bluuebunny/crossref_metadata_2025 huggingface dataset:
DISTRIBUTION OF CARBON DIOXIDE IN THE AQUEOUS PHASE OF AEROBIC SOILS
Authors: GREENWOOD D. J.
Published: July 2006

Theory predicts that in the aqueous phase of aerobic soils carbon dioxide concentration/distance gradients are 1·35 times as large as those for oxygen. Because of differences in solubility, the partial pressure/distance gradients of carbon dioxide should be less than one‐twentieth of the gradients of oxygen partial pressure. Experiments were carried out to test this prediction.

In some experiments oxygen partial pressures were measured directly by means of a micro‐electrode and carbon dioxide indirectly by methods involving microelectrode determinations of specific conductance in agar‐CaCO3 gel. Measurements were made in models of water‐saturated soil consisting of yeast cells embedded in agar‐CaCO3 gel, around plant roots in agar‐CaCO3 gel and within water‐saturated soil. Oxygen partial pressures fell by 5–15 per cent of an atmosphere over distances of 0·2–0·4 cm whereas carbon dioxide partial pressures increased by less than 0·3 per cent of an atmosphere over the same distance.

In other experiments different thicknesses of water‐saturated soil were incubated with their upper surfaces exposed to air. The mean oxygen partial pressure fell by 7–13 per cent of an atmosphere with increasing the thickness from 0·2 to 0·4 cm whereas the carbon dioxide partial pressure never increased by more than 0·2 per cent of an atmosphere.

Both sets of evidence confirm the theoretical prediction. It is concluded that the partial pressure of carbon dioxide in the aqueous phase of soils containing no oxygen‐free zones, would never, even at the surfaces of roots, be more than 1 per cent of atmosphere greater than in the gas phase.
EFFECT OF SOIL CLAY TYPE ON THE ‘AVAILABILITY’ OF ZINC IN SOME MEDITERRANEAN RENDZINA SOILS
Authors: NAVROT J. , GAL M.
Published: July 2006

The influence of soil clay type on the ‘availability’ of zinc was studied in six rendzina soils from Israel. The quantities of zinc extracted by EDTA—(NH4)2CO3, were higher in the soils with a lower total of zinc content. Values of extracted zinc calculated on the basis of soil minus CaCO3 were higher in soils with attapulgite than in soils with montmorillonite as the predominant mineral. Thus, it appears that zinc is more strongly bound to montmorillonite. This was confirmed by a greenhouse experiment in which total zinc uptake after zinc fertilization was higher from rendzinas containing attapulgite than from montmorillonitic rendzinas.
OPALINE SILICA OF RECENT VOLCANIC ASH SOILS IN JAPAN
Authors: SHOJI SADAO , MASUI JUN‐ICHI
Published: July 2006

Soil samples were investigated from three different climatic regions of Japan. The soil profiles were well drained and consisted of a number of buried soils. Organic matter and free iron oxides were removed from the samples which were then fractionated. Laminar opaline silica particles occurring in the 0.2 to 5 μm fractions were examined electron‐optically following ultrasonic and cold 5 per cent sodium carbonate treatment.

Four types of opaline silica particles were distinguished: circular, elliptical, rectangular, and rhombic. The opaline silica particles are extremely thin. They show fine‐grained uneven surfaces and weathered and alkali‐treated opaline silica particles appear to be very porous suggesting that the particles are actually composed of extremely fine silica spheres. Opaline silica panicles occur only in the 0.2 to 5 μm fractions and are most abundant in the 0.4 to 2 μm fractions. Of the four types the circular and elliptical types predominate. The elliptical type is the most common in the fine fraction and the circular type in the coarse fraction.

Compared with B‐ or C‐horizons, the A‐horizon of a profile tends to be relatively rich in opaline silica. Opaline silica particles are abundant in recent volcanic ash soils, particularly in Hokkaido soils < 500 years old. Soils of this area more than 7000 years old contain opaline silica particles whereas they are rare in Kanto soils > 6000 years old and in Kyushu soils > 4000 years old.

Hokkaido has much lower mean annual temperatures and rainfall than Kanto or Kyushu. This may have caused slower weathering of opaline silica in the Hokkaido soils.

Conditions for formation of opaline silica may be less favourable in subsoils because supersaturation of silica and concentration of bases is less likely to occur in subsoils than in surface soils.
A PHOSPHATE SORPTION INDEX FOR SOILS
Authors: BACHE B. W. , WILLIAMS E. G.
Published: July 2006

Phosphate sorption isotherms covering a wide concentration range (10−6 to 5 × 10−3m phosphate) were determined for 42 soil samples at 20 °C by a standardized technique. The slope of a plot of the sorption, x, against the logarithm of the equilibrium solution phosphate concentration, log c, measured at c= 10−4M, proved a suitable reference index to characterize the phosphate sorbing properties of the soils. Several single‐point methods were tested by statistical correlation against this reference index. Of these, the sorption, x, from one addition of 150 mg P/100 g soil gave r= 0.951, but r= 0.974 when the equilibrium concentration was also taken into account in the quotient x/log c. This quotient is therefore suggested as a simple yet adequate way of indicating a fundamental soil property, its phosphate sorption isotherm.
LEACHING OF EUPHRATES SALINE SOIL IN LYSIMETERS
Authors: AL‐NAKSHABANDI G. A. , ALZUBAIDI A. , ISMAIL H. N. , AL‐RAYHANI F. , AL‐HADITHY E.
Published: July 2006

A saline soil from Euphrates alluvium at Abu‐Ghraib was leached in two lysimeters with river water and the changes in composition of the soils and of the leachates were measured as well as the hydraulic conductivity. The results show that the presence of gypsum prevents the soils becoming sodic as leaching with irrigation water of favourable composition proceeds.
THE APPLICATION OF MULTIVARIATE ANALYSIS TO SOIL STUDIES. III. SOIL VARIATION
Authors: NORRIS J. M.
Published: July 2006

Three stages in the study of soil variation are recognized: the identification of major soil types and gradients, the establishment of the location of types on the ground and on a map, and the understanding of the causes of soil variation. Evaluation of the causes of variation may be hindered if the stages are not kept separate and a strategy is suggested to achieve this separation. Principal components analysis and numerical classification are used first to produce a rigorous description of soil variation which is presented in map form. This description is a basis for the generation of hypotheses about the causes of soil variation. This strategy is used to examine soil variation in some beech woods and farmland of the mid‐Cotswold Hills, Gloucester shire, and a hypothesis is suggested that variation in soil moisture is most important in this area.
NUMERICAL ANALYSIS OF SOILS: A COMPARISON OF THREE SOIL PROFILE MODELS WITH FIELD CLASSIFICATION
Authors: MOORE A. W. , RUSSELL J. S. , WARD W. T.
Published: July 2006

Fourteen field and laboratory attributes of 49 south‐east Queens land soils were examined by numerical analysis. Three different models were used for description: the soils were viewed (1) as arrays of layer‐attributes, (2) as sets of depth functions (orthogonal polynomials) each of which describes an attribute, and (3) as sequences of layers of soil material. Dendrograms derived from Euclidean distance similarity matrices were constructed for the 49 profiles. Very similar dendrograms were obtained using (a) layer‐by‐layer comparisons (with layers weighted by an exponential depth function) and (6) orthogonal polynomials, with equal weight given to profile mean (size parameter) and five coefficients (shape parameters). The dendrogram derived from sequential analysis differed markedly from the others and seemed less meaningful; the divisive approach that had to be adopted to delineate groups of profile‐layers may have resulted in a sub‐optimal classification.

An independent field study which related the soils to geomorphic units and to differences in parent material provided a further, separate classification. The groups derived by numerical analysis, using models I and 2, agreed well with the field classes even though the strategies used were different and independent. It is concluded that existing techniques of numerical analysis can provide immediate useful support in field surveys.
TRENDS OF SOIL CLASSIFICATION IN TANZANIA I. THE EXPERIMENTAL USE OF THE 7TH APPROXIMATION
Authors: KESSEBA A. , PITBLADO J. R. , URIYO A. P.
Published: July 2006

A review is made of the trends in soil classification in Tanzania, indicating the need for an alternative to the traditional catena concept. An attempt to use the 7th Approximation is reported, in view of the demand for high category soil classification, using forty‐three typical soil profiles and discussing the particular problems related to placing three intimately studied profiles into the orders Alfisol, Ultisol, and Oxisol. An unrevised version of the 7th Approximation is not recommended for use in Tanzania. However, by using the central concepts of the system and further defining the soil classes at all levels, the use of the 7th Approximation could greatly assist in the assessment of the nation's soil resources and the ultimate development of agriculture in this country.
HYSTERESIS OF FLUX‐GRADIENT RELATIONS FOR SATURATED FLOW OF WATER THROUGH CLAY MATERIALS
Authors: NOVÁK V.
Published: July 2006

The relation between flow velocity (v) and hydraulic gradient (7) was studied for two porous materials. The volume of the sample was allowed to change during experiment. For the kaolinite, the relation between v and I is non‐linear, the hydraulic conductivity k becomes dependent on time and varies for both increasing and decreasing 7. After some time, k tends to some constant value. For bentonite, k remains constant as 7 increases. However, when I starts to decrease, k decreases accordingly. Hysteresis in the relationship between v and 7 remains unchanged with time. The observed deviations from Darcy's law may be due to deformation of the voids.
VERTICAL DISTRIBUTION OF EXTRACTABLE IRON AND ALUMINIUM IN SOIL PROFILES FROM A BROWN EARTH‐PEATY PODZOL ASSOCIATION
Authors: BALL D. F. , BEAUMONT P.
Published: July 2006

Fe and Al extractable by 3 per cent oxalic acid and by 0.1M potassium pyrophosphate at pH 10 have been determined in horizon samples of two soil profiles of each of three subgroups (Brown Earth, Brown Podzolic Soil, and Peaty Podzol) developed in North Wales on parent materials derived from Silurian shales. The vertical distribution of Fe and Al together with the relationship between pyrophosphate‐extractable (‘fresh’ hydrous oxides) and oxalic‐extract‐able Fe or Al (‘fresh’+‘aged’ hydrous oxides) can assist classification and interpretation of the course of podzolization in these soils. If podzolization is defined as sesquioxide transport, then its degree of development in the soils studied differs according to whether Al or Fe are used as the index element. The evidence supports continued recognition of soils of Brown Podzolic type as an intergrade subgroup.
THE RELATION BETWEEN BULK DENSITY, AVAILABLE WATER CAPACITY, AND AIR CAPACITY OF SOILS
Authors: ARCHER J. R. , SMITH P. D.
Published: July 2006

The effect of bulk density on moisture content at 50 mb tension in four soils of different textures was studied. The volumetric water content increased linearly with bulk density over a wide range of densities. Depending on texture, a maximum bulk density was reached above which continued compaction decreased the water content. This is shown to be the point at which the air capacity of the soil at this tension approaches zero. Accepting that the gravimetric wilting point depends mainly on texture, the available water capacity varies in a manner similar to the 50 mb water content.

If the relationships described are valid in the field, the available water capacity and air capacity may be optimized using cultivation techniques to adjust the bulk density. The available water capacity of coarse‐textured droughty soils may be increased by increasing the bulk density provided that the air capacity remains above acceptable lower limits (10–15 per cent). Conversely, the air capacity of compacted soils with large available‐water capacities could be increased by reducing the bulk density to a value corresponding to an acceptable available‐water capacity. In very compacted soils a decrease in bulk density will benefit both available‐water capacity and air capacity.
THE ORIGIN OF SOIL POLYSACCHARIDE: TRANSFORMATION OF SUGARS DURING THE DECOMPOSITION IN SOIL OF PLANT MATERIAL LABELLED WITH 14C
Authors: CHESHIRE M. V. , MUNDIE C. M. , SHEPHERD H.
Published: July 2006

Incubation of soil with 14C‐rye straw for 448 days resulted in the evolution of about 50 per cent of the carbon of the substrate as CO2 The two main sugars of the straw, glucose and xylose, were degraded to approximately the same extent (70 per cent). The same results were obtained whether the soil was derived from granitic or basic igneous parent material.

There was very little transformation of the substrate to galactose, mannose, arabinose, rhamnose, or fucose, and a much slower rate of degradation than with soil incubated with 14C‐glucose over a similar period.

Hydrolysis of the soil samples by a preliminary treatment with 5 N H2SO4, before treatment with 24 N H2SO4, followed by heating with N H2SO4 did not release significantly greater amounts of sugar than treatment with 24 N H2SO4 and N H2SO4 alone. Separate analysis of the hydrolysates showed that 90 per cent of each of galactose, mannose, arabinose, xylose, rhamnose, or fucose had been extracted by 5 N H2SO4, but only 50 per cent of the glucose.

Fractionation of the straw‐soil mixture after 224 days incubation showed that the specific activity of the glucose was higher in the humin fraction than in the fulvic acid, as would be expected if the remaining 14C were still in the form of unchanged plant material.

This evidence that plant polysaccharide persists in soil could explain the presence of much of the xylose in the soil organic matter.
THE DISTRIBUTION OF IRON, MANGANESE, AND SCOTLAND ALUMINIUM IN SOME SOILS FROM NORTH‐EAST SCOTLAND
Authors: MOORE T. R.
Published: July 2006

Twenty‐four soils from north‐east Scotland have been subjected to differential extraction techniques to determine the effect of hydromorphism on various Fe, Mn, and A1 fractions. There were pronounced losses of dithionite‐extractable Fe and Mn from gleyed horizons, but the 'silicate‐Fe’fraction appeared to be relatively unaffected. The oxalate‐extractable Fe and A1 fractions also decreased in response to gleying. The ratio of the oxalate‐ to dithionite‐extractable Fe fractions (Fe0/Fed) increased in gleyed horizons, presumably due to variations in the rate of ageing and crystallization of amorphous Fe oxides and hydroxides.
MINERALOGY AND RADIOISOTOPE RETENTION PROPERTIES OF A CHRONOSEQUENCE OF SOILS DEVELOPED IN BASALTS OF VICTORIA, AUSTRALIA
Authors: MOKMA D. L. , JACKSON M. L. , SYERS J. K. , GIBBONS F. R.
Published: July 2006

The mineralogical composition and retention properties for radioisotopes (20Sr and 137Cs) of soils developed in five basalt flows of age varying from 6000 years to about four million years occurring in western Victoria were investigated. The trend of mineral weathering has been almost exclusively to amorphous material, kaolinite‐plus‐halloysite, and chlorite, the more soluble products of weathering having been removed. The most significant changes in clay mineralogical composition with time are the progressive decrease in the Si02/Al2O3 molar ratio of the amorphous material in the clay fraction of the surface horizons, from an initial value of approximately 4 to values of approximately 2, and the progressive increase in the amount of kaolinite‐plus‐halloysite, both in the topsoil and at depth, with age of the basalt flow. The amount of kaolinite plus halloysite increases from approximately 20 per cent of the clay of soil developed in the basalt flow 6000 years old to approximately 50 per cent of that of soil in basalt about four million years old. Evidence for the presence of halloysite was obtained by electron microscopy studies. The amorphous material and chlorite contents, each of which constitutes between 20 and 50 per cent of the clay fractions, decrease concurrently with the increase in kaolinite‐plushalloysite content.

Fixation of Sr by whole soil samples was controlled by the organic matter and free iron oxide contents rather than by the mineralogy of the samples. A high proportion of the added Cs was sorbed by whole soil samples. Much of the sorbed Cs was not readily replaced by CaCl, washings but was replaced in part by subsequent washing with NaCl of pH 5.3 and almost entirely by subsequent NH4Cl washings. Much of the Sr and Cs deposited on these soils by rainfall and dry fall‐out would be sorbed; the ease of replacement suggests that these elements would be available for further movement through the food chain.
SOIL CLASSIFICATION WITH PARTICULAR REFERENCE TO THE SEVENTH APPROXIMATION
Authors: MITCHELL C. W.
Published: July 2006

The fundamental objective of soil classification is the achievement of an agreed world–wide system of maximum usefulness to the widest possible range of users. Such a classification should be natural rather than artificial because soils are natural bodies. Further, it should be hierarchical rather than co–ordinate because hierarchies are readily comprehensible and memorable, can be constructed on the basis of a few characters, and do not need to give equal weight to all criteria used in classifying soils. They also have the advantage of closely denned, mutually exclusive classes which can still make allowance for occasional aberrant profiles or pedons.

The historical development of soil classifications is discussed with particular reference to the Russian and French and especially the U.S. Dept. Agric. 7th Approximation. The latter is defended against the main criticisms that have been levelled against it. It is maintained that it has been desired by sound inductive as well as deductive reasoning, that it treats soils as polythetic individuals, that it considers pedons three–dimensionally and that it permits non–hierarchical sub–classifications. Attention is given to the more practical criticisms that there is an undue emphasis on soil moisture and temperature regimes, unknown genetic criteria and the shallower horizons, and that it handles ses‐quioxidic soils inadequately. Positive advocacy is made on the ground that the 7th Approximation will facilitate and speed soil research especially in developing countries.
CALCULATING THE ECONOMIC BENEFITS OF SOIL SURVEY
Authors: BIE S. W. , ULPH A. , BECKETT P. H. T.
Published: July 2006

A farmer (or other users of land) achieves greatest net return by using each soil for the crop and management which gives maximum return.

A soil map indicates the boundaries between soils requiring different management for optimum returns. The benefits from a soil survey increase with the ‘purity’ of the soil units as mapped.

The cost of soil survey increases sharply with the ‘purity’ to be achieved. So it is necessary to recognize the stage beyond which the costs of yet more detailed soil survey are unlikely to exceed the benefits to be expected from mapping units of greater ‘purity’.

This paper reports a simple algorithm for calculating the probable benefits from further soil survey to produce a map of higher ‘purity’ than so far achieved.
MINERALOGY AND MORPHOLOGY OF SALT EFFLORESCENCES ON SALINE SOILS IN THE GREAT KONYA BASIN, TURKEY
Authors: DRIESSEN P. M. , SCHOORL R.
Published: July 2006

Samples from fifteen salt crusts from the central Great Konya Basin, Turkey, were studied in the laboratory. Chemical analyses data were combined with the results of X‐ray diffraction.

In the mineralogical systems studied, three types of salt efflorescences of different morphology were distinguished, with mirabilite/thenardite, bloedite, and bloedite/epsomite/halite as major mineral associations. These crusts seal the surface soil more or less effectively, thus reducing evaporation and thereby preventing cracking of the saturated soils. The effectiveness of this sealing depends on the morphology of the accumulated salt minerals rather than on their chemical composition. Reclamation of salt‐encrusted spots therefore requires understanding of the mineralogy and the morphology of the efflorescent salts.
LATERITIC DEEP WEATHERING OF GRANITE
Authors: GILKES R. J. , SCHOLZ G. , DIMMOCK G. M.
Published: July 2006

Chemical and mineralogical analyses of two representative laterite profiles developed from granite in south‐western Australia have shown that several depth zones defined by particular mineral suites and geochemistry may be recognized. These zones are not simply related to the conventional morphological pallid, mottled, and ferruginous zones.

Changes in geochemistry in both profiles can be related to the stability of the major mineral species and to the common isomorphous substitutions occurring in them. Ca, Na, and Mg, which are mainly present in plagioclase feldspars and ferromagnesian minerals, are removed during the earliest stage of alteration of the parent granite. K, Mn, Zn, and residual Ca, Na, Mg, and Sr decrease as microcline and micas alter to kaolin. Al and Fe are most abundant in the surface zones which contain secondary sesquioxide minerals.
THE UNIQUENESS OF THE MOISTURE CHARACTERISTICS
Authors: POULOVASSILIS A.
Published: July 2006

Experiments, designed to test the non‐uniqueness which has been reported in the relationship between moisture content and suction in porous materials during transient flow conditions, are escribed. When a vertical column of sand was brought to uniform moisture content and uniform suction in a draining condition by percolating a constant flow through it until apparent equilibrium conditions ensued and then placed horizontally at the same time as the flow was stopped, the suction was found to decrease with time over a period of a day, indicating that the sand was now wetting up. This decrease was smaller the drier the sand. However, when the column was left in a vertical position with the water percolating through it for three hours after apparent equilibrium conditions were reached, a small adjustment of moisture content and suction was observed; when it was then placed horizontally as in the previous experiments little decrease of suction was observed. No change in suction was observed in either case if the equilibrium condition was reached in a wetting porous material.

These experimental results and those of previous workers are explained by the hypothesis that, during drainage, some water is left in pores from which the air‐water interface has already retreated to drain through film flow, more slowly, subsequently to the continuous water body.

Additional experiments showed that the release of entrapped air may have a small effect on the uniqueness of the moisture characteristics.
TRANSFORMATION OF SUGARS WHEN RYE HEMICELLULOSE LABELLED WITH 14C DECOMPOSES IN SOIL
Authors: CHESHIRE M. V. , MUNDIE C. M. , SHEPHERD H.
Published: July 2006

Incubation of soil with 14C hemicellulose from rye straw for 448 days resulted in the evolution of about 70 per cent of the substrate as CO2. The two major sugar components of the hemicellulose, xylose (50 per cent) and arabinose (5 per cent), were almost completely decomposed. After 56 days only 5 per cent of the xylose remained and after 448 days only 1‐2 per cent. Similar results were obtained for soil derived from either granitic or basic igneous parent material.

Almost 4 per cent of the hemicellulose was transformed to glucose and I per cent to mannose during the first 14 days of incubation.

Fine grinding of 14C rye straw increased the extent of its decomposition on incubation but after 448 days 20 per cent of both its xylose and arabinose remained.

It is suggested that the isolated hemicellulose is decomposed faster because it has been made water soluble.
ETHYLENE GLYCOL SORPTION BY HOMOIONIC MONTMORILLONITES
Authors: ELTANTAWy I. M. , ARNOLD P. W.
Published: July 2006

Experimental procedures giving complete unimolecular surface coverage of montmorillonite by ethylene glycol (EG) are described. The EG sorption data, excluding rate effects, are independent of the nature of the exchangeable cations associated with the clay surfaces. The amount of EG sorbed (0.357±0.007 g EG/g montmorillonite) is larger than that obtained following previously recommended techniques based on low pressure equilibration with CaCl2‐EG mixtures (solvates) of relatively small EG content or on dynamic approaches. In both of the latter, the extent of EG sorption is determined by the exchangeable cation‐EG interaction and not by the real extent of the surface. Na‐ and K‐saturated montmorillonite‐EG complexes are less stable than those formed from Ca or Mg clay.
MICRO‐STRUCTURAL DIFFERENCES BETWEEN ARABLE AND OLD GRASSLAND SOILS AS SHOWN IN THE SCANNING ELECTRON MICROSCOPE
Authors: LOW A. J. , STUART P. R.
Published: July 2006

The scanning electron microscope has been used to compare the microstructure of an old grassland soil with that of an arable soil of the same soil series. The micrographs give more direct evidence than previously available of the presence of an adherent, presumably organic, matrix binding the clay and other particles of the old grassland soil. Fungal hyphae were also observed. Neither of these features was present to the same extent in the old arable soil.
A LANGMUIR TWO‐SURFACE EQUATION AS A MODEL FOR PHOSPHATE ADSORPTION BY SOILS
Authors: HOLFORD I. C. R. , WEDDERBURN R. W. M. , MATTINGLY G. E. G.
Published: July 2006

For forty‐one soils (pH > 5.0) from southern England and eastern Australia, the Langmuir equation was an excellent model for describing P adsorption from solutions < 10‐3M P, if it was assumed that adsorption occurs on two types of surface of contrasting bonding energies. For most of these soils, which were relatively undersaturated with P, this equation may be written as:

image

where x = adsorption, k = adsorption/desorption equilibrium constant, xm= monolayer adsorption capacity, and c = equilibrium solution concentration. The relative magnitude of the parameters for each surface were approximately: xm= 0.3 x″m=0.3 and k′= 100 k. More than 90 per cent of the native adsorbed P occurs on the high‐energy surface in most soils.
DECOMPOSITION OF SOIL POLYSACCHARIDE
Authors: CHESHIRE M. V. , GREAVES M. P. , MUNDIE C. M.
Published: July 2006

Polysaccharide material was isolated by absorption on charcoal from the acidified, non‐humic fraction extracted by alkali from three soils. The polysaccharides were used as substrates in soil incubation, perfusion, and suspension experiments. Concordant results were obtained with freely drained Countess‐wells and Insch Association soils derived from acidic and basic igneous parent materials respectively. Polysaccharide material added to soil at low concentration (I per cent) was apparently totally decomposed after 8 weeks when the amounts of polysaccharide in control and amended soils were statistically indistinguishable. At higher concentrations (2‐3 per cent) a significant difference in reducing sugar, equivalent to about 30 per cent of the substrate, remained after 32 weeks. Partial neutralization of the polysaccharide material with calcium hydroxide increased the rate of decomposition in Countesswells Association soil but had an opposite, smaller effect in Insch Association soil. Soil polysaccharide material was decomposed slightly faster in perfusion and suspension experiments than in moist soil. Only 20 per cent of the carbohydrate in the unfractionated alkali–soluble organic matter of soil was decomposed during incubation in soil for up to 133 weeks. There was usually little change in the carbohydrate content of soil incubated alone. The soil microbial population showed a marked increase in response to added polysaccharide material but only slight qualitative changes were detected.

It is concluded that the persistence of naturally occurring polysaccharide in soil is related to inaccessibility caused by chemical combination, complexing or insolubility but not to a biologically‐stable molecular structure.
SANDSTONE‐DERIVED SOILS OF A CATENA AT IPERU, NIGERIA
Authors: OGUNWALE J. A. , ASHAYE T. I.
Published: July 2006

Chemical and mineralogical properties of five soil profiles of a catena in Iperu, Western State of Nigeria, are reported. The pH values of the subsoils are extremely acid. Acidity decreases with improved drainage in the subsoils (pH 4.0–5.8). The cation exchange capacity (C.E.C.) of the soils range from 3.0 to 16.2 me/100g of soil.

The silt: silt+clay ratio, calcium: magnesium ratio and Fe2O3:Al2O3 ratio are used as weathering indices. The low values of the silt: silt + clay index indicate that the soils must have undergone advanced weathering. The magnitude of the Ca: Mg ratio indicates that more calcium than magnesium is available in the soils. The values for sodium and potassium are extremely low. More iron than aluminium was extracted from the soils by the dithionite‐citrate method.

Kaolinite is the most abundant clay mineral. Halloysite, interstratified clay materials, vermiculite, quartz, and mica are present in considerable amounts. The silt fraction in which quartz is the most abundant mineral, also contain some kaolinite and mica.
TYPES OF SOIL DEGRADATION ON LOESS NEAR KRAKOW
Authors: KORELESKI K.
Published: July 2006

Humus content, thickness of the accumulation horizon, soil texture, and depth of decalcification are all related to the slope of the soil surface in loess soils near Kraków.

For example, humus content declines from 75 to 65 tonnes/ha as slope increases from 2 to 12°. Depth of decalcification which is about IOO cm on soils with slopes less than 2° is only about 50 cm on slopes of 12°.

Such observations may prove helpful in the evaluation of the intensity of soil erosion processes on other loess areas physiographically similar to the region near Kraków.
THE INFLUENCE OF PYRITE OXIDATION PRODUCTS ON THE ADSORPTION OF PHOSPHATE BY COAL‐MINE WASTE
Authors: PULFORD I. D. , DUNCAN H. J.
Published: July 2006

Loss of fertilizer phosphate by adsorption on coal‐mine waste can increase the cost of reclamation schemes. Samples were taken from four typical coal‐mine tips in Central Scotland and the relationships between phosphate adsorption, Tamm A1 and Fe, pH, fraction less than 2 mm, and acetic soluble calcium and sulphate were studied. Only Tamm Fe was shown to be correlated with phosphate adsorption.

Unburned (black) shale adsorbed more phosphate than burned (red) shale.

Heat has also been shown to influence the levels of Tamm Fe and phosphate adsorption. This is of practical significance as high temperatures can be generated within the tips as a result of spontaneous burning of the waste material.
A QUANTITATIVE ANALYSIS OF THE FACTORS AFFECTING PLANT NUTRIENT UPTAKE FROM SOME SOILS
Authors: BALDWIN J. P.
Published: July 2006

A model of solute uptake by a growing root system is discussed in relation to the ability of a soil to support the nutritional requirements of plants. It is quantitative, and should apply to the absorption of nitrate, phosphate, and potassium by grasses and arable crops. The principles, if not the detail, are relevant to all soils.

The model was tested in an experiment in which the nitrogen and potassium taken up by a rape plant were measured. The results suggest that the model has identified the significant variables in the absorption process.

The principal factors affecting the supply of nutrient to a given plant are the total quantity of diffusible nutrient, the rate at which the nutrient can move, and the distance it has to travel to a root surface. The exact relevance of each factor for the different nutrients is readily determined.

The diffusion coefficients of potassium and phosphate are often low. Mass flow contributes little to their supply, and an adequate exploitation of the soil reserves depends on a well‐developed root system. Nitrate, on the other hand, can usually move easily to roots, either by diffusion or mass flow. The whole rooting volume is depleted fairly quickly, and the amount absorbed depends solely on the quantity present in the rooting volume.

These ideas have practical significance. In particular, they suggest that the soil properties which influence root growth may deserve as much attention as soil chemical composition in the drawing up of fertilizer recommendations.
QUANTITATIVE PEDOLOGICAL STUDIES ON SOILS DERIVED FROM SILURIAN MUDSTONES
Authors: EVANS L. J. , ADAMS W. A.
Published: July 2006

The uniformity of the parent material between and within five soil profiles representing a typical catenary sequence in upland mid‐Wales was investigated using as criteria of uniformity the constancy of the ratios Zr: Sr and quartz: illite in the silt fractions. No lithologic breaks could be detected in the soil profiles. ZrO2, TiO2, quartz, and tri‐acid residue were assessed for use as internal standards. TiO2 appeared to be mobile during pedogenesis. Of the other three standards tri‐acid residue was considered to be most suitable.
THE REACTION OF FLUORIDE WITH SOILS AND SOIL MINERALS
Authors: PERROTT K. W. , SMITH B. F. L. , INKSON R. H. E.
Published: July 2006

The reaction of sodium fluoride solution with soils and soil minerals at constant pH has been assessed as a possible single‐value characteristic in the classification of soils, particularly those containing significant amounts of poorly ordered inorganic material. A suitable method involves reaction of the soil or clay at 25°C with 0·85 M sodium fluoride at pH 6·8, the amount of OH− released after 25 min being taken as the single‐value characteristic.

There was a statistically significant correlation between the amount of OH− released and the amount of alumina extracted with cold 5 per cent sodium carbonate solution from both freely drained and poorly drained Scottish soils. The multiple correlation coefficients were improved for freely drained soils by including the dithionite‐extracted ferric oxide and the silica soluble in 5 per cent sodium carbonate solution. The procedure is not suitable for surface soils, because of interference by organic matter, or for carbonate‐containing soils unless carbonate is removed.
THE SPECIFIC ADSORPTION OF DIVALENT Cd, Co, Cu, Pb, AND Zn ON GOETHITE
Authors: FORBES E. A. , POSNER A. M. , QUIRK J. P.
Published: July 2006

The specific adsorption of divalent Cd, Co, Cu, Pb, and Zn on goethite is measured as a function of pH. For each mole of heavy metal adsorbed approximately two moles of H+ ions are displaced from the interface. Using these results the heavy metal adsorption data are expressed as functions of the solution concentrations of both H+ and metal ions, and the interfacial reaction is described by the equation,

2SH+M2+= S2M+2H+.

The adsorption data are consistent with an electrochemical model of the simultaneous adsorption of H+ ions and divalent metal ions on to the oxide. The intrinsic affinities of the metal ions for the oxide surface increase in the order, Cd < Co < Zn < Pb < Cu. However, besides the affinity of the metal ion for the surface, the adsorption curves are considered to be influenced by surface charge, the adsorption density of the metal ions and their size.

The analysis of the data in terms of H+ and M2+ ion adsorption is considered to be complementary to the hydrolysis model for heavy metal adsorption.
INTERNAL STRUCTURE OF TILLED SOIL
Authors: DEXTER A. R.
Published: July 2006

Samples of tilled soil were impregnated with paraffin wax and were sectioned by sawing. The distribution of angles of incidence between voids and aggregates on the sections were investigated using random lines in three orientations. The angular distributions were found to be isotropic. Incidence angles near to normal were found to be more probable than in idealized beds of spherical aggregates.

Distributions of aggregates and voids were examined along horizontal lines on the soil sections using an approach developed in communications theory. Soil structures in the size range from I to 5 mm were defined exactly by sets of sixteen transition probabilities. Differences were observed in the tilths produced by a mouldboard plough, a tine cultivator, and a rotary cultivator. The soil structures were different at different depths and changed with time after tillage.

Transition probabilities measured in this way can be used in stochastic processes to simulate large tilths in a computer. The techniques described here could be adapted to the study of the distribution of soil structural features at any scale.
PLASTIC LIMIT DETERMINATION USING A DROP‐CONE PENETROMETER
Authors: CAMPBELL D. J.
Published: July 2006

The drop‐cone method, in which a 30° cone of mass 80 g is allowed to sink into a soil sample at a selection of moisture contents, was used to determine the moisture content/cone penetration curve in the region of the plastic limit for eighteen soils.

The moisture content corresponding to the minimum of the curve is shown to be always numerically less than, but to correlate closely with, the plastic limit. It is suggested that the plastic limit be redefined as the moisture content corresponding to the minimum of the moisture content/cone penetration curve, with the advantages that the test is more closely related to soil behaviour, less subjective, at least as reproducible as the Casagrande test and may be carried out simultaneously with the liquid limit test.
ADSORPTION OF PHOSPHATE BY GIBBSITE
Authors: HELYAR K. R. , MUNNS D. N. , BURAU R. G.
Published: July 2006

The effects of the salts were studied using I per cent suspensions of gibbsite at pH 5.5 and 26°C. At 480μM phosphate and I mM calcium, the kinetic pattern was an initial rapid adsorption reaction, which approached equilibrium in 24 h, revealing a slower reaction. Adsorption isotherms determined at 24 h, with a range of final phosphate concentrations from 0.1 to 1000 μ in solution, were not affected by 20 mM sodium or potassium chloride or 10 mM magnesium chloride. Increasing calcium chloride from o to 20 TIM increased the adsorption of phosphate over the range from 1 to 100 μM final phosphate concentration. At lower (0.1 μM) and higher (1000 μM) phosphate, the effect of calcium was smaller.

These results help to explain several effects of the various cations on the adsorption of phosphate by clays and soils, when effects of neutral salts on pH are also considered.
SODIUM‐CALCIUM EXCHANGE EQUILIBRIA IN SALT‐AFFECTED AND NORMAL SOILS
Authors: POONIA S. R. , TALIBUDEEN O.
Published: July 2006

Sodium‐calcium exchange equilibria in soils with a range of cation exchange capacity (CEC) and surface charge density (SCD), showed calcium preference whether the results were interpreted by a thermodynamic treatment, by an electric diffuse double layer equation, or by an empirical approach. Surface soils preferred Ca more than the corresponding sub‐soils, which was mainly attributed to their higher SCDs and organic carbon contents (OC). Significant correlations between OC and (ΔGo)ca→Na, and OC and SCD, suggest the effect of OC on Ca preference to be mainly through increased SCD rather than to specific ion exchange sites.

Significant correlations between ΔGo and SCD, ΔGo and KG (the Capon constant), and between corrected SCD and KG, suggest that all three approaches can be used to describe Na:Ca exchange equilibria in these soils, and that the equilibria are related to intrinsic soil properties.
LIME‐INDUCED CHLOROSIS
Authors: SCHINAS S. , ROWELL D. L.
Published: July 2006

The following properties were measured on 22 soil samples from seven sites in the south east of England: total CaCO3, active CaCO3 apparent solubility product, particle size distribution of the CaCO3, and pH. Active CaCO3 was between one quarter and one half of the total for all sites except one. Apparent solubility products varied for each parent material, and increased with depth in each profile and ranged from 0.93 to 4.87 × 10−9. Soil pH was directly related to apparent solubility product. Active CaCO3 was closely related to the surface area.

pH measured in 0.01 M CaCl2 was the best index of yield of cauliflower, tomato, sweet white lupin and bitter blue lupin, with chlorotic symptoms increasing and yield decreasing as pH increased. The apparent solubility product of the soil carbonates and pH measured in water were also closely correlated with yield. Total and active CaCO3 were only related to yield above limits of 20 and 10 per cent respectively and even then were poor indices of yield.
EFFECT OF ORGANIC CONSTITUENTS AND COMPLEXED METAL IONS ON AGGREGATE STABILITY OF SOME EAST ANGLIAN SOILS
Authors: HAMBLIN A. P. , GREENLAND D. J.
Published: July 2006

Paired soils of high and low organic matter content from the East Anglian silts were used to determine the role of different organic constituents and complexed metal ions in relation to aggregate stability. Although leaching with periodate and borate caused some loss of stability for most of the soils, the changes were much less than those due to extraction of the soils with pyrophosphate or acetylacetone which were more effective in removing organic materials complexed with iron and aluminium. Amounts of iron and aluminium extracted were not well correlated with changes in stability. The results indicate that in these soils polysaccharides are less important to aggregate stability than organic matter bonded to the clay particles through association with aluminium or iron.
THE MEASUREMENT AND CHARACTERISATION OF VOIDS IN SOIL THIN SECTIONS BY IMAGE ANALYSIS. PART I. PRINCIPLES AND TECHNIQUES
Authors: MURPHY C. P. , BULLOCK P. , TURNER R. H.
Published: July 2006

The introduction of the image analysing computer (Quantimet 720) makes possible the rapid and accurate measurement of components in thin sections and extends the range of measurements possible. Two techniques for presenting material for analysis are outlined. Models are used to demonstrate the measurement of size, irregularity and orientation of components and their discrimination according to shape.
CATION EXCHANGE PROPERTIES OF SPHAGNUM PEAT: EXCHANGE BETWEEN TWO CATIONS AND PROTONS.
Authors: ANDRÉ J. P. , PIJAROWSKI L.
Published: July 2006

Parameters of the exchange equilibria for three pairs of cations of agricultural interest (K/NH4 – Ca/Mg – K/Ca) were experimentally determined. The selectivity coefficient of the two homovalent pairs was found to be constant, whereas that of the mono‐divalent pair depended on the total concentration of cations in the solution and on the exchange capacity. Equations are given which describe the exchange equilibria in peat, which take into account its pH‐dependent exchange capacity.
PROTON‐DECOUPLED PULSE FOURIER‐TRANSFORM 13C MAGNETIC RESONANCE OF SOIL ORGANIC MATTER
Authors: WILSON M. A. , GOH K. M.
Published: July 2006

The structure of some humic acids, fulvic acids and lipid fractions of soil organic matter have been investigated by 13C‐n.m.r. spectroscopy. Signals from aromatic groupings were normally absent in humic and fulvic acids. There were differences in spectra from extracts prepared from different sources or by different techniques. 1 3C‐n.m.r. spectra of lipid fractions were generally similar to each other but there were some distinct differences that may be used to a ‘fingerprint’ the lipids.
INFLUENCE OF ORGANIC MATTER ON THE PHYSICAL PROPERTIES OF SOME EAST ANGLIAN SOILS OF HIGH SILT CONTENT
Authors: HAMBLIN A. P. , DAVIES D. B.
Published: July 2006

A comparison was made of the physical properties of pairs of silt soils differing only in organic matter content. Within the textural group studied, the member of the pair with more organic matter had better physical properties relating to both plant growth and soil management. Increased organic matter give higher water holding capacities and porosities, and decreased compaction, breaking strength and bulk densities. Organic matter content alone was not sufficient to explain differences in aggregate stability to water.
ADSORPTION ON HYDROUS OXIDES I. OXALATE AND BENZOATE ON GOETHITE
Authors: PARFITT R. L. , FARMER V. C. , RUSSELL J. D.
Published: July 2006

The adsorption of oxalic acid on synthetic goethite (α‐FeOOH) was studied using adsorption isotherms. Infrared spectra were obtained for goethite‐oxalate complexes at several points on the isotherms. On a goethite preparation with a phosphate sorption capacity of 200|μmolg−1 the amounts of oxalate strongly adsorbed varied from near zero at pH 8 to about l00μmolg−1 at pH 4 and below. At pH 3.4, the first l00μmolg−1 of oxalic acid added was strongly adsorbed as a binuclear complex (FeOOC–COOFe), replacing two singly‐coordinated OH groups by ligand exchange. At higher concentrations a further 200 μrnol g−1 of oxalic acid formed a monodentate complex (FeOOC–COOH) so that more oxalate could be accommodated.

Benzoic acid was weakly adsorbed on goethite with one benzoate oxygen replacing one singly‐coordinated OH. The other oxygen of the COO group fitted into the goethite surface so that the benzene ring was at a high angle to the (100) face.
MECHANISMS OF PHOSPHATE SORPTION BY SOILS AND HYDROUS FERRIC OXIDE GEL
Authors: RYDEN J. C. , McLAUGHLIN J. R. , SYERS J. K.
Published: July 2006

Data for the sorption of added inorganic phosphate (P) by contrasting soils and iron oxide gel were resolved by a method of successive approximation of the Langmuir sorption constants. Three distinct Langmuir equations described the overall isotherm irrespective of the experimental conditions used. Free energies of sorption (ΔG) for a particular region were similar for each soil and for iron oxide gel under all experimental conditions. In contrast, the sorption maximum for each region was influenced by the sorbent and experimental conditions.

Because of the pronounced similarities in their P sorption characteristics iron oxide gel was used as a model surface for P sorption by soils. Three mechanisms for P sorption by iron oxide gel and by soils are proposed: (i) chemisorption at protonated surface sites, (ii) chemisorption by replacement of surface hydroxyls, and (iii) a more‐physical sorption of P as a potential‐determining ion.
ADSORPTION OF HERBICIDE‐DERIVED p‐CHLOROANILINE RESIDUES IN SOILS: A PREDICTIVE EQUATION
Authors: VAN BLADEL R. , MOREALE A.
Published: July 2006

Relationships between the adsorption of p‐chloroaniline and the original adsorbate concentration were investigated for five soils ranging in organic matter content from 1.7 to 8.1 per cent and in clay content from 0.5 to 21 per cent. Adsorption data were analyzed applying the linear form of the Freundlich equation. To evaluate the general relationship between adsorption of p‐chloroaniline by soils and the solution concentration (C0), values of partition coefficient (Kp), reflecting the magnitude of distribution of chemical at equilibrium between soil colloids and solution were calculated.

The experiments showed that the regression parameters were significantly correlated with the soil organic matter content. A comparison of the experimental results obtained with other soils and the calculated values gave satisfactory agreement.
SHRINKAGE IN CLAYEY SUBSOILS OF CONTRASTING STRUCTURE
Authors: REEVE M. J. , HALL D. G. M.
Published: July 2006

Shrinkage was measured on subsoil samples from two clayey alluvial soils of contrasting structural development and two boulder clay soils also of contrasting structure. Of the four phases of shrinkage recognized, the proportion of shrinkage attributable to the structural shrinkage phase is shown to be dependent on structural development and organic carbon levels in the subsoil. The importance of structural shrinkage to the maintenance of good structure in clay soils under intensive cultivation is briefly discussed.