bluuebunny/crossref_metadata_2025 huggingface dataset:
Survival of the take-all fungus in the presence and absence of susceptible grasses
Authors: Cotterill PJ , Sivasithamparam K
Published: April 2005

A field trial was conducted to compare the effect of depth on inoculum of Gaeumannomyces graminis var. tritici under grasses and bare-fallow. Soil was sampled from 0-5, 5-10 and 10-15 cm depths in March, October and December 1986. Sample bioassays were carried out to determine infectivity, propagule number and to evaluate the contribution of different sized particles to the total soil-borne inoculum. A pot experiment examined the conduciveness of the respective soil samples to take-all. Grasses were effective in the carry-over of the field inoculum of the take-all fungus. In grass plots, infectivity was similar at the three sampling dates, although propagule number increased with time. In fallow plots, infectivity and propagule number declined progressively. Inoculum level fluctuated with time in both treatments, mainly in the 10-15 cm layer, and was most stable in fallow plots at 5-10 cm. Infectivity increased with increase in propagule size and the larger propagules were more infective at l2�C rather than 20�C. There was no difference between the conduciveness of soils from each layer in fallow plots, but in grass plots conduciveness increased with depth. Infectivity and propagule number of the fungus at respective depths appeared to be related to organic matter, conduciveness and fertility of the soil.
Phosphorus cycling in wheat pasture rotations .II. The role of the microbial biomass in phosphorus cycling
Authors: Mclaughlin MJ , Alston AM , Martin JK
Published: April 2005

The incorporation of phosphorus derived from fertilizer and plant residues into the soil microbial biomass was studied under field conditions by using isotopic double labelling. The 33P-labelled medic residues (Medicago truncatula cv. Paraggio) and 32P-labelled fertilizer were added to a solonized brown soil (Calcixerollic xerochrept) before sowing of a wheat crop ( Triticum aestivum cv. Warigal). Amounts of 31P, 32P and 33P in the microbial biomass were determined at 0, 7, 18, 32, 46, 61, 81 and 95 days after sowing of the wheat. Throughout the experiment, amounts of 31P in the microbial biomass were closely related to gravimetric soil water content, with a large and rapid increase in the amount of 3 1 ~ in the microbial biomass being observed in the first 7 days after wetting of the (initially) dry soil. Due to banding of the fertilizer at sowing, little (<5%) of the 32P was recovered in the microbial biomass throughout the experiment. Of the 33P applied in the medic residues, 22-28% was recovered in the microbial biomass. Most of the P taken up by the microbial biomass was derived from native soil P (i.e. not added that season).
Effects of urea rates, farmyard manure, CaCO3, salinity and alkalinity levels on urea hydrolysis and nitrification in soils
Authors: Kumar V , Yadav DS , Singh M
Published: April 2005

The effects of urea concentration, farmyard manure, CaCo3, pH and EC levels on urea and nitrification rates in different Indian soils at constant temperature (25 � 1�C) and moisture (50% WHC) were studied. The hydrolysis rate of urea was not proportional to the amount of urea added. In all cases, hydrolysis was completed within 6 days, except with 16.64 dS m-1 EC and 4% and 8% CaCO3 treatments. An increase in CaCO3, pH and EC levels inhibited urea hydrolysis. The NH4+ concentration increased up to 6 days and then decreased up to 24 days, with a corresponding increase in the NO3- concentration. The maximum NO2- concentration was observed at 12 and 18 days and decreased at 24 days. However, accumulation of NO2- continued up to 24 days at higher CaCO3, EC and pH levels. An increase in urea levels decreased the rate of nitrification. The nitrification rate was fast in the presence of farmyard manure and slow at the higher CaCO3, pH and EC levels.
Nutrient cycling by mound building termites in low fertility soils of semi-arid tropical Australia
Authors: Coventry RJ , Holt JA , Sinclair DF
Published: April 2005

The capacity of three species of mound-building termites, Amitermes vitiosus Hill, Drepanotermes perniger (Froggatt), and Tumulitermes pastinator (Froggatt), to turn over plant nutrients was quantified in a semi-arid tropical woodland near Charters Towers in north-eastern Queensland. Various chemical attributes of the red and yellow earth soils, of low inherent fertility and unmodified by recent termite activity, are compared with those of the mounds of the three termite species and with the underlying, termite-modified soils. The mounds contain 21 Mg ha-l of soil, representing only 1% of the total mass of soil in the Al soil horizon but 5-7% of the plant nutrients in this system. Nutrients in the termite mounds, temporarily withheld from plant growth, are eventually returned to the soil surface by erosion of abandoned mounds. We estimate that the termites can turnover annually 300-400 kg ha-1 of soil material with nutrient levels 2-7 times that of the Al soil horizon.
Predicting the effects of land disturbances on stream salinity in southwest Western Australia
Authors: Schofield NJ
Published: April 2005

A model developed by A. J. Peck to predict the effects of land disturbances on stream salinity has been extended to take account of increased stream runoff, and applied to the jarrah forest region with improved parameter estimates. Validation on Wights experimental catchment suggests that the model is capable of reliable predictions in the case of agricultural clearing. However, the extended model did not provide discernibly better predictions than the original model. When applied to rainfall zones of the northern jarrah forest of W.A., the model predicted that agricultural clearing would result in average stream salinity increases of -70 mg 1 for the high rainfall zone (> 1100 mm yr-1), of -270 mg L-1 for the intermediate rainfall zone (900-1100 mm yr-1), and of ~3400 mg L-1 for the low rainfall zone (<900 mm yr-1). In the case of bauxite mining followed by reforestation, the model was limited to consideration of long-term effects, and neglected transient effects. Predicted stream salinity increases were considerably smaller than for agricultural clearing, primarily because mining involves clearing smaller areas, and these areas are reforested. The model is sensitive to variations in parameter values which implies that a wide range of stream salinity increases could occur within any one rainfall zone, due to the variation of local conditions.
Effects of flow velocity variation on rain driven transportation and the role of rain impact in the movement of solids
Authors: Moss AJ
Published: April 2005

Rain-flow transportation in, and airsplash from, shallow sheet flows of varying velocity were investigated experimentally by using four drop sizes at constant intensity (64 mm h-1). Whereas airsplash yields were negligible, rain-flow transportation reached rates of up to 3 g m-1s-1 and exhibited two distinct modes of operation, or regimes, depending on whether the unimpacted flows were laminar or transitional to turbulent. In the first of these regimes, clouds of particles, suspended by individual drop impacts, were moved downstream before settling back to the bed. In the second regime, general turbulence, imposed by drop bombardment, made the flow everywhere able to entrain and transport particles without direct dependence on individual drop impacts. These findings are combined with those of previous studies to make an assessment of the roles of rain and flow in water erosion.
Evaluation of the influence of sample preparation and extraction technique on soil solution composition
Authors: Menzies NW , Bell LC
Published: April 2005

Soil solutions were extracted by immiscible liquid displacement with trichlorotrifluoroethane and by centrifuge drainage from surface and subsoil samples having a wide range of chemical and physical properties. Extractions were performed on field-moist samples and on air-dry samples which were re-wetted to different matric suctions and for different lengths of time. The composition of the soil solution obtained was the same with both methods of extraction when samples had been pre-wet to a matric suction of 0-1 bar. Immiscible liquid displacement extracted solution from a krasnozem surface soil at suctions as great as 15 bar; in contrast, centrifuge drainage failed to extract solution from this soil at >3 bar. The concentration of ions in solutions extracted by displacement from soils with increasing matric suction rose to a far greater extent than that anticipated if concentration was the only mechanism operating. In re-wet air-dry samples, major cations and anions were at equilibrium levels in solution after incubation for 1 day; longer incubation times resulted in an artificial elevation of ionic strength through mineralization of organic matter in some surface samples. The levels achieved after 1 day were similar to those present in solutions extracted from field-moist samples.
Phosphate sorption characteristics of soils of the north Queensland coastal region
Authors: Toreu BN , Thomas FG , Gillman GP
Published: April 2005

Phosphate-sorption curves covering the range of supernatant P concentration, 0-1 �g nil-1, have been determined for a number of agriculturally important soils in the high rainfall (2000-4000 mm) region of tropical Queensland. Where possible, soil samples were taken from both virgin and cultivated sites within a soil series. The soils occur on four major parent materials, namely basaltic, granitic and metamorphic rocks, and on alluvium derived from one or more of these rocks. The shapes of the P-sorption curves and the differences in magnitude of P sorption were related to the mineralogical composition of the clay fraction which, in turn, was determined by parent material. Past applications of phosphatic fertilizer have lessened soil P-sorption capacity, despite a reduction in soil organic matter resulting from clearing and cultivation.
Utilization of non-exchangeable soil potassium in relation to soil type, plant species and stage of growth
Authors: Memon YM , Fergus IF , Hughes JD , Page DW
Published: April 2005

The stage of growth at which three plant species, a grass, a legume and a cereal, absorbed initially non-exchangeable potassium (Kn) from two soils, a red podzolic and a krasnozem, was examined by sequential harvesting in a glasshouse experiment. Large amounts of Kn were removed from the red podzolic soil, which contained greater amounts of micaceous material, in the order setaria > maize > lucerne. Uptake of Kn appeared insignificant after exchangeable Kn as measured on the bulk soil, had been depleted by about 60%, and its contribution to total plant uptake thereafter was independent of species. For setaria and maize, plant K concentrations at this time were above the critical level, so that Kn represents a potassium resource that can be exploited during normal growth of an appropriate species. Uptake of Kn from the krasnozem was relatively small. The red podzolic soil yielded much more Kn than a similar soil in earlier experiments. This was attributed to differences in clay mineralogy, possibly associated with differences in the weathering stages reached by the two soils. Thus, it is not possible to infer the pattern of release of Kn simply from a knowledge of Great Soil Group and parent material.
Racemization of amino acids in agricultural soils - an age effect
Authors: Griffin CV , Kimber RWL
Published: April 2005

Preliminary results of an investigation into the extent of racemization of amino acids in agricultural Ap horizons reveals significant differences between soils from a wheat-fallow rotation and from permanent pasture and between the readily and less readily hydrolysable fractions of these soils. Some possible interpretations of the data, including evidence of heterogeneity in the residence time of soil amino acid nitrogen, indicate that amino acid racemization reactions may have significant application for long-term nitrogen turnover and fertility studies.
Spatial variation in salinity of some alluvial aquifers in central Queensland - a steady state analysis
Authors: Dowling AJ , Gardner EA
Published: April 2005

This paper reports on the spatial variation of salinity in the alluvial groundwaters of the Callide Valley, central Queensland. The spatial distribution of salinity in this area is very complex with substantial variation occumng over small (< 1 km) and large (> 10 km) distances. This complexity has been attributed to variable leakage of highly saline water into the alluvium from adjacent hard rock aquifers. A simple but elegant steady-state dimensionless analysis is introduced to clearly establish if salt additions or subtractions are occurring in the alluvial groundwaters. By using ions not normally complicated by precipitation reactions (sodium and chloride), our analyses show that solutes are conserved, with excellent agreement between the measured data and theory. This result strongly supports a hypothesis of progressive concentration of a localized source of salt, introduced near the headwaters, with increasing distance down discrete alluvium-stream valleys. We conclude our paper with a caution on the delayed effects of distributed salt import into alluvial aquifers with large solute response times.
Weighted method of characteristics solutions for solute transport models
Authors: Prathapar SA , Reddell DL
Published: April 2005

Method of characteristics (MOC) solutions are widely employed in solute transport models to estimate tracer concentration. The conventional approach to obtain average tracer concentration for a particular cell is to arithmetrically average the concentration of moving points within the cell during a particular time step. This results in the prediction of a stepwise or a 'jerky' dispersion front unless a large number of moving points are introduced and/or smaller grid size are used. Criteria proposed in the past to avoid this 'jerky' behaviour are unsuitable if the flow is non-uniform and/or unsteady or if the grid size is large. To overcome this problem, a distance weighted criterion was incorporated in a solute transport model which utilizes the method of characteristics. Results were compared with those from analytical solutions and the conventional arithmetical averaging algorithm. The distance weighting algorithm performed as well as the arithmetic averaging algorithm for small grid sizes. When the grid size was large and/or the seepage velocity was low, the conventional approach resulted in a stepwise dispersion front, whereas the distance weighting approach resulted in a smoother dispersion front, consistent with analytical solution. Application of the proposed method should facilitate the selection of larger grid size for simulating solute transport in porous media.
Crop growth across a toposequence controlled by depth of sand over clay
Authors: Hamblin A , Richards Q , Blake J
Published: April 2005

Sand soils containing, by definition, less than 5% clay, may give substantial variation in crop growth, even where they have apparently similar chemical and physical properties. This work tests the proposition that crop growth in a winter-rainfall environment is dependent upon the depth of a uniform sand profile, and that crop growth can be negatively correlated with depth to clay because of the low water and nutrient storage capacity of such soils. Spring wheat and barley, cereal rye, and narrow-leaf lupin were grown at three adjacent sites across a toposequence having a 3� slope with increasing sand depth (from 0.6 to >2.5 m) downslope. The experiments were conducted over two years, the first wetter than average, the second drier. In both years there was a significant decline in dry matter accumulation and crop yield with increasing sand depth in which the wheat biomass and lupin grain yield were most affected. Water uptake and nutrient distribution patterns within the profiles showed that available water was least and leaching most severe on the deepest sand, where no fine-textured materials at depth occurred to trap water and nutrients for later-season use within the rooting zone. Maximum rooting depths were estimated to average 2.0 m for wheat, and 2.4 m for lupin and cereal rye. However, on the deepest sand where roots grew to >2.5 m, yields were reduced to half, even under the high fertilizer conditions of the experiments. It is concluded that depth of sand provides the most reliable prognosis for crop growth and yield where there are no distinctive differences in clay content or chemical reaction.
A comparison of soil porosity and solute leaching after six years of direct drilling or conventional cultivation
Authors: Francis GS , Cameron KC , Kemp RA
Published: April 2005

The soil porosity, pore size distribution, micro-morphology and the leaching of surface-applied solutes after six years of continuous winter wheat planted by direct drilling (DD) or conventional cultivation (PL) were compared. The total porosity of the PL soil was greater than that of the DD soil throughout most of the cultivated depth. This was mainly due to the greater volume of pores >300 �m diameter in the PL than DD soil. Pores in this size range were, however, more stable in the DD than PL soil, with the differences between tillage treatments being more apparent at the winter than summer sampling occasion. The most common macropores in PL soil were compound packing voids with only a few variably oriented biotic channels (>5 mm) being present. In contrast, the DD soil consisted mainly of a system of vertically or subvertically oriented biotic channels which were frequently linked with planar voids (< 1 mm). The probable differences in tortuosity and continuity of these contrasting pore systems were related to the leaching characteristics observed under the two tillage treatments. The breakthrough curves showed extensive preferential flow under both ponded infiltration and simulated-rainfall input conditions. More rapid leaching through DD than PL soil was observed for both 'equilibrated' and 'non-equilibrated' surface-applied solutes under ponded infiltration conditions. This implied that large pores were more continuous in uncultivated than cultivated soil. In contrast, it is suggested that there was no difference in the continuity of the smaller pores involved in water and solute flow under simulated rainfall since both tillage treatments had similar breakthrough curves under these conditions. More solute was recovered in 1.5 pore volumes of leachate under simulated rainfall than ponded infiltration conditions.
Effects of the amount of stubble mulch and overland flow on erosion of a cracking clay soil under simulated rain
Authors: Loch RJ , Donnollan TE
Published: April 2005

A field study by using simulated rain and run-on water was carried out to determine the effects of different amounts of wheat stubble mulch (ranging from 0.1 to 3 t ha-1) and increasing discharge on erosion. Rain-flow erosion decreased with increasing amounts of stubble. Concentrations of bed-load sediment carried by rain-flow decreased with increasing plot discharge. As discharges increased, overland flow probably became too deep for drop impact to effectively disturb the soil surface and entrain sediment. Only plots carrying 0.1 t ha-1 stubble showed definite scour by overland flow. However, sediment concentrations produced by scour were well below those measured in rill flow on bare soil at this site, showing that even very small rates of stubble mulch can, in some situations, significantly reduce erosion. Discharges at which rilling develops fully must be much larger than those at which scour by overland flow is initiated. Future work will need to consider discharges much larger than those used in this study.
Impact droplets and the protection of soils by plant covers
Authors: Moss AJ
Published: April 2005

Impact droplets, the fine drops splashed from the impact sites of larger drops on plant elements, were investigated experimentally to assess their role in water erosion. It was found that impact droplets rarely strike the soil surface before decelerating markedly from their sometimes high initial velocities. This, and their small sizes, render them almost non-erosive. Their production therefore represents a major soil-conserving mechanism in that large, potentially erosive drops are converted to almost harmless drizzle. Conversion rates of incident-drop water to impact droplets were found to be about 10-25% by weight for large, effectively semi-infinite targets, but rose rapidly to about 90% as impact points approached within half a drop diameter of target edges. Most impacts on plant elements are edge-affected and elements of about the same diameter as a raindrop (e.g. those of fine grasses) produce double-edge effects, almost entirely converting incident drops into impact droplets. These results, combined with previous findings, allow consideration of the abilities of different arrays of plant elements (i.e. 'covers') to combat water erosion generally. Closely spaced, near-ground, plant elements, about 1-3 mm in diameter, display a peculiar overall effectiveness in this respect.
Development of a soil water dispersion index (SOWADIN) for testing the effectiveness of soil-wetting agents
Authors: Sawada Y , Aylmore LAG , Hainsworth JM
Published: April 2005

Computer-assisted tomography (CAT) applied to gamma-ray attenuation measurements has been used to develop an index termed the soil water dispersion index (SOWADIN), which describes quantitatively the amount and distribution of water in soil columns. The index, which is determined by classifying pixels in a scanned slice into three categories according to their attenuation coefficients, contains two numerical values. The first value corresponds to the water content of the scanned slice and the second value is a measure of the dispersion of the water throughout the slice. Artificially wetted zones were created in soil columns to give one-third of the scanned layer wetted with various patterns of wetted-area distribution. The SOWADIN values obtained accurately reflected the differences in water distribution associated with the different patterns. Application of SOWADIN to columns of a water-repellent sand before and after treatment with a soil-wetting agent clearly illustrates both the increase in water content and improvement in water distribution in the soil column following treatment.
The effect of wetting pre-treatment on the desorption moisture characteristic of vertisols
Authors: Thorburn PJ , Gardner EA , Geritz AF , Coughlan KJ
Published: April 2005

Four experiments were conducted by using individual aggregates and ground samples of different soils and a range of wetting pre-treatments to investigate the effect of wetting on the desorption moisture characteristic of Vertisols. Wetting rate was varied by manipulating the energy of the water used to wet up the soil. Fast wetting was found to increase moisture uptake in Vertisols over a wide range of matric potentials (to -38 MPa in one soil). At high matric potentials, additional water uptake ranged up to 0.26 g g-l. These results were attributed to the creation of planar voids within soils between small water-stable aggregates on fast wetting. These voids retained water at matric potentials as low as -90 kPa. At this potential, 40% of additional water taken up on fast wetting was still retained in one soil. At -1500 kPa, fast wet soils retained up to 1.2 times more moisture relative to slow wet soils. The effect of wetting at potentials of -1500 kPa and less appeared to be related to the smectite content of the soil clay fraction and the degree of order of clay quasi-crystals. The soil which showed the greatest effect of fast wetting at these potentials had a less well ordered clay micro-structure. These findings have relevance to field studies, as variations in maximum field soil moisture content, with depth, could be reproduced by tension wetting pre-treatments. This result indicates that reduced rate of subsoil wetting may be responsible for the decrease in maximum field water contents with increasing soil depth, which has been observed in Vertisols. Such profiles have previously been attributed to the effect of overburden and stress potentials alone.
Non-destructive measurement of soil clod volume using hexane displacement
Authors: Ross PJ , Prebble RE
Published: April 2005

A non-destructive method of measuring soil clod volume is described. Clods, suspended in a sling, are weighed in air, in hexane and in air again after excess hexane has been drained at 25 mm hexane suction. Measurements were made to test the accuracy of the method and to compare it with the kerosene saturation technique. It was found to be faster, more accurate and more convenient than the kerosene method. An illustration is given of its use for monitoring the change in porosity with water content of a swelling soil.
Causes and prediction of changes in extractable phosphorus during flooding
Authors: Willett IR
Published: April 2005

In a laboratory experiment, samples of 18 soils, which are known to be flooded in the field, were flooded for up to 32 days. Both untreated and phosphate-treated (50 mg P kg-1) soils were studied. It was attempted to identify which chemical properties measured on the dry untreated soils, and the changes in pH, Eh and extractable Fe and Mn over the flooding periods, controlled the changes in sodium acetate buffer (pH 3.0) extractable phosphorus during flooding. It was shown that the reduction of iron(III) oxides was the dominant source of the P released during flooding. However, the amount of P released was strongly inhibited by re-sorption. Direct measurement of the amount of iron(III) reduced during flooding and measurement of phosphate sorption were required to predict the amount of P released during flooding. Organic matter contributed toward the P released during flooding. Its contribution appeared to be by mineralization, rather than by accelerating FeIII reduction. The reduction of MnIII and MnIII was a minor source of P in the untreated soils. Changes in soil pH during flooding were responsible for desorption of freshly applied P, but did not appear to affect P release in the untreated soils. The Vertisols and some of the Alfisols showed very little, or no release of P during flooding.
Simulation of phosphate leaching in acid sandy soils
Authors: Gerritse RG
Published: April 2005

Prediction of changes in amounts of phosphate leaching from soils with changes in management practices requires a detailed knowledge of the adsorption and desorption characteristics of the soils for phosphate. Non-equilibrium soil distribution of inorganic phosphate was determined at various rates of flow from time courses of phosphate in the leachates of small columns of sandy soils sampled from the Swan Coastal Plain in south-west Western Australia. Equilibrium distribution isotherms were estimated by extrapolating to zero rate of flow. Time courses of phosphate concentrations in the leachates were also calculated with a numerical compartmental simulation model. First-order transport rate equations with time-dependent rate coefficients adequately described the experimental time courses of the leachate concentrations. Kinetic parameters were based on a consideration of the physical/chemical distribution of ortho-phosphate only. The error due to this approach was evaluated by measuring the (biochemical) fixation of phosphate in soil organic matter.
Allophane and halloysite content and soil solution silicon in soils from rhyolitic volcanic material, New Zealand
Authors: Singleton PL , Mcleod M , Percival HJ
Published: April 2005

The relationship between Si in soil solution and allophane and halloysite content was studied by using a drainage sequence of three New Zealand soils from rhyolitic volcanic alluvium. Clay mineralogy was compared with soil colour and drainage. Allophane and halloysite contents of two morphologically similar soils from rhyolitic volcanic ash were also studied and possible reasons for differences in mineralogy were determined. Allophane was estimated by acid oxalate and pyrophosphate dissolution. The Al/Si ratio of the allophane was determined and the allophane content of the soil was estimated from the Si extracted in acid-oxalate. Halloysite was estimated by differential thermal analysis of the whole soil. Soil samples were centrifuged with a dense water-immiscible organic liquid to displace the soil solution from between soil particles. The Si in soil solution was then determined by spectrophotometry. Allophane was predominant when Si in soil solution was <10gm-3, and halloysite was predominant when Si in soil solution was >10gm-3. Low Si in soil solution and the presence of allophane was associated with well drained horizons which could be identified by their ochreous colour. High Si in soil solution, the absence of allophane and predominance of halloysite, was associated with poorly drained horizons. These horizons could be identified by their pale colour (chroma <2). In two morphologically similar soils, the change from allophane dominance in one soil to hahoysite dominance in the other soil also corresponded to an increase in Si in soil solution. This was probably the result of slightly slower horizon permeability which increased Si in soil solution to a level favouring halloysite formation.
Aluminum determination in soil solution. 1. Evaluation of existing colorimetric and separation methods for the determination of inorganic monomeric aluminum in the presence of organic acid ligands
Authors: Kerven GL , Edwards DG , Asher CJ , Hallman PS , Kokot S
Published: April 2005

Colorimetric methods of analysis and separation procedures were evaluated for their ability to selectively measure the inorganic monomeric forms of aluminium (Al) toxic to plant roots. An Al-fulvate complex of natural origin was prepared and characterized by gel filtration chromatography and 2 7Al NMR to act as a model organic complex of Al. All five colorimetric methods tested failed to adequately discriminate between inorganic monomeric and organically complexed forms of Al. Best discrimination was achieved by the 15 s 8-hydroxyquinoline method, with only 46% of the organically complexed Al being measured as inorganic monomeric Al. All methods with longer reaction times measured >80% of the complexed Al as inorganic monomeric Al. Separation procedures by using cation exchange resins to remove inorganic monomeric Al from aluminium fulvate solutions were found to produce a decrease in sample pH of 0.8, even though the resin was used in the potassium form to eliminate H+ ion exchange. The decrease in sample pH caused the Al complex to dissociate and 34% of the Al was retained on the resin. With buffered Chelex 100 in the potassium form, change in sample pH was reduced to 0.2 pH units, but 23.5% of the Al was still retained on the resin. Separation of organically complexed forms of Al from inorganic monomeric forms by gel filtration chromatography (GFC) was shown to be ineffective when sulfate is present due to co-elution of the SO4-Al complex with the fulvic acid-Al complex.
Hydrolysis of FeIII solution to hydrous iron oxides
Authors: Lewis DG , Cardile CM
Published: April 2005

A range of hydrous iron oxides was prepared from ferric nitrate solutions by varying the rate and manner of hydrolysis. The properties of the resultant products were determined by using various techniques including size fractionation with Amicon Diafilters, rate and extent of dissolution in acid ammonium oxalate solution, X-ray diffraction and Mossbauer spectroscopy. The variation in properties is interpreted in terms of the conditions under which the various materials had been formed. The products of spontaneous hydrolysis at low pH and low FeIII concentration had properties distinctly different from those samples in which hydrolysis was induced rapidly by addition of alkali. The low-pH products were far more resistant to dissolution in acid ammonium oxalate and were relatively well ordered as determined by X-ray diffraction and Mossbauer spectroscopy at 77 K. The crystallographic and magnetic ordering of the rapidly formed phase is normally very limited, but these properties were increased significantly if formation occurred in the presence of low-pH polymeric material which may act as a template for freshly precipitating oxides.
Boron retention within a catena of rhyolitic soils and Its effect on radiata pine growth and nutrition
Authors: Ryan PJ
Published: April 2005

Boron deficiency in Pinus radiata (D. Don) plantations in N.S.W. has been particularly evident on soils derived from acid igneous parent materials. A slope sequence (catena) of soils on a rhyolitic parent material was selected to study the amount of boron retention and its relationship to soil development. The soils at three positions, a hillcrest, mid-slope and lower slope, were described and various soil chemical and physical properties were determined for each horizon. Tree height, deformity, survival and foliar chemistry of 6 year old P. radiata were measured in plots adjacent to the three soil profiles studied. Boron adsorption isotherms varied within individual soil profiles by horizon and also between the different soil profiles in the catena. Boron adsorption was highest in the hillcrest soil B horizons and lowest in the bleached A2 horizons of the lower slope soil. The Freundlich isotherm constant k was found to be significantly correlated with clay content (r = 0.88), exchangeable aluminium (r = 0.79, exchangeable potassium (r = 0.68), and dithionite-citrate extractable iron (r = 0.66). Leaching and illuviation of iron oxides and clay has been accentuated in the two soil profiles on the hillslope sites of the catena. As clay, aluminium and iron oxides have been removed from the surface horizons of the lower slope soil, the ability of these horizons to adsorb and therefore retain boron has been greatly diminished. Position on the catena also affected P. radiata growth survival and foliar chemistry. Tree height decreased while the incidence of deformity increased down the slope. It is suggested that the progressive deterioration in tree growth down the slope is mainly caused by the trees being increasingly affected by boron stress as a result of decreasing capacity of the soils to retain boron by adsorption against leaching towards the lower slope.
Leaching of applied calcium and potassium from an oxisol in humid tropical Queensland
Authors: Gillman GP , Bristow KL , Hallman MJ
Published: April 2005

Downward movement of Ca and K applied to a north Queensland Oxisol has been studied in the field where rainfall is approximately 4000 mm per annum. After cultivating the soil to about 15 cm depth, Ca was applied as lime (5 tha-1) and gypsum (8.6 t ha-1) and K as potassium chloride (760 kg ha-1), the experiment being replicated five times. On three occasions, covering a six week period, known amounts of artificial rainfall (225 mm in total) were uniformly applied and, after 1 or 2 days, soil cores were taken to 1 m depth. Most of the Ca from the lime treatment remained in the top 10 cm but, in the gypsum treatment, Ca moved to about 30 cm. Potassium was extremely mobile in the profile and was rapidly distributed to about 50 cm depth. The hydraulic and electro-chemical properties of the soil were well characterized, and the observed movement of water and solute could be explained in terms of these properties.
Evaluation of three soil erosion models for clay soils
Authors: Freebairn DM , Silburn DM , Loch RJ
Published: April 2005

The Universal Soil Loss Equation (USLE) and two modified USLE models were assessed for their ability to predict soil erosion on contour bay catchments on the Darling Downs, Queensland. The models were applied using USLE handbook values as well as optimized values determined by fitting the models to the experimental data. All three models explained greater than 80% of the variance in measured soil loss with no single model being consistently superior to the others. Cover reduced erosion more than that predicted by the USLE.
Variation in soil physical properties between and within morphologically defined series taxonomic units
Authors: Di HJ , Kemp RA
Published: April 2005

Eyre, Templeton and Wakanui series are morphologically defined taxonomic units which are used to partition alluvial soil variation across the Canterbury Plains near Lincoln College in New Zealand. The wider significance of the classification criteria is here assessed by quantifying the variability of physical properties of hydraulic significance ['field-saturated' hydraulic conductivity (Kfs), moisture content and bulk density] between and within the three taxonomic units. The overall effectiveness of the morphologically based classification system in partitioning variation in soil physical properties is considered by using analysis of variance. The classification of soils according to texture and mottling criteria is generally effective in separating soils in terms of the selected soil physical properties. Although some topsoil physical properties do not differ significantly between pairs of taxonomic units, all subsoil properties are clearly distinguishable between Templeton and Wakanui series. The differences are mainly attributable to spatial changes in soil texture and pore characteristics. Different amounts of variation in physical properties, however, are still present within each taxonomic unit. The variation in physical properties amongst the combined series taxonomic units is reduced to differing extents by the classification. More than half of the variance in moisture content at both topsoil and subsoil depths amongst Templeton and Wakanui taxonomic units, for instance, is accounted for by the classification, and is thus due to differences between the two series. Little contribution is made by the classification in reducing the heterogeneity of Kfs in topsoils. The classification is particularly effective in separating Wakanui from Templeton taxonomic units in terms of subsoil Kfs, an important property controlling water movement and storage.
Prediction of exchangeable sodium percentage in soils by mechanistic and layer models
Authors: Kapoor A , Pal R , Poonia SR
Published: April 2005

An experiment was conducted in Plexiglass columns ( i d . 5.6 cm) to study depth distribution of adsorbed Na+ in Ca-saturated loamy sand, sandy loam and clay loam soils on percolating different volumes of 0.1M NaCl solution. The exchangeable sodium percentage (ESP) decreased gradually with depth and increased with increase in volume of solution percolated. The depth development of ESP of the soils was computed by using a numerical solution of a one-dimensional convective-dispersive partial differential equation (model I) and a conceptual layer model (model II). To account for the effect of adsorption on cation flow, the slopes of the nonlinear adsorption functions fitted to the normalized adsorption isotherms of Na+ were employed in model I , and the Gapon equation was employed in model II. As the Gapon selectivity coefficient (Kg) is dependent on Na saturation, its values were calculated from the regression equation: Kg = 0.22 + 0.0043SAR (where SAR is the sodium adsorption ratio). Model I overpredicted ESP of loamy sand and sandy loam soils throughout the column depth; the overprediction was more pronounced in the former. The coefficient of determination, calculated on the basis of pooled data of three soils and two solution volumes showed that the accuracy of prediction of model II was considerably higher (r2 = 0.80) than that of model 1 (r2 = 0.54).
Chemical attributes of some Queensland acid aoils. II. Relationships between soil and soil solution phase compositions
Authors: Bruce RC , Bell LC , Edwards DG , Warrell LA
Published: April 2005

Relationships were sought between soil and soil solution attributes by using the data of Bruce et al. (Part I). There was a strong linear relationship between EC of soil solutions and EC of 1:5 soil : water extracts (r2 = 0.904). In subsoils, the activity of Al3 + in soil solution was dependent on soil solution ionic strength and soil Al saturation, and was described by the following multiple regression equation: loge(Al3+) = -6.97 + 1.96logeIss + 0.0777Alsat.%
Measurement of the oxidation rate of elemental sulfur in soil
Authors: Watkinson JH
Published: April 2005

Equations have been derived for surface reaction rates for various shaped particles of known size distribution, assuming that the reaction rate per unit area was constant and that the effect of reaction products on the rate was negligible. These have been applied to the oxidation of elemental sulfur (So) in soil, assuming that the S� particles were either highly porous or were blocky shaped. Published incubation data for some New Zealand soils under pasture from five soil groups over a 70 day period and with up to 98% oxidation of added So were fitted with R2 of 95%. The average rate constants for the soil groups ranged from 48 to 76 S �g cm-2 day-1. These were similar to a value for an Australian soil, but 10-15 times greater than values for Canadian soils. The higher rate possibly resulted from the greater activity of thiobacilli, the reduction of lag time errors by long incubation times, and the avoidance of possible loss of oxidation products by direct determination of residual So. The addition of phosphate rock (50 g kg-1) gave an increase in rate for mineral soils, but not for organic soils, of 15 �g cmW2 day-1, and was attributed to enhanced aeration through better soil porosity.
The extraction of Al, Fe and Si from a range of New Zealand soils by hydroxylamine and ammonium oxalate solutions
Authors: Lee R , Taylor MD , Daly BK , Reynolds J
Published: April 2005

The elements Al, Fe and Si were extracted with acid oxalate and acid (HCl) hydroxylamine by using 36 samples from eight different soils, and the results for each extractant were compared. Parent materials were largely volcanic in nature, but eight samples were from soils derived from quartzo-feldspathic materials. Oxalate extracted significantly greater amounts of Fe from most samples than hydroxylamine. Results for Al and Si were less consistent. Compared with oxalate, hydroxylamine (soil : solution, 1:250) extracted significantly greater amounts of Al and Si from some samples and less from others. Taken over all samples, however, there was no significant difference between the two methods in the amounts of Al and Si each extracted. A decrease in the soil:solution ratio for hydroxylamine from 1:250 to 1:400 had little effect of Fe and Si values, but it did increase the amount of Al extracted in several cases. Soil mineralogy appeared to bear little relationship to observed differences, although the presence of magnetite probably contributed to higher oxalate-Fe values. Although statistically significant, differences between individual values were generally small. Results are compatible with previous studies which indicated that hydroxylamine provides an approximation of oxalate values for Al and Fe. Unlike previous work, however, the present results also suggest that approximate values can be obtained for Si.
The role of Ca-organic interactions in soil aggregate stability .I. Laboratory studies with glucose 14C, CaCO3 and CaSO4.2.H2O
Authors: Muneer M , Oades JM
Published: April 2005

14C-glucose with or without CaCO3 or CaS04.2H2O was incubated in a leached fine sandy loam under controlled temperature and humidity for 120 days. The addition of CaSO4.2H2O decreased the release of 14CO2, compared with soil with 14C-glucose and CaCO3 and 14C-glucose only. Addition of CaCO3 initially stimulated release of 14CO2 but subsequently the release of 14CO2 was inhibited compared with treatments with no calcium additions. Addition of both CaSO4.2H20 and CaCO3 resulted in more residual 14C in the soil at the end of the incubation period than in the control soil to which no calcium was added. The addition of CaSO4.2H2O and CaCO3 led to increases in water-stable aggregates 50-250 �m diameter, and decreased the amount of dispersible clay. In the presence of calcium and glucose, the stabilization of aggregates >1000�m occurred and they persisted for a longer time than when no additions of calcium were made.
The role of Ca-organic interactions in soil aggregate stability .III. Mechanisms and models
Authors: Muneer M , Oades JM
Published: April 2005

Serial additions of glucose after drying-wetting cycles led to substantial aggregation of the surface soil from a red-brown earth. Addition of glucose and Ca compounds resulted in up to 80% of the soil bound in particles >2000�m with only a small portion of the soil in particles 4 0 �m. Treatment of the soils with Na4P2O7 caused dispersion of most of the clay but did not disrupt larger aggregates. More disaggregation was caused by treatments with HCI (0.02 M and 0.1 M), indicating the presence of pyrophosphate-resistant binding mechanisms which were presumed to be due to Ca bridging. Addition of Ca to the soil reduced the efficiency of extraction of organic materials by NaOH. This effect was eliminated by a pretreatment with 1 M HCl, indicating a 'bridging' effect of Ca between polycarboxylic macromolecules (humic acids) and clays. The role of Ca in clay and organic matter flocculation, the bridging of clay aggregates to organic materials and interactions of these colloidal aggregates with the biologic cycle is illustrated in some pictorial models.
Estimates of effective rooting depth for predicting available water capacity of burdekin soils, Queensland
Authors: Baker DE , Ahern CR
Published: April 2005

Estimates of rooting depth are necessary parameters in predicting available water capacity (AWC) of soils. In a recently assembled database for the Burdekin River Irrigation Area, no single criterion, commonly used to estimate rooting depth, was available for all sites. Therefore a number of methods of estimating rooting depth which give interchangeable results were required. This paper compares eight methods of estimating rooting depth within three AWC models and compares the outcome with field determinations. Soil properties used to estimate rooting depth were laboratory-based (two chloride methods, electrical conductivity and pH), morphological (carbonate and mottling) and two fixed depths (0.9 and 1.0 m). For all soils tested, the laboratory-based methods used within one AWC model (based on regression equations by using -1500 kPa water retained) resulted in predicted AWC values not significantly different (P< 0.05) from field measurements. The suitability of mottling was limited to cracking clays and sodic duplex soils and other rooting depth methods had varying applicability depending on soil type. This work shows that a range of rooting depth methods can be used to predict AWC of Burdekin soils. The results should have application to soils of other areas.