bluuebunny/crossref_metadata_2025 huggingface dataset:
A model to predict the effects of prostrate ground cover on wind erosion
Authors: Findlater PA , Carter DJ , Scott WD
Published: April 2005

This paper presents a simple physical model which assumes that the loss of soil is proportional to the fraction of the uncovered ground, when the aerodynamic roughness is small. Integration shows that the total soil loss decreases exponentially with the fraction of ground covered. The model is compared with the soil flux generated in a portable wind tunnel over prostrate lupin residues and results from other studies. The data are well described by the model. Unexpectedly, the same data seem to predict soil fluxes that are not necessarily proportional to the cube of the excess wind speed above the threshold level.
The movement and distribution of manganese added to soil
Authors: Uren NC
Published: April 2005

Autoradiography was used to trace the movement and distribution of divalent manganese (Mn) labelled with 54Mn after addition to samples of two whole soils and to the natural aggregates of one of the soils. Various treatments involving waterlogging, incubation at 100 cm suction and air-drying were imposed. Given time, irrespective of the treatment, the 54Mn tended to accumulate at spots of varying size inside the aggregates and throughout the whole-soil samples. Since divalent Mn added to the two soils is converted rapidly to easily reducible forms by a process inhibited by microbial poisons, the spots represent presumably centres where the divalent Mn is oxidized microbially to insoluble oxides of Mn.
Accession of SO2-4 sulfur from Tongan rainfall
Authors: Manu VT , Kipton H , Powell J , Banks L , Sheat A , Widdowson JP
Published: April 2005

Accession of SO42- S from rain in Tonga has been assessed as approximately 6 kg S ha-1 year-1 from analysis of rainwater collected at three sites on two islands over a period of 365 days. The accession is of similar magnitude to crop removal of soil S. This accounts for the absence of S deficiencies in crops grown on andesitic soils which, on the basis of low to very low levels of adsorbed sulfate and low plant yields in glasshouse trials, were considered S-deficient. From consideration of ion ratios, it was established that sea spray/marine aerosol is the major source of SO42- S in Tongan rainwater.
Seasonal variations in soil S flush and possible contributions from plant roots in the measurement of soil microbial sulfur, phosphorus, potassium and nitrogen
Authors: Perrott KW , Sarathchandra SU
Published: April 2005

The seasonal changes of the flush of soil sulphur (S) after CHCl3 fumigation were studied in a two-year field trial on a high-producing pastoral soil. The pattern was different from that observed for microbial P, and this may be explained by seasonal changes in the contribution of roots to the soil S flush. Roots extracted from sieved (<4 mm) soil were used to estimate the contribution of plant roots in the determination of soil microbial P, K, N and S. Increases in P, K and N extracted from roots after CHCl3 fumigation made only a small contribution to the increases for the soil (4%, 2% and 7% for P, K and N respectively). The contribution of roots to the increase in S extracted from soil after fumigation was about 22%.
The effects of fire on the soil in a degraded semiarid woodland .II. Susceptibility of the soil to erosion by shallow rain impacted flow
Authors: Kinnell PIA , Chartres CJ , Watson CL
Published: April 2005

Small (500 by 250 by 100 mm) soil monoliths collected from experimental plots subjected to various fire frequencies in a semi-arid woodland near Coolabah, N.S.W., were tested for their susceptibility to erosion by rain-impacted flows under laboratory conditions. In the tests, the erosive stress applied to the soil surfaces was controlled by using drops of uniform size (2.7 mm) falling 11.2 m onto flows whose depths were controlled between 1 and 2.7 drop diameters. Experimental data and thin-section observations showed that cryptogams provide a high degree of protection against erosion. Sediment concentration (measured in g L-1) from cryptogam-covered plots was considerably less than that from both bare-crusted surfaces and surfaces dominated by depositional material. Surfaces with cryptogamic crusts were generally free of debris, but showed only minor signs of erosion, whereas bare-crusted and depositionary surfaces suffered pronounced lowering and tended to disintegrate. Because increasing fire frequency reduces the spatial distribution of the cryptogamic cover on the soil surface in the semi-arid woodlands, increasing fire frequency must increase the erosion hazard.
An ammonia budget for Australia
Authors: Denmead OT
Published: April 2005

The paper reviews research into sources and sinks of ammonia (NH3) in the Australian landscape and presents an NH3 budget for the continent. Emissions from uncultivated land areas were reckoned to be the most important source, followed by excreta from domestic animals, emissions from fertilized fields, and biomass burning. Coal burning and excreta from wild animals (kangaroos) were of minor importance. The total emission of NH3 was estimated to be 1.9 Tg N y-1, 1.6% of the global total. In a comparable budget for the globe, biomass burning was listed as the biggest source, but this and emissions from uncultivated land areas are the biggest unknowns in both budgets. Ammonia concentrations and deposition rates in Australia are presently too small to constitute serious pollution problems as they do in parts of Europe, but the depositions may be large enough to play an important role in the nitrogen (N) economy of native plant and microbial ecosystems.
Sorption-desorption behaviour of caesium in some Western Australian soils
Authors: Singh B , Gilkes RJ
Published: April 2005

Soil caesium-137 derived from past atmospheric nuclear tests is increasingly being used as an indicator of soil erosion and deposition on the basis that fallout 137Cs has been retained by soils, although this assumption has not been thoroughly tested for different soils. The sorption behaviour of some Western Australian soils indicates that Cs is differentially sorbed as a consequence of differences in clay mineralogy. Kaolinitic sandy soils of low exchange capacity sorb Cs in preference to Ca and Na, with the specificity for Cs being higher at lower concentrations of Cs in solution. lllitic and smectitic soils sorbed more Cs than kaolinitic soils and retained more than 50% of sorbed Cs after a series of extractions with salt solutions. Retention by kaolinitic soils was less but, for the concentrations of Cs likely to occur in soils, it seems that most Cs is retained so that it is probable that the 137Cs technique can be used with confidence for the measurement of soil erosion and deposition for many Western Australian soils.
Effects of increased levels of soil CaCO3 on Lupin (Lupinus angustifolius) growth and nutrition
Authors: Jessop RS , Roth G , Sale P
Published: April 2005

Little published evidence exists which relates narrow-leafed lupin growth to lime levels in soils when compared with growth on a soil with minimal or zero levels of lime. This pot experiment measured lupin growth and nodulation plus plant levels of Ca and Fe by using mixtures of a gilgaid black earth soil with varying quantities of free lime. A sand control allowed a plant growth comparison at minimal levels of lime. Iron sequestrene was added to all treatments to eliminate iron chlorosis. Plants harvested 68 days after sowing showed adequate levels of Fe. However, plant height, branch number, shoot and root dry weight and nodulation were markedly lower for plants grown on the low lime depression soil than those from the sand. Further major reductions in all aspects of growth occurred with increasing levels of the mound (high lime) soil. These effects were strongly related to soil and plant Ca levels; it is suggested that poor lupin growth on highly calcareous soils may be related to adverse direct effects of Ca.
A comparison of the effects of mineral and organic nitrogen sources on the distribution of wheat roots in a leaching environment
Authors: Diggle AJ , Bowden JW , D'Antuono MF
Published: April 2005

Wheat was grown under leaching conditions in columns in a glasshouse. Marked differences were observed in the root density profiles which resulted from addition of nitrogen in the form of either calcium nitrate or ground lupin leaves. The root profiles from the lupin leaf treatment had the highest density of roots at the surface and a continuous reduction in density with depth. Where calcium nitrate was added, total root growth was reduced, but there was enhanced growth of roots at depth associated with the leached nitrate. Water use was greater where lupin leaves were added, and the amount of top growth was also greater, although the difference was not significant. Nitrogen uptake was greater where calcium nitrate was added. Comment is included on the suitability of analysis of variance and repeated measurement methods for comparing profile data of the type collected here.
Effect of time of application and continuity of rainfall on leaching of surface applied nutrients
Authors: Mclay CDA , Cameron KC , Mclaren RG
Published: April 2005

The effect of time of rainfall relative to solute application, and the effect of rainfall continuity, was studied using undisturbed soil lysimeters. Immediate leaching with a surface-applied pulse of nitrate was compared with delayed (24 h) leaching of sulfate in a non-adsorbing soil. Preferential flow of water and solutes through natural soil macropores resulted in: (i) peak solute concentrations occurring before 1.0 pore volume of drainage, and (ii) incomplete leaching of applied solutes after 2.0 pore volumes of drainage. The immediate application of rainfall resulted in faster leaching rates compared with a delayed application. It is considered likely that the delay before rainfall allowed sufficient time for some solute to diffuse into intra- and inter-aggregate pore space and thus be bypassed by water flowing through soil macropores. Under intermittent rainfall, there was a series of time periods during which diffusion could occur into soil micropores and therefore the rate of leaching of surface-applied solute was slower than under continuous rainfall.
Effect of phosphate on the adsorption of 2,4-D on lepidocrocite
Authors: Madrid L , Diaz-Barrientos E
Published: April 2005

The competitive effect of phosphate on the adsorption of 2,4-D on an iron oxyhydroxide is studied. The adsorption isotherms of the herbicide with no phosphate present are strongly pH-dependent and are concave, suggesting a competition with solvent molecules. The presence of phosphate causes a strong decrease in 2,4-D adsorption and a progressive change in the isotherm from concave to convex. The relationships between the adsorbed amounts of both adsorbates show that in their regions of maximum slope the loss of one site for herbicide adsorption is accompanied by the adsorption of at least 10 phosphate groups, and this number increases as the amount of 2,4-D present decreases. It is shown that the proportion of sites lost for 2,4-D adsorption only depends on the amount of phosphate adsorbed and is independent of the total 2,4-D present in the system, and this conclusion can be explained in terms of the Stern model. The order of addition of both adsorbates has little effect on the final distribution of either adsorbate, although P adsorption seems to be slightly retarded by the presence of 2,4-D previously adsorbed. It is suggested that 2,4-D retention is mainly due to electrostatic forces.
Self mulching behavior in clay soils - Its definition and measurement
Authors: Grant CD , Blackmore AV
Published: April 2005

The history of the self-mulching concept is reviewed and from this a definition is proposed. Observation of the phenomenon to date has been quite subjective and qualitative, and the causes and mechanisms are little understood. A numerical index is developed to help redress these deficiencies. The self-mulching property embodies the ability of a soil to re-aggregate its clay in the course of wetting and air drying after the natural structure has been disrupted by puddling. A comparison of the clay released by such puddling with the clay released by shaking after drying and slaking of the puddle, forms the basis of the components for the numerical index. Suitable parameters for these components were extracted from experiments using typical Australian self-mulching soils. These soils also displayed a degree of subplasticity in at least part of their aggregated clay fraction. The numerical index values were compared with field structure ratings, made by pedologists, for 47 (mostly surface) soils from Australia and other parts of the world, and good agreement was found. The index is relevant to further work on mechanisms and modifications in self-mulching or potentially self-mulching soils.
The effects of minimum cultivation after three years on some physical and chemical properties of a red-brown earth at Forbes, NSW.
Authors: Cavanagh PP , Koppi AJ , Mcbratney AB
Published: April 2005

Reducing cultivation may improve many soil physical and chemical properties of a red-brown earth. A trial was set up in 1986 on a red-brown earth near Forbes, N.S.W., comparing direct-drilling and conventional-cultivation crop establishment techniques. The surface soil (0-100 mm) was sampled at the end of the third year and assessed for macropore structure, infiltration characteristics, bulk density, pH, electrolytic conductivity, organic carbon and total nitrogen content. Cultivation degraded some desirable soil physical properties as indicated by data obtained from image analysis and infiltration. Bulk density did not mirror differences in macroporosity. Organic carbon, total nitrogen and electrolytic conductivity levels were higher in direct-drilled soil in comparison to conventionally tilled soil. It ib concluded that the improvement of soil chemical and physical properties afforded by a reduction in tillage would lead to an increase in soil water infiltration rate and storage.
Rain impact soil crust. I. Formation on a granite derived soil
Authors: Moss AJ
Published: April 2005

The formation of soil crusts caused by raindrops (rain-impact soil crusts), on a granite-derived aqualf, was studied experimentally with the aid of optical microscopy. Crust development was initiated when rigid 10-50 pm particles were concentrated on the surface by preferential removal of both coarser and finer material in the airsplashing environment. The resulting silt concentrate was spread over the surface by lateral outflow sheets from the drops, forming a closely packed, dilatant, bed-load layer about 0-5 mm thick. This layer strongly resisted deformation by raindrop impacts and also suppressed hydraulic penetration, which tends to enhance loose packing. Compaction of the underlying soil, to a depth of about 5 mm, followed the establishment of the silt layer. This compaction was attributed to the action of stress waves, notably primary waves, propagated when drops impacted the effectively near-rigid surface of the silt layer.
Rain impact soil crust. IV. Packing of sand and silt fractions by raindrops
Authors: Moss AJ
Published: April 2005

Comparison of resistance to fast and slow deformation by rain-packed and artificially prepared sand and silt fractions showed that, whereas sands are left in loosely packed states after accrual under rain impact, silts are left more densely packed, i.e. below critical void ratio. This contrast is attributed mainly to the declining importance of hydraulic penetration with pore size. Rain-packed silt is dilatant and cannot deform without expansion which, in turn, requires water entry at a rate compatible with the required deformation. In the short duration of rain-impact events, hydrodynamic time lagging occurs because water can move only slowly through the small silt pores. Consequently, densely packed silt remains essentially rigid. However, drop-outflow sheets are able to entrain silt and distribute it over the surface as densely packed bed-load deposits, thus maintaining its dilatancy. Sand, its larger pores invaded by hydraulic penetration jets which maintain loose packing, cannot behave in this manner. Relative stability of the silt layer on soil surfaces, and its suppression of hydraulic penetration, allow transmission of drop-generated stress waves which cause the immediately underlying soil to become compacted into the main structural element of the rain-impact soil crust.
Mossbauer spectroscopic evidence of a IVFe3+ intermediate in the oxidation of Fe(Oh)2 to α-FeOOH
Authors: Cardile CM , Lewis DG
Published: April 2005

Mossbauer spectroscopy was used to study the oxidation of Fe(OH)2 under high pH conditions with the aim of detecting the formation of Fe(OH)3. The Mossbauer spectral parameters indicated that a small IVFe3+ component was initially present in the Fe(OH)2. The Mossbauer spectra were recorded at 77 K, thus any Fe species in solution would also be observed in the frozen state. The small IVFe3+ component increased progressively with the oxidation of the Fe(OH)2, maximizing with the onset of �-FeOOH formation. As �-FeOOH formation increased, the IVFe3+ component decreased, with �-FeOOH being the final sole phase. It is suggested that the Mossbauer spectral parameters indicate that a component such as Fe(OH)2 may form at high pH values as used in this study. Furthermore, any Fe3+ produced by the initial oxidation of Fe(OH)2 is exsolved from the solid and at the high pH of the surrounding liquid produces Fe(OH)-4 until the formation of the more stable �-FeOOH begins. This suggests Fe(OH)2 could be the building blocks for �-FeOOH in alkaline solution. No apparent Fe(OH)3 phase was observed as anticipated.
Predicting exchangeable cation distributions in soil by using exchange coefficients and solution activity ratios
Authors: Phillips IR , Black AS
Published: April 2005

A simple model which predicts the distribution of surface-applied chemicals in soil following leaching is described. The applied cation is considered to reach equilibrium between the solution and exchange phases prior to moving into the underlying soil layer. The distribution between the solution and exchange phases is defined by the Gapon relationship. The Gapon exchange coefficient is derived from exchange isotherms determined using a batch technique. Movement of the applied cation through successive layers and cation exchange with the soil continues until the activity ratio in solution equals the equilibrium activity ratio determined from the exchange isotherm. The applied cation remaining in solution is then considered to move 'freely'. A number of physical and chemical processes have been omitted in developing the model to retain simplicity and to ensure that the required parameters can readily be obtained using simple and well established laboratory procedures. In particular, only a binary cation exchange system is considered, and it is assumed that the rate of exchange is instantaneous. The inputs to the model are the amount of cation added, the Gapon exchange coefficient and corresponding solution activity ratio, the equilibrium activity ratio, the initial exchangeable and solution cation concentrations, and the average volumetric moisture content of soil during leaching. The simple model satisfactorily predicted the distribution of exchangeable K+ and Mg2+, and percentage of applied K+ or Mg2+ leaching 'freely' in the soil solution in homogeneous columns of soil having varying texture, clay mineralogy, and initial cation composition.
Changes in the physical properties of a vertisol following an irrigation of cotton as influenced by the previous crop
Authors: Hulme PJ , Mckenzie DC , Abbott TS , Macleod DA
Published: April 2005

Structural degradation of Vertisols depresses cotton lint yield by extending the period of waterlogging following irrigation or heavy rainfall. Break crops such as wheat and safflower are often grown without irrigation to improve the macroporosity of degraded Vertisols, by encouraging deep cracking, after several years of cotton production. Investigations were made into the effects of cultivated fallow, wheat and safflower on soil structure, and the growth of a subsequent cotton crop. The tests reported in this paper, done over a 12-day period following irrigation, were: soil water content and potential, core and clod bulk density, air-filled porosity, an index of macropore continuity using Rhodamine dye, and penetration resistance. The results, when compared with established limits of aeration and penetration resistance to cotton root growth, indicate that soil physical conditions at 0.25 m should have impeded root growth regardless of water content. However, cotton roots continued to extract water in this hostile soil environment; this favourable performance was attributed to the better conditions for root growth in the interaggregate fissures than those within aggregates. Apart from water content, all indicators of soil structure were able to differentiate consistently between the three crop treatments to a depth of 0.25 m. Below 0.8m, the cropped plots, particularly safflower, had lower water contents than the fallow plots.
The effect of irrigated crop production on the properties of a sodic vertisol
Authors: Mckenzie DC , Abbott TS , Higginson FR
Published: April 2005

Irrigated cotton yields in the lower Macquarie Valley, New South Wales, declined within a decade of the inception of irrigation, particularly on grey clays. Degradation of subsoil structure was thought to be involved. Two adjacent sites, one used for irrigated cotton production since 1968 ('cultivated'), the other for native pasture and grazing ('uncultivated'), were compared. The soil at each site, a sodic grey cracking clay (Vertisol), was described and sampled for a range of physical and chemical analyses. In the cultivated soil there was increased surface sodicity, greater dispersion of soil aggregates at 0 - 0-3 m, decreased organic carbon levels to 0 - 3 m and increased subsoil compaction. Also, the cultivated soil was observed to have more massive structure, with fewer macropores, between 0.2 and 0.7 m than the uncultivated soil. Probable reasons for this degradation of chemical and physical fertility following 15 years of intensive irrigated farming are discussed.
Water tables and soil colour as an indicator of saturation in some soils of the Waikato, New Zealand
Authors: Singleton PL
Published: April 2005

Seasonal fluctuation in water tables in some alluvial soils in the Waikato was determined to establish time, depth and duration of saturation. Duration of saturation could then be related to soil colour to test whether colour could be used as an indicator of saturated conditions in these soils. The results confirmed that there were different watertable regimes between soil series and that there could be different depths and durations of water-table within a series. In the soils studied, colour can be used as a general indicator of whether or not saturated conditions have occurred. However, soil colour did not give any indication as to the time of year or continuous duration of a water table, or whether or not soil wetness had changed as a result of improved drainage. The results of this study highlight the dynamic water-table relationships between and within Waikato soils. For detailed land-use interpretations based on depth to a water table it is advisable to take watertable measurements at the site itself rather than to rely on assessments based on soil colour. When measurement is not practical, the worst conditions indicated by soil colour should be used for interpretations and planning soil management.
Soil flux measurements using a portable wind erosion tunnel
Authors: Leys JF , Raupach MR
Published: April 2005

A portable wind erosion tunnel was used to measure the wind erodibility of a range of soil types under two treatments (bare uncultivated and bare cultivated) in south-west New South Wales. The erodibility was characterized by the soil flux function Q(u*) where Q is the streamwise soil flux (measured with a modified Bagnold soil trap) and u* is the friction velocity (obtained by fitting a logarithmic wind profile law to a wind profile measured in the tunnel). An average over 10 replicate plots for each surface type was necessary to smooth the large scatter in Q and the smaller scatter in u*. The Q values spanned three decades of magnitude, from the highly erodible sand, through the weakly erodible sandy clay loam to the basically nonerodible clay. Cultivation increased the erodibility of the sand and the sandy clay loam by about a factor of 10, but slightly decreased the erodibility of the clay. The function Q(u*) is well described by the Owen (1964) soil flux equation (J. Fluid Mech. 20, 225-42) but the threshold friction velocity is not well described by existing simple models.
Stone cover and rain intensity - Effects on infiltration, erosion and water splash
Authors: Agassi M , Levy GJ
Published: April 2005

The effects of level of stone cover, stone size and rain intensity on infiltration, erosion and water splash from a silty loam soil (Calcic Haploxeralf) were studied using a laboratory rainfall simulator. Square asbestos cement plates (5 mm thick), measuring 100 and 2500 mm2, were used to simulate stones. Three levels of surface cover (0, 25 and 50% cover) and two rain intensities (21 and 45 mm h-1) were studied. An increase in the level of stone cover increased infiltration and reduced erosion. The size of the asbestos cement plates had no effect on either infiltration or erosion. An increase in rainfall intensity resulted in a moderate increase in infiltration and a significant increase in soil erosion. Water splash from bare soil (control) reached 15.9% of the applied rain, thereby signifying its importance in simulated rainfall studies. An increase in the level of stone cover reduced water splash. By mulching with small plates, a lower percentage of water splash occurred, compared with large plates and the control. Rain intensity had no effect on water splash.
A soil sulfur test for pastures and crops
Authors: Blair GJ , Chinoim N , Lefroy RDB , Anderson GC , Crocker GJ
Published: April 2005

Soil testing for S has generally been unsuccessful when using extractants that remove only sulfate from the soil. An assessment of a range of extractants to predict S status was undertaken on soil samples taken from 18 field trials in northern N.S.W. The extractants were water, 0.01M monocalcium phosphate (MCP) and 0.5M NaHCO3, 0.25 M KCl heated for 3 h at 100, 80, 40, or 25�C. The highest correlation between soil S test level and % maximum yield was found in the 40�C KCl extractant (r2 = 0.73). This compares with an r2 value of 0.47 for the widely used MCP extractant. A study using a soil from a pot experiment where rice was grown showed that the KCl extract removed more S from the HI reducible (ester sulfate) fraction than did MCP. This S fraction is believed to be important in supplying S to plants. A comparison of the specific radioactivity of soil extractants and rice plants confirmed that the KCl 40�C extract removes S from similar soil pools as do plants. The procedure is recommended for wider evaluation.
Soil structure and plant growth
Authors: Passioura JB
Published: April 2005

Soil structure affects plant growth in many ways. Roots grow most rapidly in very friable soil, but their uptake of water and nutrients may be limited by inadequate contact with the solid and liquid phases of the soil. This contact is much more intimate in hard soil, but then the growth of the roots is strongly inhibited, so that their foraging ability is poor, and the plant may eventually become short of water or nutrients. However, many soils, even if hard, contain continuous macropores that provide niches for the roots to grow in. The presence of such macropores increases the extent of the root system, but because the roots are clumped within them, the rate at which the roots can extract water and nutrients from the soil between the macropores is considerably slowed. These macropores also provide niches for microorganisms, both symbiotic and pathogenic, so that the response of roots to different tillage treatments may differ markedly on this account alone. Soil structure not only affects the ability of roots to grow and to supply the leaves with water and nutrients; if adverse, it also induces them to send hormonal signals that slow the growth of the shoot, even if they are currently able to take up adequate water and nutrients.
Soil fauna and soil structure
Authors: Lee KE , Foster RC
Published: April 2005

Significant effects of soil fauna on soil structure are achieved mainly by a few groups among the larger soil invertebrates that are widely distributed and generally present in large numbers. Of these groups the most important are earthworms, termites and ants. The review deals mainly with earthworms, which are distributed throughout all but the coldest and the driest regions of the world. The effects of termites and ants on soil structure are also discussed. These groups of soil animals are also widely distributed, but are most common and most effective in influencing soil structure in tropical and warm temperate regions. A brief section deals with the influence of microarthropods, which are commonly found in large numbers, but because of their small size are unable to make large burrows in the mineral soil horizons, and are largely confined to pre-existing voids in litter and surface soil horizons. Their faecal pellets are granular and largely organic, with little included mineral soil material, and they sometimes make up the major proportion of forest litter layers. Quantitative assessment of the influence of earthworms on soil structure is available, but information on other groups is largely qualitative. The burrows of earthworms contribute to macroporosity and so influence water infiltration and aeration. Anecic species, that live in semi-permanent burrows opening to the soil surface and feed at the surface, provide more or less vertical channels for water infiltration and gas exchange. Endogeic species, that burrow continuously in search of food within the soil, provide more horizontally oriented, frequently extensive and intersecting networks of macropores that promote water movement and gas diffusion. Burrows that penetrate soil surface crusts are particularly important for water entry to the soil. Water movement through pores of the dimensions of earthworm burrows is important only when rainfall or irrigation supplies water at rates that exceed the capacity of the soil surface for capillary uptake. The combination of increase in surface area available for capillary uptake through the burrow walls and of hydraulic pressure resulting from the column of water in a water-filled burrow increases infiltration. Occupied burrows of anecic species may be sealed with soil or plant litter by the resident earthworm when water is ponded on the soil surface, or blocked by the earthworm's body, so as to be ineffective for water infiltration. When burrows are air-filled they provide surfaces that penetrate below ground and facilitate gas exchange.
The measurement of soil structure - Some practical initiatives
Authors: Coughlan KJ , Mcgarry D , Loch RJ , Bridge B , Smith GD
Published: April 2005

Soil structure has many aspects, and it is difficult to measure and characterize, particularly in soils where structure changes with wetting and drying. There is a need for soundly based methods robust enough to be used routinely on a range of soils. Such methods should also provide parameters for use in soil, hydrological and agronomic process models to enable the effect of soil structure to be simulated. This paper describes five methods and presents some results of indices which are proving useful in soils studies. An index of aggregate breakdown is derived from the proportion of sizes <0.125 mm formed in the soil surface under simulated rain. This index closely relates to infiltration and erodibility in the field. Disc permeameters, operated at a range of tensions, offer a convenient way to identify the various size classes of larger pores that are available to transmit water into soil under low energy wetting. The presence of many pores in the 0-7-3.0 mm range is linked with farmer observations of better soil structure in the field. It has been used to compare treatments and provide soil hydrologic parameters in soils that do not seal or are protected from heavy rain. In Vertisols, characterizing structure degradation and also the propensity for self-mulching present difficulties. Indices derived from clod shrinkage studies can discriminate between different treatment histories and different field soil structure. The proportion of oriented clay can also be used to diagnose soil structural damage by farming operations. Self-mulching is an important phenomenon in some Vertisols which is not, in general, well understood. Further work is needed to validate and improve each of the indices reviewed. Studies using the methods outlined could provide sufficient understanding of structural processes for them to be modelled. Key criteria for use in system simulations and quantitative land evaluation might then be measured (or modelled) by simplified, routine methods.
Interaction of soil deformations, structure and permeability
Authors: Kirby JM , Blunden BG
Published: April 2005

Soil deformations, structure and permeability are linked in consistent and qualitatively predictable ways. The critical state concept of soil mechanics provides a useful framework for the description of deformations and the changes in structure and permeability in agricultural operations. Changes in structure are limited until yield (the onset of permanent deformation) occurs either in uniaxial compression or shear. Following yield, changes are more pronounced and may be expansive or compressive. Expansion during shear is accompanied by localised zones of aligned fabric, while compression during shear results in more general rearrangement of structure. Uniaxial compression and compression during shear both result in decreases to permeability. Expansion during shear leads to increases or decreases in permeability, depending on the initial structure. In all cases, shearing appears to cause a change in permeability towards a unique set of relationships among the stresses, void ratio and permeability. Quantitative predictions of changes in structure and permeability resulting from soil deformation cannot be made using current information. Systematic studies of the interaction between soil deformations and structure are required, together with further systematic studies of the interaction between soil deformations and permeability. The critical state concept suggests useful directions in which to explore these interactions.
The effectiveness of zinc fertilizers as measured by DTPA soil extractable zinc, dry matter production and zinc uptake by subterranean clover in relation to soil properties of a range of Australian soils
Authors: Brennan RF
Published: April 2005

The effectiveness of zinc fertilizer (Zn) on a wide range of Australian soils was examined using subterranean clover (Trifolium subterranean cv. Nungarin) as a test crop in a glasshouse experiment. The initial effectiveness (IE) of zinc fertilizer as measured by dry matter production (DMP), and zinc content (uptake) of subterranean clover (clover) was found to vary markedly among the soil types. No simple linear retationship between the initial effectiveness measured by either dry matter production or uptake and any one soil property was found. IE values were found to be related to the pH (1 : 5 soil :water) (pHw) and the level of DTPA soil extractable zinc measured in the unfertilized soil (Zno). IE based on Zn uptake by clover tops was also related to the organic carbon (OC) (%) content of the soils. The model for IE measured by DMP in a stepwise linear regression was IEDMP = 2.682 - 0.107 pH,-4.852 Zn, (n = 45; r2 = 0-86). IE based on Zn uptake by clover tops was: IEuptake = 10.842 - 0.882 pH, - 0.310 OC (%) - 1.349 Zn, (n = 54; R2 = 0.85). The IE of zinc fertilizer measured by DTPA soil extraction (IEDTPA-zn) was also found to vary markedly among soil types. The level of zinc extracted by DTPA after the addition of Zn fertilizer was found to be affected by clay (%), organic carbon (%) and calcium carbonate (CaCO3) (%) content of the range of Australian soils. This relationship could be described by: IEDTPA - Zn = 0.178 + 0.0.002 Clay (%) + 0.014 OC (%) + 0.018 CaCO3 (%) (N = 54, r2 = 0.84)
Factors affecting dryland salinity in two wheat belt catchments in Western Australia
Authors: Mcfarlane DJ , George RJ
Published: April 2005

We investigated why the Wallatin Creek Catchment in the Western Australian wheatbelt had an appreciable area of secondary salinity whereas the adjoining North Baandee Catchment had almost none. The Wallatin Creek Catchment, which is long and narrow, had a shallow regolith over granite bedrock. Although this catchment had less salt stored in the regolith than the wider North Baandee Catchment, the groundwaters came close to the ground surface because the regolith was thin and the valley cross-section narrow. Management practices which increase recharge (e.g. using level banks to control runoff), are likely to result in increased salinity in the short term in the Wallatin Creek Catchment. We also investigated whether retaining areas of remnant vegetation had reduced the amount of secondary salinity in a sub-catchment of the Wallatin Creek Catchment. At comparable positions in the landscape, groundwater levels were up to 7 m lower under the remnant vegetation. The vegetation appears to have delayed, if not prevented, the development of salinity in nearby and downslope areas.
Relationships between extractable Al, selected soil properties, pH buffer capacity and lime requirement in some acidic Queensland soils
Authors: Aitken RL
Published: April 2005

The objectives of this study were to examine (1) interrelationships between various forms of extractable A1 and selected soil properties, (2) the contribution of extractable A1 to pH buffer capacity, and (3) investigate the use of extractable A1 to predict lime requirement. Aluminium was extracted from each of 60 Queensland soils with a range of chloride salts: 1 M KCl (AlK), 0.5 M CuCl2 (AlCu), 0.33 M LaCl3 (AlLa) and 0.01 M CaCl2 (AlCa). The amounts of A1 extracted were in the order AlCu > AlLa > Alk > AlCa. Little or no A1 was extracted by KC1 or Lac13 in soils with pHw values greater than 5.5 , whereas CuCl2 extracted some A1 irrespective of soil pH. The greater amounts of A1 extracted by CuCl2 were attributed mainly to A1 from organic matter, even though all of the soils were mineral soils (organic carbon 54.7%). Both AlCu and AlLa, were significantly (P < 0.001) correlated with organic carbon, whereas none of the extractable A1 measures was correlated with clay content. AlK and A~L, were poorly correlated to pH buffer capacity. The linear relationship between AlCu and pH buffer capacity (r2 = 0.49) obtained in this study supports the view of previous researchers that the hydrolysis of A1 adsorbed by organic matter is a source of pH buffering in soils. However, the change in CEC with pH accounted for 76% of the variation in pH buffer capacity, indicating that other mechanisms such as deprotonation of organic groups and variable charge minerals are also involved in pH buffering. The ability of CuCl2 and LaCl3extractable Al to estimate lime requirement depended on the target pH. The results suggest that lime requirements based on neutralization of AlLa would be sufficient to raise pHw to around 5.5, whereas requirements based on neutralization of AlCu substantially overestimated the actual lime requirement to pHw 5.5, but gave a reasonable estimation of the lime requirement to pHw 6 5.
Changes in soil pH due to long term soil storage
Authors: Slattery WJ , Burnett VF
Published: April 2005

Soil pH measured in 0.01 M CaCl2 was found to increase by up to 0.23 of a unit due to long term (7 years) storage of dried surface soil. In comparison, pH measured in water was found to increase by up to 0.55 of a unit after the same time of storage. Soils with the highest ionic strength were found to have the largest pH change. There appeared to be no relationship between soil type and pH change due to storage of soils. We suggest that caution be exercised when re-analysing soils that have been stored for long periods, for water and CaCl2 pH.
Studies of lignin degradation in mound material of the termite Nasutitermes exitiosus
Authors: Cookson LJ
Published: April 2005

Lignin degradation in the mound material of the enteric lignin degrading termite Nasutitermes exitiosus (Hill) was studied under normal and wet moisture conditions during incubation with C-14-(lignin)-Populus tremuloides Michx. There was negligible 14(CO2) evolution from mound material incubated for five weeks. However, adjacent soil when wet produced a 6.8% degradation of the 14C-(lignin)-lignocellulose.
Microbial activity and survival in soils dried at different rates
Authors: West AW , Sparling GP , Feltham CW , Reynolds J
Published: April 2005

The changes in microbial biomass C, soil respiration, microbial activity (respiration/microbial C) and the content of oxidizable organic C extracted by 0-5 M K2SO4, were measured in four soils of contrasting characteristics (a sand, two silt loam soils and a peat) which were air-dried at 22�C at three different rates in the laboratory. Respiration was also measured on samples of the drying soils rewetted with water. The rates of drying were: <10 h (fast), <33 h (medium) and <62 h (slow); drying was carried out for 6 h on consecutive days, with overnight storage. Measurements were also made on soils stored at field-moisture content over the 15 day duration of the experiment. Respiration and activity declined continuously and in a generally linear manner as the volumetric water content (W,) decreased. The decline in respiration in relation to water content W, was similar for all four soils and for the three rates of drying. Microbial biomass C also declined but generally only after a considerable initial period of drying (after the soils had reached Wv of 0-1-0.3). Extractable C values increased, but only after an initial drying period (Wv below 0.06-0.12). The increases in extractable C were approximately coincident with the decreases in microbial C, but only part of the increase in extractable C could be accounted for by the decrease in microbial C. Rewetting of dried soils caused a marked increase in respiration, particularly when the rewetted soils had reached Wv values where extractable C had begun to increase. The relationship between microbial activity and extractable C was similar for all four soils and was not affected by the rate of drying. The similarity of the microbial responses in these contrasting soils, and the absence of any detectable differences between rates of drying suggest that the microbial communities had similar survival strategies to resist desiccation, and occupied comparable physical niches in the soils, despite these soils having widely differing textures, organic matter content, and soil moisture characteristics.
Laboratory methods for measurement of soil erodibilities (K-factors) for the universal soil loss equation
Authors: Loch RJ , Rosewell CJ
Published: April 2005

This paper reports a comparison of several methods for estimating the K (erodibility) factor for the Universal Soil Loss Equation (USLE) on the basis of laboratory measurements of soil properties. All methods used the nomograph of Wischmeier et al. (J. Soil Water Cons., 1971, 26, 189-93) to calculate K on the basis of laboratory data, but the data inputs ranged from: dispersed particle sizes as originally used in the nomograph; non-dispersed particle size, measured after shaking in water; and equivalent sand size distributions, based on settling velocity distributions of particles (aggregates and sand grains) at the soil surface under rain. A further method tested with the use of aggregated particle sizes resulting from rainfall wetting was a correction of the calculated K based on average density of wet sediment >0.100 mm diameter. Estimated K factors were compared with K factors derived from field measurements of soil loss for five soils. Use of dispersed particle sizes gave poor prediction of field K values for the three clay soils, and size distributions measured after rainfall wetting gave poor predictions of field K values for the four soils that had sediment of low density. Predictions of K from the use of non-dispersed particle sizes, and from the use of particle size at the soil surface under rain combined with a correction for sediment density were good for three soils, reasonable for one, and little different to that from the nomograph for the remaining soil. These latter two methods gave similar results, and were successful in predicting field values of K. As well, both methods appear to be sensitive to effects of cropping management on soil structure and erodibility. Either method could be used, depending on laboratory resources available and possible other uses of the data obtained. Simpler methods for measuring size distributions after rainfall wetting and for estimating sediment density are suggested.
The influence of dispersible clay and wetting/drying cycles on the tensile strength of a red-brown earth
Authors: Kay BD , Dexter AR
Published: April 2005

The tensile strength of aggregates is a dynamic property under field conditions and for any given soil reflects the integration of processes leading to a strengthening and weakening of failure zones. The objectives of this study were to determine if variation in the tensile strength of natural aggregates from a red-brown earth could be related to the combined effects of (a) conditions favouring dispersion of clay and a subsequent increase in strength by cementation on drying and (b) wetting/drying cycles which would result in a decrease in strength. Aggregates were collected from the A horizon of different long-term rotations. The seasonal variation in tensile strength was assessed using data collected in 1988 and unpublished data which had been collected annually between 1978 and 1981. Trends in tensile strength over 5 years confirmed the importance of an interaction between climatic conditions which could lead to increased dispersion of clay and wetting/drying cycles. The extent of weakening of failure zones by wetting/drying cycles varied with the rotation. The nature of the impact of cropping history on tensile strength was dependent on antecedent climatic conditions.
Seasonal and fertilizer effects on the organic cycle and microbial biomass in a hill country soil under pasture
Authors: Perrott KW , Sarathchandra SU , Dow BW
Published: April 2005

A two year investigation of soil phosphorus and the soil organic cycle was carried out on a typical hill country site in the North Island, New Zealand. This included investigation of changes in soil phosphorus, as well as seasonal and fertilizer (superphosphate) effects on soil microbial phosphorus and sulfur, sodium bicarbonate extractable phosphorus and calcium chloride extractable sulfur. No net utilization of soil organic phosphorus occurred when application of phosphate fertilizer was withheld. On the contrary, accumulation of organic phosphorus was found in both fertilized and unfertilized plots. Immobilization of inorganic phosphorus into organic forms appeared to be a significant factor in fertilizer phosphorus requirements at this site. It was also a significant cause of the decline in the soil phosphorus status when no fertilizer was applied. Despite declining pasture production, there were no effects of withholding superphosphate on the soil biological cycle as measured by soil microbial phosphorus and sulfur, total organic phosphorus and sodium bicarbonate extractable organic phosphorus. However, seasonal variations occurred indicating storage and release of phosphorus by the soil organic matter and microbial biomass. Release of phosphorus occurred during periods of rapid pasture growth and could account for phosphorus uptake by the pasture at those times.