bluuebunny/crossref_metadata_2025 huggingface dataset:
A 57Fe Mossbauer spectroscopic study of a selection of Australian and other goethites
Authors: Johnston JH , Norrish K
Published: April 2005

The 57Fe Mossbauer spectra recorded at room temperature for seven Australian and two U.S.A. goethite mineral specimens of various composition and extent of aluminium substitution, particle size and origin are presented. Eight of these exhibit six-line magnetic hyperfine spectra with differing hyperfine magnetic splitting and asymmetric line broadening, resulting from super-paramagnetic relaxation effects. The results show that the relation between the decreasing magnitude of the hyperfine magnetic splitting with both increasing aluminium content and decreasing particle size, as previously reported for aluminium-substituted goethites, does not hold generally for the natural goethites studied here. For these, such a relation is more complex and appears to depend, not only on the extent of aluminium substitution, but also on the other impurity substituents in the goethite specimens. These combined effects make it difficult to use the magnitude of H to measure the particle size or to relate the type of Mossbauer spectrum with the mode of occurrence of the goethite.
Effect of rainfall data errors on the optimized values of model parameters
Authors: Boughton WC , Sefe FT
Published: April 2005

The rainfall input to a rainfall-runoff model was arbitrarily increased and decreased in order to determine the magnitude of corresponding changes in optimized values of the model parameters. The optimized capacities of moisture stores representing surface storage capacity of a catchment changed by average amounts of +24% and -20% as rainfall input was changed by +10% and -10%, respectively. Values of other parameters showed changes of similar magnitude, but there was no uniformity in the magnitude of induced changes from catchment to catchment. The results cast doubt on the validity of relating optimized values of model parameters to physical characteristics of catchments.
Reversion of calcined calcium aluminium phosphate fertilizers due to rehydroxylation of crandallite
Authors: Palmer B , Gilkes RJ
Published: April 2005

Calcium aluminium phosphate fertilizers prepared by calcination of Christmas Island C-grade ore at temperatures between 400°C and 600°C are amorphous and soluble in neutral ammonium citrate. Hydrothermal treatment of calcines at temperatures between 60°C and 150°C for periods of up to one year resulted in various amounts of reversion to an insoluble form due to rehydroxylation and recrystalization of crandalite. The rate at which reversion occurs increases with increasing temperature of hydrothermal treatment. Reversion did not occur within one year at 45°C, and is therefore unlikeley to affect fertilizer performance in the field.
A statistical method for the estimation of trend in salinity in the river Murray
Authors: Cunningham RB , Morton R
Published: April 2005

A simple statistical model is proposed for the analysis of salinity measurements, and is illustrated in detail for chloride concentrations in the River Murray at Morgan, S.A., over a period of 43 years. We conclude that a positive trend has occurred over and above that associated with a decline in waterflow. Some insight into the form of the trend is provided by a moving average of the log-chloride concentration after allowing for waterflow effects. Despite such extensive data, the linear component of this trend is not precisely established, as is clear from the wide confidence limits.
Differences in the efficacy of various soil phosphate tests for white clover between very acid and more alkaline soils
Authors: Holford ICR
Published: April 2005

Fifty-four soils, ranging in pH from 4.0 to 8.1, were analysed for exchangeable phosphate, sorptivity, and extractable phosphate by five commonly used soil tests. Phosphate uptake and yield data for white clover were obtained from two experiments conducted under identical glasshouse conditions. Marked differences were observed between the very acid soils (pH <5.6), and the moderately acid to alkaline soils in the effects of phosphate sorptivity on extraction by soil tests and plant uptake of exchangeable phosphate. On very acid soils the soil tests containing ammonium fluoride and sodium bicarbonate were unaffected by sorptivity and were less effective as indices of available phosphate than on the other soils, while the opposite situation applied to the double-acid Mehlich test. Phosphate sorptivity had no effect on the critical levels of any soil tests on the very acid soils, contrasting with the previously demonstrated effects on sodium bicarbonate tests when used on moderately acid to alkaline soils. The sodium bicarbonate tests were the most effective, and the Mehlich test was the least effective on all soils regardless of sorptivity or pH. The results suggested that the major source of plant-available phosphate in moderately acid to alkaline soils is exchangeable phosphate, whereas in very acid soils it is non-exchangeable mineral phosphates associated with iron and aluminium.
A theoretical treatment of the effects of Ionic and non-ionic competitive adsorption during solute transport in soils
Authors: Barnes CJ , Aylmore LAG
Published: April 2005

The method of characteristics is used to analyse multi-species solute movement through a non-linearly reactive soil taking dispersion into account. Both ionic and non-ionic solutes are considered, and it is shown that the shape of a solute front depends on the shape of the adsorption isotherms. At large times, overall solute movement is effected by a series of solute fronts moving independently. The composition of each front, and hence individual solute concentrations within the front, are determined by the degree of competition reflected in the adsorption isotherms. Varying water contents are considered explicitly, although the detailed analysis is restricted to uniform water contents for simplicity.
Moessbauer parameters for ferrihydrites at 4 K
Authors: Childs CW , Dickson DPE , Goodman BA , Lewis DG
Published: April 2005

The Moessbauer spectra at 4.2K for five ferrihydrites (one natural, four synthetic) have been determined. Two of the samples contained silicon (atomic ratio Si/Fe= 18%, 21%) and one contained aluminium (Al/Fe = 19%). The Moessbauer parameters were calculated from peak positions estimated by a fit of one set of six Lorentzian lines to each spectrum and by judging absorption maxima by eye. Hyperfine magnetic field (H) values were between 50.0 and 50.4 T for pure samples and between 48.3 and 49.2 T for samples containing silicon or aluminium. Variations as small as these, due to impurities, would not prevent ferrihydrite being distinguished from lepidocrocite (H= 46.0 � 0.5 T for pure, well-crystallized material) in Moessbauer spectra of soil samples at 4.2 K.
A preliminary investigation of hardpan horizons in north-west New South Wales
Authors: Chartres CJ
Published: April 2005

Micromorphological, scanning electron microscope, electron microprobe, X-ray diffraction and chemical analyses of morphologically differing hardpan horizons show a wide range of constituent materials and interparticle cements. A number of different fabric elements occur within the hardpans. These include porphyroskelic zones with amorphous silica in the s-matrix, zones composed almost entirely of amorphous silica, chlamydic zones with clay coatings on skeleton grains, and zones of calcareous material filling fissures. A further porphyroskelic fabric type, in which the plasma consists of strongly oriented clay intimately mixed with isotropic material containing amorphous silica, was also recognized in one type of hardpan. Amorphous silica is the cementing agent within some of the fabric zones identified, but in the chlamydic zones, at least, clay minerals enriched in silica, iron and titanium, and depleted in aluminium, appear to be the cementing medium. Micromorphological evidence indicates a complex development of the hardpans with alternating phases of silica, clay and carbonate deposition.
The role of organic matter in soil acidification
Authors: Ritchie GSP , Dolling PJ
Published: April 2005

The pH and buffer capacity of two soils increased or remained constant after incubation with different amounts of plant material (lucerne cham at field capacity and when air dry. For both soils, the pH changes were greater at field capacity, whereas the buffer capacities were independent of the water treatments. The pH changes observed could be explained in terms of the organic anion concentration of the plant material. The results indicate that the initial soil pH and the anion concentration (i.e. the per cent dissociation of soluble organic acids when released into the soil) determine the acidifying effect of organic matter.
The effect of soil strength on germination and emergence of wheat (Triticum aestivum L.). II. High shear strength conditions
Authors: Collis-George N , Yoganathan P
Published: April 2005

Experimental studies on limiting soil strength conditions for germination and emergence of wheat are reported. From the experimental results in a fine, dense sand a quantitative estimate of the stresses at the organ/soil interface that will prevent seed and seedling expansion and hence prevent germination and emergence is made using the Spherical Cavity Expansion Theory of Vesic. Interfacial stresses of 3.0, 2.3, 1.7 and 0.8 MPa (=30, 23, 17 and 8 bar) are found to be limiting to germination, root elongation, coleoptile elongation and emergence of wheat respectively. These results are discussed in terms of a range of soils with different mechanical properties. The limiting stresses are interpreted in terms of the results obtained by the torsional shear box.
Quantifying the contribution from the soil microbail biomass to the extractable P levels of fresh and air-dried soils
Authors: Sparling GP , Whale KN , Ramsay AJ
Published: April 2005

Levels of P extractable in 0.5 M NaHCO3 and the microbial biomass C were measured on a range of 15 New Zealand pasture soils, with and without an air-drying treatment. The microbial biomass C, estimated using a modified substrate-induced-respiration method, was decreased 11-68% by air-drying. Two soils showed no increase in extractable inorganic phosphorus (P) levels after air-drying, but increases for the other 13 soils ranged over 14-184%. In general, the biomass C was not related to the overall P, levels of moist or air-dried soils. However, the increase in P, after air-drying was related to the microbial P content of the moist soil, estimated by CHCl3 fumigation, and the proportion of the biomass C killed by air-drying. A comparison of the actual measured Pi levels of dried soils and those estimated allowing for the microbial contribution, showed excellent agreement, strongly suggesting that the whole of the Pi increase on air-drying of soils was derived from killed microbial cells. The microbial contribution to Pi levels in NaHCO3 extracts of dried soils ranged over 4-76% and was therefore a significant large proportion in some soils. A large microbial contribution to Pi in extracts is most likely on air-dried soils from under pasture with >2% organic matter and NaHCO3-extractable P values of <20 �g g-1.
Influence of organic matter and phosphate content on the point of zero charge of variable charge components in oxidic soils
Authors: Gillman GP
Published: April 2005

The point of zero charge of the variable charge components (pH,) of oxidic soils formed on basaltic parent material in humid tropical Queensland has been measured on samples from virgin rainforest and cultivated fertilized fields. The average amount of free iron in these soils is about 10%. Soils with low organic matter content and low extractable phosphorus have high pH, values. Regression analysis showed pH, to be reduced by about one pH unit for each 1% increase in organic carbon or for each 100 �g/g increase in extractable phosphorus. Implications with respect to cation and anion exchange capacities are briefly discussed.
The influence on soil properties of mould oil used in sample cores
Authors: Dowling AJ , Shaw RJ , Berthelsen S
Published: April 2005

Mould oils, with up to 10% v/v oleic acid, in a distillate carrier, are useful lubricants and release agents for thin-walled tube-core sampling of wet plastic clays and moist sandy soils. Mould oil with 2% v/v oleic acid interferes with soil organic carbon determinations because of hydrocarbon residues. There are minimal effects on electrical conductivity and gravimetric soil water content. Sparing and careful use of all lubricants in soil sampling is required, with special care where organic carbon content is a measured soil property.
The effect of rock phosphate properties on the extent of fertilizer dissolution in soils
Authors: Hughes JC , Gilkes RJ
Published: April 2005

Two soils, a West Australian Petroferric Udipsamment (WA4) and a Colombian Typic Haplustox (SA21) were incubated for up to 31 days with 23 phosphate fertilizers. These comprised 18 apatitic rock phosphates, three calcined rock phosphates, monocalcium phosphate and dicalcium phosphate. The fertilizers were mixed through the soils at rates of addition between 0.37 and 37 mg g-' soil. The extent and rate of dissolution of fertilizers were measured by determining changes in Ca using the ACa technique. Most dissolution generally occurred within one day for all fertilizers. The proportion of fertilizer that dissolved decreased with increasing rate of addition, and this proportion differed greatly between fertilizers (1-43% in WA4, 2-72% in SA21). All fertilizers dissolved to a greater extent in the Colombian soil. Calcined (1500�C) Queensland rock phosphate was the most soluble of the rock phosphates, which is consistent with its high availability to plants. The calcined iron-aluminium rock phosphates (Calciphos, Phospal) dissolved to a smaller extent than most of the apatitic rocks. The CaO/P2O5 ratio of the apatitic rock phosphate fertilizers was a slightly better predictor of the extent of dissolution than the apatite unit cell a dimension, although neither explained more than 60% of the variance. The present results are consistent with the accepted reactivity scale for the apatitic fertilizers, but the amount of each fertilizer which dissolved depended greatly on the soil to which it was applied.
Inhibition of soil urease activity and nitrification with some metallic cations
Authors: Yadav DS , Kumar V , Singh M
Published: April 2005

Investigations to study the effects of 14 metallic cations on urease activity and nitrification rate in Hansi clay loam (Typic Ustochrepts) were undertaken at Haryana Agricultural University, Hissar, Haryana (India). The metallic cations inhibited soil urease activity, and the order of effectiveness varied when compared at 100, 500 and 1000 ppm. Increasing levels of metallic cations adversely affected the urease activity. Inhibitory effects of metallic cations at 1000 pprn decreased in order: Ag+ = Hg2+ > Cu2+ >Cd2+ > Co2+ >Ba2+ > Zn2+ > Ni2+ > Fe2+ > Cr3+ > Mn2+ > Sr2+ > Pb2+ > Al3+. Effects of Cr3+, Cu2+ and Hg2+ on nitrification were also tested. Above 80% of added N was nitrified at 21 days in the control (urea alone) and 100 ppm Cr3+ treatments, whereas addition of 500 and 1000 pprn cr2+ and 100, 500 and 1000 pprn Cu2+ delayed nitrification. A considerable amount of NH+4- remained unchanged in Hg2+ -treated soils after 28 days of incubation; these soils also contained more residual NO-2 than other treatments.
The dispersal of automotive lead from metropolitan Adelaide into adjacent rural areas
Authors: Tiller KG , Smith LH , Merry RH , Clayton PM
Published: April 2005

About 600 surface samples and key horizons of 240 soil profiles from a 90 x 20 km study area extending from the metropolitan area of Adelaide, South Australia, to its rural hinterland, were analysed for lead. Atmospheric fallout was collected monthly at 19 locations for 2 years, and up to 3 years at fewer sites in the same area. Lead in atmospheric fallout showed little year-to-year variation and tended to be seasonally controlled with highest values in winter. Collection of lead in fallout was unaffected by the filtering action of vegetation. The lead content of surface soils and atmospheric fallout showed that part of petrol-lead emitted within Adelaide from automotive exhausts has measurably contaminated the rural landscape to about 50 km downwind of the city. The variation in lead content of surface soils in the agricultural region near Adelaide can be largely explained in terms of accessions of aerosol-lead of automotive origin. This research complements previous investigations which showed that the lead isotopic compositions of selected soils were close to the composition of the lead tetraethyl used in South Australia. An environmental budget showed that only 3% of the lead in petrol burned in Adelaide has been dispersed via the atmosphere beyond the immediate highway zone, and deposited on the land surface within 50 km of the city centre. On the assumption that no more than 35% of the lead is retained within the vehicle, and that about half of the total burned lead is deposited near the roadway, the 30% of the total lead which cannot be accounted for (about 200 t at the time of this study) has probably dispersed beyond the study region and should be viewed as a contribution to continental and global pollution. Lead levels measured in rainfall, air and soils were low in relation to the accepted standards and experience. Although the lead levels were low, this investigation indicates the likely dispersal pattern of other pollutants with similar atmospheric residence times, and thus provides guidance to planning decisions concerning placement of polluting industries, and in relation to possible industrial accidents which cause pollution.
The absence of leaching of molybdenum in acidic soils from Western Australia
Authors: Riley MM , Robson AD , Gartrell JW , Jeffery RC
Published: April 2005

A glasshouse experiment was conducted to estimate the extent of leaching of molybdenum on acidic sandy soils from Western Australia. Sodium molybdate, at a rate equivalent to 40 g of molybdenum per hectare, was added to pots of soil either before or after leaching a column of the soil with the equivalent of 500 mm water. Molybdenum concentrations were determined in the leachate and in the wheat plants grown on the soils in pots after leaching. Approximately 10% of added molybdenum was removed with leaching from two grey sands, while negligible quantities were removed from three more acidic sandy soils. Leaching does not appear to be an important factor in the occurrence and recurrence of molybdenum deficiency on the yellow-brown acidic sandplain soils of the Western Australian wheatbelt.
Accumulation of plant nutrients and changes in soil properties of sandy soils under fertilized pasture in southeastern South-Australia .II. Total sulfur and nitrogen, organic carbon and pH
Authors: Lewis DC , Clarke AL , Hall WB
Published: April 2005

The accumulation of total sulfur in sand over clay soils growing improved pastures was measured in three areas of the south-east of South Australia. Accumulation rates in the top 10 cm of soil ranged from 4.6 to 6.3 kg ha-1 yr-1 and in the 10-30 cm layer from 1.3 to 3.7 kg ha-1 yr-1. Assuming all of this sulfur came from applied single superphosphate, the recoveries of applied sulfur in the sand layer were 42, 63 and 57% for the Hundreds of Coles, Willalooka and Senior respectively. Using a 'balance sheet' approach, the calculated annual maintenance superphosphate rates, that will supply sufficient sulfur, ranged from 110 to 250 kg ha-1. Total soil nitrogen accumulation rates were 55, 48 and 37 kg ha-1 yr-1 for the Hundreds of Coles, Willalooka and Senior respectively. The enhanced nitrogen accretion in Coles was attributed to improved legume production resulting from both increased superphosphate dressings and higher average annual rainfall in that area. Organic carbon levels were highly correlated with pasture age, with increases in the top 10 cm of soil ranging from 0.022% to 0.034% per year. Soil pH was highly correlated with pasture age, with decreases as large as 0.036 units per year in the top 10 cm and 0.025 units per year in the 10-30 cm layer measured in the Hundred of Willalooka.
The size and horizon of origin of fragments produced by deep ripping texture contrast soils
Authors: Blackwell PS , Green TW , Olsson KA
Published: April 2005

Two texture contrast soils were cultivated by deep ripping when they were drier than their lower plastic limits. The size distribution and soil horizon-of-origin of the resulting fragments were measured. One soil, a transitional red-brown earth, had either been previously uncultivated below the A horizon or had been deep ploughed and gypsum added two years previously. There was much fragmentation and mixing of soil from both of the horizons. Fine soil (<2 mm diam.) from the A horizon reached the lower depths of the trough made by the ripping and coarse soil from the B horizon (>50 mm) was brought to near the surface. The fragment size distributions were characteristically bimodal. Fragments of the fine mode (<2 mm) came mainly from the A horizon, fragments of the coarse mode (11-25 mm or larger) came mainly from the B horizon. In the laboratory, clods from the deep ripped soil were crushed at the same low water potential (air dry). The crushing energy per unit mass (specific crushing energy) was inversely proportional to the normalized geometric mean diameter of the fragments produced. Suggestions are made for modelling the effects of deep ripping.
Corrigenda - The effect of Aeolian accessions on soil development on granitic-rocks in south eastern Australia. I. Soil morphology and particle-size distributions
Authors: Walker PH , Chartres CJ , Hutka J
Published: April 2005

Four Alfisols in south-eastern Australia were studied to determine their genesis with special reference to textural profile development and aeolian accession. Sampling sites were located in erosional terrain developed from granitic rocks of similar composition and in hillcrest positions to reduce the chance that colluvial deposition had affected pedogenesis. The sampling transect was placed in such a way that differences in regional aeolian accession could be reflected in soil properties. The chemical and physical characteristics of these soils indicated that strong leaching had been important in their genesis. Detailed particle-size data confirmed that the coarsest fractions in all profiles were derived from weathered granite. The A horizons tended to have a single size mode in the sand range and very little clay-size material. The B horizons tended to be bimodal with the greatest amount of clay in the 0.12-0.06 �m size class and a mode in the sand range close to that of the A horizons. The appearance of a peak in the 62-31 �m size class, which is progressively stronger in the western sites, probably relates to a fine aeolian accession which has penetrated the B and C horizons. The amount of clay contributed by aeolian accession to textural B horizons is unknown. At erosional sites in south-eastern Australia, where the probability of colluvial and fluvial sedimentary layering is minimal, aeolian accession of fine fractions has complicated the interpretation of pedogenesis.
Comparison of microbial C, N-flush and ATP, and certain enzyme activities of different textured soils subject to gradual drying
Authors: West AW , Sparling GP , Speir TW , Wood JM
Published: April 2005

A clay loam, a silt loam and a sand soil were gradually dried from field moisture content to air-dryness at 25�C in the laboratory. Microbial C measured by substrate-induced respiration (SIR), fumigation-incubation (FI) and fumigation-extraction (FE), microbial N-flush measured by FI and FE, microbial ATP content, and soil phosphatase and sulfatase activities were monitored throughout a drying period of approx. 60 h achieved over 16 days. All the microbial and enzyme variables declined as the gravimetric soil water content ( W) decreased to air-dryness. In general, the relationship between microbial C or N-flush and W was linear, but was exponential between ATP or phosphatase and W. Soil texture appeared to affect the rates of decline and also the amounts of the microbial and enzyme variables remaining in air-dry soil; e.g., the lowest rate of microbial C decline and the largest amount remaining at air-dryness occurred in the clay loam soil. Sulfatase activity was not significantly affected by soil drying. Agreement between the SIR and FE estimates of microbial C was good (r = 0.92***). These two methods were applicable over a wide range of water contents. Microbial N-flush, estimated by the FE method, also showed a consistent trend and correlated highly with microbial C estimated by SIR or FE. In contrast, microbial C and N-flush estimated by the FI method were not significantly correlated with W or any of the other variables. ATP and phosphatase activity appeared to relate more closely to microbial activity (CO2 respiration/microbial C) than microbial mass. The reliability of the methods to measure the biomass and the influence of soil texture, water and carbon contents on microbial survival are discussed.
Indexes of residual shrinkage to quantify the comparative effects of zero and mechanical tillage on a vertisol
Authors: Mcgarry D , Smith KJ
Published: April 2005

Differences in the soil physical condition of the surface layer of a Vertisol (near Warwick, Queensland) under a zero versus mechanical tillage trial were investigated by using indices derived from a limited part of the soil's shrinkage curve. Shrinkage data were generated by coating initially air-dry clods in SARAN resin, then oven-drying them in six temperature increments to 105�C. Values of both the slope and y-axis intercept of a straight-line fit to the data were significantly greater in the mechanically tilled treatment. This showed that mechanical tillage led to decreased bulk density (increased porosity) and caused the soil to have greater shrinkage potential.
A description of acid soils and the relationships between properties of acid soils and the nutrient status of grazed pastures in the southeast of South Australia
Authors: Hodge TJV , Lewis DC
Published: April 2005

Areas of low soil pH in the south-east of South Australia were delineated by using previously submitted soil samples and soil association maps. A survey was then undertaken in the major soil associations to determine the severity and characteristics of highly acid soils. The acid soil types identified were a siliceous sand over clay (Db/Dy) and a siliceous sand over organic matter/sesquioxide pan (Uc). The top 2.5 cm of both soil types was significantly less acid than the remaining portion of the A horizon, with pH decreasing rapidly with depth until the B horizon, where a substantial soil pH increase occurred. As soil pH (0.01 M CaCl2) decreased below 4.5, extractable soil aluminium (0.01 M CaCl2) increased rapidly, to a maximum extractable concentration of 17 �g g-l. These soil types were also found to be deficient in both phosphorus and potassium, with 65% of the sites having extractable phosphorus concentrations below the critical value of 20 �g g-1 and 35% below the critical value for extractable potassium of 80 �g g-l. For subterranean clover, significant positive correlations were observed between soil pH and plant calcium and sulfur, and between extractable soil aluminium and plant aluminium. Significant negative correlations were observed between soil pH and plant manganese and between extractable soil aluminium and plant calcium and magnesium. For ryegrass, significant positive correlations were observed between extractable soil aluminium and plant aluminium and manganese. Significant negative correlations were observed between soil pH and plant manganese and between extractable soil aluminium and plant calcium. No other significant correlations were obtained. The results are discussed in relation to further acidification and management of these acid siliceous sands.
Generation of microcracks in molded soils by rapid wetting
Authors: Grant CD , Dexter AR
Published: April 2005

Tillage of compacted or of puddled and remoulded soils is a major agronomic problem internationally. The natural regeneration of microcracks (tilth mellowing) prior to the cultivation of such soils can reduce the energy needed to work them. Rapid wetting, under certain conditions, plays a major role in developing cracks in structurally damaged soils. This study reports the use of different initial water contents and wetting rates to examine the development of 'new' soil structure, described mechanically by tensile strength, and optically by measurements of the relief of fractured soil surfaces. New terminology is introduced to describe the rate of wetting needed to induce mellowing and to describe the rugosity of soil fracture surfaces. Rapid wetting was found to induce microcracking in soils, even with initial matric potentials as wet as -1.0 to -1.5 MPa. Implications for water management are briefly considered. Visual and analytical evidence from photographs and computer images indicates that internal microcracking is almost always detectable whenever the wetting rate is sufficiently high to reduce the soil tensile strength.
Shallow soil monoliths for laboratory studies on soil erosion from undisturbed soil surfaces
Authors: Kinnell PIA , McLachlan C
Published: April 2005

Details of a sampling frame for obtaining 500 mm long, 250 mm wide and 100 mm high soil monoliths for soil erosion studies under laboratory conditions are given. A procedure for obtaining and transporting the monoliths intact to the laboratory is outlined. Preliminary results from tests on the susceptibility of a few soil surfaces to erosion by rain-impacted flow are presented.
The role of Ca-organic interactions in soil aggregate stability .II. Field studies with 14C-labeled straw, CaCO3 and CaSO4.2.H2O
Authors: Muneer M , Oades JM
Published: April 2005

Uniformly 14C-labelled straw with or without CaCO3 or CaSO4.2H2O was incubated in a leached, fine sandy loam in the field. The addition of both Ca salts increased the residual 14C in the soil after several months decomposition, CaSO4.2H2O being more effective than CaCO3 in this respect. Addition of the Ca salts decreased the amount of dispersible clay and increased the proportion of particles 50-250 �m diameter. The addition of 14C-labelled wheat straw (with or without CaSO4.2H2O or CaCO3) increased the stability of aggregates >2000 pm diameter. Addition of Ca during decomposition of straw resulted in a synergistic stabilization of aggregates >1 mm. Moreover, the stabilization was prolonged in the presence of Ca.
Rill erosion of a self-mulching black earth. II. Comparison of sediment transport equations
Authors: Loch RJ , Maroulis JC , Silburn DM
Published: April 2005

Data obtained from a study of the effects of three tillage treatments on rill erosion of a self-mulching black earth were used to assess three sediment transport equations that are used, or suggested for use, in process-based models of soil erosion. The equations tested were those of M. S. Yalin, of C. T. Yang as developed by I. D. Moore and G. J. Burch, and a simplified equation reported by Yang. The three tillage treatments studied caused differences in rill flow that were reflected in Manning's n values ranging from 0.028 to 0.069 at the highest discharge. The two Yang equations gave better predictions of measured sediment concentrations than that of Yalin, with the simplified equation of Yang giving the least variable predictions. Both Yang equations appeared to be overly sensitive to variations in values of Manning's n coefficient.
The physical environment of two semi-arid tropical soils with partial surface mulch cover
Authors: Bristow KL , Abrecht DG
Published: April 2005

The seedbed microenvironment in soils with partial surface mulch cover will be affected by the width of the bare row zones. In this paper we compare seedbed conditions under four bare row widths [0 cm (completely mulched), 5 cm, 15 cm and completely bare] during a drying cycle in a loamy sand and clay loam soil in a semi-arid, tropical environment. It is shown that for both soils the rates of drying were greatest in the bare soil and least in the mulched soil, with the 5 and 15 cm bare row width treatments showing trends which were intermediate between the two extremes. Although soil surface temperatures were not noticeably different between the two soils, differences at depth became substantial as the soils dried, with the maximum temperature at 5 cm depth in the loamy sand exceeding that in the clay loam. There was also a steepening in the temperature gradient with depth as the soils dried. Under both wet and dry conditions, maximum temperature at 5 cm depth increased significantly with bare row width up to a width of about 25 cm which, for mulch of negligible height, approximates a bare soil. Results of this work demonstrate the benefits of maximizing surface mulch cover in the semi-arid tropics.
Rapidly extracted (0.02 M CaCl2-soluble) reactive aluminum as a measure of aluminum toxicity in soils
Authors: Close EA , Powell HKJ
Published: April 2005

This paper examines the use of short extraction times, and the determination of aluminium with chrome azurol S (CAS), for the estimation of 0.02 M CaCl2-soluble aluminium in soils. It reports the correlation between CAS-reactive aluminium in 5 min extracts and percent maximum yield of white clover (Trifolium repens) for a series of acid soils. The reactivity of soluble and colloidal aluminium species with the metallochromic reagent CAS has been assessed. ~ l ( a q ) ~ + , simple hydroxy species and complexes of weakly binding ligands (salicylic acid, tannins) are CAS-reactive (2 rnin). In contrast, complexes of strongly binding ligands (citric acid, fulvic acid) are not CAS-reactive ([Al] ~ [L] ~ [CAS] ~ 1-2~10-5 M). For a series of six limed phosphated topsoils and subsoils (pH 4.2-5.5), 0.02 M CaCl2- soluble aluminium, as determined with CAS, was negatively correlated against the percent maximum yield of white clover; r2 = -0.73** (5 min extraction), n = 20. This correlation is similar to that for yield against total aluminium as determined by atomic absorption spectroscopy after 60 min extraction (r2 = -0.77**). However, the colorimetric analysis is more convenient and sensitive; further, it does not measure colloidal and polymeric aluminium species (which may not be plant-available). The satisfactory correlation achieved for short extraction times suggests use of CAS for a rapid field method for aluminium toxicity in soils.
A field method for exchangeable (1M KCl extractable) aluminum(III) in soils
Authors: Close EA , Powell HKJ
Published: April 2005

A rapid method for estimation of exchangeable (1 M KCl extractable) aluminium(III) in soils is reported. It involves a 5 min extraction of a measured volume of soil, followed by incremental addition of the supernatant to the metallochromic reagent chrome azurol S (CAS) in hexamine buffer (pH 4.9). Formation of Al (CAS) (purple) from CAS (amber) is rapid. Iron(III) is masked by ascorbic acid. The intermediate colour of the resultant solution containing complexed and non-complexed CAS is compared with standards in polystyrene cuvettes. Tests on 17 soils with KCI-extractable aluminium levels in the range 50-850 mg kg-1 established that aluminium extracted in 5 min (X, mg kg-') is related to the 16 h value (Y, mg kg-1) by Y = 1.43X+ 32; r2 = 0.962**); an approximate conversion factor of 1.5 (Y = 1 .50 X) was applied to all measured values to estimate soil alumimium values.
The influence of alternative tillage systems on the distribution of nutrients and organic-carbon in some common Western Australian wheatbelt soils
Authors: White PF
Published: April 2005

The effect of reduced cultivation on the chemical fertility of three agricultural soils important in Western Australia was investigated. The experiment compared the effect of different tillage systems for continuously cropping wheat on the distribution of extractable P, extractable K, total N, organic C and pH for soils ranging from a sand to a sandy clay loam. Three tillage systems were applied (conventional cultivation, direct drilled with a combine, direct drilled with a triple disc drill) and the distribution of nutrients was measured to a depth of 25 cm. Developments were monitored for a period of 9 years. Clear differences between treatments were evident within the first 3 years of the experiment. Relative differences between treatments remained constant after this time. The concentrations of extractable P, extractable K, total N and organic C in the soil were all higher with direct drilling than with conventional cultivation, regardless of soil type or environment. The concentration of these elements declined in all treatments throughout the duration of the experiment. Major differences between treatments occurred in the surface 5-10 cm of the soil, although trends differed slightly depending on the element measured. Ammonium nitrate application substantially reduced the pH of the sandy soil, regardless of tillage treatment, but had no effect on the other soil types. Conventionally cultivated sandy and sandy clay loam soils also had a slightly higher pH than the direct drilled soils. The yield of plants was not directly related to the concentration in the soil of any elements measured. Accumulation of nutrients near the surface indicated that, if the surface soil is dry, then nutrients may be less available to plants established with direct drilling than with conventional cultivation. Further research is needed to establish whether present 'soil testing-P recommendation' relationships, based on conventional cultivation systems, are appropriate under direct drilling systems in Western Australia. Changes in pH with different tillage systems may have a bearing on fertilizer application strategies. Finally, the decline in organic C with conventional cropping indicates that the structure of soils in this experiment remains fragile even with direct drilling.
Use of the neutron method in assessing the changes in soil strength of undisturbed and ameliorated transitional red-brown earths during soil drying cycles
Authors: Jayawardane NS , Blackwell J
Published: April 2005

The relationships between penetrometer resistance (qp) and volumetric moisture content (�v) measured using the neutron method in an undisturbed transitional red-brown earth and after an~elioration by application of surface gypsum and slotted gypsum were examined. A very highly significant (P < 0.001) negative correlation was obtained between qp and �v in all treatments. The low r2 values of the regressions were attributed to heterogeneity in strength characteristics of the soil matrix, due to presence of cracks and macropores and the associated wetting patterns. The qp at any given e, was significantly reduced in the slots with lower bulk density compared to the undisturbed soil. The differences in qp- �v relationship of the undisturbed part of the soil under different ameliorative practices were attributed to changes in the swelling characteristic, and hence in the bulk density at any given �v of the undisturbed soil, caused by the presence of gypsum and the slots. Regression equations between qp and neutron count rate (n) for the undisturbed soil and for the slots were developed by combining the qp on �v relationships with the neutron meter calibration for �v measurements. The use of these regression equations and measured n values to predict changes in soil strength profiles during a wheat crop drying cycle in an undisturbed and ameliorated transitional red-brown earth was evaluated on another experimental site. There were no significant differences between the predicted and measured qp values in the non-ameliorated soil and the gypsum-slotted soil. Significant differences were observed between the predicted and measured qp values in the surface gypsum applied soil. The study shows the potential for using the neutron method as a convenient in-situ field technique to predict qp profile changes, preferably using qp on n relationships developed at the experimental site.
Resistance to water uptake by irrigated potatoes on a duplex soil
Authors: Rab MA , Olsson KA , Willatt ST
Published: April 2005

Resistances to water flow were analysed for the soil-root system of a potato crop growing on a duplex soil-where soil hydraulic properties varied with depth-under two irrigation regimes: 'wet' (irrigated weekly) and 'dry' (irrigated twice only during the growing season). The relative magnitudes of the soil and plant resistances controlling root water uptake were evaluated over depth and time using field-measured soil hydraulic properties and root length densities in successive soil layers. Resistance to water flow in the root system is likely to be the dominant resistance in the liquid phase, although soil resistance increased more rapidly than plant resistance with decreasing soil-water matric potential and root length density. Soil resistance reached similar values to plant resistance only when the soil-water matric potential was in the range -900 kPa to -1500 kPa (corresponding soil hydraulic conductivities of 10-7 and 10-8 m day-1 respectively), depending on the root length beneath unit ground area in the soil layer, La. Poor utilization of water from depth of this soil was attributed to resistance in the root system (possibly radial) associated with low La. Practical considerations for improved water management of the potato crop on clay soils are discussed.
Acidification of soils on a transect from plains to slopes, south western New-South-Wales
Authors: Chartres CJ , Cumming RW , Beattie JA , Bowman GM , Wood JT
Published: April 2005

Samples were collected from unimproved road reserves and adjacent paddocks on a 90 km transect crossing red-brown earth soils in the west and red earth soils in the east. Measurements of pH in water and CaCl2 indicated that the red earths have been acidified by approximately 0.5 pH units over the last 30-40 years. Small increases in CaCl2-extractable A1 were also recorded for the acidified red earths. The red-brown earths do not appear to have been markedly affected by soil acidification to date. Clay mineralogical data and measurements of cation exchange capacity of the <2 �m fraction indicate that red-brown earths are better buffered against acidification than red earths. However, small differences in management practices and rainfall along the transect may also be partially responsible for differences in acidification between soil types.
Long term trends in fertility of soils under continuous cultivation and cereal cropping in southern Queensland .VIII. Available nitrogen indexes and their relationships to crop yield and N uptake
Authors: Dalal RC , Mayer RJ
Published: April 2005

Six major soil series of southern Queensland were studied for the changes in the levels of available N indices (determined by both biological and chemical methods) and nitrate-N, with continuous cultivation and cereal cropping for up to 70 years. The biological N indices, measured in soil collected at planting of winter cereals, were anaerobic mineralizable N, aerobic mineralizable N and nitrate-N down to 1.2 m depth. The chemical indices were autoclave N and oven N. The predictive capabilities of various available N indices, and total N and organic C, were assessed from dry matter and N uptake of winter cereals in the field in 1983 as well as in the glasshouse. Anaerobic mineralizable N levels increased with mean annual rainfall but decreased with mean annual temperatures of the sampling sites of the six soil series. Therefore, it was possible to predict closely anaerobic mineralizable N from soil total N, and mean annual rainfall and temperature. Autoclave N showed no such trends. Anaerobic mineralizable N declined with period of cultivation, exponentially in Waco, Langlands-Logie and Cecilvale soils (0.112, 0.111 and 0.247 year-1, respectively) and linearly in the other three soil series. No consistent trends were discerned in autoclave N and oven N in four of the soil series with period of cultivation. Generally, nitrate-N (measured at planting) declined with period of cultivation. However, in Billa Billa soil, it increased in the soil profile (0-1.2 m) during the initial 7 years of cultivation and declined rapidly after 12 years. Although a number of available N indices, including total N and organic C, were significantly correlated with crop dry matter yield and N uptake, the best prediction of crop performance was provided by a combination of anaerobic mineralizable N (0-0.3 m) and nitrate-N (0-0 6 m) in the six soil series.
Soil erosion processes and nutrient loss. II. The effect of surface contact cover and erosion processes on enrichment ratio and nitrogen loss in eroded sediment
Authors: Palis RG , Okwach G , Rose CW , Saffigna PG
Published: April 2005

Thirty-five erosion experiments, involving four levels of surface contact cover by corn stalks and corn leaves (the latter represented by flat metal sheets) on three slopes, were carried out under simulated rainfall to investigate the effect of fractional surface contact cover and type on the loss and enrichment ratio (ER) of nitrogen in eroded sediment. All experiments were in a tilting flume of the simulated rainfall facility with a sandy clay loam soil. Experiments with rainfall detachment as the only erosion process were conducted on a low slope of 0.1%, to prevent entrainment occurring. The simulated rainfall rate was 100 mm h-1, and sediment samples were collected at the flume exit for up to 40 min. In experiments with entrainment as the only erosion process, clear water was applied as runon at the top of the flume. A stream power of 0 33 W m-2 was used and maintained with entrainment alone and in experiments with rainfall and runon combined for both 3 and 6% slopes. Sediment samples were fractionated through a series of sieves and total nitrogen was analysed for each size range to give the enrichment ratio (ER). The aggregate size or settling velocity characteristics, enrichment ratio (ER), and total nitrogen loss of the eroded sediment varied considerably with slope and cover types for the different erosion experiments. As cover by corn stalks increased, the settling velocity characteristics of eroded sediment became finer; the degree of this fineness was greater than when simulated leaves provided the same cover. For the rainfall detachment alone experiments, values of ER were greater than unity for both cover types and slopes, and greater than values for all other experiments. For the combined rainfall and runon experiments, ER was higher for corn stalks than simulated leaves. For experiments with entrainment alone, values of ER were close to unity for both cover types and slope, even by the early sampling time of 0.6 min. It may be concluded that the effectiveness of cover in reducing nutrient loss lies in reducing sediment loss, not in reducing ER. When rainfall detachment and entrainment were applied together, sediment concentration and total nitrogen loss were substantially increased over the sum of the contribution of rainfall detachment and entrainment acting alone. This finding indicates synergism in nutrient loss between these two erosion processes.