rill flow compared with sheet flow. Rainfall was found to influence the settling velocity characteristics of eroded sediment substantially when sheet flow predominated. This was thought to be due to lower flow velocities under rainfall (and therefore smaller contribution to soil loss by entrainment). The findings reported in this study have important implications when assessing nutrient losses from eroded sediment, and in predicting the spatial redistribution of eroded sediment.
The study of soil structure - Science or art
Authors: Letey J
Published: April 2005

Soil structure is the size, shape and arrangement of the solid particles and voids which is highly variable and associated with a complex set of interactions between mineralogical, chemical and biological factors. Science is based on quantitative measurements which can be reproduced. Soil structure does not lend itself to quantification. Numerical values of soil structure indices almost always depend on the measurement procedure and therefore the study of soil structure may be considered as being largely art rather than science. Furthermore, most soil scientists studying soil structure are not primarily interested in soil structure per se but rather the functionality of soil structure as a medium for crop growth or chemical transport. Studies in the laboratory, frequently on fragmented samples, do not always lead to an understanding of the functionality of soil structure under field conditions. Development of a comprehensive understanding of soil structure requires a combination of principles based both on science and art.
Sustainable agricultural systems - What are the appropriate measures for soil structure
Authors: Hamblin A
Published: April 2005

Sustainable agriculture implies time-scales which are long relative to human lifespan, and the maintenance of productive capacity from the resource base. To evaluate whether agricultural systems are sustainable we need appropriate biophysical and socio-economic measures. Monitoring the status of soils will need some description of their capacity to store and transmit water, nutrients and gases for plants and microorganisms. Most physical and chemical properties of soils which regulate this storage and transmission are time-consuming and complex to measure. Moreover, they are not readily adapted to the requirements of large-scale, long-term environmental monitoring. Robust surrogates are required which can be unambiguously interpreted. A range of such surrogates and their application at different spatial scales is discussed.
Fungal hyphae and structural stability of soil
Authors: Tisdall JM
Published: April 2005

This review describes the possible mechanisms by which fungal hyphae, especially those of vesicular-arbuscular mycorrhizal (VA) fungi, bind microaggregates of soil (<0.25 mm diameter) into stable macroaggregates (>0.25 mm), and suggests a model of the formation of a stable macroaggregate by fungal hyphae. Factors which affect the growth of VA mycorrhizal hyphae in soil and their production of extracellular polysaccharides are discussed in relation to stable macroaggregates. The interactions between clay particles and hyphae are described. The review suggests areas of future research on stabilization of aggregates by VA mycorrhizal hyphae.
Micromorphology of soil structure - Description, quantification, application
Authors: Ringrose-Voase AJ
Published: April 2005

Micromorphological observation can provide insights into soil structure and aid interpretation of soil behaviour. Undisturbed samples are taken in the field and impregnated. They are used to prepare thin sections or images of the macropore structure using fluorescent photography. Sections can also be obtained at macro, meso and submicroscopic scales. The various elements of soil structure observed micromorphologically can be classified into pore space, physical, distribution and orientation fabrics, and associated structures. Examples of the importance of features in each category are given. Image analysis, especially when computerized, provides a way of parameterizing micromorphological observations. To date it has been used primarily on images of macropore space at the meso and microscopic scales. Such images can be digitized and segmented to show pore space and solid. The pore space can be allocated to pore types. This aids the estimation of 3-D parameters from I-D and 2-D measurements made on the image using stereology. Various ways of using structural parameters to compare structures are discussed. Applications for micromorphological observations, especially when quantitative, include comparison of structures formed by different management techniques. Structural measurements can aid interpretation of soil behaviour as described by physical measurements. They also have a role in estimating the representative elementary volume, on which physical measurements should be made, and in calibrating field estimates of soil structure.
Aggregate hierarchy in soils
Authors: Oades JM , Waters AG
Published: April 2005

An Alfisol, a Mollisol and an Oxisol were fractionated into different particle sizes after a range of disaggregating treatments from gentle to vigorous. The Alfisol and the Mollisol appeared to break down in steps; macroaggregates >250 �m diameter breaking down to microaggregates 20-250 �m diameter before particles <20 �m were released. Vigorous disruption led to particle size distributions similar to those obtained by classical methods used to determine particle size distributions. The Oxisol was stable to rapid wetting treatments but when aggregate disruption was initiated by vigorous treatments particles <20 �m diameter were released and there was no evidence of aggregate hierarchy. Scanning electron microscopy of particles of different sizes showed distinctly single grain particles and aggregates. The microscopic studies indicated the potential role of roots and hyphae in the stabilization of larger aggregates, and for fragments of roots as nuclei for smaller aggregates. Plant debris was not visible in aggregates <20 �m but clay microstructure was evident. It is suggested that aggregate hierarchy occurs in Alfisols and Mollisols because organic materials are the dominant stabilizing agents in larger aggregates but in the Oxisol oxides are dominant stabilizing agents and prevent the expression of aggregate hierarchy caused by organic materials.