bluuebunny/crossref_metadata_2025 huggingface dataset:
The management of soil physical properties limiting crop production in Australian sodic soils - a review
Authors: Jayawardane NS , Chan KY
Published: April 2005

Sodic soils occur extensively on the agricultural lands of Australia. The poor crop productivity of sodic soils is often associated with their low infiltration rates and restricted drainage. This is caused by low macroporosity and macropore instability, due to the presence of sodium on the clay surfaces. To achieve long-term improvements, tillage techniques to increase macroporosity have to be combined with chemical and biological techniques to improve macropore stability. Macropore stability is improved by addition of chemical ameliorants and organic matter. Maintenance of macroporosity also requires protection of the tilled soil from recompaction during flood irrigation, raindrop impact and trafficking. Adverse effects of sodicity of surface soil layers can be corrected by incorporating gypsum and by using conservation farming practices to add organic matter and to protect the surface from mechanical disturbance and raindrop impact. Subsoil sodicity can be corrected by combining deep ripping with chemical ameliorant additions, but the beneficial effects are often quickly lost under flood irrigation and trafficking. Longer term increases in crop production can be achieved by providing surface and subsurface drainage, bed farming and gypsum-slotting. Advantages and disadvantages of these techniques, their application in dryland and irrigated cropping and the areas for future research are discussed. In soils such as Vertisols with high shrink-swell potential, strong-rooted crops such as safflower could be used for biological soil loosening, through deep soil profile drying. The effectiveness of soil ameliorative techniques can be evaluated by assessing the soil factors limiting crop growth during a growing season in a non-ameliorated soil, and the subsequent changes in these soil factors due to the ameliorative practices. A technique which can be used in field studies to monitor these changes through the cropping season, based on the concept of the 'non-limiting soil water range' for crop growth, is described. Irrigation management of sodic soils and re-use of saline drainage waters require an understanding of the changes in soil hydraulic properties with changes in water quality parameters. The 'equivalent salt solution' concept can be used to predict such changes in soil hydraulic properties. These predicted values could then be used in existing water flow models for assessing water and salt flow through irrigated sodic clay soils.
A transfer function approach to modeling the leaching of solutes to subsurface drains .II. Reactive solutes
Authors: Heng LK , White RE , Scotter DR , Bolan NS
Published: April 2005

Leaching losses of sulfate-sulfur (S) through mole drains at 450 mm depth in two adjacent paddocks were measured for three years. Sulfur was applied in autumn at the rate of 50 and 30 kg S ha-1 in the first and second years respectively, as single superphosphate to one paddock and as elemental sulfur to the other. The concentration in the drainage was mostly between 5 and 10 g S m-3 from the superphosphate-treated paddock, and between 1 and 5 g S m-3 from the elemental S treated paddock. Simultaneous collection and analysis of suction cup and soil samples from 250 mm depth on a number of occasions provided data from which a sulfate adsorption isotherm was constructed. Soil sampling suggested 60% of the superphosphate was immobilized within a week of application. After that net mineralization of sulfate occurred. Sulfate S drainage concentrations were successfully simulated for most of the drainage periods, by using a transfer function derived from chloride and bromide leaching data from the same site and the measured sulfate adsorption isotherm. Oxidation of elemental S, net mineralization, rainfall addition, and herbage uptake of S were incorporated into the model through their effects on the sulfate concentration of the solution entering the soil's transport volume. This meant the convolution integral in the transfer function equation had to be evaluated numerically. Inadequate description of the dynamics of mineralization appeared to be the main weakness of the model, rather than the simplifying assumption that the soil's transport volume could be treated as a well mixed system.
Causes for the reduced reactivity of phosphate rock residues in partially acidulated phosphate rocks
Authors: Di HJ , Condron LM , Campbell AS , Goh KM , Cornforth IS
Published: April 2005

The agronomic effectiveness of partially acidulated phosphate rock (PAPR) fertilizers depends on the proportion of water soluble P present and the long-term release of P from the unacidulated residual phosphate rock (water-insoluble residue) in the soil environment. The relative reactivity of water-insoluble residues in a range of partially acidulated phosphate rock (PAPR) fertilizers was assessed according to chemical solubility, and was found to be lower than the corresponding original PRs. Two causes were identified for the reduced formic acid solubility of water-insoluble residues: (i) some preferential dissolution of more reactive apatite components (i.e. higher carbonate substituted apatite) during partial acidulation as indicated by reductions in the molar apatite C:P ratio of the residual PRs compared with the corresponding original PRs, and (ii) acid-insoluble metal (Fe-Al-Mg)phosphate and/or fluoride complexes formed on the surface of residual PRs during partial acidulation with commercial-grade phosphoric acid, which were partially soluble in alkaline ammonium citrate. These two mechanisms accounted for most of the solubility differences observed for 'medium' reactive PRs (Khouribga, Arad), compared with only half for more reactive PRs (North Carolina, Gafsa). The conclusion from this study is that partial acidulation may not be an ideal method for the manufacture of fertilizers containing fast and slow release (i.e. PR) components, particularly when highly reactive PRs such as North Carolina are used.
Soil pH changes under Victorian pastures
Authors: Crawford DM , Baker TG , Maheswaran J
Published: April 2005

The severity and extent of surface soil acidification was assessed at 107 pasture sites across Victoria. At each site, soil samples (0.20 cm depth) were taken from the pasture area and an adjacent reference (undisturbed) area for analysis of soil pH (1:5 0.01 m CaCl2 or water). Acidification was evident in the 0.10 cm depth of sites with moderately and slightly acid (pH [water] 5.5-7) reference soils, while alkalinization was evident in the 0.20 cm depth of sites with strongly acid (pH [water] <5.5) reference soils. Causes of pH changes were not clearly evident from the relationships between site factors and changes in soil. It was evident that site factors were confounded since sites that had acidified often supported subterranean clover and had slightly to moderately acid reference soils, while sites which had alkalinized often supported white clover-based pastures under higher rainfall and had more acidic reference soils. An understanding of the causes of acidification in pasture-based agricultural ecosystems will only be gained through more fundamental studies at individual sites.
The indexing of self-mulching behavior in soils
Authors: Wenke JF , Grant CD
Published: April 2005

Past work on self-mulching behaviour in soils has produced numeration o various components of this behaviour, but no explicitly defined and tested index of self-mulching has emerged, with the exception of Grant and Blackmore's ISM (Aust. J. Soil Res. 1991, 29, 155-73). Grant and Blackmore's index is not obviously based on mechanisms of self-mulching and is to this extent called into question. An index involving the actual dynamics of soil structural regeneration is required, and so procedures for a dynamically based index, SMI, have been developed and values of this compared with those of ISM. A high degree of correlation was found and it is concluded that both measures are valid and that the choice for use can be based primarily upon whether a static or dynamic assessment of self-mulching structure is required.
Surface soil-pH map of Queensland
Authors: Ahern CR , Weinand MMG , Isbell RF
Published: April 2005

Surface soil pH can influence biological activity, nutrition and various chemical processes in the soil. Low pH or acidity is causing major concern in southern Australia, prompting requests for details on the extent, severity and distribution of acidic soils in Queensland. By creating a soil pH database, using an appropriate base map, rainfall isohyets and GIS technology, a coloured pH map of surface soils was produced at a 1:5000000 scale for the entire State. As most samples were from virgin or little disturbed sites, the map generally reflects naturally occurring soil pH. Developed horticultural, agricultural and fertilized pastoral areas are likely to have lower pH than that mapped. About two thirds (63.1%) of Queensland's soils have acidic surfaces, 9.5% neutral and the remaining 26.9% are alkaline. The major proportion (74%) of the > 1200 mm rainfall zone is strongly acid, and the remainder is medium acid or acid. Much of the sugar growing areas occur in this zone. Surface soil pH generally decreases as rainfall increases and to a lesser extent from subtropical to tropical climate. In addition to climate, identification of the soil type assists with predicting pH, as the organic, coarse and medium textured soils and massive earths are more likely to be acid and have low buffering capacity. Depending on the land use, such soils may require regular liming or minimizing of net acidifying practices for long term sustainability.
Comparison of cation/anion exchange resin methods for multi-element testing of acidic soils
Authors: Mclaughlin MJ , Lancaster PA , Sale PG , Uren NC , Peverill KI
Published: April 2005

Increasing laboratory costs and time constraints have stimulated development of techniques which allow the simultaneous extraction of many elements from soil. We assessed several techniques using cation/anion exchange resins which allow the simultaneous extraction of Ca, Mg, K, Al, Mn and P from soil. Elements are extracted by shaking soil either with resin beads or resin membranes in distilled water. The resin is separated from the soil and elements are desorbed using BaCl2/HCl. Concentrations of elements in solution are then determined by conventional chemical methods. Using 50 soils which varied in acidity/fertility, a comparison was made between concentrations of elements extracted by the resin methods and commonly used extraction procedures. Apart from Al, concentrations of elements extracted by the resin procedures correlated well with conventional extraction procedures, although P was less well correlated (R2 < 0.8) than cations (R2 > 0.8). All the resin procedures have the potential to reduce the time required for analysis of Ca, Mg, K, Mn and P in soils. The resin membrane method offers considerable speed and cost advantages over the unconfined resin bead method.
Exchange and solution phase chemistry of acid, highly weathered soils .I. Characteristics of soils and the effects of lime and gypsum amendments
Authors: Menzies NW , Bell LC , Edwards DG
Published: April 2005

Exchange and solution phase characteristics were evaluated on surface and subsoil horizons of 60 acid, highly weathered soils in the unamended state, and on 39 of the surface horizons following addition of CaCO3 or CaSO4.2H2O. Soil solutions from unamended surface samples were dominated by Na (median concentration 0.65 mM), while the other major cations were present at lower levels (median concentrations: Ca, 0.09; Mg, 0.14; K, 0.28 mM). This pattern was more pronounced in the subsoil samples where the median concentrations of the nutrient cations were < 0.05 mM, whereas the median concentration of Na was 0.28 mM. The cation exchange capacity of surface samples was dominated by Ca, Mg and Al, while Al was the major exchangeable cation in the subsoil. Addition Of CaSO4.2H2O decreased soil solution pH and increased electrical conductivity and the concentration of Ca, Mg, Na, K and Al in the soil solution. The soil solution pH change resulting from CaSO4.2H2O addition could not be predicted on the basis of the characteristics of the soil in the unamended state.
Study of free and occluded particulate organic matter in soils by solid state 13C Cp/MAS NMR spectroscopy and scanning electron microscopy
Authors: Golchin A , Oades JM , Skjemstad JO , Clarke P
Published: April 2005

A simple densimetric method for the separation of free and occluded particulate organic materials was developed and applied to five virgin soils. The free organic matter was isolated by suspending the soil in sodium polytungstate solution (d = 1.6 Mg m-3) and decanting the light material. The remaining soil was disaggregated by sonification for liberation of occluded organic materials. The free light fraction consisted of large, undecomposed or partly decomposed root and plant fragments. This fraction comprised 0.59-4.34% of soil dry weight and accounted for 6.9-31.3% and 5.9-22.1% of total soil carbon and nitrogen respectively. Identifiable components of the occluded fraction were small particles of incompletely decomposed organic residues, pollen grains, particles of plant tissue such as lignin coils and phytoliths. This fraction comprised 0.69-1.81% of soil dry weight and represented 9.2-17.5% and 6.2-14.1% of the total soil carbon and nitrogen. The proportion of soil organic carbon recovered as the occluded fraction was high in soils with high clay contents. The chemical composition of occluded and free organic materials was investigated by solid-state 13C CP/MAS NMR spectroscopy. Despite the differences in soils, environmental conditions and vegetation, the organic structure of the free light fraction was similar in four of the five soils. This fraction consisted of 55-63% O-alkyl C, 18-25% alkyl C, 14-18% aromatic C, and 5-7% carbonyl C. In the other soil, this fraction showed a higher proportion of alkyl C (31%) and lower O-alkyl C (46%). Most of the differences between soils were associated with organic materials contained in the occluded light fraction. The differences in chemical structure between the occluded light fraction and free light fractions were similar in all examined soils. The NMR data showed that the proportion of O-alkyl C was lower and alkyl C higher in the occluded light fractions than in the free light fractions. The proportion of aromatic and carbonyl carbon was higher in the occluded fractions of three soils while the percentage of these two types of carbon remained unchanged in the two other soils. It is considered that the occluded organic matter is an old pool of carbon that has been accreted within aggregates during decades of root growth and it is that pool which is lost due to cultivation.
Microbiotic soil crusts - a review of their roles in soil and ecological processes in the rangelands of Australia
Authors: Eldridge DJ , Greene RSB
Published: April 2005

Microbiotic crusts are assemblages of non-vascular plants (mosses, liverworts, algae, lichens, fungi, bacteria and cyanobacteria) which form intimate associations with surface soils. They play a major role in infiltration processes through changes to soil physico-chemical properties, and through their influence on soil surface roughness. Whilst some research suggests that they may restrict infiltration, Australian experience is that they are generally associated with enhanced infiltration. Unlike physical soil crusts, microbiotic crusts stabilize the soil against water and wind erosion, increasing landscape stability, particularly in areas of low vascular plant cover. Microbiotic crusts are thus useful indicators of soil surface condition, and cyanobacteria in the crusts fix nitrogen which may be utilized by developing vascular plant seedlings. Little is known, however, about how they interact with vascular plants and soil invertebrates. Their role in rangeland ecosystems has received renewed attention over the past few years with an increasing interest in ecologically sustainable development of arid and semi-arid grazing systems. In this review we discuss the characteristics and distribution of microbiotic crusts in the rangelands of Australia, their roles in soil and ecological processes and the impacts of fire and grazing. Finally we propose a new system for classifying crusts into functional groups and identify areas requiring further investigation.
Evaporation from bare soil in south-western Australia - a test of two models using lysimetry
Authors: Yunusa IAM , Sedgley RH , Tennant D
Published: April 2005

Physical models of the soil water balance components are useful where direct methods of determination are costly and time consuming. Information from such models is useful in developing more efficient soil and crop management practices. The simplicity of such models sometimes encourages their use in new regions without proper testing. In this study, two models of soil evaporation (Es), developed by Ritchie (Water Resour. Res., 1972, 8, 1204-13) and Boesten and Stroosnijder (Netherlands J. Agric. Sci., 1986, 34, 75-90) were evaluated in the dry mediterranean environment of the cereal belt of south-western Australia under a wide range of evaporative demand by using lysimetry. Both models treated soil evaporation as a two-stage process, but in the Ritchie model, second-stage evaporation varied with the square root of time, whereas in the Boesten and Stroosnijder model, Es varied with the square root of the potential evaporation (Eow). In the Boesten-Stroosnijder model, only the parameter � was stable over a wide range of potential evaporation Eow, whereas in the Ritchie model, both the parameters U and C varied with E(ow). However, interdependence between U and C was conservative, and higher values of U under low Eo were compensated by lower values of C, and vice versa. For the soil used in this study, the following values were found to be appropriate for the parameters: U, 4.7 mm; C, 4.0 mm1/2 ; and �, 1 . 5 mm1/2. For dry environments where seasonal Eo fluctuates widely, low U values and high C values are recommended. The Es estimated by the models agreed poorly with Es measured by the lysimeter on a daily basis. However, when the daily values were accumulated over periods of at least 6 days, good agreement was obtained, indicating that the errors associated with the daily estimates cancel out each other over time. Hence, both models gave satisfactory short-term and long-term predictions of Es, but in both cases variation between predicted and observed values was least in the Ritchie model. This is consistent with the conclusion from other studies in the region, which show that second stage evaporation dominates Es, and hence should depend more on soil moisture supply than on Eo.
Evaluation of some methods for measuring transient hydraulic properties of rain-induced surface seals on two clay soils
Authors: Silburn DM , Foley JL
Published: April 2005

Surface sealing of soils can markedly affect infiltration under rain. Robust infiltration models and methods for measuring hydraulic properties are needed. A review of methods of measuring seal hydraulic properties indicated that methods differ greatly in the hydraulic boundary conditions used and this may affect results and make a systematic analysis difficult. Two methods ('post-rain' suction permeameter and rainfall in situ) of measuring seal flux and conductivity under appropriate hydraulic boundary conditions were tested in a laboratory for two clay soils under simulated rain. The suction permeameter tests showed that conductivity of surface seal samples is altered by the suction applied during the measurement. This occurred in the absence of rain and appears to be more general than previously reported. Transient infiltration and conductivity measured by the two methods were in close agreement from ponding time onwards, provided suction equal to that measured under the seal was applied in the suction permeameter. The suction permeameter can provide conductivity data under a wider range of conditions than the rainfall in situ method, including prior to ponding, but requires measured subseal suction data. The two methods are seen to be complementary. The transient conductivity behaviour of the two soils was markedly different-the well aggregated, swelling clay exhibited an exponential decay, similar to commonly used models; the less aggregated, non-swelling clay did not. Desorption moisture characteristic curves (MCC) and measured subseal moisture content gave useful estimates of subseal suction after commencement of surface ponding, provided: (a) a correction from desorption to adsorption is not made, as desorption occurs in the subseal soil after time of ponding; and (b) MCC are measured using appropriate pre-treatment (rainfall wetting of sample in 10-20 mm depth in a soil bed).
Sulfur leaching from soil columns treated with S-35 labeled urine
Authors: Till AR , Blair GJ , Boswell CC
Published: April 2005

Pasture improvement has led to increased stocking rates which has potentially increased sulfur losses in urine patches and in sheep camps in merino enterprises. A study was undertaken using soil collected from a camp and non-camp area of an aeric ochraqualf soil. 35S-labelled urine was applied to these soils and the columns were leached daily for 7 days or subjected to wet/dry treatments for 7 cycles. The amount of S leached was dependent on the soil S level and the nature of the wetting and drying cycles. There were significant losses of unlabelled soil S in the leachate and retention of 35S in the profile which indicates that the sulfate in the profile moves en masse, most likely through continuously dynamic adsorption/desorption reactions.
Allocation of new individuals to continuous soil classes
Authors: Mcbratney AB
Published: April 2005

Objective methods of identification of unknown objects are reviewed briefly. Particular emphasis is given to diagnostic keys, diagnostic tables and taxonomic distance. A method for allocating new individuals to continuous soil classes is presented and detailed examples given. This method is compared with more conventional methods of soil identification.
Sorption non-equilibrium during cadmium transport through soils
Authors: Kookana RS , Naidu R , Tiller KG
Published: April 2005

We studied the sorption behaviour of cadmium during its transport through laboratory soil columns packed with two different soils (a Spodosol and an Oxisol). Models based on both equilibrium and time-dependent sorption reactions were used to describe observed breakthrough curves (BTCs) of cadmium. Under batch conditions, the sorption of cadmium was essentially complete within 3 h for the Spodosol and within 24 h in the Oxisol. However, sorption in the Oxisol tended to increase at a very slow rate after 10 h up to 300 h. Simulations carried out using batch sorption data, which followed the Freundlich equation, failed to describe the observed cadmium BTCs satisfactorily. A sharp BTC front was expected due to the nonlinear nature of the sorption isotherm. However, a more dispersed front with significant asymmetry was observed in both soils, indicating the occurrence of non-equilibrium sorption during cadmium transport. The presence of non-equilibrium conditions was further supported by the observed decrease in Cd concentrations in the effluent fractions collected after stopping the flow through the columns. The Cd BTCs were adequately described only when the bi-continuum (two-site/two-region) approach of solute transport modelling was utilized. Only a small degree of asymmetry was noted in chloride BTCs for both soils, thus suggesting the presence of a small physical non-equilibrium component. It is concluded that the sorption non-equilibrium observed during Cd transport is likely to be due to both sorption related (chemical) and transport-related (physical) mechanisms.
Modeling the dissolution rate of reactive phosphate rock in New Zealand pastoral soils
Authors: Watkinson JH
Published: April 2005

Equations are proposed that describe the dissolution rate of phosphate rock (PR) incorporated at maintenance rates into pastoral soil. They are restricted to PR particles of equal-sized, equivalent spheres dissolving independently of each other. The rate-limiting step is considered to be steady-state diffusion through a concentric shell of soil around the PR particles. Models are examined in which the shell is either of a fixed outer diameter or of a fixed thickness. Both permit analytical solutions to the diffusion equation. They are consistent with the Kirk and Nye model for dicalcium phosphate dihydrate under appropriate conditions, and also with field dissolution of PRs applied alone, mixed with elemental sulfur or as the unreacted component in partially acidulated PRs.
Sodium-fluoride pH of South-Western Australian soils as an indicator of P-sorption
Authors: Gilkes RJ , Hughes JC
Published: April 2005

Phosphate sorption by the surface horizon of 228 acid to neutral Western Australian (W.A.) soils is more closely related (r(2) = 0.76) to the content of oxalate-extractable aluminium than to any other soil constituent. This fraction corresponds to poorly ordered inorganic and organic Al compounds that release considerable amounts of OH- to NaF solution. Thus the abundance of these compounds in soil may be estimated by measurement of the pH of a NaF extract (pH((NaF)) This association enables the rapid and moderately accurate prediction in the field of the P-sorption capacity of soils (r(2) = 0.72) by measuring pH(NaF) With a. simple, portable pH meter. For many W.A. soils, it is probable that well crystalline aluminium and iron oxides, clay minerals and other soil constituents are of secondary importance in determining P-sorption and that most P-sorption is due to poorly ordered and organically complexed forms of Al.
Rock phosphate dissolution and bicarbonate-soluble-P in some soils from South-Western Australia
Authors: Hughes JC , Gilkes RJ
Published: April 2005

Samples were collected from 228 soils from the main agricultural areas of Western Australia (W.A.) and their chemical and textural properties analysed. Soils were incubated for 7 days with North Carolina rock phosphate at a rate equivalent to 1022 �g Ca g(-1) and 383 �g P g(-1) soil. Subsequently, the amount of rock phosphate (RP) that had dissolved was determined by measuring the increase in extractable calcium (�Ca) and changes in plant-available P were estimated by a sodium bicarbonate extraction (�Bic-P). Only 29 soils dissolved more than 40% of the added RP and these occur in the wettest area of W.A., to the west of the 800 mm rainfall isohyet. They represent a variety of soil types including Vertisols, Spodosols, Alfisols and Ultisols. Simple and multiple regressions were carried out to investigate the soil properties responsible for RP dissolution and associated P availability. No single soil property adequately predicted RP dissolution or concomitant changes in bicarbonate-P. Titratable acidity and sand content together explained 61% of the variance in RP dissolution; titratable acidity was the most predictive single variable for bicarbonate-P but only explained 56% of the variance. Stepwise regression showed that titratable acidity and pH(CaCl2) together explained 79% of the variance in bicarbonate-P. The most suitable soils for RP application are sandy, humic or peaty podzols where much of the dissolved P remains available to plants. The other soils (mainly red and yellow earths and Vertisols) which dissolved much RP contain larger amounts of extractable aluminium (by dithionite or oxalate) which is the soil component largely responsible for P-sorption in these W.A. soils. These results indicate that RP fertilizers will be most effective on the humic, sandy podzols of the western and southern coastal plains of WA.
Nature of interstratified kaolin-smectites in some Australian soils
Authors: Churchman GJ , Slade PG , Self PG , Janik LJ
Published: April 2005

The clay minerals in the < 2 �m, and finer, size fractions of several horizons from each of five Australian soils of different types and from different locations have been analysed by X-ray diffraction, infrared spectroscopy, transmission electron microscopy and X-ray fluorescence. Samples from each profile contained a phase in which layers of smectite and of kaolin (positively identified as kaolinite) were randomly interstratified with each other. The relative proportions of the two types of layers varied widely. One interstratified phase contained 70% smectite. This value for smectite content of kaolin-smectites is as high as any reported in the literature. The charges associated with the interstratified smectite layers also differed substantially. Discrete kaolinite commonly occurred along with interstratified kaolinite-smectite, Towards the surfaces of the soils, the proportions of kaolinite in the interstratified phases increased at the expense of smectite.
Evaluation of the CREAMS model. 4. Derivation of interrill erodibility parameters from laboratory rainfall simulator data and prediction of soil loss under a field rainulator using the derived parameters
Authors: Evans KG , Loch RJ , Silburn DM , Aspinall TO , Bell LC
Published: April 2005

This study investigated the use of laboratory rainfall simulator data for the derivation of CREAMS (chemicals runoff, and Erosion from Agricultural Management Systems) interrill erodibility parameters K and nbov. The laboratory rainfall simulator method of collecting erosion data was validated using the surface of an Irving clay (black earth). Reliable CREAMS K and nbov values for this Irving clay had previously been determined from field rainulator data. In this study, CREAMS erodibility parameters were derived for the same soil type using laboratory rainfall simulator data. The values of these parameters fell within the 90% confidence region for parameters derived from non-rilled field rainulator plots. Both nbov and K, determined from laboratory data, varied with slope, indicating that the slope gradient response predicted by CREAMS may not be applicable for interrill erosion on short, steep slopes. For slopes < 8%, a default value of nbov = 0.01 with K = 0.37 (English units) gave good predictions of observed soil losses. However, for slopes > 8%, there was an over-prediction of observed soil loss up to 60% when these parameter values were used. The data indicate that for predictions of interrill soil loss from steeper slopes, nbov and K values should be adjusted to achieve greater accuracy. When values of K = 0.37 and nbov = 0.01 were used with field data obtained from a site with a slope of 4%, predicted interrill soil losses correlated well with both the estimated interrill component of measured field soil losses and observed soil losses from interrill field plots. It is concluded that the laboratory rainfall simulator used in this study produces hydrology and erosion data that can be used to derive realistic CREAMS parameters for interrill erosion.
Krasnozems - a profile
Authors: Isbell RF
Published: April 2005

Since the first soil map of Australia by Prescott in 1931, acid red soils developed from basalt have been specifically recognized in spite of their very limited area of occurrence in eastern Australia from North Queensland to Tasmania in a rainfall zone of about 1000 to 4000 mm. Until the early 1950s these soils were known as red loams, but the term krasnozem became formalised in 1953 with the publication of Stephen's Manual of Australian Soils. Over the past 40 years, these soils have been extensively studied because their favourable agronomic properties have led to intensive land use. The krasnozems are red to brown, acid, strongly structured clay soils (50-70% clay) ranging in depth from less than 1 m to over 7 m. Their clay mineralogy is dominated by kaolin and iron and aluminium oxides, and this ensures that the soils have variable charge properties with low cation exchange capacity and usually a significant anion exchange capacity. Free iron oxide contents range from about 7 to 18% Fe. Red basalt-derived soils occur in a number of other countries, and the 'typical' Russian krasnozems appear to have similar mineralogical and chemical properties but apparently lack the characteristic strong polyhedral structure of the Australian soils and are only about one metre deep. The Australian krasnozems are mostly classified as Oxisols in Soil Taxonomy and Ferralsols in the FAO-Unesco scheme. In the new Australian classification they are classed as Ferrosols and a more specific definition and subdivision of this class into lower categories is given, together with their relationship to morphologically similar soils.
Role of plant cover and stock trampling on runoff and soil-erosion from semi-arid wooded rangelands
Authors: Greene RSB , Kinnell PIA , Wood JT
Published: April 2005

Relationships between plant cover, runoff and erosion of a massive red earth were investigated for a runoff zone of an intergrove area in a semi-arid wooded rangeland in eastern Australia. The measurements were carried out in small experimental paddocks with different stocking rates of sheep and kangaroos. A trailer-mounted rainfall simulator was used to apply rainfall at a time averaged rate of 30 mm h-1 to obtain runoff rates and sediment concentrations. There was a significant negative relationship (r2 = 0.58; P < 0.01) between final runoff rate and plant cover. It is probable that the plants increase infiltration and decrease runoff by (i) funnelling water down their stems and (ii) providing macropores at the base of the plant through which water can rapidly enter the soil. However, there was no significant effect of plant cover on sediment concentration. Probable reasons for this are: (i) even though plant cover will absorb raindrop energy and decrease the erosive stress on the soil, the nature of the plants investigated is such that they may not be 100% effective in protecting the soil beneath them, and (ii) the distribution of contact cover provided by the base of the plants is highly patchy and thus relatively inefficient at reducing sediment concentration. At zero cover final runoff rates from paddocks with a high and low stocking rate were similar, i.e. 23.4 and 22.3 mm h-1 respectively. However, at zero cover, the sediment concentration from the high stocking rate paddock was significantly (P < 0.01) greater than that from the low stocking rate paddock. Greater hoof activity and lower organic matter (and hence lower structural stability) of the 0.20 mm layer in the high stocking rate paddock caused the soil surface to be more susceptible to erosion. These results show that grazing by removing perennial grasses and pulverizing the surface soil can have a major impact on local water balances and erosion rates respectively within the intergrove areas. The implications of these results for the long-term stability of semi-arid mulga woodlands is briefly discussed.
Seasonal variations in forms of extractable sulfur in some New Zealand soils
Authors: Tan Z , Mclaren RG , Cameron KC
Published: April 2005

Seasonal variations in different forms of extractable sulfur (S) were examined in three New Zealand soils under permanent pasture. The concentrations of total extractable S, extractable inorganic sulfate-S (SO2-4-S), and extractable organic HI-reducible sulfur (HI-S) and carbon-bonded sulfur (C-S) were determined in field moist samples using four different extractants. During the course of the year, extractable SO2-4-S levels varied substantially. Concentrations of SO42--S in the soils peaked in the early spring and, for two of the soils, remained at relatively low levels throughout the rest of the year. The third soil, however, following a decrease in concentration in late spring, showed a continuous increase in SO2-4-S during the summer and autumn period. Concentrations of extractable organic C-S in soils were generally highest in the winter and declined significantly during the spring. Extractable organic HI-S concentrations fluctuated throughout the year with no clear trends. The proportions of the three forms of extractable S in soils also varied seasonally. The proportions of extractable organic HI-S in soils were more constant compared with the other two forms of S and generally accounted for less than 20% of the total extractable S. The seasonal changes in the proportions of SO2-4-S appeared to be inversely related to the changes in extractable C-S. This suggests that under the field conditions, the extractable organic C-S fraction is readily mineralized to sulfate when conditions are favourable for mineralization to take place.
Chemical fertility of krasnozems - a review
Authors: Moody PW
Published: April 2005

Krasnozems (Ferrosols) characteristically have high contents of citrate-dithionite extractable Fe and moderate to high contents of clay throughout the profile. They typically have low cation exchange capacity (2-20 cmolc kg-1), high P sorbing ability, and a significant anion exchange capacity at depth. The chemistry of krasnozems is dominated by the variable charge characteristics of the organic matter and the oxy-hydroxides of Fe and Al which occur in the predominantly kaolinitic clay fraction. The effects of surface charge characteristics, organic matter, and extractable iron and aluminium on the cation and anion exchange capacities, P sorbing abilities and pH buffer capacities of Australian krasnozems are reviewed. A selection of reports of nutrient deficiencies and toxicities in these soils is presented and briefly discussed. Published data on the chemical composition of the soil solutions of krasnozems are reviewed. Data from a suite of paired (undeveloped and developed) krasnozem profiles from eastern Australia indicate that exchangeable Ca and Mg, effective cation exchange capacity (ECEC), pH buffer capacity (pHBC) and total N decrease significantly (P < 0.05) in the A horizon following development, while exchangeable K, ECEC and pHBC decrease (P < 0-05) in the B horizon. The decreases in the A horizon are shown to be a direct consequence of the decline in organic matter which occurs following development. Because of the crucial role that organic matter plays in the chemical fertility of krasnozems, they are less likely to maintain their fertility under exploitative conditions than other productive clay soils such as Vertosols. It is concluded that the sustainable use of krasnozems will depend on maintenance or enhancement of organic matter levels, maintenance of surface and subsoil pH by regular application of amendments, minimization of erosion, and replacement of nutrients removed in harvested products.
Corrigenda - Chemical fertility of krasnozems - a review
Authors: Moody PW
Published: April 2005

Krasnozems (Ferrosols) characteristically have high contents of citrate-dithionite extractable Fe and moderate to high contents of clay throughout the profile. They typically have low cation exchange capacity (2-20 cmolc kg-1), high P sorbing ability, and a significant anion exchange capacity at depth. The chemistry of krasnozems is dominated by the variable charge characteristics of the organic matter and the oxy-hydroxides of Fe and Al which occur in the predominantly kaolinitic clay fraction. The effects of surface charge characteristics, organic matter, and extractable iron and aluminium on the cation and anion exchange capacities, P sorbing abilities and pH buffer capacities of Australian krasnozems are reviewed. A selection of reports of nutrient deficiencies and toxicities in these soils is presented and briefly discussed. Published data on the chemical composition of the soil solutions of krasnozems are reviewed. Data from a suite of paired (undeveloped and developed) krasnozem profiles from eastern Australia indicate that exchangeable Ca and Mg, effective cation exchange capacity (ECEC), pH buffer capacity (pHBC) and total N decrease significantly (P < 0.05) in the A horizon following development, while exchangeable K, ECEC and pHBC decrease (P < 0-05) in the B horizon. The decreases in the A horizon are shown to be a direct consequence of the decline in organic matter which occurs following development. Because of the crucial role that organic matter plays in the chemical fertility of krasnozems, they are less likely to maintain their fertility under exploitative conditions than other productive clay soils such as Vertosols. It is concluded that the sustainable use of krasnozems will depend on maintenance or enhancement of organic matter levels, maintenance of surface and subsoil pH by regular application of amendments, minimization of erosion, and replacement of nutrients removed in harvested products.
Soil structure and carbon cycling
Authors: Golchin A , Oades JM , Skjemstad JO , Clarke P
Published: April 2005

Samples from the surface horizons of six virgin soils were collected and separated into density fractions. Based on the spatial distribution of organic materials within the mineral matrix of soil, the soil organic matter (SOM) contained in various density fractions was classified as: (a) free particulate OM, (b) occluded particulate OM, and (c) colloidal or clay-associated OM. The compositional differences noted among these three components of SOM were used to describe the changes that OM undergoes during decomposition when it enters the soil, is enveloped in aggregates and eventually is incorporated into microbial biomass and metabolites and associated with clay minerals. The occluded organic materials, released as a result of aggregate disruption, were in various stages of decomposition and had different degrees of association with mineral particles. Changes in the degree of association of occluded organic materials and mineral particles with decomposition are discussed and form the basis of a model which illustrates the simultaneous dynamics of microaggregates and their organic cores. This model indicates a major role for carbohydrate-rich plant debris in formation and stabilization of microaggregates.
Environmental consequences of soil sodicity
Authors: Fitzpatrick RW , Boucher SC , Naidu R , Fritsch E
Published: April 2005

Australia has the highest ratio of salt-affected soils in relation to total surface area of any continent in the world, with approximately one third of the land mass being covered by sodic soils and 5% affected by soil salinity. Sodicity often coincides with the distribution of duplex soil profiles. In many areas these duplex soils are under agriculture. Sodicity substantially limits agricultural productivity. Although sodicity is considered to be an intrinsic property of the clay fraction of an affected profile, its full impact may be revealed through interactions with hydrological processes, resulting in various forms of both on-site and off-site environmental degradation. Some of the concepts, criteria and properties used to diagnose and classify sodic soils are discussed as a prelude to reviewing the nature and causes of the complex interactions which exist between related environmental problems such as dryland salinity, water erosion, waterlogging and water quality. There is a need for detailed studies to evaluate more thoroughly pertinent soil variables which link sodicity to both current and future environmental hazards, so that appropriate management strategies can be formulated.
Soil attributes related to water repellency and the utility of soil survey for predicting its occurrence
Authors: Harper RJ , Gilkes RJ
Published: April 2005

The incidence and severity of water repellency was related to five soil class (FC I-V), based on the field texture and dry consistence of the soil surface horizons, derived from a soil survey near Jerramungup, Western Australia. Water repellency was most severe on the FC I soils (median clay content 1.5%), with 66% of samples having water repellency based on the water drop penetration time (WDPT) test >10 s. Corresponding values for the FC II and III soils (2.5%, 4.0% clay) were 37% and 20%. Water repellency did not occur on the most clayey FC IV (8.1% clay) and FC V (22.1% clay) soils. Following stratification of Ap horizon soils by 1% increments of clay content, highly significant linear relationships occurred between log [water drop penetration time (WDPT)] and log [organic carbon (OC)] for the 1-2, 2-3 and 3-4% clay classes, these respectively explaining 50, 35 and 37% of the variation in water repellency. The role of organic carbon in promoting water repellency decreases markedly with increasing clay content, with WDPT being proportional to OC4.5, OC3.9 and OC3.0 for each of these clay classes. A multivariate relationship using measures of amorphous iron, clay and organic matter explained 63% of the variation in water repellency, and this multivariate dependency provides an explanation of the poor bivariate relationships between either clay or organic carbon content and water repellency reported in previous studies. There is a strong geomorphic control of the clay content in the soil surface horizons. Given the effect that clay content has on water repellency, the susceptibility of soils to water repellency can be mapped across farms, with the actual expression of water repellency depending on soil organic matter content, and hence land use. Such discrimination will allow the prediction of water erosion hazard and identify soils requiring ameliorative treatments.
Ultrasonic dispersion of soil in water - the effect of suspension properties on energy dissipation and soil dispersion
Authors: Raine SR , So HB
Published: April 2005

The application of ultrasonic energy to soil-water suspensions for particle size analysis has been widely adopted and more recently applied to aggregate stability assessment. However, suspension properties have been reported to affect both the energy applied and the degree of aggregate breakdown. This paper investigates the effect of suspension concentration, suspension volume, gas saturation, depth of ultrasonic probe insertion and particle size distribution on the power (energy per unit time) applied by an ultrasonic probe. It also investigates the effect of suspension concentration, suspension volume, gas saturation and method of wetting the soil on the dispersion produced by ultrasonic energy applications. Where the power applied was expressed per unit soil mass, the quantity of dispersed material released by ultrasonic action was not affected by either the volume or concentration of the suspension. However, decreasing the dissolved gas concentration in suspension decreased the dispersion produced. The method of soil wetting significantly affected initial disruption but had no effect on the maximum amount of <2 and <20 �m material produced by sonification. The power applied by the ultrasonic probe was found to decrease with suspension temperature, increase with dissolved gas concentration and increase with the depth of probe insertion. Recommendations are made on the range of suspension properties that should be used for standard measurements of aggregate stability assessment using ultrasonic energy.