bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphology and genesis of silt and clay coatings in the vesicular layer of a desert loam soil
Authors: Sullivan LA , Koppi AJ
Published: April 2005

The microscopic and submicroscopic characteristics of the vesicles in a Desert Loam (Haplic Durargid) soil were examined. The surface roughness of the vesicles depended on the texture of the material in which they formed. Plate-like silt and coarse clay particles on the vesicle surface were strongly oriented having a pavement-like appearance. Silt and clay coatings lined many of the vesicles and interconnected channels. Many vesicles occurred in clusters and contained layered coatings of different thickness: clay coatings up to 200 �m, silt coatings up to 300�m, and composite coatings up to 1 mm. Some radially cracked clay coatings also contained silt depositions within the cracks. The probable genesis of the clay coatings involves the translocation of clay particles from an external source, through the raindrop-disturbed surface layer, and around entrapped air bubbles within vesicles. The morphology of the coating indicates that the vesicles in this soil layer have considerable durability.
Phosphorus sorption in relation to soil properties for the major soil types of South-Western Australia
Authors: Singh B , Gilkes RJ
Published: April 2005

The P sorption characteristics of 97 soils that are representative of the agricultural areas of Western Australia were described using Langmuir and Freundlich equations. The Langmuir P maximum (xm) ranged from 11 to 2132 �g g-1 soil and the Freundlich k coefficient ranged from 1 to 1681. Clay content, DCB Fe and Al, oxalate Fe and AL, and pyrophosphate Al were positively related to xm and k. By using stepwise regression analysis, the combination of DCB and oxalate-soluble A1 predicted more than 75% Of the variation in the P sorption coefficients. Reactive Al compounds may thus be responsible for much of the P sorption by these soils. Soil pH in 1 M NaF (pH 8.2), which is normally used for the detection of allophanic material, was strongly related to the P sorption coefficients and might therefore be used as a quick test for predicting the P sorption capacity of soils.
The influence of soil-pH on the saprophytic growth in soil of the take-all fungus Gaeumannomyces graminis var tritici
Authors: Glenn OF , Sivasithamparam K
Published: April 2005

Experiments were conducted firstly, to determine whether there was a difference in saprophytic growth response of the pathogen to pH in soil from that on agar. Secondly, we examined whether the response to liming involved a sensitivity of the fungus to the concentration of hydrogen (H+) or calcium ions (Ca2+). The saprophytic growth of the take-all fungus showed that, although it is sensitive to soil pH, each strain behaves differently, and this behaviour cannot be predicted from agar studies. It seems unlikely, therefore, that the observed disease response to soil pH resulted from direct effects on the saprophytic phase of the fungus. There was no indication that increase in the Ca2+ in soil played any part in the growth response of the fungus. The potential for other indirect effects of pH on nutrient availability to the plant and to other stages in the disease cycle is discussed.
Towards a model for soil structural behavior
Authors: Quirk JP , Murray RS
Published: April 2005

Clay particle interaction as mediated by water is considered within the context of attractive and repulsive inter-particle forces-van der Waals forces, ion correlation forces responsible for the potential minimum between Ca-clay particles, cation hydration, ion induced structural forces and diffuse double layer forces especially in relation to the threshold concentration concept. In relation to diffuse double layers, the surface potentials, as determined by co-ion exclusion, are shown to be near constant with respect to concentration. Consideration is also given to the nature of the matrix within which the interparticle forces operate, that is the domain and quasicrystal entities. The particle separations within these entities are defined by the application of the Kelvin equation to the low temperature N2 desorption isotherms. The close agreement between the surface areas obtained from the application of the BET equation to the nitrogen adsorption isotherm and the areas obtained from the desorption isotherms leads to the concept of intrinsic failure; that is the presence of pores external to domains and quasicrystals which permit ready access to the total surface area. The role of electrolyte concentration in controlling the permeability of sodic soils (the threshold concentration concept) is reviewed and discussed with respect to recent studies on the behaviour of red-brown earth soils. At a macroscopic level some consideration is given to the role of oxides and organic matter in stabilizing soil aggregates against slaking. The interaction of rainfall, structure and wheat yield for red-brown earth soils is discussed in terms of a critical rate of wetting which causes incipient failure. In relation to incipient failure the hypothesis is advanced, that the role of organic mater in protecting against slaking, is in strengthening coarse pores; it appears that the pores involved are those with a high probability of continuity and which are responsible for the rapid attainment of field capacity.
The P fertilizer requirements of subterranean clover, and the soil P status, sorption and buffering capacities from two P analyses
Authors: Dear BS , Helyar KR , Muller WJ , Loveland B
Published: April 2005

The phosphorus fertilizer requirement of subterranean clover (Trifolium subterraneum) was determined on a number of soils in field and glasshouse experiments. The solution phosphorus concentration in a 0.01 M CaCl2 extract (SPC0) determined from a phosphorus sorption curve was found to be closely related (R2 = 0.80 to 0.84) to relative yield. The critical SPC required to achieve 90% of relative yield (SPCc) was 0-128 �g P mL-1 in the field and 0.106 �g P mL-1 in the glasshouse experiments. Phosphorus sorbed at an SPC of 0.10 �g P mL- l (Ps0.1 at SPC0.1) was highly correlated with the phosphorus requirement of subterranean clover in both the field and glasshouse, accounting for 89% and 73% respectively of the variation in phosphorus requirement. A modified two-point sorption curve was found to give a good estimate of phosphorus sorbed at both SPC0.1 (Ps0.1) and SPC0.3(Ps0.3), and greatly increased the number of soil samples that can be processed, compared with a five-point sorption curve. The two-point test involved the addition of solutions containing 0 and 8 �g P mL-1 at a soil: solution ratio of 1:10. The sorption curve constructed using this method was suitable for assessing soils with Ps0.1 levels up to 90 �g P g-1. The soil phosphate buffering capacity at SPC0.1 (PBC0.1) was also accurately estimated using calculations from the two data points, but PBC0.3 values were poorly estimated. It was concluded that the two-point sorption curve is a sensitive and efficient method of predicting the present phosphorus status of clover pastures, their phosphorus fertilizer requirements, and of calculating PBC0.1, a useful soil characteristic.
An Australian comparison of Penman's potential evapotranspiration estimates and class A evaporation pan data
Authors: Chiew FHS , Mcmahon TA
Published: April 2005

Estimates of potential evapotranspiration are required to serve as an aid for estimating actual evapotranspiration. Penman's combination equation is generally accepted as an appropriate method for estimating potential evapotranspiration. However, as all the climatic data required to calculate Penman's potential evapotranspiration are seldom available, potential evapotranspiration is more commonly approximated as a factor times standard evaporation pan reading. In this paper, linear regression equations relating Penman's potential evapotranspiration for land surfaces to Class A evaporation pan data over several time periods are developed for various climatic regions throughout Australia. The analyses indicate that the correlations between daily estimates of Penman's potential evapotranspiration and pan data are poor, and therefore, pan data should be treated with caution if used to approximate daily potential evapotranspiration. The correlations improve over longer time periods, and the equations developed for three-day and weekly totals may be used as a last resort to approximate potential evapotranspiration in areas where climatic data required to calculate potential evapotranspiration are not available.
Potassium-calcium exchange in some New Zealand soils
Authors: Parfitt RL
Published: April 2005

The preference of some New Zealand soils to retain potassium over calcium under simulated field conditions has been measured by using Gaines and Thomas selectivity coefficients. All samples showed a preference for potassium over calcium (and magnesium), although the soils contained much more exchangeable calcium than exchangeable potassium. The preference for potassium decreased as more potassium was added to the samples. Oxidic, allophanic and ultic soils had the least preference for potassium; brown soils, formed mainly in loess, had the greatest preference, and this was probably due to the presence of many potassium-selective sites on vermiculite and mica clays in the soils. The results suggest that calcium, rather than potassium, is likely to be leached from all of the soils tested. This was consistent with data from laboratory leaching experiments using an allophanic soil.
Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter
Authors: Sparling GP
Published: April 2005

The sensitivity of soil organic carbon (Corg) and microbial carbon (Cmic) measurements, and the Cm~,/Co,, ratio, to reflect climatic, vegetation, cropping and management history was investigated using a range of topsoils in New Zealand. The Cmic generally comprised 1-4% of Corg, with the proportion being consistently greater under pastures, than the equivalent soil under native forest, exotic forest or arable cropping. However, absolute values differed markedly between soils and were greatly influenced by texture, mineralogy and the Corg content. The Cmic recovered more rapidly than Corg on returning to pasture following cropping. There was a generally greater Corg content in those soils from the areas with higher precipitation, but the precipitation-evaporation quotient proposed by Insam et al. (Soil Biol. Biochem. 1989, 21, 211-21) to predict the relationship between Cmic and Corg, greatly underestimated the Cmic content of New Zealand soils and there was too great a scatter in the data to derive a revised regression formula. The Cmic and the Cmic/Cor, ratio are useful measures to monitor soil organic matter and both provide a more sensitive index than COrg measured alone. However, under typical climatic and land use conditions in New Zealand, the values do not appear readily transferrable between soils. To ascertain whether a soil has achieved equilibrium in organic matter status, it will be necessary to establish reference values to which a tested soil can be compared.
Surface charge in some New Zealand soils measured at typical ionic strength
Authors: Parfitt RL
Published: April 2005

The positive and negative surface charges of some New Zealand soils used for horticulture were measured at different pH values using 0.002 M CaCl2 solutions, Which have a similar ionic strength to soil solutions in New Zealand. The surface negative charge increased with pH for all soil samples including those containing mica and smectite. This behaviour was mainly due to the presence of organic matter and allophane both of which had an appreciable amount of variable negative charge. Allophanic soil B horizons had a higher positive charge than that of the Oxidic soils, which was less than 1 cmol kg-1 at pH 5.
Manganese oxide accumulations associated with some soil structural pores .I. Morphology, composition and genesis
Authors: Sullivan LA , Koppi AJ
Published: April 2005

The morphology and composition of manganese oxide accumulations associated with the structural pores in a black earth (Typic Pellustert) subsoil layer were examined using light microscopy, electron microscopy, X-ray diffraction and electron micro-analytical techniques. Birnessite was identified as the crystalline manganese oxide phase. There were significant positive correlations between cobalt, calcium and manganese and a significant negative correlation between iron and manganese. It was most probable that both microbial oxidation and auto-oxidation of Mn2+ contributed to the formation of the manganese oxide accumulations in this soil.
Genesis of podzols on coastal dunes in southern Queensland .I. Field relationships and profile morphology
Authors: Thompson CH
Published: April 2005

This paper is the first of a series reporting studies in the genesis of podzols and humus podzols on coastal dunes in a chronosequence that spans >700K yrs. It is concerned mainly with temporal changes in profile morphology across a podzol chronosequence and with brief descriptions of sites chosen for genetic studies. It summarizes the geology, geomorphology and general mineralogy of dune systems at Cooloola and North Stradbroke Island and briefly discusses the effects of parent material, geomorphic component, climate, dune denudation and vegetation on soil development. Its purpose is to provide a field and morphological framework for other papers in the series dealing essentially with laboratory investigations and interpretations of the chemistry, mineralogy and genesis of these subtropical soils.
Physical limitations to plant growth on tailings from sandy alluvium
Authors: Emerson WW , Hignett CT , Thomas DA
Published: April 2005

It is proposed to rework surface alluvium derived from earlier mining of gold-bearing quartz. After grinding and extraction, tailings would be pumped back into the excavation as a thick slurry. In pot trials of the tailings in winter, it was found that oats failed to establish despite fertilizer addition. To find the reason for this, the particle size distribution, water retention, bulk density, ease of dispersion and hydraulic conductivity of tailings and the starting alluvium were compared. Also tailings were slowly dried in stages and, at each stage, the increase in cone penetrometer resistance was measured. The penetration resistance of tailings was found to be proportional to matric suction and independent of whether the alluvium was ground coarse or fine. The effect of reduced particle size is compensated for by the decrease in bulk density. The suction required to initiate air entry into tailings is greater than the depth of tailings used in the pot trial, so that aeration would have been inadequate. Further, in the case of tailings resulting from fine grinding, when 10% of the volume of the wet tailings has drained to give adequate aeration, the penetration resistance is already 2.5 MPa, too high for root penetration. It is deduced that none of the water present is available for plant growth. After coarse grinding only, there is a small amount of available water. Possible ways of improving conditions for plant growth on the tailings are briefly discussed.
Manganese oxide accumulations associated with some soil structural pores .II. Composite coatings and translocation
Authors: Sullivan LA , Koppi AJ
Published: April 2005

The morphology and composition of some composite coatings-containing manganese oxide coatings and impregnations-that were associated with the structural pores in a black earth (Typic Pellustert) subsoil layer were examined using light microscopy, electron microscopy, and electron micro-analytical techniques. Detailed examination of composite coatings indicates, firstly, that subsurface coatings and impregnations of manganese oxides had been formed by the burial of surface accumulations of manganese oxides with coatings of other soil components, and secondly, that fine-textured soil material had been translocated and deposited in a form which was virtually indistinguishable from that of the soil matrix.
Utilization of labeled mineral and organic phosphorus sources by grasses common to semi-arid mulga shrublands
Authors: Armstrong RD , Helyar KR
Published: April 2005

We examined whether the differing growth responses to varying concentrations of soil P by grasses common to the mulga shrublands of south-west Queensland were due to differences in their ability to utilize sparingly soluble sources of P in two glasshouse trials. The uptake of three sparingly soluble sources of mineral P (amorphous FePO4, crystalline FePO4 (strengite), and amorphous AlPO4) was compared with that of a soluble P source, KH2PO4, over 34 days. All P sources were uniformly labelled with 32P. For the four grasses studied (Cenchrus ciliaris, Aristida armata, Digitaria ammophila and Thyridolepis mitchelliana), the addition of strengite produced the lowest yields and plant P content, followed by FePO4, and then AlPO4 and KH2PO4. Recovery of the labelled P by the grasses was in the order: strengite < FePO4 < AlPO4 < KH2PO4. C. ciliaris recovered more of the added strengite, but less FePO4 and AlPO4, than the other grasses. There were no differences in specific activity between the grasses for KH2PO4. Where soil treatments were the same, there was no evidence that these species differed in their ability to utilize sparingly soluble sources of mineral P. The reutilization of P from 32P labelled plant residues by two grasses was examined in a second experiment. The experiment consisted of a factorial combination of two species (D. ammophila and A. armata ) and a control (non-planted pots), two phosphorus systems (low and high P), and four harvests (15, 23, 31, and 39 days). The net release of P from the residues was significantly increased in the presence of plants but was not affected by the species present. D. ammophila and A. armata obtained similar proportions of their P content from the added residues (6.6%).
Interrill erodibilities based on the rainfall intensity flow discharge erosivity factor
Authors: Kinnell PIA
Published: April 2005

Interrill erodibilities are often determined using a model which considers the interrill erosion rate to vary directly with rainfall intensity (I) squared. However, it has been shown that the sediment discharge from an interrill area varies directly with I rather than I2 when factors such as flow discharge are also considered. Analysis of data from the experiments used to determine interrill erodibilities in the Water Erosion Prediction Project (WEPP) in terms of a model that uses both rainfall rate and flow discharge indicates that the susceptibilities of some soils to interrill erosion may differ considerably from the erodibilities determined from the WEPP model. Apart from the need to use models which better account for the variations in erosive stress, consideration has to be given to the fact that erodibility is a dynamic factor that can vary rapidly between two extremes. One of these extremes is associated with detachment-limiting conditions that may often be controlled by cohesion. The other extreme is associated with the complete protection of the soil matrix by a layer of pre-detached particles. When this extreme results, interrill erodibilities are controlled by the particle size and density characteristics of the pre-detached particles. Difficulties arise in extrapolating information from one scale to another, and from one soil where erodibility experiments have been performed to others where they have not because of the dynamic nature of the rain-flow-soil surface interaction. Also, the effect of slope gradient in the interrill erosion environment varies between soils and experimental conditions because of this interaction and the differing susceptibility of soils to rilling.
Efficiencies of sediment samplers for wind erosion measurement
Authors: Shao Y , Mctainsh GH , Leys JF , Raupach MR
Published: April 2005

We investigate the efficiency of three sediment samplers used for studies of wind erosion: a vertically integrating trap (an active, modified Bagnold trap for measuring vertically integrated streamwise sediment fluxes, designed for use in a portable wind tunnel); and two single-point, passive traps, the Leach trap (a small sampler of simple design, mainly for use in wind tunnels) and the Fryrear trap (a rugged sampler for field use). The vertically integrating trap is calibrated using a 'weighed sediment supply' technique in which a weighed sediment source is blown away completely during a calibration run. The single-point traps are calibrated against an accurate isokinetic sampler. The collection efficiency of all three traps is determined both in bulk and as a function of particle size. The results for overall efficiency E (for aeolian sand-sized particles) are: for the vertically integrating trap, E = 1.02 �.05; for the Leach trap, E = 0.85 � 0.05 with a slight tendency to increase with wind speed; and for the Fryrear trap, E = 0.90 � 0.05 (with or without a rain hood). Particle size analyses, carried out on the sediments collected by the traps under test and also the isokinetic sampler (assumed to have E = 1 for all particle sizes), show that the particle size distributions of the trapped sediments do not differ significantly from those of the isokinetic sampler. This uexpected result is a feature of the soils used for the tests, for which clay particles are mainly transported as small aggregates or clay skins upon sand grains.
Water repellency in a New Zealand development sequence of yellow brown sands
Authors: Wallis MG , Horne DJ , Palmer AS
Published: April 2005

A series of sands on the west coast of the lower North Island, New Zealand, were studied to investigate the effects of time, topography and vegetation cover upon the development of soil water repellency. Severe repellency was measured with the molarity of ethanol droplet (MED) index in the Waitarere and Motuiti dune phase sands, of age <130 years and c. 500 years respectively. In each dune phase, the dune sands were more repellent than the lower lying soils of the sand plains. Low or zero MED values were measured in the 1600-6000 year old Foxton dune phase sands and 10 000-25 000 year old Koputaroa dune phase sandy loams under either pasture or native bush. There was no consistent relationship between bush or pasture cover and repellency severity in the Foxton and Koputaroa soils, however, the species composition of the pasture and bush differed. The Waitarere sand was the most repellent soil, despite a low organic carbon content. The carbon content profiles of most of the soils did not appear to be related to the respective MED profiles of repellency severity. The MED values of the surface layer from five dune sands were generally related inversely to the fulvic acid (FA) content and proportionally to the humic acid to fulvic acid ratio (HA/FA), which were measured in a previous study. The pH of the five soils ranged from 5.61 to 6.89, with no apparent relationship between pH and MED. A study of soil water content indicated that repellency reduced rainfall infiltration into the Waitarere and Motuiti sands and the Himatangi sand, found on elevated sand plains. The most severely repellent sands had the greater variability in soil water content after rainfall.
The nature, distribution and management of sodic soils in New-South-Wales
Authors: Mckenzie DC , Abbott TS , Chan KY , Slavich PG , Hall DJM
Published: April 2005

Accurate data on the distribution of the various types of sodic soils in New South Wales are not available. However, general observations suggest that large areas are affected by structural instability as a result of sodicity, particularly on grey clays and red-brown earths of the Murray-Darling Basin. There is a strong need for new sodicity surveys because the production of crops and pasture often is well below potential on these lands. Exchangeable sodium data on their own do not adequately describe sodic soil behaviour, so information is also required about related factors such as electrical conductivity, exchangeable magnesium, clay mineralogy, pH, calcium carbonate content, degree of remoulding, and the frequency of continuous stable macropores. Critical limits for sodicity that are used by soil management advisory services need to be redefined. Considerable research into the reclamation and management of sodic soils has occurred in the irrigation areas and rainfed cropping districts of the Murray-Darling Basin in New South Wales. Mined and by-product gypsum, and to a lesser extent lime, have been shown to greatly improve the physical condition and profitability of production from soils with a dispersive surface. However, the responses to these treatments are less likely to be economical when sodicity is confined to the subsoil. Adequate supplies of gypsum and lime are available in New South Wales, but further research is required to determine economically optimal and environmentally acceptable rates and frequencies of application, particle sizes and chemical compositions for different farming systems that utilize the various types of sodic soil.
Soil sodicity in Victoria
Authors: Ford GW , Martin JJ , Rengasamy P , Boucher SC , Ellington A
Published: April 2005

This paper gives a broad overview of the distribution and agricultural importance of sodic soils in Victoria. Sodic soils are estimated to occupy at least 13.4 Mha, representing at least 73% of Victoria's agricultural land. Most of this land is used for dryland farming; about 85% of the cropped land and 66% of the land sown to dryland pastures occurs on sodic soils. The largest sodicity class is 'alkaline sodic', dominated by a diverse range of soils (red duplex, yellow duplex, calcareous earths and self-mulching cracking clays). Alkaline sodic soils comprise half of the total agricultural land area, or about 24% of the area of land currently used for dryland cropping and 21% of the land under sown pasture. Land degradation problems are recognized as affecting most agricultural land in Victoria, and to be substantially limiting its productivity. The nature, extent and severity of the various forms of land degradation are a consequence of both intrinsic soil properties and of management practices. There is an urgent need to improve current farming practices to prevent further deterioration of the soil resource. Existing knowledge of the behaviour of sodic soils under both dryland and irrigated agriculture is reviewed. It is concluded that substantial gains in productivity are possible, but will require effective collaboration between soil scientists, agronomists, and land managers. Collation and integration of current knowledge on the properties and management of sodic soils in Victoria, and the acquisition of additional relevant information by targeted long-term research is required. Key issues for future research are identified.
Sodicity in South Australia - a review
Authors: Naidu R , Merry RH , Churchman GJ , Wright MJ , Murray RS , Fitzpatrick RW , Zarcinas BA
Published: April 2005

The current knowledge of the nature and distribution of sodic soils in South Australia is reviewed. The agriculturally developed area of South Australia lies south of latitude 32-degrees-S. and is mainly used for low intensity grazing and dry land cereal/sheep production. A high proportion of the State, including much of the high rainfall area, has soils which are sodic (>6% ESP) through a significant proportion of the profile but information on the precise nature of sodicity in these soils is limited. Where exchangeable cation data axe available, the analytical techniques used often did not precisely delineate between soluble salts in the soil and ions on exchange sites. Therefore, many of the datasets have major weaknesses and may be unreliable. Since many soils with ESP <6 also show dispersive characteristics typical of sodic soils, there is an urgent need for new sodicity studies relating to distribution and the criteria (ESP) used to identify dispersive soils. Information on the effect of sodicity on nutrient requirements of plants, especially the modern varieties, is scarce both locally and internationally, making development of management strategies for economically sustainable crop production difficult. Further, many different grades of gypsum are available in South Australia. Preliminary studies show the presence of impurities drastically influences gypsum dissolution characteristics. More effort is needed to assess the quality and reactivity of South Australian gypsum. Some effort has been directed by land managers towards reclamation and management of sodic soils by using both gypsum and lime either separately or as mixtures. However, there is neither a scientific basis for the application of gypsum-lime mixtures nor crop production data to support such management strategies.
Distribution of the native earthworm fauna of Australia - a continent-wide perspective
Authors: Abbott I
Published: April 2005

Based on nearly 2000 available records, the broadscale geographical distribution of the native earthworm fauna of Australia was mapped. Native earthworms were recorded from south-eastern, eastern and northern Australia within 400 km of the coast. Isolated faunas were present in Tasmania and south-west Western Australia, and apparently isolated faunas occurred in the Adelaide area/Fleurieu Peninsula of South Australia and the ranges of central Australia. All but 30 locality records occurred where annual rainfall averaged or exceeded 400 mm; 16 of these records were instances of moisture-gaining sites (moist caves, waterholes, banks of large rivers, edge of granite domes). A collecting strategy to both fill in gaps in the distribution map and discover additional anomalous occurrences (with respect to the 400 mm isohyet) is outlined.
The effect of pre-detached particles on soil erodibilities associated with erosion by rain-impacted flows
Authors: Kinnell PIA
Published: April 2005

In shallow rain-impacted flows, particles detached from the soil matrix will produce a layer of pre-detached particles on an eroding surface when entrainment by flow is absent. This layer provides a degree of protection to the underlying soil matrix and material from the layer also contributes to the discharge of sediment across the downstream boundary of an eroding area. The development and effects of the layer are dynamic. The layer tends to be more protective at low flow velocities and with coarse particles than at high velocities and with fine particles. The ease by which particles can be detached from the soil matrix also influences the development of the layer. The dynamic nature of the layer results in the susceptibility of a surface to erosion by rain-impacted flow varying in time and space. The consequence of this is examined with respect to erodibilities associated with an erosivity index that is based on the product of runoff rate and the rate of expenditure of rainfall kinetic energy.
The strength of remolded soils as affected by exchangeable cations and dispersible clay
Authors: Barzegar AR , Murray RS , Churchman GJ , Rengasamy P
Published: April 2005

The tensile strengths of remoulded samples of five Australian soils with differing clay type, texture and shrink-swell potential were measured as a function of exchangeable cations (Na, Ca and Mg) and exchangeable sodium percentage (ESP). Spontaneously and mechanically dispersible clays were also determined as a function of ESP. The tensile strength changed with the nature of the exchangeable cation, clay content and amounts of spontaneously and mechanically dispersible clay. In Ca-soils, the tensile strength was highly correlated with clay content and CEC. Regression analyses of data for soils containing various amounts of exchangeable sodium showed that mechanically and spontaneously dispersible clay were individually correlated with the tensile strength of remoulded soils. However, multiple regression analyses of these data indicated that spontaneously dispersible clay alone was a major predictor of the tensile strength of remoulded sodic soils. This suggests that measurement of spontaneously dispersible clay adequately accounts for the differences in tensile strengths of dry remoulded soils as influenced by ESP values. Analysis of variance of data for all the soils with varying ESP values showed that spontaneously dispersible clay was strongly correlated with clay content. Analyses of data for individual soil type showed that spontaneously dispersible clay was highly correlated with ESP. For each soil studied, increase in ESP resulted in increase of dispersible clay and hence in tensile strength. Although tensile strength increased with ESP, the rate of change of strength with ESP was different for each soil. Soil with the highest clay content gave rise to the greatest rate of change. The effect of exchangeable magnesium on tensile strength was similar to calcium. However, in two of the soils, exchangeable magnesium, in the presence of sodium, increased the strength slightly more than calcium, confirming the ionic radius effect of these elements.
Carbon dynamics in vertisols under several crops as assessed by natural abundance 13C
Authors: Skjemstad JO , Catchpoole VR , Lefeuvre RP
Published: April 2005

The effects of three annual crops (oats, C3, Avena sativa; sorghum, C4, Sorghum bicolor; black gram, C3, Vigna mungo) and a grass pasture (green panic, C4, Panicum maximum) on the content and turnover of organic carbon (0-0.15 m) in Vertisols in south-eastern Queensland were measured. Monocultures of the crops and pasture were grown for 11 years in two blocks (1 and 3) established by cultivating a 44 year old C4 Rhodes grass (Chloris gayana) pasture. The site was previously under C3 brigalow (Acacia harpophylla) scrub. In block 1 on Paleustollic Pellusterts, the organic carbon in both the <1.6 Mg m-3 and the >1.6 Mg m-3 fractions decreased linearly with time in the cultivated plots and increased linearly with time in the green panic pasture. In block 3, the organic carbon content of the light fraction (<1.6 Mg m-3) and the heavy fraction (>1.6 Mg m-3) in the oats and green panic plots on Typic Pellusterts also showed a linear relationship with time, decreasing in the cultivated plots and increasing under pasture. The organic carbon content of the soil fraction >1.6 Mg m-3 from the black gram and sorghum plots on Paleustollic Chromusterts showed an initial rapid decline over 2 years with a subsequent slower linear decline. The proportions of organic carbon in the soil due to the original C3 brigalow forest and the subsequent C4 pasture were calculated from the �13C values of the heavy soil fractions. In block 1, cultivation resulted in a decline in both the C3 and C4 pools. In block 3, cultivation resulted in a more rapid decline in the older C3 pool than the C4 pool. The rate of decline in block 3 was associated with soil type and, upon cultivation, the C3 carbon in the Chromusterts declined more rapidly than that in the Pellusterts. Organic carbon which was part of the resistant pool under pasture therefore contributed significantly to the labile pool on cultivation. There appeared to be major differences in the mechanisms protecting the organic matter from microbial degradation in the different soil types. In the Chromusterts, a proportion of the older C3 pool which may have been physically protected under pasture was rapidly mineralized on cultivation. The mechanisms protecting the C3 pool in the Pellusterts appeared to be more stable to physical disruption and therefore more resistant to degradation.
Correction
Authors: Grant CD , Blackmore AV
Published: April 2005

Modifications to Self-Mulching (I(Sm)) Behavior and Their Implications (Vol 31, Pg 574, 1993)
Comparison of single and dual probes for measuring soil thermal properties with transient heating
Authors: Bristow KL , White RD , Kluitenberg GJ
Published: April 2005

Storage and transfer of heat in soils is governed by the soil thermal properties and these properties are therefore needed in many agricultural and engineering applications. In this paper we discuss solutions of the heat flow equation applicable to single and dual probe transient heating methods, and describe measurements made on air-dry sand to show how these methods can be used to obtain soil thermal properties. Measurements show that the two methods yield similar values of thermal conductivity. When determining thermal conductivity from the single probe data, it is best to use nonlinear curve fitting and to include a correction term in the model to account for the presence of the probe. Measurements of volumetric heat capacity made by using the dual probe heat-pulse method agreed well with independent estimates obtained using the de Vries method of summing the heat capacities of the soil constituents. The advantage of using the dual probe method together with the appropriate heat-pulse theory rather than the single probe is that all three soil thermal properties, the thermal diffusivity, volumetric heat capacity, and thermal conductivity, can be determined from a single heat-pulse measurement. Instantaneous heat-pulse theory can be used with the dual probe method to determine heat capacity from short duration heat-pulse data, but it should not be used to determine the thermal diffusivity and thermal conductivity.
Rate of recycling of sulfur from urine, feces and litter applied to the soil surface
Authors: Blair GJ , Till AR , Boswell C
Published: April 2005

The recycling of S from plant litter, dung and urine is an important process for supplying S for pastures. A pot experiment was conducted where 35S-labelled litter (25% white clover/38% ryegrass/21% weed) and S-35-labelled urine and faeces collected from sheep fed the same herbage as was used as litter was surface applied to pots and the fate of the applied S was followed for 100 days with ryegrass as the test plant. In camp soil, 45% of the S applied in urine was taken up by ryegrass plants within 12 days of application. In non-camp soil, the uptake of urine-S was about 20% over the same period. Cumulative uptake of 35S from urine in camp soil was subsequently restricted, with a maximum of 60% eventually measured in plants after 100 days. Mean rates of release of S (0-37 days) from litter and faeces was respectively 16.2 and 4.5 mg g-1 day-1. The calculated half-times from S in the two materials were respectively 43 and 154 days under controlled environmental conditions with adequate moisture. Litter S followed organic matter (OM) decomposition, but faecal S release was initially more rapid than faecal OM decomposition. There was little S release from faeces after day 25. Rather, S was immobilized in faeces during the 25-100 day period. The decomposition of litter and faeces was divided into an initial rapid process during which soluble S and more labile S was released, followed by a slower process involving the release of S from tissues more resistant to mineralization. The uptake of 35S from labelled materials was initially more rapid than would be expected for total S released from the added litter and faeces and the 35Suptake effect was short-lived relative to the continued effect of added material on total S uptake. The preferential uptake of 35S from the surface-applied material appears to be due to limited root development at the early stages of the experiment. Movement of 35S into the soil organic matter pool was very rapid; 58.4% of urine S was in the soil organic matter fraction in the non-camp soil by day 6. The amount of applied S in the organic matter equilibrated at about day 75. The accumulation of applied S from the materials added was greater than that recorded in previously reported studies for inorganic sulfate (e.g. about 50%). Soil P and S status had little effect on rates of release of S. from the applied materials, however, the effect of the camp and non-camp soil on total S recycling was markedly different as a result of the different amounts of plant growth and thus S uptake in the two soils. The decomposition of litter indicated peak rates of S release at two specific times over the 100 days and indicated successional changes in micro-organism activity. With faeces, the experiment was not continued for sufficiently long to show micro-organism effects.
Effects of calcium and aluminum in the soil solution of acid, surface soils on root elongation of mungbean
Authors: Menzies NW , Edwards DG , Bell LC
Published: April 2005

Short term root growth bioassays using mungbean (Vigna radiata (L.) Wilczek) were conducted on 39 surface soils in the unamended state and following the addition of CaCO3 or CaSO4.2H2O. Root length after 48 h growth was related to solid phase and soil solution Ca and Al attributes. Suitable diagnostic indices for the prediction of Ca limitations to root growth were either Ca saturation of the cation exchange capacity or Ca activity ratio (CAR) defined as the ratio of the activity of ca2+ in the soil solution to the summed activities of Ca2+, Mg2+, Na+, K+ and Al3+. Values corresponding to 90% relative root length were 34% for Ca saturation and 0.10 for CAR. The activities of Al3+ and AlOH2+ were the Al attributes most strongly correlated with root growth; an Al3+ activity of 1.9 �m~ and an AlOH2+ activity of 0.46 �m corresponded to 90% relative root length. The results suggest that organically complexed Al and the ion pairs Al(OH)+2, Al(OH)04 and AlSO+4 are not plant-toxic. The most effective diagnostic criterion for A1 toxicity in this study was the calcium-aluminium balance (CAB), defined as 2 log(Ca2+) - 6 log(Al3+). The CAB value corresponding to 90% relative root length was 31. The correlation between root growth and CAB was further improved by inclusion of a pH term; this may indicate toxic effects of H+ per se.
Properties of iron-oxides from red soils derived from volcanic tuff in West Java
Authors: Prasetyo BH , Gilkes RJ
Published: April 2005

The properties of iron oxide concentrates of Oxisols and Alfisols on volcanic tuff in West Java, Indonesia, were studied by XRD,TGA, TEM and chemical analysis.Goethite and hematite are the co-dominant iron oxides and are present in all samples. Iron content of the soils (dithionite-soluble Fe) ranges from 6.0 to 15.4%. Aluminium substitution in goethite and hematite ranges between 11 and 26 mol% and 0 and 9 mol% respectively. The Al substitution in hematite increases at about half the rate for goethite within the same samples. Crystal size of goethite and hematite was measured from line broadening of the 110 reflections and ranges between 7 and 18 nm for goethite with a mean value of 10 nm and between 7 and 28 nm for hematite with a mean value of 18 nm. The dehydroxylation temperature of goethite is in the range 290-320 �C and is linearly related to Al substitution by the equation y = 280 + 1.53x, (R(2) = 0.53). The goethite and hematite in these Indonesian soils are very similar to these minerals in tropical and Mediterranean soils from other regions.
Long-term effects of lime on soil-phosphorus solubility and sorption in eight acidic soils
Authors: Holford ICR , Schweitzer BE , Crocker GJ
Published: April 2005

Measurements of phosphorus (P) sorption, isotopically exchangeable, KCl soluble and extractable P (Bray(1)) were carried out on limed and unlimed soils from eight pasture experiments on the Northern Tablelands of New South Wales at intervals of 1, 2 and 3 years after lime application. Lime increased soil pH by a minimum of 0.5 to a maximum of 1.55 units, and there were corresponding decreases in soluble aluminium and manganese. Lime decreased P sorptivity in every soil and at every sampling, but decreases were usually largest at the first sampling. They were attributed to the pH-induced increase in surface negative charge and the smaller increases in calcium concentrations of these freely drained soils, compared with undrained potted soils, of a previous glasshouse experiment. Isotopically exchangeable P was increased by the highest lime rate (5 t/ha) in all but one soil at the first sampling, while soluble P was increased by both lime rates in all soils. Increases in exchangeable P tended to decline at successive samplings, but increases in soluble P sometimes increased and sometimes decreased with time. In general, lime-induced increases in soluble P were consistent with decreases in P sorptivity, although the primary cause of the increases was probably the dissolution of iron and aluminium phosphates. All these changes were conducive to the increased plant availability and uptake of soil and fertilizer P.
Forms of sulfur extracted from soils after different methods of sample preparation
Authors: Tan Z , Mclaren RG , Cameron KC
Published: April 2005

Three forms of sulfur (S) were determined in extracts from field-moist, air-dried and conditioned (i.e. maintained at 20�C and 75% field moisture capacity for 2 weeks) soils by using four extractants-water, CaCl2, KH2PO4 and Ca(H2PO4)2. The amounts and proportions of inorganic sulfate (SO2-4-S), organic HI-reducible S (HI-S) and carbon bonded S (C-S) in extracts varied with soil type, method of sample preparation and the extractant used. Substantially less S overall was extracted from field-moist soil compared with air-dried and conditioned soils. For soils with pH values close to or above 6, water and phosphate extractants removed similar amounts of SO2-4-S. However, phosphate solutions removed greater amounts of SO2-4-S than water from soils with relatively low pH or with a large capacity for sulfate adsorption. The CaCl2 solution extracted the smallest amounts of sulfate from the soils studied. There was no consistent ratio between extractable sulfate-S and extractable organic S. Extracts from air-dried soil contained the greatest amounts and proportions of organic S, particularly in phosphate extracts. The conditioning of soils decreased the extractable organic S and increased the sulfate-S, indicating that extractable organic S is readily mineralizable. The relative proportions of extractable organic S present as HI-S and C-S varied considerably. Comparison of the conditioned and air-dried soils indicated there was no difference between the two forms of organic S in their ease of mineralization.