bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship between mineralogy and elemental composition in strongly developed soils using principal components analysis
Authors: Garcia-Gonzalez MT , Aragoneses FJ
Published: April 2005

The distribution rate of major, minor and trace elements in different size fractions of highly developed soils of central Spain was determined and related to the mineralogy of the soils. Analysis of variance, factor analysis and contingency tables were used. The principal trace element carriers were the 2 : 1 phyllosilicates and the Fe and Mn-oxides; kaolinite did not play a role in this regard. Factor analysis indicated that the principal difference is found between samples rich in clay-kaoliniteAl2O3 and samples rich in quartz-SiO2. Alkaline and alkaline-earth elements (K, Na, Rb, Ba and Sr) show a similar behaviour, being directly related to the contents of illite and feldspars. Co and Pb contents are found to be related to the Mn-oxides, while Cu and Zn showed a relatively erratic distribution. Vanadium content was clearly associated with the Fe-oxides, but other metals, such as Cr, Ni and La, showed distinct associations depending on particle size.
A collection system for measuring runoff and soil erosion with a mobile rainfall simulator on sealed and stony red earth soils
Authors: Greene RSB , Sawtell GR
Published: April 2005

A collection system was developed for use with a Grierson and Oades rainfall simulator. The collection system enabled measurements of runoff and soil erosion to be made on massive red earth soils with severe seals (or crusts) and stones at their surface. In our design, the collection flume was separated from the other three sides of the plot frame. This allowed the collection flume to be initially inserted with minimum disturbance to the soil hydraulic properties and then connected to the other three sides of the plot frame. Runoff data obtained with this collection system, from a stony, sealed, surface soil, are presented.
Seasonal changes in pathways of dissolved organic carbon through a hillslope soil (Xeralf) with contrasting texture
Authors: Chittleborough DJ , Smettem KRJ , Cotsaris E , Leaney FW
Published: April 2005

The pathways of dissolved organic carbon (DOC) through a podzolic soil (Xeralf) with strong texture contrast are described. During winter, most of the DOC passes through macropores in the profile and flows laterally through the B horizons. During summer the presence of dry, hydrophobic organic matter on the soil surface and the A1 horizon causes DOC to flow overland. DOC concentrations vary seasonally. Highest concentrations are measured during summer overland flow. For all horizons, the longer the dry period the greater the DOC concentration in the subsequent flow. During storm events there is a marked flushing effect in the B horizons but in the A horizon and the surface, DOC concentrations tend to rise. There was a marked decrease in DOC concentration in flow from the B3 compared to the upper horizons. This may be due to adsorption by fine clays lining the macropores.
The effect of agricultural development on the physical and hydraulic properties of four Western Australian soils
Authors: Mcfarlane DJ , Howell MR , Ryder AT , Orr GJ
Published: April 2005

Changes to the physical and hydraulic properties of four wheatbelt soil types after agricultural development were determined so that the effect of clearing the soils on runoff and erosion could be estimated. Development resulted in an increase in the bulk density of three of the four soils and an increase in the dispersion in the surface of a sandy soil. It also decreased the water repellency of one of the soils. After agricultural development the average sorptivity of the soils, as determined using a disc permeameter, increased from 8.0 to 24.4 mm h-0.5 when the water was added at a 10 mm suction and from 6.5 to 10.4 mm h-0.5 when added at a 40 mm suction. The average steady state infiltration rate, also determined using a disc permeameter, increased from 12.6 to 475 mm h-1 after clearing for a 10 mm suction and from 6.1 to 11.3 mm h-1 for a 40 mm suction. A rainfall simulator added water at a rate of about 40 mm h-1 for 30 min to the four soils. Runoff was generated from all of the uncleared soils but from only one of the cleared soils. On three of the cleared soils, increasing the rate to 60 mm h-1 and the duration to 40 min still failed to produce runoff. The increased infiltration after clearing was unexpected and conflicts with previous results obtained using infiltrometer rings. We believe that methods which disturb the surface crust on uncleared soils are likely to result in higher infiltration rates than occur under natural rainfall events. Localized runoff is likely in uncleared areas with enhanced infiltration at nearby sites. Therefore the lower infiltration rates that we recorded do not necessarily result in higher runoff from uncleared areas. Infiltration in cleared areas is more uniform and the closure of high infiltration sites can result in more runoff from catchments. The point measurements of infiltration cannot be used to accurately predict runoff from large catchments.
Evaluations of the CREAMS model. III. Simulation of the hydrology of vertisols
Authors: Silburn DM , Freebairn DM
Published: April 2005

The CREAMS hydrology model was evaluated for two Vertisols, each with three fallow management strategies, by comparing predictions of runoff, soil moisture and drainage with 5-8 years of measured data. Model parameter values were derived by: (i) using a combination of measured site characteristics and published values, and (ii) optimizing selected parameters, particularly the runoff parameter (curve number). With parameter values from published sources, runoff was overpredicted by 1 to 39%; good estimates of total soil moisture were obtained. Using optimized curve numbers, runoff was predicted well (daily, r2 = 0.83; monthly, r2 = 0.92; annual, r2 = 0.94). Total soil moisture values were predicted well, the main source of error being from overprediction of transpiration. Errors in predicted runoff caused little of the error in predicted total soil moisture. The distribution of soil moisture in the soil was poorly predicted. Drainage predictions were similar to estimates from steady-state solute mass balance. Optimized curve numbers derived in this study provide parameter values for modelling the water balance of self-mulching Vertisols. Values of other model parameters, derived from field measurements and published sources were near optimal, and predictions were not improved by adjusting the more sensitive of these parameters. The model is considered adequate for many practical applications. Some enhancements to the model are suggested.
Determination of dissolved carbonate/bicarbonate in the presence of sulfide
Authors: Fordham AW
Published: April 2005

Sulfide interferes with the determination of carbonate/bicarbonate in soil solutions by pH-titration methods. Its effect, and that of other weakly acidic but oxidizable anions, can be detected and eliminated by prior treatment of the solution with hydrogen peroxide.
The relationship between soil pH measurements in calcium chloride and water suspensions
Authors: Little IP
Published: April 2005

The relationship between the pH in a 1:5 soil/water suspension and the pH in 0.01 m CaCl2 has always been considered to be linear, but recent findings favour a non-linear relationship. This trend was confirmed with a set of 1342 surface soils from acid to neutral red duplex and gradational soils from the Lachlan Shire in central western New South Wales. The linear relationship was consistent with that found by earlier workers, but inclusion of the second and third powers of pH(w) accounted for significantly more of the variation in pH(ca) resulting in a sigmoidal curve. It is suggested that the deviation from linearity is due to the buffering effect of Al at low pH and to the presence of carbonate at high pH. Several other attributes were shown to influence pH, namely the ionic strength as indicated by the electrical conductivity of the 1:5 soil/water suspension, exchangeable cations (Na, K, Ca,Mg and Al) and Al and Mn extracted with 0-01 m CaCl2, and their effect varied at different pH levels.
Yield responses and nitrogen fertilizer requirements of wheat in relation to soil nitrate levels at various depths
Authors: Holford ICR , Doyle AD
Published: April 2005

Wheat grain yield responses and estimates of fertilizer nitrogen requirements in 57 experiments over five years (1985-9) were related to soil nitrate values at various depths (to 90 cm) in the soil profile. These experiments were on representative soils of the north western slopes and plains of New South Wales. Profile distributions of nitrate differed in the first three years, when nitrate concentrations at 15 or 30 cm intervals declined regularly with depth, to the last two years, when it was much more uniformly distributed and much lower in the top 30 cm. This was apparently caused by very high mid-fallow (pre-sampling) rainfall that occurred in the last two years but not in the earlier years. There were large differences in relationships of N fertilizer responsiveness and requirements to soil nitrate values between the two time periods. For each period, responsiveness and requirements were closely related to soil nitrate values at 0-15 cm and deeper depths, but not at 0-10 cm, with >50% of the variance being accounted for. The optimum sampling depth was 0-15 or 0-30 cm. Fertilizer responsiveness and requirements in relation to soil nitrate values (0-90 cm) were much lower in the last two years than in the first three years. This was attributed to very low in-crop rainfall in the last year and excessive rainfall in the penultimate year causing significant nitrate leaching beyond 90 cm depth. The critical nitrate concentrations varied from 24 mg N/kg at 0-15 cm down to 12 mg N/kg at 0-90 cm depth for 1985-7 and from 6 to 7 mg N/kg for all sampling depths in 1988-9. It was concluded that relationships obtained for the first three years were representative of years when normal or above average (but not excessive) rainfall occurred in the fallow and crop growth periods, while those for the last two years represented years when excess pre-sampling rainfall leached soil nitrate beyond the sampled depth or when yield responses to fertilizer were limited by in-crop conditions such as low rainfall.
The reaction of copper ions and hypochlorite with minesite soils in relation to fungicidal activity
Authors: Gerritse RG , Adeney JA , Baird G , Colquhoun I
Published: April 2005

Phytophthora cinnamomi is a soil-borne pathogenic fungus and is the primary cause of dieback disease in the jarrah forests of south-west Western Australia. Treatments are needed to eliminate the fungus from infected soils. Compounds containing cupric ions (Cu2+) or hypochlorite (ClO-) have a known fungicidal activity against P. cinnamomi, but their efficacy is affected by soil factors. This study explores the possibility of containing P. cinnamomi by treatment of surface materials for haul roads at minesites in infected areas with these compounds. Solution concentrations of Cu2+ between 50 and 100 mg/L are considered to be fungicidally effective against P. cinnamomi. In samples from the lateritic regolith at the Huntly minesite of Alcoa in Western Australia, concentrations in this range are obtained after adding about 0-5 g (range = 0.3-1 g) of Cu2+ per kg of regolith material. Soil materials from mineral sand areas on the Swan Coastal Plain in Western Australia adsorb Cu2+ less strongly than the regolith materials from the Huntly minesite. Addition of about 0.1-0.2 g Cu2+ per kg is sufficient to reach a fungicidal concentration in solution in these soil materials. Movement of Cu2+ from treated surfaces of haul roads to groundwater and surface water can present a problem. For a single application, travel times of Cu2+ in both lateritic regolith and sandy soils were calculated to be = 200 years per metre. A single treatment of materials from the lateritic regolith would be effective for a period of 2-10 years, depending on the selected material. Sandy soils would have to be treated once or twice a year. Colloidal particles in both surface runoff and throughflow can contribute significantly to the spread of copper in the lateritic regolith, but much less in sandy soils. Hypochlorite is rapidly reduced to chloride by organic matter in soils. At additions of about 0.5 g ClO- per gram of organic carbon, however, hypochlorite can be an effective fungicide against P. cinnamomi.
Effect of Ca:Mg ratio on soil sodicity at different levels of sodium adsorption ratio and electrolyte concentration
Authors: Astaraei AR , Chauhan RPS
Published: April 2005

A laboratory study on loamy soil (19.6% clay) with different quality waters varying in Ca : Mg ratio (1 : 1, 1 : 2, 1 : 4, 1 : 6, 1 : 8) at two levels each of salinity (6 and 12 dSm-1) and SAR (10 and 50) was carried out. Exchangeable sodium (ES), exchangeable sodium percentage (ESP), Na: (Ca+Mg) ratio and degree of dispersed clay in soil increased with increasing Mg concentration at both the levels of EC(iw) and SAR(iw). The percentage of dispersed clay was more with increasing Mg concentration at higher SAR(iw) with a lower level of EC(iw), while the reverse trend was observed with hydraulic conductivity of soil. The Ca : Mg ratio in the exchange complex decreased with increasing Mg concentration, EC(iw) and SAR(iw). Further Mg concentration in the exchange complex increased with Mg in water and EC(iw) and decreased with the rise in SAR(iw). The multiple correlations between different water parameters and soil characteristics, namely ESP, degree of dispersion and hydraulic conductivity, were calculated and regression equations were developed. The relative contributions of water parameters to ESP, degree of dispersion and hydraulic conductivity of soil were in the order SAR(iw) > EC(iw) > Ca : Mg; EC(iw) > Ca : Mg > SAR(iw), EC(iw) > SAR(iw) > Ca : Mg, respectively.
Impact of soil erosion on production in cropping systems .I. Development and validation of a simulation model
Authors: Littleboy M , Silburn DM , Freebairn DM , Woodruff DR , Hammer GL , Leslie JK
Published: April 2005

A computer simulation model to analyse risks of soil erosion to long-term crop production is described. The model, called PERFECT, simulates interactions between soil type, climate, fallow management strategy and crop sequence. It contains six main modules; data input, water balance, crop growth, crop residue, erosion and model output. Modules are arranged in a framework that allows alternative modules to be used as required for the potential range of applications. The model contains dynamic crop growth models for wheat, sorghum and sunflower. Validation of PERFECT against small catchment and contour bay data collected throughout Queensland showed that PERFECT explained up to 84% of the variation in total available soil water, 89% of the variation in daily runoff, and up to 75% of the variation in grain yield. Average annual soil erosion was accurately predicted but daily erosion totals were less accurate due to the exclusion of rainfall intensity in erosion prediction. Variability in climate dominates agricultural production in the subtropical region of Australia. The validated model can be coupled with long-term climate and soils databases to simulate probabilities of production and erosion risks due to climatic variability. It provides a method to determine the impact of soil erosion on long-term productivity.
Soil Science, soil protection and productivity opening address - National soils conference
Authors: Smiles DE
Published: April 2005

Australia will continue to rely on its soils to maintain national well being. At the same time society will be more demanding that the soil resource be managed sustainably. Soil scientists are therefore challenged to be more effective in helping formulate policy, contributing to public understanding and in applying their knowledge to meet national need. Close consultation with land managers to define important problems is necessary as is increasing confidence that the knowledge we have is appropriate to the task. It is also important to recognise that much of our science was generated as a reductionist response to difficult problems and it is now necessary to integrate our knowledge to deal with those problems. Collaboration across organisations to ensure most effective use of that knowledge is necessary. Important opportunities to demonstrate application of soil science are identified. A plea is made to teach the subject, not just as an intellectual exercise but as a basis for problem solving across the whole range of uses to which soils are put. Case studies for guidance and to identify knowledge gaps are sought. There is also need to recognise that different client industries demand different communication models to ensure that soil science knowledge is applied appropriately.
A brief history of national soil classification in Australia since the 1920s
Authors: Isbell RF
Published: April 2005

Modern soil science concepts and ideas relating to classification were introduced into Australia in the late 1920's by J. A. Prescott who, in 1931 and 1944, also produced the first maps of Australia showing the broad soil zones. This was followed up in the fifties by C. G. Stephens who formalised the Great Soil Group concept in his Manual of Australian Soils (1953) and in 1961 produced a map and publication titled The Soil Landscapes of Australia. Around this time however, other ideas were being put forward, notably by E. G. Hallsworth and colleagues, and especially by G. W. Leeper, whose original ideas on classification were to provide the foundation for the Factual Key of K. H. Northcote (1960a), which was used as the basis of the Atlas of Australian Soils project (1960-68). The Great Soil Group concept of Stephens was amplified in 1968 in A Handbook of Australian Soils (Stace et al. 1968) which was produced for the Adelaide International Society of Soil Science Congress. This review also considers the role of numerical methods and of Soil Taxonomy in Australia and concludes that while neither are likely to provide the most suitable scheme for Australia, the use of the latter to identify our soils must be encouraged so that the rest of the world is able to relate to our published soil research. Currently, the Factual Key and Handbook classifications are both used in Australia. Both are obsolescent as they date from the early sixties and the vast amount of soils knowledge accumulated since then, particularly in tropical Australia, has not been incorporated into either system. Their deficiencies have led over the past seven years to the development of a new Australian Classification System (a five-level hierarchial general purpose scheme with mutually exclusive classes identified by keys). This scheme is now being tested throughout Australia.
Urban soil contamination in Australia
Authors: Tiller KG
Published: April 2005

The current knowledge of the pollution of Australian urban soils was reviewed with special reference to heavy metals. Increased community concern in recent years has resulted m a major upsurge in the investigation and rehabilitation of contaminated soils. This has led to a concomitant reassessment and development of regulatory procedures, and the establishment of some new environmental agencies. This review considers sources and extent of contamination, and approaches to the establishment of reference background levels in urban and rural areas. Assessment of contaminated sites has been largely based on overseas experience but site specific approaches relevant to Australian soils and climates are needed and are being developed by State authorities in collaboration with the Australian and New Zealand Environmental and Conservation Council and the National Health and Medical Research Council. The need for soil-based research and for standardized soil sampling procedures for site evaluation and action is stressed. Many opportunities exist for soil scientists in solving problems of soil contamination and rehabilitation.
Water extraction by isolated trees and its possible impact on building foundations on clay soils
Authors: Misra RK , Sands R
Published: April 2005

Spatial and temporal variation in soil water content and bulk density was measured near Melaleuca and Ulmus trees, with neutron and gamma gauges, on a Duplex soil in Melbourne, in order to examine water extraction patterns of these trees and foundation movement arising from water extraction. The experiment simulated the situation of isolated trees growing on city pavements. Results indicated that both trees extracted similar amounts of water. However, Ulmus, the exotic, deciduous species, extracted water from a greater depth near the tree than Melaleuca, the Australian native, evergreen species. Melaleuca extracted water from a greater distance than Ulmus. Data on bulk density indicated differential swelling and shrinkage of greater magnitude near Ulmus than Melaleuca, although seasonal shrinkage adjacent to Melaleuca was higher than Ulmus. The results are discussed in relation to variation in compressibility factor of overburden and damage to building foundations.
The manganese oxide mineral, lithiophorite, in an oxisol From Hawaii
Authors: Golden DC , Dixon JB , Kanehiro Y
Published: April 2005

The mineralogical composition of the surface soil horizon (0-15 cm) of Wahiawa soil (Tropeptic Eutrustox) was investigated by X-ray diffraction (XRD), high gradient magnetic separation (HGMS), transmission electron microscopy (TEM), and infrared methods. The concentration of lithiophorite decreased with particle size and none was present in the clay fraction as indicated by XRD. Lithiophorite was further concentrated from the crushed sand-sized fraction by HGMS. Hexagonal, electron-dense, often twinned lithiophorite particles were identified by electron diffraction. Differential infrared (DIR) spectra obtained by dissolving Mn oxides in acidified hydroxylamine hydrochloride (HAHC) indicated lithiophorite as the HAHC-soluble Mn-phase. Lithiophorite compositiion, as revealed by chemical analysis of the HAHC extracts, consisted of appreciable amounts of Mn, Al, Zn, Co and Mg, and less than stoichiometric amounts of Li. Sodium hydroxide treatment apparently altered the lithiophorite, as revealed by the DIR spectrum of the hydroxylamine-soluble fraction of the NaOH-treated sample compared with the untreated sample. The high crystallinity of the lithiophorite was suggested by its resistance to chemical dissolution and narrow X-ray diffraction lines. No evidence for the presence of todorokite or birnessite was found, contrary to earlier reports. Examination of sand-sized nodules by scanning electron microscopy indicated large (2-5 �m) platy lithiophorite crystals at the surface of these nodules. Electron microprobe analysis of these platy particles indicated iron enrichment near the surface. The freshly fractured nodule surface revealed numerous unaltered platy crystals of lithiophorite filling the veins of the nodule.
Shrinkage of some New Zealand soils and its implications for soil physics
Authors: Allbrook RF
Published: April 2005

Aggregates from three New Zealand soils were used to produce shrinkage curves. Each soil had a clay mineralogy dominated by a different mineral, namely allophane, halloysite and kaolinite.The curves showed marked differences. Only the allophanic soil showed structural shrinkage, and only the halloysitic soil showed residual shrinkage. When the slope of the normal shrinkage line is about unity, this indicates the soil is liable to crack- this was only shown by the allophanic soil. The implication for soil physics is that, since all soils with at least a moderate clay content shrink, bulk densities change with moisture and this must be allowed for in such calculations as soil moisture on a volume basis.
Phosphate sorption by soil in relation to exchangeable cationcComposition and pH
Authors: Curtin D , Syers JK , Bolan NS
Published: April 2005

The influence of exchangeable cation composition on the sorption of phosphate (P) was studied using samples of an acid, clay loam subsoil which had been saturated with Ca2+ or Na+. The Na-soil always sorbed less P than the Ca-soil but the difference between the two systems was strongly pH-dependent. Sorption by the Na-soil declined rapidly as pH increased, to the extent that at pH 7.6 it was only 22% of that sorbed at pH 4.1. Although sorption by the Casoil also decreased with an initial pH increase, it increased again once pH exceeded approximately 5. The difference in sorption between the Ca, and Na-soils was only about 20% at low pH but it increased considerably above pH 5. At the highest comparable pH value (6.7), the Ca-soil sorbed almost 4 times as much P as the Na-soil. The observed cation-induced differences in P sorption by this soil cannot be explained simply by the formation of insoluble Ca-P compounds or surface Ca-P complexes in the Ca-saturated samples. A more plausible interpretation appears to derive from the effect of cation saturation on electrostatic potential. A model of P sorption which incorporates electrostatic potential effects indicated that the pH-dependence of the cation effect is likely to be due to a more rapid decrease in potential in the Na- than in the Casoil as pH is increased. However, in the absence of any measured values for potential, it is not possible to apply this model in a general way.
Sediment transport by shallow flows impacted by pulsed artificial rainfall
Authors: Kinnell PIA
Published: April 2005

In many experiments using rainfall simulators, rainfall is applied to the target as a high intensity pulse so that there are often long periods when the soil receives no rain and there are short periods when the soil receives rain at an extremely high intensity. Because concerns exist about the use of such methods of applying rain in experiments designed to help predict erosion under natural conditions, experiments using intermittent and continuous artificial rainfall were performed and analysed in terms of a recently developed theory on erosion by rain-impacted flow. The results indicate that the manner in which the rain is applied does not significantly influence the time-averaged sediment discharge from the sediment transport perspective. However, if high intensity, high energy pulses of rain influence factors which affect the susceptibility of the soil to erosion differently to continuous rain, then concerns about the use of intermittent rainfall in soil erosion experiments remain.
Effect of superphosphate addition on N mineralization in some Australian forest soils
Authors: Falkiner RA , Khanna PK , Raison RJ
Published: April 2005

Pinus radiata stands are reported to accumulate increased N on addition of phosphatic fertilizers. Field and laboratory studies were initiated to determine if addition of superphoshate increases soil N mineralization in forest soils. In a field experiment, application of 200 kg P ha-1 as superphosphate to trenched plots in a Pinus radiata stand increased accumulated soil mineral-N contents by 122% and 82% above the control on two occasions. Application of 500 kg P ha-1 as superphosphate either alone or in combination with lime (10 Mg ha-1) increased in situ soil net N mineralization in a dry sclerophyll eucalypt forest from 20.7 (control) to 28.3 (+P) and 30.2 (+P+lime) kg N ha-1 yr-1 20 cm-1. Uptake by the vegetation accounted for all of the mineralized nitrogen. In a 180 day laboratory incubation using undisturbed soil columns (0-20 cm) from nine forest sites, seven soils showed a positive response to superphosphate (100 kg P ha-1) addition, with increases in N mineralization ranging from 14% to 117%. The response of N mineralization to superphosphate addition was not related to initial soil organic C, total N or P content in the 0-20 cm layer. However, soil pH and organic C combined to account for 76% of the variation in N mineralization response (P < 0.01). In the 0-5 cm layer of untreated soils, soil organic P content could explain 71% of the variation in net N mineralization. Addition of superphosphate appears to increase N mineralization in several Australian forest soils and the improved availability of N will enhance tree growth rates. The mechanisms underlying the response are still poorly understood and thus also our ability to predict its significance for tree nutrition on specific forest sites.
Runoff as a factor influencing experimentally determined interrill erodibilities
Authors: Kinnell PIA
Published: April 2005

In most modern models of interrill erosion, the effect of surface-water flow on interrill erosion is ignored. On the basis of an interrill erosion model developed from a theory on sediment transport by rain-impacted flow, it is shown that failure to consider the hydrology of interrill areas may lead to errors in the determination of interrill erodibilities.
Correction
Authors: Watkinson JH
Published: April 2005

Oxidation Rate of Elemental Sulfur Particles With a Wide-Range of Sizes (Vol 31, Pg 68, 1993)
Rill erosion on a structurally degraded sandy loam surface soil
Authors: Murphy BW , Flewin TC
Published: April 2005

This study reports on the degree of rill erosion from a 0.65 ha site with a hardsetting red duplex soil having a structurally degraded surface soil. Rill erosion was measured after a series of relatively low intensity rainfall events (all <1 yr return period) that resulted in above average rainfall over a period of 78 days. The rill erosion was estimated by measuring the volume of rills in the field. The soil characteristics indicated that the soil was a structurally degraded soil with low aggregate stability (2-5% of total soil), very low organic matter levels (0.91% for 0-50 mm) and relatively high bulk density (1.56 g/cm3). The low aggregate stability resulted in the rapid breakdown of soil aggregates and settling of the soil under rainfall causing surface crusting and low infiltration rates (4.08 mm/h) as well as decreasing depressional storage. This resulted in high runoff and rill erosion, the total volume and mass of soil loss being equivalent to 48.3 m3/ha and 78.0 t/ha respectively. This high level of soil loss was considered to result from the combination of the poor structural condition of the soil, the tilled or loosened soil condition at the onset of the rainfall events, the duration and number of the low intensity rainfall events and the low evaporation rates between rainfall events. The results suggest that to reduce soil loss to acceptable levels under the conditions of the study, it is necessary to adopt management practices that increase surface cover, maintain infiltration rates, reduce tillage and increase soil aggregate stability in combination with erosion control earthworks. The study also looked at the prediction of soil loss using the USLE equation, and confirmed that the equation should not be used to predict erosion for individual events or erosion resulting from concentrated flow, rather it should be used to estimate expected long-term soil loss for a particular soil under a given set of management practices.
Anion exclusion effects on estimates of soil chloride and deep percolation
Authors: Slavich PG , Petterson GH
Published: April 2005

Anion exclusion affects estimates of deep percolation determined using chloride mass balance models. This paper evaluates potential errors arising from ignoring anion exclusion in both soil analysis methods and model assumptions. Soil chloride analysis from saturated paste and 1:5 soil/water extracts are compared with that of field soil water extracted using a filter paper technique. The influence of anion exclusion on estimates of soil water chloride concentration (Clsw mmol/L) and chloride content per unit mass of soil (CIT mmol/kg soil), both which are required by chloride mass balance models, is examined for these methods. The relative importance of total electrolyte concentration and sodium absorption ratio (SAR) on the anion exclusion volume of a clay was also determined using a simple laboratory leaching technique. The chloride concentration of soil water at field moisture contents was more closely related to estimates calculated from saturated paste extracts than from 1:5 soil/water extracts. Although the amount of excluded water estimated in the saturated paste was larger than that estimated at the field water content, the proportion of non-excluded water in each was similar. The ClT was overestimated when analysis from saturation extracts was used. Electrolyte concentration and SAR were shown to have similar (but opposite) relative effects on the exclusion volume. However, because these variables were positively correlated, their effects were not apparent in the field samples. For the clay soil under study, deep percolation could be overestimated by up to 1.64 times if anion exclusion effects were ignored when using 1:5 extracts to estimate Clsw. The errors were considerably less if saturation extracts were used to estimate Clsw and ClT.
Al toxicity of wheat grown in acidic subsoils in relation to soil solution properties and exchangeable cations
Authors: Carr SJ , Ritchie GSP
Published: April 2005

Toxic concentrations of soluble A1 in the subsoil decrease the yield of wheat grown on many yellow earths in the eastern wheatbelt of Western Australia. In our previous research (Carr et al. 1991), we observed variable plant response to high concentrations of soluble Al in subsoils of yellow earths in different regions of the wheatbelt. Environmental conditions (e.g. water supply) and/or an unidentified soil mitigating factor may have contributed to the variable plant response to soluble Al in some of the regions studied. We collected ten soils from four regions of the eastern wheatbelt of Western Australia. In a glasshouse experiment using these soils, we studied the effect of soil solution and KCl extract properties on wheat growth under uniform environmental conditions. The concentration of Al in a 0.005 M KCl extract was able to explain 97% of the variation in root fresh weight of wheat grown in the 10 soils, even though the soil solution properties were found to differ markedly between regions. For example, 97% of the variation in root fresh weight (RFW) was explained by the total [Al] in soil solution extracted from soils in one region (Merredin). In comparison, 58% of the variation in RFW was explained by the total [Al] in the soil solution extracted from soils collected from all four regions studied. Ionic strength differences and possibly [SO4] were the major chemical properties that differed between Merredin and the other regions studied. These chemical differences presumably altered the toxic proportion of Al in the soil solution, and hence, the plant response in some regions. The effect of ionic strength on toxic Al appeared to be simulated by extraction of the soil with 0.005 M KCl.
Carbon and nitrogen mineralization in cultivated and grassland soils in subtropical Queensland
Authors: Robertson FA , Myers RJK , Saffigna PG
Published: April 2005

Availability of N in the clay soils of the brigalow region of Queensland declines rapidly under sown pasture, but under continuous cultivation and cropping, it remains high enough to supply the needs of cereal crops for at least 20 years. The aim of this work was to determine whether the low availability of N under pasture was due to low microbial activity or to rapid re-immobilization of mineralized N. Microbial biomass C and N (0-28 cm) were 420 and 68 �g g-1 respectively in pasture soil but only 214 and 41 �g g-1 respectively in cultivated soil. Pasture soils respired more CO2 (Cresp) and mineralized less N (Nmin) than cultivated soils (219 and 93 �g C g-1 and 3.1 and 5.9 �g N g-1 respectively) during 10-day incubations over 2 years. Increased Crop under pasture was due to an increase in the amount rather than the specific activity of the microbial biomass. The smaller Nmin in grassland soils was due to more rapid immobilization rather than reduced gross mineralization of N, as the ratio Cresp : Nmin was larger and the ratio Nmin :biomass N was smaller in the grassland than in the cultivated soil. On prolonged incubation. with progressive loss of CO2 through respiration, Nmin increased and N immobilization decreased in the grassland soils. Prolonged incubation of the cultivated soils reduced Nmin because of C limitation. The above patterns of C and N mineralization in the grassland and cultivated soils helped to explain the differences in N availability in the two systems.
The effect of fire on carbon and nitrogen mineralization and nitrification in an Australian forest soil
Authors: Bauhus J , Khanna PK , Raison RJ
Published: April 2005

The causes of onset of nitrification in a soil collected under an ashbed which was produced when heaped slash was burned, and for its absence in an unburnt soil, were investigated for an acid forest soil from south-eastern Australia. The occurrence of nitrification in ashbed soils was assessed in laboratory incubations extendig to 151 days to determine if it could be attributed to (a) an increase in pH, (b) an additional supply of P, (c) the removal of chemical inhibitors, and (d) the lack of competition with heterotrophs killed during soil heating. The treatments were: percolated and unpercolated ashbed soil from 0-5 and 5-10 cm depth; unburnt soil from 0-5 cm untreated and with added lime or added P; and burnt and unburnt soil from 5-10 cm depth. In addition, each treatment had an identical where the soil was inoculated with nitrifying garden soil. Compared with the unburnt surface soil (0-5 cm), ashbed soil had higher pH (3.6 units), higher mineral N (3 times) and slightly elevated NaHCO3-extractable P. During 151 days of incubation, microbial respiration in surface ashbed soil, measured as CO2 evolution, initially exceeded the values obtained in unburnt soil but then decreased to only 72% of unburnt soil at the end of the incubation period. In ashbed soil, the microbial biomass N content was low but its C/N ratio was high. Net N mineralization (Nmin) in ashbed soil was not significantly different from unburnt or phosphate fertilized soils (13.1, 14.7 and 17.8 mg N,in kg-' respectively) but was lower than in limed soil (59.3 mg Nmin kg-1). Percolation of surface ashbed soil with distilled water removed high amounts of salts and increased microbial respiration and N mineralization. Inoculation of soils with a slurry from a nitrifying garden soil induced nitrification in every treatment, regardless of their ammonium content, pH or other limiting component. Nitrification was also stimulated in unburnt surface soil on the addition of lime and P. Autotrophic nitriflers were active only in surface ashbed soils and probably in limed soils. P addition promoted heterotrophic nitrification. It was concluded that soil heating reduced competition between autotrophs and heterotrophs for ammonium and that ash supplies nutrients, such as K and Ca which stimulate nitrification. Low pH was not a limiting factor for nitrification but a high pH may promote the establishment of autotrophic nitrifiers.
Sodic soils - New perspectives
Authors: Sumner ME
Published: April 2005

There are large areas of the world where soils are adversely affected by the presence of sodium (Na) as an exchangeable cation. Unlike their saline counterparts which are more extensive, sodic soils have received less attention in the literature. There has been considerable disagreement concerning the definition of sodicity, owing largely to the fact that many experiments used in the development of definitions did not account for the presence of salts in the water used to measure hydraulic properties. These problems are discussed and the conclusion is reached that a single simple definition is no longer possible. This problem is further exacerbated by the fact that many soils which would never have fallen into a previously defined sodic category, do in fact exhibit sodic properties. The major focus of this account of sodicity will therefore be the soils which contain relatively low levels of exchangeable Na. As such soils are widespread in both humid and subhumid areas of the world and are responsible for the production of a large proportion of the world cereal crop, they deserve special attention. Because swelling and dispersion are the primary processes responsible for the degradation of soil physical properties in the presence of Na, an account of clay behaviour in relation to Na and electrolyte concentration is presented before exploring these new realms of sodicity. Pure clay systems are not always suitable for use as models of soil behaviour in terms of dispersion and flocculation. However, as far as swelling is concerned, the correspondence is much better. Nevertheless, the effects of the exchangeable cations on dispersion are predictable albeit usually only qualitatively. This is partly due to the phenomenon of 'demixing' in which the cations are not distributed over all surfaces in the same proportions. The effects of Na and electrolyte concentration in relation to hydraulic conductivity, infiltration, crusting, runoff, erosion and hardsetting are discussed from which it emerges that the effects of Na are manifested in measurable and often sizeable proportions down to very low levels far below those previously used to define sodic soils. The primary processes responsible for physical degradation are swelling at relatively high levels and clay dispersion throughout the range of exchangeable Na percentage (ESP). Provided that the total electrolyte concentration (TEC) is below the critical flocculation concentration (CFC), clays will disperse spontaneously at high ESP values, whereas at lower ESP levels, inputs of energy are required for dispersion. The TEC of the ambient solution, because of its effects in promoting clay flocculation, is crucial in determining soil physical behaviour.
Sodic soils - an introduction to their formation and distribution in Australia
Authors: Chartres CJ
Published: April 2005

This paper briefly summarizes existing Australian data about causes of sodicity and the distribution of sodic soils in Australia. Sources of salts and sodium include atmospheric accession, salts released by weathering processes and saline groundwaters. A traditional model of sodic soil pedogenesis is contrasted with more recent data demonstrating the role of several factors including mineralogy, EC/ESP relationships and exchangeable magnesium percentage on development and behaviour of sodic soils. Limited data about the national distribution of sodic soils are presented. There has been very little recent innovative research in Australia to increase understanding of soils affected by sodicity. A number of research needs are indicated.
Influence of clay minerals and organic matter on effects of sodicity on soils
Authors: Churchman GJ , Skjemstad JO , Oades JM
Published: April 2005

This review shows that the permeability of soils decrease because exchangeable sodium causes aluminosilicate clay minerals to swell and disperse in water. Among common soil minerals, only smectites with a high percentage of exchangeable Na show extensive swelling. Illites often remain dispersed in solutions of high electrical conductivity, partly because the shapes of their particles prevent strong cohesion. Smectites are often highly mobile, consistent with their small particle sizes. The dispersion of kaolinites varies with solution pH since a significant proportion of their charge can be variable. The sensitivity of soils to pH may be more strongly influenced by other, variably charged components than by the dominant aluminosilicates. Of these, metal oxides, hydroxides and oxyhydroxides can restrain the dispersion of aluminosilicate clay minerals. Organic matter can aid the dispersion of sodic soils while suppressing swelling. It can also be mobilized in a soluble form and probably also in a colloidal form under sodic conditions. Exchangeable Mg enhances dispersion from sodicity, but apparently to a greater extent in illitic soils than in smectitic soils. Exchangeable Al tends to prevent dispersion but the influence of clay mineralogy on its effect is apparently untested. The effect of sodicity upon soils is amplified by fineness of texture and by mechanical disturbance. Studies of soil fabric should increase the current poor understanding of the macroscopic effects of sodicity in terms of interparticle interactions of the pure components.
The distribution of sodic soils in Tasmania
Authors: Doyle RB , Habraken FM
Published: April 2005

It is estimated that sodic soils (ESP>6) occupy at least 23% of Tasmania's land area based on the present limited soil data set. Sodic soils are mostly restricted to lower rainfall areas (<800 mm/y) of eastern Tasmania, occurring primarily in the Launceston Tertiary Basin, the Derwent, Coal, Jordan and Huon River Valleys and on Flinders Island. In Tasmania, sodic soils have formed predominantly from Triassic and Permian mudstones and sandstones, Tertiary clays and unconsolidated Quaternary deposits. However, profiles with sodic features have also developed above granite, Jurassic dolerite and Tertiary basalt. Sodic soils most commonly occur on lowland plains, river terraces and in valley floors. In Tasmania, sodic soils are characterized morphologically by: (i) abrupt separation of a sandy, bleached A2 horizon from a moderately sodic (ESP 6-15) clay subsoil; (ii) coarse prismatic, columnar and/or angular blocky pedality in the subsoil, which may exhibit vertic properties; (iii) hardsetting sandy A2 horizons in some profile classes; (iv) fine sandy crack infills and clay-organic coatings on ped faces in the upper B2 horizon; and (v) thick, sticky and greasy fine clay argillans on ped faces, and clay infills in cracks and other voids in the lower B2 horizon that contribute to reduced porosity and permeability. Sodic soils in Tasmania have traditionally been utilized for pasture production with occasional cultivation for fodder crops and pasture renewal. Under a pastoral system, few sodicity problems have been recognized as such. However, in the last 10 years there has been increased cropping, particularly for poppies and more recently potatoes. Soil structure decline and drainage problems have become key factors limiting production. Management problems are mainly due to poor internal and external drainage, with poor structure in the A2 horizons which liquefy in winter and often set hard in summer. Salinity in associated drainage depressions is a problem gaining increasing recognition.
Catenary relationships of downland soils derived from loess, South Canterbury, New Zealand
Authors: Webb TH , Burgham SJ
Published: April 2005

Very limited information is available on soil variability within the large soil map units of the loess-mantled downlands of the east coast of South Island, New Zealand. In this study eight profiles were sampled in a catenary transect across a valley to assess the morphological, chemical and particle-size changes both within and between soil profiles for both sunny and shady aspects. Profiles from each landform element had similar sequences of horizons but thickness of horizons varied. Profiles on shoulder slopes had thinnest topsoil and subsoil horizons above underlying fragipans. There was a rapid thickening of topsoils and depth to fragipans immediately below the point of slope inflection between planar midslopes and concave lower slopes. The most striking difference in soil morphology was the overthickened topsoil horizons in footslope sites. This was attributed to effects of cultivation, either directly, through mechanical movement of soil material during cultivation operations, or indirectly, through the promotion of soil erosion. There was no indication of the expected catenary relationship involving translocation of exchangeable bases from upper to lower slopes. Differences in P-retention, KCl-extractable aluminium and clay content were identified in soils with different aspects but were not attributed to climatic differences.