bluuebunny/crossref_metadata_2025 huggingface dataset:
The distribution and pedology of soil mosaics, Barossa District, South Australia
Authors: Wells CB
Published: April 2005

Black earths and Australian brown earths occur in ways contrary to normal expectation in the red brown earth zone of southern Australia. The soil pattern is an intimate fine-grained mosaic of the three great soil groups changing within a few yards from one to another in an erosional landscape and quite out of accord with the underlying Precambrian metamorphic rocks. Field studies reported here ascribe the black earths to thin intermittent remnants of a lacustrine Tertiary clay as parent material, and the brown earths to a mixture of the clay with the normal weathering products of the underlying rocks. A substantial part of the evidence for this is derived from their distribution as a horizontal lamina tracing out a contour band in the mid and upper mid slope topography. There is a nice accordance between the elevations of this band and of an adjacent, elevated, dissected black clay plain. The three soils are everywhere found in places which are consistent with the postulate that their parent materials were put there by processes of erosion, dissection, and redistribution of distinctly separate hill and high plain landscapes.
A hydrologic investigation of salt-affected soils in an alluvial plain of the Hawkesbury River, N.S.W
Authors: Collis-George N , Evans GN
Published: April 2005

An alluvial plain had noticeable salinization of low-lying surface soils after a succession of wet years. Piezometric investigations showed that the water-table was permanent and of low hydraulic gradient. Salinity measurements provided the ground water pattern of salinity and the soil-salt distribution relative to water-table depth. The critical depth for the water-table associated with surface salinization was 3 ft. The influence of a neighbouring saline-water bearing sedimentary shale deposit is examined, and the probable source of salt in the alluvial plain soils is suggested. A possible method of controlling this salt, by control of the input potential of the watertable, is discussed.
Studies on soluble silica in soils. II. The release of monosilicic acid from soils
Authors: Beckwith RS , Reeve R
Published: April 2005

The release of monosilicic acid into solution from soils has been studied under near-neutral and acid conditions. For all soils examined the final concentration of silica decreased with decreasing soil : solution ratio but larger total amounts were released into the larger volumes of extractant. The amount of silica extracted from any one soil varied with pH in a manner similar to that reported previously for residual amounts of monosilicic acid added to soil suspensions, viz. release was minimal at pH 7-9 and increased continuously with acidity. Citrate ions promoted release of native silica from soils as well as partially preventing sorption of added monosilicic acid. The inference of Part I, that much readily soluble silica may be derived from sorption sites in soils, has thus received additional confirmation. Studies have also been made of the release of silica both from some clay minerals and from synthetic sesquioxides on which monosilicic acid was previously sorbed. The release of sorbed monosilicic acid from sesquioxides resembles release from soils in its dependence on pH; iron and aluminium oxides are considered to be responsible for most of the retention of monosilicic acid by soils. Much of the silica rapidly dissolved from soils by N hydrochloric acid is also believed to be derived from sorption sites, and the use of an acid extractant for assessing the 'reactive silica' status of soils is briefly discussed. Suspensions of fine quartz or amorphous silica were partly converted to sorbed silicic acid in the presence of sesquioxides, and it appears that finely divided silica, even quartz, is not stable at near-neutral pH values in the presence of excess sesquioxides. The results of the investigations have been discussed briefly in relation to the availability of soil phosphate and the amounts of sorbed silicic acids occurring in various soils.
The reaction of polyvinyl alcohol with montmorillonite
Authors: Emerson WW , Raupach M
Published: April 2005

The interaction of montmorillonite with low concentrations (1-5 %) of completely hydrolysed polyvinyl alcohol (PVA) has been investigated. As there was no release of cations from the clay on adding PVA it is concluded that the exchangeable cations, in particular divalent cations, are not directly involved in the bonding of PVA to montmorillonite. This is consistent with an earlier hypothesis (Emerson 1960) that PVA is hydrogen-bonded to the clay. Efforts to inhibit the formation of these bonds by the addition of various low molecular weight polyhydroxy compounds were not successful. The linkage of PVA to Na-montmorillonite was strongly influenced by the order of addition of small amounts of sodium chloride. Adding salt after the PVA increased the viscosity of the clay suspensions far more than adding salt first. This difference in bonding was also reflected in the swelling behaviour of flakes prepared by filtering and drying the suspensions. It appears that in the presence of salt, the clay crystals come together before many clay PVA bonds are formed, resulting in smaller flocs and looser links due to the unabsorbed segments of the polymer chains. This sensitivity of PVA to salt is in contrast to that of anionic polymers, where the presence of a Stern layer of cations improved the efficiency of bonding. The effective bonding of PVA to the clay is considered to be by OH . . . O bonds along single chains to the clay oxygens. The basal (001) spacing observed on X-ray examination of complexes formed at higher PVA concentrations arises from the crossing of two chains, attached to adjacent silicate sheets.
The influence of the microflora on the physical properties of soils. II. Field studies on water repellent sands
Authors: Bond RD
Published: April 2005

The water repellence of sandy soils has been investigated at sites in the upper south-east of South Australia by observation of infiltration patterns and measurement of contact angle of wetting. Water penetrated into repellent sands through narrow channels, the intervening soil remaining dry. Such dry areas persisted through the winter months and were responsible for a mosaic pattern of bare and grassed areas in severely affected paddocks. The intensity of water repellence has been found to vary with species of plant cover, age of pasture, and also management practices.
Structure variation within two red-brown earth profiles
Authors: Sleeman JR
Published: April 2005

Stereomicroscopic and thin-section studies of structure and fabric features of two red-brown earth profiles from the Riverine Plain of south eastern Australia are assessed in relation to depositional layering and soil formation as suggested by field evidence. Internal fabric in relation to mode of occurrence suggests that some of these features are inherited from, and characteristic of, the original depositional layer whilst others have been formed or accumulated during soil formation subsequent to the cessation of deposition. Trends in the degree of development of these features with increasing depth suggest that the Hanwood profile consists of five depositional layers with evidence for a depositional time break, accompanied by soil formation, at the top of the fourth layer below the present surface. The Deniboota profile includes three depositional layers with evidence for a time break at the top of the second layer below the present surface.
Development and distribution of soils in the Merredin area, Western Australia
Authors: Bettenay E , Hingston FJ
Published: April 2005

The soil pattern in the Merredin district of Western Australia is closely related to a number of readily recognizable landscape features. An understanding of these relationships is proving useful in broad-scale mapping in semi-arid Western Australia and the units so obtained can be readily subdivided for more detailed mapping. Soil and topographic relationships of the five surfaces recognized are described in detail. These are an expression of erosional modifications of a mature Tertiary landscape resulting from changes in landscape stability. Deep lateritic weathering has influenced the chemistry and morphology of large areas of soils. Smaller areas of soils are developed from less weathered material exposed by complete removal of the lateritic profile, and from lake parna resulting from wind deflation of salinized alluvial sediments. The physical and chemical properties of samples from representative soils are summarized and discussed with reference to profiles which are arranged in groups on the basis of origin of parent material.
Aspects of the hydrologic cycle and related salinity in the Belka valley, Western Australia
Authors: Bettenay E , Blackmore AV , Hingston FJ
Published: April 2005

Factors involved in increasing salinity, which has followed clearing in the Western Australian wheat belt, have been investigated in a typical valley. Field and laboratory studies show that salinity is associated with a three-component hydrologic system involving surface, soil, and aquifer waters. The amounts of surface and soil water have increased after clearing. The third component, which is not thus affected, consists of a confined and continuous fine-textured aquifer which extends under most of the area and which has its intakes adjoining rock outcrops. This aquifer is the major repository for water and salt in the landscape, and salinity of overlying soils results where capillary contact with the surface occurs in the valley bottoms. The increase in volume of surface water does not lead directly to increased salinity, but rather, ultimately, to a removal of salts from the system via the main drainage lines. Increased soil water, however, serves to affect salinity in two ways. Firstly, it increases the area and duration of capillary contact between the confined aquifer and the soil surface in valley floors. Secondly, it leads to the development of seepage spots in the coarse-textured soils on valley sides, thus resulting in the formation of saline patches. The main part of the salt in the landscape has accumulated through atmospheric accession.
The slaking of soil crumbs as influenced by clay mineral composition
Authors: Emerson WW
Published: April 2005

The water adsorption and swelling of dry orientated flakes of a Ca-illite and a Ca-kaolinite have been measured at high relative vapour pressures and finally immersed in solution. Portions of the flakes equilibrated in the vapour phase were immersed in solution, either in air or under vacuum, and the degree of slaking observed. Whereas the pore space of illite was filled at p/po = 0.92 and slaking was inhibited, that of kaolinite was incompletely filled at p/po = 0.985 and the clay still slaked severely. Slaking of both clays only occurred if air was present initially in the flakes. The swelling of dry Ca-montmorillonite flakes in water was increased if the flakes were immersed in air rather than under vacuum. It is suggested that the pressures developed by entrapped air, and hence the amount of slaking due to this cause, depend not only on the initial size of the air-filled pores but also on how much the clay swells. Further, the thickness of the clay particles controls not only the pore size distribution but also how far the shear stresses due to swelling can be reduced by bending of the particles. Some of the observed properties of kaolinite flakes are explained in terms of a simple model. Two examples are given of kaolinitic soils which appear to slake and collapse to an appreciable depth on rapid wetting.
Chemical and mineralogical transformations accompanying the weathering of basic volcanic rocks from New South Wales
Authors: Craig DC , Loughnan FC
Published: April 2005

An investigation has been made of the chemical and mineralogical transformations which have accompanied the weathering of six basic volcanic rocks from eastern New South Wales. Montmorillonite is initially formed from the destruction of the olivine, pyroxene, and plagioclase in the parent rock, but, in the near-surface horizons, this mineral is unstable and may form kaolinite, halloysite, or a poorly crystalline montmorillonite. The alumina content shows a steady increase up the profiles, whereas the alkalis, alkaline earths, and some of the silica have been lost in the ground-waters during the mineral transformations. Marked concentrations of iron and titanium occur at specific levels in some of the weathering profiles and explanations of these phenomena are given.
Determination of hydraulic conductivity as a function of depth and water content for soil in situ
Authors: Rose CW , Stern WR , Drummond JE
Published: April 2005

A theory is presented to calculate hydraulic conductivity from successive measurements of water content profiles for soil in situ. With unsaturated soil, potential gradients are inferred using moisture characteristics, but with saturated soil these gradients must be measured directly. The weight of overburden can affect in situ soil water suction, and a method for determining this effect is given. The theory was applied to a soil profile with marked changes in moisture characteristics and texture, and conductivity was determined for several depths as a function of water content.
Water movement through a swelling material
Authors: Blackmore AV , Marshall TJ
Published: April 2005

The effect of the drag of a fluid on the porous material through which it flows is examined for a swelling material. It is shown that, when equilibrium is established between drag and swelling in films of oriented sodium montmorillonite, there is a decrease in void ratio in the material in the direction of flow. This effect of drag increases with decreasing electrolyte concentration of the permeating solution, in accord with double-layer theory, and with increasing drop in hydrostatic pressure across the film. Hydraulic conductivity was found to increase with decreasing electrolyte concentration of the permeating solution, contrary to usual experience. The cause of this is considered to be the increase in spacing corresponding to decrease in concentration. Hydraulic conductivity of unconfined film at equilibrium was found to decrease with increasing drop in hydrostatic pressure across the film. An increase in the pressure drop causes a decrease in the spacing of the clay, particularly towards the base of the film, so that the hydraulic conductivity of the whole film is lowered. Consequently Darcy's law does not hold for these films. Implications for less ordered swelling systems are considered briefly. The effect of drag on soils under field conditions will ordinarily be negligible.
The effect of flow above the water-table on tile drain design in Murrumbidgee Irrigation Area soils
Authors: Talsma T
Published: April 2005

Most tile drainage systems in the Murrumbidgee Irrigation Areas are installed in soils that are relatively impermeable at a short distance below the drain level, and these systems are designed to discharge excess water at a rate much less than the average hydraulic conductivity of the soil profile. The contribution of unsaturated flow above the water-table under these conditions may be considerable, and the effect of ignoring this contribution upon drainage design is therefore investigated. Capillary conductivity-suction relationships of Murrumbidgee Irrigation Area sods are characterized by the absence of a critical suction value, above which capillary conductivity declines rapidly from the saturated hydraulic conductivity. The presence of a critical suction value, however, is a basic assumption in acceptable analyses of capillary flow and immediate application of these analyses in our case is not justified. An approximate analysis is therefore presented, dividing flow above the water-table into a saturated capillary fringe as conventionally defined and a region above this fringe, where flow is in the unsaturated state and mainly vertical. The latter region is evaluated from the capillary conductivity-depth profile during vertical infiltration from the soil surface to the water-table. It is found that flow above the water-table is accounted for by adding a layer of 10 cm or less to the saturated flow region. The maximum error in design spacing, resulting from neglect of flow above the water-table, is about 6%. Capillary flow may therefore be safely ignored for practical design purposes. If necessary, more accurate solutions may be obtained numerically by solving the Laplace equation for the stream function rather than for the potential function.
Studies of the relative importance of iron and aluminium in the sorption of phosphate by some Australian soils
Authors: Bromfield SM
Published: April 2005

Phosphate sorption by 47 acid surface soils was correlated with the amounts of iron and aluminium extracted from them by ammonium oxalate at pH 3.2. The correlation coefficients, when all soils were considered, were highest for sorption and aluminium. For certain groups of soils, iron or iron plus aluminium gave higher coefficients than did aluminium. The relative contributions of iron and aluminium to phosphate sorption could not be accurately assessed from these correlation coefficients because iron and aluminium themselves were positively correlated. Eleven of the forty-seven soils were chosen for determinations of the effect of selective removal of iron and aluminium on their ability to sorb phosphate. Soils usually sorbed less phosphate after various amounts of their iron and aluminium had been extracted chemically. Many of them, however, still sorbed large amounts of phosphate in spite of the removal of reducible iron and acid-soluble aluminium. Soils and haematite extracted with sodium dithionite in acetate at pH 5.0 usually sorbed more phosphate than untreated samples. This was due largely to the incomplete removal of reduced iron and could be prevented by washing with dilute acid. Acid washing after dithionite treatment caused sorption by the soils to fall below the values for the untreated samples and virtually destroyed that of the oxide. It also removed much aluminium from the soils. The amount by which sorption fell below that of the untreated samples could be accounted for largely by this aluminium. It was concluded tentatively that, for most of the soils, phosphate sorption was due to acid-soluble aluminium and to sorption sites which were non-reducible and insoluble in dilute acid. The contribution of reducible iron in the original soils remains in doubt, but it could be a minor one.
The nature of the mechanical impedance to seedlings by soil surface seals
Authors: Arndt W
Published: April 2005

The nature of seedling emergence through soil surface seals under a variety of field and model situations is described. In this process the importance of the shear and compressive strengths of the seal has been demonstrated. Resistance to emergence has been shown to be also due to gravity, soil cohesion, and friction between structural parts. The mechanics of seedling emergence is too variable and complex to be expressed by a single index, such as the tensile strength of free samples, as in the modulus of rupture determinations of Richards (1953). Direct measurement of mechanical impedance is preferable to refining the use of such indices, and provides a basis for a better understanding of the relation between seedlings and soil properties influencing emergence.
The influence of soil strength on the penetration of a loam by plant roots
Authors: Barley KP , Farrell DA , Greacen EL
Published: April 2005

Wheat and pea roots were grown through soil crumbs until they encountered cores of more finely structured earth. The cores were prepared from a loam at various bulk densities and matric suctions. Over a range commonly found in the field, the penetration and growth of the roots were controlled chiefly by the strength of the soil. Soil strength should be regarded as a property that has a general influence on root elongation, rather than as a limiting condition encountered in unusual soils.
An examination of a forest site which has exhibited the ash-bed effect
Authors: Humphreys FR , Lambert MJ
Published: April 2005

A site which has shown the 'ash-bed effect' to a marked degree was examined 9 years after planting with Pinus radiata. Trees grown in the ash-beds were found to be 1.2 to 1.4 times the height and more than twice the volume of trees grown next to the ashbeds. Chemical analysis of their foliage revealed that phosphorus levels were significantly higher in the ash-bed trees than in the normal trees, while the calcium, magnesium, sodium, potassium, aluminium, nitrogen, and manganese were the same. Soil analyses showed that the ash-bed soils had higher pH and exchangeable calcium contents and lower 'phosphorus adsorption capacity', exchangeable aluminium, and Tamm's oxalate-soluble aluminium than the normal soils, while no difference could be found in the loss on ignition, total nitrogen, ammonium nitrogen, 'total' phosphorus, Tamm's oxalate-soluble iron, exchangeable potassium, sodium, or magnesium. The soil phosphorus was fractionated and it was found that the ratio of the phosphorus associated with aluminium to the 'total' phosphorus was significantly greater in the ash-bed soils than the other soils. In the material examined the 'ash-bed effect' is associated with increased phosphorus availability. This could arise from a change in the composition of the soil phosphorus, a reduction in phosphorus adsorptivity, a reduction in aluminium ion concentration, an increase in phosphorus solubility because of more favourable pH conditions, and increased calcium levels. The possibility of a nitrogen x phosphorus interaction in earlier years is discussed.
Morphology and origin of patterned ground in a humid tropical lowland area, New Guinea
Authors: Haantjens HA
Published: April 2005

Two types of patterned ground occur on rolling to undulating plains consisting of weathered Pleistocene deposits under a warm climate with an annual rainfall between 1650 and 2000 mm and low seasonality. Pitted soils occur on gentle slopes and are characterized by sharply defined holes or unconnected trenches developed in coarser textured upper-soil horizons, above slowly permeable, finer textured subsoils. Sorted stripes are found locally on moderate slopes and consist of a network of gravel strips aligned at about 25� to the maximum slope and separating low earthen rises. There is no evidence that deformation by swelling and shrinking, loading, or liquefaction has caused the pitted soils. On the other hand, there are strong indications that this micro-relief is produced by large earthworms. Worms are also considered to build up the earthen rises of the sorted stripes, but, in this case, are likely to act upon a pre-existing pattern of gravel distribution and differentiation in gleying caused by denudation, and minor deformation due to differential swelling and shrinking, loading, and rheo-tropic disturbance. It is suggested that the microrelief caused by worms is not older than 400-800 years.
Stone distribution in a stony tableland soil
Authors: Mabbutt JA
Published: April 2005

Texture-contrast profiles on a stony tableland showed concentration of stone in the A horizon, very little stone in the B horizon, and marked recurrence of stone below. The stone was identical with that in an underlying silcrete duricrust. There had been only slight lowering of the soil surface to form the present pavement, and no other stone appears ever to have been exposed. The contours of the surface soil are inconsistent with stone derivation from a higher-lying siliceous horizon. Heavy minerals indicate that the profiles are residual and that the stone-free clay B horizon is not a depositional layer. Upward displacement of stone within the profile by swelling and shrinkage of the clay subsoil alone explains the consistent relationship between soil horizons and the distribution of stone. There appears to have been little or no associated gilgai formation, probably owing to the mulching effect of a thick, coarse textured, stony surface soil. A bleached A2 horizon and a horizon of salt accumulation developed after stone displacement, and indicate cessation of subsoil movement and withdrawal of the wetting front with change to a drier climate.
The association of trace elements with manganese minerals in Australian soils
Authors: Taylor RM , McKenzie RM
Published: April 2005

In widely different types of Australian soils birnessite and lithiophorite appear to be the common forms of occurrence of mineralized manganese. These mineral forms were dissolved out of the soil by hydrogen peroxide acidified to pH 3 with nitric acid and analyses of the extracts were made. It was found that the concentration of trace elements is generally quite high in these minerals. In particular, most of the soil cobalt (average 79%) was contained in or associated with these minerals where they were present.
The measurement of the diffusion of oxygen in saturated porous media
Authors: Smiles DE , Griffin DM
Published: April 2005

Methods of measurement of oxygen diffusion in saturated porous media are examined and established results of the analysis of ground water flow are applied to the 'bare platinum microelectrode technique'. Some physical consequences of the analysis when applied to simple biological situations are discussed.
Soil properties in relation to the sulphur and phosphorus status of some basaltic soils
Authors: Spencer K
Published: April 2005

Twenty-three basaltic soils from elevated areas in northern New South Wales were examined for sulphur and phosphorus status by growing Phalaris tuberosa L. in pots in a glasshouse. Sulphur deficiency was more common and more severe than was phosphorus deficiency. To determine whether there may be some topographic control of sulphur or phosphorus status, soil colour was examined, as in general the reddest soils were found in the highest positions in the landscape. The soils were first considered as one group and then as subgroups of sedentary, colluvial, and alluvial soils. Using redness to rank the soils, there was no overall relationship to sulphur or phosphorus status. However, colour of the sedentary soils was significantly correlated with sulphur status (r = 0.92***), the reddest soils being the most deficient. The sulphur status of the brown colluvial and greyish brown alluvial soils showed no relationship to colour; they were uniformly severely deficient. Phosphorus deficiency was not associated with soil colour. Neither soil pH nor redox potential was related to the sulphur and phosphorus status of the soils. There was only a weak correlation (r = 0.60**) between the water-soluble sulphur content of all soils, but a stronger correlation (r = 0.81**) when only the sedentary soils were considered. Several soil phosphorus fractions could be satisfactorily used to distinguish between phosphorus-deficient and phosphorus-sufficient soils.
The adsorption of poly(vinyl alcohol) by natural soil aggregates
Authors: Williams BG , Greenland DJ , Quirk JP
Published: April 2005

The adsorption of poly(viny1 alcohol) by natural aggregates and undisturbed core samples of Urrbrae loam has been investigated. The factors studied included the size, shape, and structure of the polymer, the physico-chemical properties of the soil, and external physical and chemical factors. The rate of adsorption has been interpreted in terms of polymer diffusion in a porous medium and the significance of these studies in relation to the use of synthetic soil conditioners has been discussed.
Mineralogical and weathering study of a red-brown earth formed on granodiorite
Authors: Green P
Published: April 2005

The development of a red-brown earth has been studied by means of mineral and fabric analyses. Data from particle-size analysis and zircon distribution indicate relative uniformity of the parent material throughout the profile, with a possible minor disconformity near the bottom of the B horizon. Calculations of gains and losses of major minerals during soil formation, based on the zircon content of each soil horizon and of the rock, show a break in the progressive increase in weathering towards the surface, suggesting that the soil is in fact a two-storied profile; micromorphological evidence supports this postulate. The constancy of the qualitative mineral assemblage, however, shows that both sola were formed entirely from the underlying weathered granodiorite. The top four horizons are interpreted as being a separate soil, probably developed from a surface movement layer composed of some material from the upper horizons of the older profile with accessions from weathering granodiorite boulders. Both soils are considered to have been formed dominantly by in situ weathering of primary minerals and removal of the weathering products by leaching; clay illuviation does not appear to have been more than a very minor soil-forming process.
The geometrical description of linear and simple planar features in soils
Authors: Willoughby DR
Published: April 2005

A quantitative graphical method of describing the spatial orientation of all linear and planar features in soils is presented. The method is then applied, on two black earth samples, to obtain solutions for planar particles and planar pores in one soil, and the plant root system and planar pores in the other. The solutions from each of these components are not only suitable for comparison with each other but, more importantly, are an expression of certain aspects of soil mechanical behaviour.
Leaching of tile-drained saline soils
Authors: Talsma T
Published: April 2005

Leaching experiments were conducted on three tile-drained saline soils, each soil having a different average hydraulic conductivity. The experimental plots consisted of the area between two parallel lateral drains and the main disposal drain. Fresh irrigation water was alternately ponded to a depth of 15 cm and drained to slightly above tiledrain depth. Chloride removal was measured on soil samples taken after completion of each draining cycle and, independently, from frequent sampling of the tile effluent. The quantity of drainage water and chloride removed through the drains was smaller than the total drainage water, estimated from the water balance and total chloride loss from the soil profiles, indicating that all seepage water did not discharge through the tiles. Analysis of results shows that during the ponding stage desalinization proceeds more rapidly near the drains than midway between, while during the falling water-table stage desalinization is more even over the whole area. This is explained by the difference in surface inflow rates across the area between drains during the two stages. Comparison of continuous ponding with alternate ponding and draining shows that in the latter case complete desalinization is achieved with considerably less leaching water. The leaching efficiency is not very high under conditions of continuous ponding.
The tensile strength of soil cores containing polyvinyl alcohol
Authors: Williams BG , Greenland DJ , Quirk JP
Published: April 2005

The indirect tensile strength (I.T.S.) of cores formed from a clay soil treated with polyvinyl alcohol (PVA) solutions has been determined using the Brazilian core test. With increasing amounts of adsorbed PVA the I.T.S. values increased up to a maximum of about three times that of cores containing no PVA. Further amounts of adsorbed PVA then resulted in a decrease of I.T.S. Increasing the water content of the soil-PVA complexes resulted in a marked decrease in the I.T.S. values, although they did not decrease to the same extent as in untreated cores. PVA having various molecular characteristics produced different degrees of strengthening. The results are interpreted in terms of the strength of
Numerical analysis of the convection and diffusion of solutes to roots
Authors: Passioura JB , Frere MH
Published: April 2005

A numerical method is given for solving a partial differential equation describing the radial movement of solutes through a porous medium to a root. Computer programmes based on the method were prepared and used to obtain solutions of the equation for an idealized root-soil system in which a solute is transported to the root by convection but is not taken up by the root. Various patterns of water uptake were considered, the most complex being a diurnally varying uptake from soil in which the water content is decreasing. The solutions suggest that the maximum build-up of solute at the surface of a root is trivial if the root is growing in a medium such as agar, in which the diffusion coefficient of the solute is high, but may be considerable, with a concentration up to 10 times higher than the average concentration in the soil solution, when the root is growing in a fairly dry soil. The application of the method to systems other than the one considered in detail is discussed.
Release of amino acids from soil humic acids by proteolytic enzymes
Authors: Ladd JN , Brisbane PG
Published: April 2005

Direct evidence for the occurrence of peptide bonds in soil humic acids has been obtained by showing that the proteolytic enzyme pronase releases a-amino acids from each of 10 humic acids. The maximal amounts of amino acids liberated by pronase accounted for 27.6-39.4% of those released by hot acid hydrolysis. The susceptibility of humic acids to proteolytic attack showed an approximate inverse relationship with their aromatic content, based on their absorbance at 260 or 450 m�. Both pronase and papain attacked casein less readily when it was incorporated into a phenolic polymer prepared from p-benzoquinone. Papain was inactive towards soil humic acids. Similar amino acids were released by pronase from each of five humic acids tested. The amino acid patterns showed no basic amino acids but relatively high proportions of leucine (isoleucine) as compared with those obtained by acid hydrolysis. The action of pronase on humic acids had little effect on the molecular weight distribution of the humic components.
The solubility of potassium from soil illites. III. Reactivity towards other ions
Authors: Tucker BM
Published: April 2005

The potassium equilibrium solubility and the potassium extracted from five illitic soil clays by various solutions have been measured. The solutes were chlorides of inorganic monovalent and divalent ions, of amines, and of heterocyclic nitrogen bases; and in addition other salts of sodium and calcium, several amino acids, and a few non-ionic compounds were used. The amounts of potassium displaced from these clay preparations depended on the size and shape of the displacing cations-generally the smaller the cation the more readily did it release potassium-and this effect continued to control release down to quite low levels of potassium solubility. This confirms the previous view that the potassium left in these clays after extensive treatment with sodium and calcium chloride lies in the interlayer spaces of the illite minerals, and provides a partial verification of the original hypothesis that potassium release from these interlayer spaces is a complex reaction involving hydrogen ions. There is some evidence that the potassium removed comes from a limited number of interlayers which show decreasing accessibility to larger ions. There are no positive indications that chemical attack of the clay mineral structure is responsible for potassium release when the clay is not heated or dried. Amino acids are able to displace potassium with an effectiveness which decreases at greater molecular weights and approaches that of primary amines of similar size in spite of the presence of the negatively charged carboxyl groups. Otherwise the release of potassium depends almost entirely on displacement by other cations and is unaffected by anions or non-ionic compounds.
The solubility of potassium from soil illites. V. Interlayer hydrogen ions; heats of reaction; and synopsis
Authors: Tucker BM
Published: April 2005

When potassium is readsorbed at interlayer sites in soil illites after displacement in calcium chloride solution, hydrogen ions are released in proportions ranging from 1/6 to 1/10 of the potassium adsorbed. This supports the conclusions of earlier work that release of potassium by calcium ions from these sites requires the intervention of hydrogen ions in the approximate ratio of one hydrogen ion to three calcium ions. The release of potassium increased about 1.4 times for a temperature rise from 10 to 30�C. The heat of reaction was 3 or 4 kcal/mole potassium released. This is consistent with a reaction between ions and charged sites as the heats of many ionic reactions are of this magnitude; and it appears to be less than the heats of decomposition of the clay mineral lattice. A summary of the findings of Parts I-V of this series appears in the Synopsis
An examination of the use of ammonium fluride as a selective extractant for aluminium-bound phosphate in partially phosphated systems
Authors: Bromfield SM
Published: April 2005

The release of phosphate from aluminium-bound, iron-bound, and calcium-bound phosphates by the solutions proposed by Chang and Jackson (1957) and by Fife (1959b) for the estimation of aluminium-bound phosphate in soils was examined. Release was studied in the presence and absence of iron and aluminium oxides. Ammonium fluoride solutions released most of the aluminium-bound phosphate and in addition variable amounts of the other two types of phosphate. The proportion of these phosphates extracted by ammonium fluoride was decreased by the presence of iron oxides and, in certain cases, by the presence of aluminium oxides. It is suggested that many reported estimates of aluminium-bound soil phosphate obtained using the procedures of Chang and Jackson and of Fife are in error. Examples of how these errors arise are discussed. The practice of equating ammonium-fluoride extractable soil phosphate to the aluminium-bound phosphate content of the soil does not appear valid.
Changes in charge charactistics of soils after treatment with 0.5M calcium chloride at pH 1.5
Authors: Tweneboah CK , Greenland DJ , Oades JM
Published: April 2005

The kinetics of the removal of iron, aluminium, and silicon from soils and clays in the pH range 0-3 have been studied using a number of oxides, clay minerals, and soils. At pH 1.5, aluminium is removed but little iron or silicon. An initial rapid rate of aluminium extraction is followed by a slower constant rate. The rapidly released aluminium is extracted in approximately 12 hr using 0.5M CaCl2 at pH 1.5.reatment of a range of soils and clays by this method reduced the positive charge developed at low pH very substantially but had little effect on the negative charge. It is suggested that the positive charges in the soils studied are mostly due to the 'active' aluminium oxides.
Microrelief features in a humid tropical lowland area. New Guinea, and their earthworn acctivity
Authors: Lee KE
Published: April 2005

Haantjens (1965) has reported patterns of micro-relief on lowland soils bordering the Sepik river floodplain in New Guinea, and has attributed their formation primarily to excavation and heaping of casts by Pheretima tumulifaciens Lee, a large earthworm associated with the micro-relief features. Evidence is presented to show that the micro-relief is probably not due to earthworm activity. It is proposed that the micro-relief results from a combination of wind and water erosion, acting on a landscape partially bared by man-made fires. The association of earthworms with the micro-relief features is probably a necessary ecological adaptation for the survival of a previously forest-dwelling species to the change to grassland induced by fire. The physical and chemical composition of the casts and soil are discussed and evidence is presented to show that the ridges and mounds observed are composed of material from the upper and not from the underlying soil horizons.
The theory of absorption in aggregated media
Authors: Philip JR
Published: April 2005

The question of the applicability of the 'diffusion analysis' to transient flows in unsaturated aggregated media has been, till now, an open one. It has been uncertain whether significant deviations from the predictions of the diffusion analysis occur as a consequence of local disequilibrium. The present paper develops the theory of absorption in aggregated media and so provides a means of studying this question. An aggregated medium is regarded as one made up of macroporosity, through which flow on the Darcy scale occurs, and microporosity, which is free to exchange water with the macroporosity. Absorption in such a medium is analysed with the aid of two extreme models of macropore flow, one a wet-front model and the other a linearized model (the mathematical details of which are developed elsewhere). The wet-front analysis leads to an integral equation that is solved by means of the Faltung theorem of the Laplace transformation. It is found that there is little difference between the solutions for the two models. The wet-front model is chosen for further study since it appears to be more realistic and is more versatile. Various models of absorption into the microporosity are studied, and are found to lead to essentially similar results. All models (and general physical considerations) indicate that the aggregated medium behaves initially as a classical medium with sorptivity equal to that of the macroporosity S; and that the apparent sorptivity increases with time, ultimately approaching a limiting value (> S). The cumulative uptake into the microporosity appears to be proportional to time initially, but is finally proportional to (time)1/2. The characteristic time of absorption into the microporosity tends to be small for most media of interest. Ln such cases, deviations from the diffusion analysis due to aggregation occur only during a short initial period. These considerations hold also for other transient phenomena such as infiltration and capillary rise in various geometries. It is concluded that the diffusion analysis may usually be applied to aggregated media. The present work provides means of analysing the exceptional cases where this is not so, such as media containing large aggregates of low sorptivity.
Diffusion, dead-end pores, and linearized absorption in aggregated media
Authors: Philip JR
Published: April 2005

Transient diffusion in a porous medium containing dead-end pores will not behave as simple diffusion if local disequilibria of concentration (between neighbouring active and dead-end porosity) are significant. The problem of the diffusion consequent on a step-function change of concentration at the surface of a semi-infinite column of such a medium is solved by means of the Laplace transformation. The solution, simpler than those already in the literature, is well adapted to the detection of dead-end porosity by diffusion observations, a matter of current interest in soil physics. The diffusion initially follows a (time)) law and, at sufficiently large times, follows a second law of this type. The ratio of the two coefficients is a simple function of the ratio of dead-end porosity to active porosity. A study of the characteristic time of local equilibration indicates, however, that deviations from simple diffusion are limited to a small initial period, during which the diffusion process penetrates into the medium no further than a few pore dimensions. It therefore appears that, in systems of interest in soil physics, the existence of dead-end porosity will be difficult to confirm experimentally and is, in any case, of little practical importance. The experiments of Goodknight, Klikoff, and Fatt were not for molecular diffusion but for the physically different process (better fitted to exhibit significant local disequilibria) of the flow of a compressible gas. In any case, since their 'dead-end porosity' consisted of orifices and chambers of large dimensions, their experiments are not evidence that dead-end porosity produces significant deviations from simple diffusion behaviour (even for the process they studied) in real media. The formalism developed to solve this problem applies also to the linearized model of absorption of water into an unsaturated aggregated medium. The connections between the two problems are established, but details of this application are given in Philip (1968a). Two further applications are indicated: transient diffusion of soluble gases in porous media, and transient heat conduction in composite media.
Water transport in soil with a daily temperature wave. II. Analysis
Authors: Rose CW
Published: April 2005

The results of a field experiment investigating water transport in soil with a strong daily temperature wave have been analysed according to theory, both theory and results having been given in Part I (C. W. Rose 1968a). Analysis yielded the history, for six days and nights following saturation, of separate net flux densities into two contiguous layers of the soil profile which were 1-3 cm and 3-12 cm below the soil surface. In this experiment, where maximum daytime temperature gradients in the soil approached 10 degCcm-1, net vapour flux densities into both soil layers were of comparable magnitude to transfer in the liquid phase, even at suctions as low as 200 cm of water. At suctions greater than about 5000 cm of water, changes in water content were achieved almost entirely by vapour transport. From the commencement of observations liquid phase water flux caused by gravity was small compared with that arising from gradients in soil water suction, and, as will commonly be the case, liquid flux arising directly from temperature gradients was also relatively unimportant. In contrast with the dominantly upward liquid phase movement through the profile, the direction of vapour flux oscillated in response to the diurnal temperature gradient, vapour flux therefore being downward during the day, except in a very shallow surface layer. It was upward during the night when the surface was cooler than the soil below, this being the main reason for the pronounced night-time increase in water content of the surface layers. Maximum errors arising from both experimental and analytical sources were analysed as uncertainties in a vapour flux enhancement factor defined in the theory. Despite these uncertainties there was some evidence of enhancement of the vapour flux, and analysis showed that the assistance to vapour flux that can be provided by a discontinuous liquid phase was the most likely cause of such enhancement in this experiment. Some implications of the work described are briefly reviewed.
Calibration and assessment of soil tests for estimating fertilizer requirements. II. Fertilizer requirements and an evaluation of soil testing
Authors: Colwell JD
Published: April 2005

The estimation of the phosphorus and potassium fertilizer requirements of wheat and potatoes from soil test calibration equations is described. The procedure is based on the estimation of yield response to fertilizer at the site represented by the soil test and the application of economic principles to the function thus established. Soil testing may be justified on the basis of statistical tests of significance on these estimates. Since, however, testing can be expensive it should also be justified on economic grounds, such as by comparison of the profit obtained from the use of soil test estimates of fertilizer requirement with the profit from the use of some alternative estimate of fertilizer requirement. A preliminary evaluation may be made from a comparison of profits from soil test and average regional estimates of fertilizer requirement, using the calibration equation for the estimation of profits at different soil test levels. This method of evaluation separates the benefit due to testing from that due to the application of fertilizers. It is shown by this procedure that a soil test for the phosphorus fertilizing of wheat and for potassium fertilizing of potatoes in southern Ontario is worth while, given sufficient diversity of nutrient level within the region.