bluuebunny/crossref_metadata_2025 huggingface dataset:
Long term trends in fertility of soils under continuous cultivation and cereal cropping in southern Queensland. III. Distribution and kinetics of soil organic carbon in particle size fractions
Authors: Dalal RC , Mayer RJ
Published: April 2005

Distribution of soil organic carbon in sand-, silt- and clay-size fractions during cultivation for periods ranging from 20 to 70 years was studied in six major soils used for cereal cropping in southern Queensland. Particle-size fractions were obtained by dispersion in water using cation exchange resin, sieving and sedimentation. In the soils' virgin state no single particle-size fraction was found to be consistently enriched as compared to the whole soil in organic C in all six soils, although the largest proportion (48%) of organic C was in the clay-size fraction; silt and sand-size fractions contained remaining organic C in equal amounts. Upon cultivation, the amounts of organic C declined from all particle-size fractions in most soils, although the loss rates differed considerably among different fractions and from the whole soil. The proportion of the sand-size fraction declined rapidly (from 26% to 12% overall), whereas that of the clay-size fraction increased from 48% to 61% overall. The proportion of silt-size organic C was least affected by cultivation in most soils. It was inferred, therefore, that the sand-size organic matter is rapidly lost from soil, through mineralization as well as disintegration into silt-size and clay-size fractions, and that the clay fraction provides protection for the soil organic matter against microbial and enzymic degradation.
Numerical analysis of soil development in a chronosequence on Fraser Island, southeastern Queensland
Authors: Little IP
Published: April 2005

Analytical data for K, Na, Ca, Mg, Al and Fe on acid extracts of samples from 52 profiles from Fraser Island, south-eastern Queensland, were used to investigate soil development in a chronosequence of podzol soils on sand, dating from mid-Pleistocene to the present. The variation observed could be accounted for by two factors, one associated with K, Fe and Al, and the other with Na, Ca and Mg. The first was most closely associated with the podzolisation process involving the weathering of minerals and the removal of the products by leaching and the deposition of Fe and A1 in the B horizon (a katamorphic factor). The second was seen as a biotic factor related to surface accumulation by the present-day vegetation. In the A horizon, both factors were related to age, implying that the soils become more impoverished with increasing age. The biotic factor, which was strongly related to the C and N contents, was also related to depth, decreasing exponentially to approximately 1.5 m, implying that this was the limit of the effect of the modern plant cover on the soil. In the B horizon, factor scores for the katamorphic factor increased markedly, indicating an increase, but not necessarily an accumulation, of K, Fe and Al. There was no relationship, however, with depth, age or carbon content. Factor scores related to the biotic factor showed a significant relationship with age, with Ca and Mg accumulating to a lesser degree in older B horizons. Several lines of evidence indicate that spodic horizons at depths greater than 1.5 m are not now in equilibrium with the surface horizons.
An investigation of the base status of soils from the Lockyer Valley uplands, and some implications for land use
Authors: Little IP , Smith KJ
Published: April 2005

Samples were examined from 129 profiles representing the major soils on all of the parent material types occurring in the Lockyer Valley Uplands. The base status and CEC were determined by an unbuffered silver thiourea method and pH, and conductivity of the 1:5 soil/water suspensions measured. A factor analysis of the data showed that 62.5% of the variation could be accounted for by three factors, each of which described a different facet of soil development. Factor 1 was related to the balance between Ca and Na+Mg. Factor 2 was mainly concerned with salinity, pH and cation saturation, whereas factor 3 was related to the balance between Ca and exchangeable Al. The soils were classified into seven groups according to the factor 1 scores for the Al horizon, and the factor 2 and 3 scores for the B horizon. Parent material and Great Soil Group classification proved only to be a general guide to base status. Nearly all the soils had Ca-dominant surface soils with low base saturation and salinity. They became more Na + Mg dominant, and more saline, with increasing depth, and many of the podzolic soils had acid B horizons with high exchangeable Al. The best agricultural soils are the yellow-brown earthy soils, and sands developed on Ma Ma Creek Sandstones, and these tend to be Ca dominant and non-saline at least in the upper solum. Of the clay soils, although most possessed Ca-dominant surface soils, they became Mg dominant at a depth greater than 10-20 cm, and may be intractable for that reason. This includes many of the soils developed on basalt, or material derived from basalt.
Groundwater recharge and discharge response to rainfall on a hillslope
Authors: Talsma T , Gardner EA
Published: April 2005

Groundwater recharge was investigated within a representative hillslope segment of a small forested catchment, where the depth to the water table increased when progressing upslope from a free water outlet. Catchment soils varied with progression upslope from grey through yellow to red earths, which were underlain by low hydraulic conductivity B horizons and permeable substrata. The catchment was equipped for measuring stream discharge, rainfall characteristics, water table position, soil water content and soil hydraulic properties. Measurements commenced when soil water was severely depleted by drought, and were continued to monitor infiltration and redistribution with depth after more than 1000 mm of rainfall. Water movement occurred under approximately unit hydraulic gradients to the layer of restricted hydraulic conductivity; with movement through this layer proceeding under gradients considerably in excess of unity. Between rainfall events water movement in the soil profiles with deep water tables occurred by redistribution, with the capillary flux exceeding the gravitational flux. Where water tables were shallow (7 m) it took many months for the soil water deficit to be replenished by rainfall. Recharge to groundwater in this case commenced with a flux of about 0.5 mm day-1 and decreased to an estimated value of 0.3 mm day-1 some 5 months later. Following winter rain more than 30% of the annual groundwater discharge from the catchment originated from a relatively small but expanding area near the free water outlet.
Effects of atmospheric evaporativity, soil type and redistribution time on evaporation from bare soil
Authors: Jalota SK , Prihar SS
Published: April 2005

Several reports in the literature show that atmospheric evaporativity (Eo), water transmission characteristics of soil and distribution of water in the profile influence the pattern of evaporation losses from soil, but few relate to their interactive effects. Experiments were conducted with silt loam, sandy loam and loamy sand soils with zero and 2 days' redistribution time before commencement of evaporation under high (15.1 � 0.50 mm day-1), medium (10.1 � 0.50 mm day-1) and low (6.3 � 0.52 mm day-1) Eo to ascertain if cumulative evaporation (CE) was always greater under higher Eo irrespective of experimental conditions, and if the evaporation rates during falling rate stage were insensitive to changes in Eo in all soils. Where evaporation commenced immediately after wetting, CE up till 30 days was always higher under higher than lower Eo values in the silt loam and sandy loam soils. In the loamy sand, however, CE under medium Eo conditions exceeded that under high Eo conditions after 2 days. When evaporation commenced after 2 days of redistribution CE under medium and low Eo values exceeded that under high Eo values after 8 and 12 days in the sandy loam, and 2 and 6 days in loamy sand, respectively. Where evaporation was commenced after the 2-day redistribution, CE at 30 days in the silt loam and sandy loam was 12% less than where evaporation commenced immediately after infiltration under all the Eo values. In loamy sand these differences were 17% and 40% under low and high Eo values, respectively. CE as well as evaporation rate (ER) were sensitive to Eo in the initial period of falling rate stage in the silt loam and the sandy loam but not in the loamy sand.
Effects of exchangeable sodium on crusting behavior of a sandy loam soil
Authors: Painuli DK , Abrol IP
Published: April 2005

Field and greenhouse studies were conducted at the Central Soil Salinity Research Institute, Karnal, India, to evaluate the effect of exchangeable sodium (ES), amount of water applied, and evaporation and temperature conditions at drying on the crusting behaviour of a sandy loam soil. The exchangeable sodium percentage (ESP) ranged from 5.8 to 30.7 in the field and from 6 to 60 in the greenhouse studies. Soil crusting behaviour was evaluated in terms of crust strength measured by a simulated seedling emergence technique. Water was applied as natural or simulated rainfall. Crust strength increased with ESP, amount of water applied, and temperature, but decreased with increasing evaporation demand. This change in crust strength was steep above ESP 30. Although drying of the crust increased its strength, beyond a certain degree of dryness the disappearance of water films surrounding the soil particles reduced strength for low ESP soils.
Tillage effects on soils - Physical and hydraulic responses to direct drilling at Lockhart, NSW
Authors: Burch GJ , Mason IB , Fischer RA , Moore ID
Published: April 2005

The effects of cultivated fallowing (maximum disturbance), direct drilling (intermediate disturbance) and direct drilling using narrow sowing points (minimum disturbance) on soil physical and hydraulic properties were assessed after 3 years of cropping treatments at Lockhart in the southern wheat-belt of New South Wales. Infiltration was measured in the field using simulated rain, before and after the site had been uniformly grazed by sheep. Minimum disturbance produced some of the highest soil strengths, aggregate stabilities and bulk densities in the top 50 or 100 mm of soil, whereas intermediate disturbance gave the lowest bulk densities. Field infiltration of simulated rain was enhanced by reducing the level of tillage disturbance. Grazing the site with sheep generally reduced infiltration, although the ranking of treatments remained similar. Measurements of hydraulic conductivity, porosity and pore continuity on soil cores recovered from the field site failed to reflect treatment differences in field infiltration, suggesting that the properties of the bulk soil were not responsible for these differences. Laboratory assessment of surface crusting using repacked top soil (0-50 mm) showed that slaking on wetting and raindrop impact produced highly impermeable crusts or surface seals that control infiltration with simulated rain. The formation of crusts or seals after 30 min of simulated rain at 42 mm/h caused a 100-fold reduction in the effective hydraulic conductivity of the surface soil. Although the tillage treatments had no significant effect on crust hydraulic conductivities, we suggest that crusts or seals formed on cultivated soils were responsible for differences observed in field infiltration. In particular, the reductions in infiltration produced by grazing the field site with sheep suggest that the surface soil may have become crusted and compacted.
Mechanical stresses on an expanding cylindrical root analog in antigranulocytes media
Authors: Richards BG , Greacen EL
Published: April 2005

Previously published studies of the mechanical impedance of granular media to root growth have shown that the rate of elongation of barley roots was halved by a lateral cell pressure of 0.02 MPa, applied externally to the growing media. It was incorrectly assumed that this lateral pressure was always the pressure on the growing root. In this paper, the stress distribution around a growing root was modelled both theoretically and experimentally by a thin cylindrical rubber tube, which was expanded radially in two granular materials in a modified triaxial cell. The theoretical model which simulated the deformation of the granular material around the expanding rubber root analogue was controlled by the elastic stiffness parameters, bulk and shear modulus in the early stages and later, at larger diameters, by the plastic yield parameters, cohesion and friction angle. This theoretical stress-strain model was validated experimentally by the good agreement with the results obtained using the thin rubber tube in the two granular materials. Using the theoretical model with root diameters similar to those for barley roots, it predicted soil pressures on the 'root' surface of 0.2-0.3 MPa for lateral triaxial pressures of the order of 0.02 MPa. This result was similar to the predictions made using earlier analytical models. The model also predicts lower mechanical impedance for finer roots, and strongly suggests that cylindrical expansion of the root behind the tip is effective in relieving soil pressure ahead of the elongating root.
Methods to experimentally control waterlogging and measure soil oxygen in field trials
Authors: Barrett Lennard EG , Leighton PD , Mcpharlin IR , Setter T , Greenway H
Published: April 2005

A method is described for the establishment of controlled waterlogging events in the field. Special plots were constructed at a site with a loamy sand overlying an indurated siliceous pan of low hydraulic conductivity. The plots were isolated from lateral water flow with polyvinyl chloride sheeting, and were either waterlogged or drained by sub-irrigation or drainage through slotted polyethylene pipe buried 0.45 m below the soil surface. In a test of the plots, waterlogging was imposed for 26 days. Samples of soil water were removed from waterlogged plots for the measurement of oxygen. Concentrations of oxygen rapidly decreased after the commencement of waterlogging, but increased again after drainage.
Behavior of Phytophthora clandestina propagules at a field site in Western Australia
Authors: Wong DH , Barbetti MJ , Sivasithamparam K
Published: April 2005

The number of infective propagules of Phytophthora clandestina, an important pathogen of subterranean clover, was estimated by the most probable number (MPN) method in soil at a field site in Western Australia. The behaviour of the propagules of this fungus was studied in relation to root disease index (RDI), disease suppressiveness index (DSI), rainfall, soil moisture and soil temperature for a period of 12 months. There was an increase in the number of infective propagules in the field soil in January and no further increase was observed until May, then marked decrease occurred in June and July with the numbers remaining low through to December. There was no significant correlation between MPN and RDI, DSI, rainfall, soil moisture or temperature. The RDI was, however, negatively correlated (P < 0.05) with DSI linearly (r = 0.76) and quadratically (r = 0.81). Subterranean clover appears to be the sole source of P. clandestina inoculum in the pasture sward of mixed plant species.
Long term trends in fertility of soils under continuous cultivation and cereal cropping in southern Queensland .V. Rate of loss of total nitrogen from the soil profile and changes in carbon : nitrogen ratios
Authors: Dalal RC , Mayer RJ
Published: April 2005

The kinetics of total N loss from the top (0-0.1 m) and the subsoil (up to 1.2 m depth) of six southern Queensland soils after different periods (0-70 years) of cultivation and cereal cropping, were studied. The equation: Nt = Ne + (No - N,)exp(- kt), where No, Ne and N, are total N concentrations initially, at equilibrium and at time t, respectively, and k is the rate of loss of total N from soil, described total N loss from only three soils. For the 0-0.1 m depth, the kw values (based on weight of total Nholume of soil) were 0.061, 0.115 and 0.275 year-1, respectively for Waco (black earth; initially grassland), Langlands-Logie (grey, brown and red clays; brigalow) and Cecilvale soil (grey, brown and red clays; poplar box). The kw values decreased to less than half at 0-0.6 m depths of those at 0-0.1 m depth. In the other three soils, Billa Billa (grey, brown and red clays; belah), Thallon (grey, brown and red clays; coolibah) and Riverview (red earth; silver-leaved ironbark), total N declined linearly over the 20-25 years of cultivation period studied. Average annual rates of N loss from the profiles of the six soils, respectively, were 31.3, 67.1, 34.5, 50.8, 35.8 and 32.0 kg N ha-1 year-1 , from Waco, Langlands-Logie, Cecilvale, Billa Billa, Thallon and Riverview soils. Except for Langlands-Logie, these losses could be accounted for by crop N removal. In the Langlands-Logie soil, besides N removal by crop (51 kg N ha-1 year-1, 1982-1984 period), leaching of N below the root-zone appeared to be the likely factor for N loss. C:N ratios generally increased with depth in the five clay soils but decreased with depth in the red earth (Riverview). Cultivation had no significant effect on the C:N ratios of Cecilvale, Thallon and Riverview soils, but it caused a decrease in Langlands-Logie soil (up to 0.6 m depth) and an increase in Waco soil (up to 1.2 m depth). It was inferred, therefore, that in the latter, remaining soil N was likely to mineralise more slowly with increasing period of cultivation, resulting in a fertility loss which may be greater than that shown by the decrease in total N.
Hydraulic properties of a duplex soil determined from in situ measurements
Authors: Rab MA , Willatt ST , Olsson KA
Published: April 2005

The hydraulic conductivity characteristics of a duplex soil profile were determined in the field from in situ measurements. For a given soil water suction, hydraulic conductivity of the subsoil was generally lower than the surface soil. Hydraulic conductivity characteristics calculated using the equations of Marshall and Millington and Quirk were in good agreement with field-measured hydraulic conductivity after matching at low soil water suctions. Implications of hydraulic properties for crop production and water management are noted.
The use of electromagnetic induction to detect the spatial variability of the salt and clay contents of soils
Authors: Williams BG , Hoey D
Published: April 2005

The apparent electrical conductivity (EC,) of a 250 ha area of the Riverine Plain in New South Wales was mapped using a Geonics EM 34/3 electromagnetic terrain conductivity meter. The EC, values obtained were highly correlated with both the total soluble salts and the total <2 km clay material to a depth of 15 m. The spatial variability of both these properties has a direct bearing on present and future land-use practices.
Accessions of atmospheric dust east of Adelaide, South Australia, and the implications for pedogenesis
Authors: Tiller KG , Smith LH , Merry RH
Published: April 2005

Atmospheric dust and rainfall were collected at 19 locations within a 90 x 10 km study area extending eastwards from the coast near Adelaide, South Australia. Monthly collections for up to 3 years established seasonal and regional trends in fallout of particulate matter. Fallout was highest in the area of highest rainfall, but correlation of monthly rainfall with fallout was generally not statistically significant. The amount of dust collected was higher under tree foliage than in adjacent open space. Annual accession of atmospheric dust within this urban-rural transect was in the range of 5-10 t km-2 but the occasional severe dust storm could contribute about half the annual rate. These accretions of dust to the landscape, 2.5-5 mm per 1000 years, were about one hundredth of the recommended soil loss tolerance adopted in many studies of soil erosion, and thus unlikely to contribute significantly to models developed for soil loss on that basis. Dust accessions were, however, similar to estimates of rates of soil formation or profile deepening on resistant rocks of 1-5 mm per 1000 years which may be appropriate to conditions in southern Australia. Incorporation of such accessions into existing soils would be difficult to identify yet may provide a significant factor in pedogenesis in the higher rainfall areas. The low rates of soil development in many Australian landscapes, with contribution from both weathering and eolian dust inputs, would encourage the adoption of soil loss tolerances in soil erosion management that are orders of magnitude lower than those commonly accepted.
Fluoride interactions with hydrous aluminum oxides and alumina
Authors: Farrah H , Slavek J , Pickering WF
Published: April 2005

Fluoride ion interaction with amorphous Al(OH),, gibbsite or alumina (Al2O3) has been investigated over a range of pH values (3-8) and F- concentrations (0.1-1 mM) . At pH <6 and total F- : Al ratios >2.5, most of the amorphous AI(OH)3 gel dissolved through formation of AlF, complexes, with the distribution of fluoro ions being determined by the equilibrium F- value. At lower F : Al ratios, some solid persisted in the pH 4-7 region and strongly sorbed F- from solution. Maximum uptake occurred in the pH 5.5-6.5 region (up to 9 mol kg-1). At lower pH, uptake declined due to preferential formation of AlFx soluble species; at higher pH, OH- displaced F- from the solid and the amount of F- sorbed or converted to complexes declined rapidly towards zero between pH 6 and 8. Similar pH trends were observed using � Al2O3, except that both substrate solubility and the adsorptive capacity was less. At a iixed pH (between 5 and 7.5) uptake varied in accordance with a Langmuir equation (maximum capacity approx. 1 mol kg-1). The amount of substrate converted into AlFx complexes in acid media increased with decreasing pH and increasing initial fluoride concentration. Gibbsite displayed the same dissolution trends, but reacted at a much slower rate. Little F was sorbed by this substrate (10-20 mmol kg-1). The study has confirmed the ability of F- to mobilize A1 and the capacity of Al(OH)3 to scavenge F- from aqueous phases in the pH 4-7 region.
Characterization of organic matter in particle size and density fractions from a red-brown earth by solid state 13C NMR
Authors: Oades JM , Vassallo AM , Waters AG , Wilson MA
Published: April 2005

Size and density fractions separated from a red-brown earth have been analysed by high-resolution solidstate 13C nuclear magnetic resonance (n.m.r.) spectroscopy. Resonances from O-alkyl carbon (mainly carbohydrate) predominated in the spectra of the largest (250-2000 �m) fractions, whereas alkyl carbon resonances (mainly polymethylene) predominated in the spectra of clay fractions. Paramagnetics, mainly Fe3+, were found to influence the amount and type of carbon seen in 13C solid-state n.m.r. spectra of clay fractions containing more than several per cent iron oxides. Removal of iron oxides by reduction with dithionite allowed aromatics, carboxyls and carbohydrates to be detected by 13C n.m.r.
Decomposition of plant material in Australian soils .IV. Decomposition in situ of 14C labeled and 15N labeled legume and wheat materials in a range of southern Australian soils
Authors: Amato M , Ladd JN , Ellington A , Ford G , Mahoney JE , Taylor AC , Walsgott D
Published: April 2005

14C- and 15N-labelled wheat straw, and tops or roots of a pasture legume (either Medicago littoralis or Trifolium subterraneum) were incorporated into topsoils at 12 field sites in southern Australia. These sites were representative of soil types widely used for wheat growing in each region. The soils varied markedly in their physical and chemical properties (e.g. pH, texture and organic matter content). Based on amounts of residual I4C (averaged for all sites), the legume tops decomposed more extensively than did wheat straw, especially soon after incorporation. To a lesser extent the legume tops decomposed more extensively than legume roots, and T. subterraneum tops more than M. littoralis tops; root decomposition for both legumes was similar. For example, after 1 year, the residual organic 14C from wheat straw, M. littoralis tops, T. subterraneum tops and legume roots accounted for 48%, 41%, 38% and 54% of their respective inputs. After two years, residual 14C of wheat straw accounted for 30% of the input. Differences in decomposition due to climate and soil properties were generally small, but at times were statistically significant; these differences related positively with rainfall and negatively with soil clay content, but showed no relationship with pH or soil organic C and N. Some N was mineralized from all plant materials, the greatest from legume tops, the least from wheat straw. After 1 year, residual organic 15N accounted for 56%, 63% and 78% respectively of input l5N from legume tops and roots and from wheat straw. The influence of climate and soil properties on amounts of residual organic I5N was small and generally was consistent with those found for residual 14C. AS an exception, the residual organic 15N from wheat straw was negatively related to soil organic N levels, whereas residual I5N of legume tops and roots and residual 14C of all plant materials were not influenced by soil organic matter levels. These results are discussed in terms of the turnover of N in soils amended with isotope labelled plant materials of different available C:N ratios.
The effect of citrate bicarbonate dithionite treatment on standard and soil smectites as evidenced by 57Fe Mössbauer spectroscopy
Authors: Cardile CM , Childs CW , Whitton JS
Published: April 2005

The 57Fe Mossbauer spectra of a selection of smectitic clay fractions of CBD-treated soil samples were measured and computer-fitted with appropriate Fe3+ and Fe2 + resonances. The shape of the Fe3+ spectral envelopes suggested that all the clays were dominated by montmorillonite, contradicting the indications of the Greene-Kelly test. Experiments with untreated and CBD-treated nontronite and montmorillonite showed, however, that the apparent contradiction was probably the result of significant disruption of the smectites by the CBD treatment. The occurrence of this disruption also casts doubt on the validity of using the Greene-Kelly test on CBD-treated samples. The computer-fitted Mossbauer spectra of nontronite with different particle sizes (specifically aggregate size) demonstrated a relationship between particle size and the line-width of the Fe3+ tetrahedral site resonance. This relationship probably reflects an increasing degree of variability in the tetrahedral site with increasing particle size.
Measurement of elemental sulfur in soil and sediments - Field sampling, sample storage, pretreatment, extraction and analysis by high performance liquid chromatography
Authors: Watkinson JH , Lee A , Lauren DR
Published: April 2005

A rapid method for measuring elemental sulfur (S0) in soil and sediments is described that is accurate and precise down to a detection limit of 0.1 mg kg-l. Elemental sulfur is extracted into chloroform and measured by high-performance liquid chromatography. For moist samples, water is added to exceed their liquid limit. The method has been used to follow oxidation of both natural and fertilizer So in soil in the laboratory and field. Sediments analysed included some from lakes, and settling ponds containing coal mine wastes. Extraction within the plastic range was incomplete and recoveries as low as 5%-65% were found for five soils selected for a wide range of plastic limit. The plastic soil aggregates were not dispersed in the water-immiscible chloroform, preventing the dissolution of occluded S0; but at moisture levels above and below the plastic range, the soil was dispersed and extraction of S0 was quantitative. Extraction into a water-miscible solvent, chloroform-methanol (50 : 50), dispersed the soil at all moistures by dissolving the water thus preventing formation of plastic soil. This was less convenient because either volume correction for moisture was needed, or excess water added later to separate the chloroform. Measurement of total sulfur (S) in chloroform by inductively coupled plasma gave comparable results where samples contained S0 fertilizer, but at the lower natural levels they were much less precise and sometimes higher because of the additional S compounds extracted. Storage of moist soil below -10�C or air-dry soil at 20�C, gave no loss of S0 after one month. Moist soil at 20�C gave 40% loss after one week, but at 4�C the loss was only 5% after four weeks. Forced air-drying at 30�C, freeze-drying and microwave drying (under a narrow range of conditions) gave losses of about 5% for fertilizer S0 (<0.15 mm fraction), and of about 20% for smaller S0 crystals. In field trials with S0, sample variability was associated mostly with the difficulty of applying the S0 uniformly and with the small number of particles applied per unit area. For particles <0.25 mm, variability from mixing of cores and sub-sampling was not so great.
Effect of temperature and moisture on kinetics of urea hydrolysis and nitrification
Authors: Yadav DS , Kumar V , Singh M , Relan PS
Published: April 2005

The effects of temperature and moisture regimes on kinetics of urea hydrolysis in soils of Hisar (Typic Camborthids) and Hansi (Typic Ustochrepts) were studied. The rate constant (K) for first-order reaction increased with temperature from 10 to 35�C. Energy of activation (Ea), activation free energy (�F*) and activation entropy (�S*) between 10 and 35�C were 33.8, 81.8 kJ mol-1 and -176.55 K-1I in a sandy loam soil, and 29.2, 81 -6 kJ mol-I and - 155.3 J K-I in a clay loam soil, respectively. The hydrolysis rate was not a linear function of moisture content but increased with field capacity (F.C.). The rate of hydrolysis in both the soils followed the order: 20% F.C. < 40% F.C. < 80% F.C. = 100% F.C. The rate for flooded soil was between those for 20% and 40% F.C. for sandy loam, and between 40 and 80% F.C. for the clay loam. The added urea was completely hydrolysed in 3 days at all moisture regimes except 20% F.C.; maximum NH4+-N was found at the third day, then decreased thereafter. The time at which NO2- first appeared varied with treatments, but then it persisted throughout the 24-day incubation in all treatments.
Accumulation of plant nutrients and changes in soil properties of sandy soils under fertilized pasture in southeastern South-Australia .I. Phosphorus
Authors: Lewis DC , Clarke AL , Hall WB
Published: April 2005

The accumulation of phosphorus applied as superphosphate over a 25-year period to pastures growing on sand over clay soils was measured in three areas of different rainfall in the south-east of South Australia. Total soil phosphorus levels increased in the 0-10 cm, 10-30 cm and 30 cm-clay layers for all areas, but no accumulation occurred in the clay layer. For every 100 kg ha-1 of single superphosphate (9.6% phosphorus) applied, 2.0, 3.2 and 3.5 kg ha-1 of phosphorus accumulated in the 0-10 cm layer for the Hundreds of Coles, Willalooka and Senior respectively. The recoveries of applied phosphorus in the sand layer for the three areas were 42, 57 and 75% for Coles, Willalooka and Senior respectively. The annual accumulation rates of organic phosphorus in the top 30 cm of soil ranged from 2.4 to 3.5 kg ha-1. By using a 'balance sheet' approach, the annual maintenance phosphate requirements for the three areas were calculated. These ranged from 60 to 165 kg ha-1 of superphosphate, and were associated with differences in leaching losses, stocking rates and organic phosphorus accumulation.
Solute transport during unsteady, unsaturated soil water flow - the pulse input
Authors: Bond WJ
Published: April 2005

A general approximate analytical solution was derived for the movement and dispersion of a solute pulse during unsteady flow of water in unsaturated soils. Two types of pulse were considered: that arising from a non-uniform distribution of solute initially in the soil, and that arising from a change in concentration of solute in the water supply. The movement of pulses of tritiated water and chloride ion was investigated experimentally for the specific case of constant flux horizontal infiltration of water into a strongly aggregated, structurally stable clay soil. Good agreement between the measured distributions of tritium and those predicted using the approximate solution confirmed the validity of the approximate solution. Agreement was much poorer for chloride. The approximate analytical solution was also used to examine factors affecting the shape of solute pulses. It was found that pulses may be asymmetric at short times, but that they rapidly become symmetric as time increases.
The chemistry of shallow groundwaters in the Murrumbidgee irrigation area, New South Wales
Authors: Williams BG , Ward JK
Published: April 2005

The chemistry of shallow groundwaters in the Murrumbidgee Irrigation Area of New South Wales, Australia, is examined in terms of the degree of saturation with calcium minerals. Many water samples were found to be saturated with calcite, especially when brought into equilibrium with atmospheric CO2 pressures; gypsum saturation was found more frequently from regions having waters of high ionic strength. A thermodynamic chemical model is used to describe the effects on water 'quality', for irrigation purposes, if the groundwaters are to be reused in mixtures with irrigation supply water. A tentative classification in terms of salinity and sodium hazard is presented and a simple relationship between both hazards has been derived. A potential exists for using between 25% and 95% groundwater in mixtures with supply water for irrigation, depending on the initial salt concentration.
Variations in the properties of iron oxides within individual specimens of lateritic duricrust
Authors: Anand RR , Gilkes RJ
Published: April 2005

The morphologically distinct materials in Darling Range lateritic duricrust (i.e. loose and cemented pisoliths, concretions, matrix, pisolith coatings and void coatings) exhibit goethite/(goethite + hematite) ratios ranging from 0.15 for individual pisoliths to 1.0 for void coatings. Mole % Al substitution ranged from 20 to 34% in goethite and from 2 to 15% in hematite. Goethite and hematite in pisoliths and concretions were mostly highly Al substituted. Al substitution in goethite was positively related (P < 0.01) to Al substitution in hematite. Al substitution in maghemite was less than 5%. Goethite crystals ranged in size from 130 to 260 A. Hematite crystals ranged from 140 to 520 A, and were systematically smaller in pisoliths. Crystal size of goethite and hematite decreased with increasing Al substitution. Hematite crystals were usually about 50% larger than goethite crystals in the same sample, and crystal sizes of goethite and hematite were positively correlated (P < 0.01). Goethite and hematite occurred as aggregates of subrounded platy crystals. Differences in the properties of goethite and hematite between morphologically distinct materials in single hand specimens are indicative of the complex history of these duricrusts.
Spectroscopic and chemical differences in organic matter of two vertisols subjected to long periods of cultivation
Authors: Skjemstad JO , Dalal RC
Published: April 2005

The nature of a number of humic fractions extracted from the 0-0.1 m layers of two cracking clay soils was studied using 13C nuclear magnetic resonance and infrared spectroscopy. By comparing samples from sites under native vegetation and nearby sites which had been under continuous cultivation for cereal cropping for 35 years, two different mechanisms which act to protect organic matter against decline are evident. In both grey clays (Langlands-Logie clay) and black earths (Waco clay), a large proportion of the organic matter receives some degree of protection through association with clay. In grey clays, this is the only significant form of protection. The humic materials display little molecular recalcitrance and contain significant amounts of long alkyl chains and proteinaceous groups. In black earths, association of organic matter with clay is also the most significant factor but, in addition, the remaining humic materials are more stable to microbial attack. This results from higher aromaticity as well as shorter, more highly branched alkyl chains. Some implications of these findings are also discussed.
Reevaluation of the well permeameter as a field method for measuring hydraulic conductivity
Authors: Talsma T
Published: April 2005

Improved theory of steady outflow of water ponded to constant depth in holes drilled in unsaturated soil is used to re-evaluate the well permeameter method for measurement of in situ hydraulic conductivity, Kg. In particular, theory predicts that neglect of unsaturated flow into soil surrounding the saturated region around a borehole may lead to serious overestimation of K0, especially when using small holes in soils with high capillarity, i.e. the capillarity factor � = 0.1-1 m-l. Field studies on 12 soils gave a values from 6 to 35 m-l, resulting in theoretical overestimates of K0 by 10-40%, for boreholes >0.3 m deep and >0.03 m radius. Comparison of results obtained by measurements with this method for four soils, however, gave permeameter values of K0 which were approximately 50% of those obtained with the augerhole or the core method. Overestimation of K0 due to neglect of capillarity was, in all cases, more than offset by reduction in K0 due to pore closure around a hole during drilling and infiltration.
Calcified filaments - an example of biological influences in the formation of calcrete in South Australia
Authors: Phillips SE , Milnes AR , Foster RC
Published: April 2005

Scanning electron microscope (SEM) studies of calcareous soils and calcretes from South Australia reveal a fossilized community of soil micro-organisms dominated by filamentous structures preserved in fine detail by calcite. In the various calcrete lithological facies, the filaments form dense mats within channels and voids, and also occur within the matrix where they are intimately associated with micrite. The calcite forming the filaments has a variety of crystal habits: the nature of the microcrystals is specific to each filament but varies significantly between adjacent filaments. In the calcareous soils there are various stages between the primary filaments and the calcite encrusted structures characteristic of the calcretes, suggesting that in vivo biochemical processes dominate the mechanisms of calcification. This hypothesis is supported by the specificity of the habit of calcite microcrystals on each filament. It is suggested that the organisms deposit calcite microcrystals within the mucilaginous sheath or in the cell wall (or both) as a detoxification mechanism in response to their highly calcareous environment. Based on the identification of structures resembling fruiting bodies, at least some of the filaments appear to have been fungal hyphae, which are known to be responsible for stabilizing macroaggregates in soils. Calcified filaments may produce permanently stabilized macroaggregates which provide the locus for further carbonate precipitation, leading to eventual induration of the soil.
Muscovite in Darling Range bauxitic laterite
Authors: Anand RR , Gilkes RJ
Published: April 2005

Darling Range bauxitic laterite contains 0-17% silt size, Na-rich, 2M1 muscovite which is most abundant in laterite developed from granitic parent rocks. Muscovite grains show evidence of dissolution, but there has been no formation of dioctahedral vermiculite. Muscovite is clearly a much more resistant mineral than the feldspar, biotite and chlorite in the parent materials that have completely altered to secondary minerals. Muscovite is therefore a significant constituent of Darling Range bauxitic laterite and consequently poses problems in bauxite processing.
Soil physical conditions after six years of direct drilling or conventional cultivation on a silt loam soil in New Zealand
Authors: Francis GS , Cameron KC , Swift RS
Published: April 2005

Soil physical conditions following six years of cereals planted by direct drilling (DD) or conventional cultivation (ploughing, PL) are compared. Bulk density was higher in the top 200 mm of the DD soil but, with ploughing, bulk density was found to increase sharply and remain higher than DD below this depth. With DD, soil strength was consistently higher at most depths and aggregate stability was also higher. Earthworm numbers were at least 1.5 times greater in the DD plots. Infiltration rates were similar under both systems despite the lower total porosity and air-filled porosity of the DD soil. This was attributed to a more open and continuous network of pores in the DD soil. Root densities measured in the same year as the soil physical conditions were significantly higher in the surface 0-100 mm of the DD soil and also tended to be higher below 200 mm depth. In the sixth year of the trial, there was a significantly greater plant emergence in the DD soil than PL soil, although harvest grain yields were similar for both treatments.
Influence of fusarium oxysporum age on proportions of C, N and P mineralized after chloroform fumigation in soil
Authors: Ross DJ , Sparling GP , West AW
Published: April 2005

The influence of age of Fusarium oxysporum mycelia on mineralization in soil of their C, N and P contents following chloroform fumigation was determined with two soils from pasture of different productivity. The mineralization factors kc and kn could vary with mycelial age and, in prior-incubated soils, were lowest in the oldest (44-day) culture with the lowest cytoplasm and total N contents. Changes in kp with mycelial age showed no consistent trends. The use of k factors derived from physiologically young cells may lead to under-estimation of C and N in the indigenous soil biota.
Uncertainties in the measurement of soil water content caused by abrupt soil layer changes, when using a neutron probe
Authors: Wilson DJ
Published: April 2005

Multigroup diffusion code calculations have been made to model the changes in the thermal flux distribution as a fast neutron source passes through an interface between two soil systems. By integrating this flux over the volume of a detector attached to the source, a relative count rate can be determined for different source positions with respect to the interface. Water densities determined from these count rates and calibration curves can be seriously in error near the interface. The magnitude of these errors depends upon the soil parameters, the detector geometry, and the proximity of the soil strata to the neutron source and detector. Unless the soil structure is well known, it would be unwise to rely on water measurements closer than about 25 cm to a soil discontinuity. It two soils merge over 30-40 cm, it is likely that the measured water density will not deviate far from the real value.
Estimation of forms of Fe and Al - a review, and analysis of contrasting soils by dissolution and Mossbauer methods
Authors: Parfitt RL , Childs CW
Published: April 2005

Three methods have been used to extract iron (Fe) and aluminium (Al) from a wide range of soils. The three extractants were pyrophosphate reagent (p), acid-oxalate reagent (o), and dithionite-citrate reagent (d), and each reagent is thought to extract different forms of Fe and Al. The forms of Fe in the soils were studied before and after extraction using Moessbauer spectroscopy. Pyrophosphate-extractable Fe (Fep) does not specifically relate to any particular form of Fe in soils and it should not be used to estimate Fe in humus complexes. In some soils (e.g., Spodosol, Ochrept) Fep arises from Fe in ferrihydrite. In other soils (Ultisol, Hydrandept) Fep arises from goethite and ferrihydrite which is dispersed by pyrophosphate. Alp corresponds to Al in humus complexes and, in most soils, can be used to estimate Al in such complexes. Al and Si in allophane and imogolite were extracted in acid-oxalate reagent, and could be estimated from Alo-Alp and Sio, provided large amounts of ferrihydrite were not present. Ferrihydrite was also extracted in acid-oxalate reagent and, assuming complete extraction, could be estimated by multiplying Feo by the factor 1.7. Dithionite-citrate reagent dissolved goethite and hematite in addition to ferrihydrite. In some soils repeated extractions were required to dissoive most of the goethite and hematite. Quantitative estimates of Fe in goethite and hematite can be made from Fed -Feo. Other techniques, however, such as X-ray diffraction and Moessbauer spectroscopy, were necessary to identify iron oxides positively in most soils.
The effects of moisture regime and incubation period on the dissolution of North Carolina phosphate rock in soil
Authors: Kanabo IAK , Gilkes RJ
Published: April 2005

The effect of soil water content on the dissolution of reactive North Carolina phosphate rock (PR) in a lateritic soil was investigated in a laboratory incubation study. Soil-PR and soil-KH2PO4 mixtures were incubated at different water contents for different periods and dissolution of PR was followed by measuring the increases in exchangeable Ca (�Ca) in the soil. The phosphorus released (�P) was calculated from the composition of the PR. Increases in bicarbonate-soluble P (�Bic P) resulting from PR dissolution were also determined. Changes in both �P and �Bic P can be described by exponential functions of the form �P or �BicP = � - Bexp (-CW), where W is the gravimetric water content of the soil and A, B and C are constants. Little additional dissolution occurred for W > 13% which was about the water content at free-draining field capacity. For an incubation period of 280 days, PR dissolution increased from 4% for air-dry soil to 13% for W = 12.5%, increasing to about 17% for W = 100%. The �Bic P/�P ratio for KH2PO4-fertilized soil was initially much higher than that for PR, but decreased for both sources with period of incubation and values almost converged at 0.20 after 50 days. The effect of wet-dry treatments on AP was also investigated for soil amended to pH values of 3.76 and 5.09. After a 33 day contact period including three 2-day drying periods, there was 40% and 38% of PR dissolved for continuously wet and wet-dry treatments, respectively, at pH 3.76. The corresponding values for pH 5.09 were 22% and 21%. Therefore, these data indicate that a short drying period does not substantially affect PR dissolution (�P) and bicarbonate-soluble P (�Bic P) levels.
Effect of pH on the adsorption of phosphate and potassium in batch and in column experiments
Authors: Bolan NS , Syers JK , Tillman RW
Published: April 2005

The effect of increasing pH, through incubation with Ca(OH)2 and NaOH, on the adsorption of phosphate (P) and potassium (K) was examined in batch and in column experiments. In column experiments, an increase in pH from 5.2 to 8.2 decreased the adsorption of P and increased that of K which resulted in an increased leaching of P and a decreased leaching of K. In a batch experiment, however, an increase in pH resulting from incubation with NaOH gave similar results to those of the column experiment, whereas an increase in pH due to Ca(OH)2 addition caused the opposite effect on the adsorption of both P and K. The difference between the batch and the column experiments in the effect of incubating soil with Ca(OH)2 on the adsorption of P and K is related to the concentration of Ca in the soil solution.
Role of positive charge in the competitive effect of phosphate on sulfate sorption by an allophanic soil
Authors: Marsh KB , Syers JK , Tillman RW
Published: April 2005

The effect of phosphate (P) on the sorption of sulfate (S) by an allophanic soil with high surface positive charge was investigated in the pH range of 5.3-7.0 obtained by incubation with Ca(OH)2. The effect of P on S sorption was directly related to the effect of P on surface positive charge. At low soil pH, P reduced surface positive charge to a larger extent than at high pH and this was associated with a larger effect of P on S sorption.