bluuebunny/crossref_metadata_2025 huggingface dataset:
THE MEASUREMENT AND MECHANISM OF ION DIFFUSION IN SOILS. VIII —A THEORY FOR THE PROPAGATION OF CHANGES OF pH IN SOILS
Authors: NYE P. H.
Published: July 2006

The way pH changes in soil are propagated by movement of acids and bases is described. In acid soils the H3O+‐H2O acid‐base pair is most important, while in alkaline soils the H2CO3‐HCO3− pair is always dominant, its effect depending directly on the pressure of CO2. In neutral and slightly acid soils, soluble organic matter and the H2PO4−‐HPO24− pair may also contribute.

A soil acidity diffusion coefficient is derived, and defined as:

image

where vl= the volume fraction of the soil solution,

fl= the impedance factor for the liquid diffusion pathway,

bHS= the pH buffer capacity of the soil,

b
HB= the pH buffer capacity of each mobile acid‐base pair,

Dl
HB= the diffusion coefficient of each mobile acid‐base pair in free solution,

and the sum is taken over all mobile acid‐base pairs.

The soil acidity diffusion coefficient may be used to predict the course of pH equilibration in practical situations. It is high in acid and alkaline soil, and at a minimum in slightly acid soil. It is little affected by variation of the ionic strength of the soil solution at concentrations less than 0.01M. When the pH buffer capacity of the soil is constant, and only the H3O+‐H2O and H2CO3‐HCO3− pairs are important, the soil acidity diffusion coefficient varies as cosh{2.303(pH—pH0)}, where pH0 is the pH at which the soil‐acidity diffusion coefficient is a minimum.
THE CHARACTERIZATION OF SOME SCOTTISH ARABLE TOPSOILS BY AGRICULTURAL AND ENGINEERING METHODS
Authors: SOANE B. D. , CAMPBELL D. J. , HERKES S. M.
Published: July 2006

Samples from fifty‐eight arable topsoils in south‐eastern Scotland were analyzed for compactability, plasticity, organic matter content, particle density, and particle‐size distribution. The samples were classified by the methods employed for engineering soils and the groupings so obtained were compared with the textural classes. The criteria for the classification of engineering soils provide useful information on the likely mechanical behaviour of arable soils in the field. Tests were made for correlation between fifteen soil properties. The organic matter content, which in the samples studied ranged from 2 to 10 per cent, was shown to influence several mechanical properties, including optimum moisture content, maximum dry bulk density, liquid limit, and plastic limit.

Maximum bulk density and optimum moisture content were strongly correlated with Atterberg limits and organic matter content. The liquid limit was more closely correlated with particle‐size distribution than was the plastic limit. Unlike soils encountered in engineering, the particle density of these soils was not correlated with particle‐size distribution but, like the Atterberg limits, was strongly correlated with organic matter content.
CHARGE DISTRIBUTION AND THE CATION EXCHANGE CAPACITY OF AN IRON‐RICH KAOLINITIC SOIL
Authors: BARBER R. G. , ROWELL D. L.
Published: July 2006

The positive charge on an iron‐rich kaolinitic soil was found to increase from 11.1 to 14.2 me per 100 g as a result of lowering the pH from 8.5 to 3.0 in M NH4Cl solution and the negative charge decreased from 22.2 to 14.1. In 0.002M NH4C1 the positive charge increased from 0 to 0.3 and the negative charge decreased from 5.6 to 3.2. The variations in charge can be explained by the presence of 3 me per 100 g of permanent negative charge, pH dependent positive and negative charge influenced by the indifferent electrolyte concentration, and the overlap of diffuse layers causing a neutralization of charge.

The ability of this soil to hold cations under field conditions is overestimated by m ammonium acetate at pH 7. Instead, a solution approximating to the pH, composition, and concentration of the soil solution should be used.
THE CLASSIFICATION OF ARID ZONE SOILS
Authors: WESTERN S.
Published: July 2006

In the arid environment of South Arabia the soils (sedosols, see Part I) are not significantly affected by pedogenetic processes. Classification of these soils is therefore in accordance with the principles outlined in Part I, being based upon a consideration of the mode of deposition rather than on considerations of pedo‐genesis. Sedimentary geomorphology, soil classification, soil mapping are discussed for two areas of South Arabia. Mapping purity was satisfactory and reliability was probably greatest in series that were wholly anthropic or wholly natural in origin. In classifying land for single‐flood irrigation agriculture, the total readily available moisture capacity is the major land classification factor. It is a function of texture and effective depth, modified in places by severe stratification.
A STUDY OF HUMIC ACID BY EQUILIBRIUM ULTRACENTRIFUGATION
Authors: POSNER A. M. , CREETH J. M.
Published: July 2006

Equilibrium ultra centrifugation is a superior method to the more conventional sedimentation velocity technique for measuring the molecular weight of poly‐disperse humic acid. The technique can be used to estimate number, weight, and Z‐average molecular weights of humic acid and a measure of the polydispersity of the acid can thus be achieved.
HYSTERESIS IN THE MOISTURE CHARACTERISTICS OF CLAY SOIL
Authors: PAVLAKIS GEORGE , BARDEN LAING
Published: July 2006

The relation between soil suction, degree of saturation, and the air and water permeabilities is experimentally investigated for two clay soils. Marked hysteresis can exist between saturation and permeability, but does not follow a unique trend. Thus permeability can be greater on a wetting or drying cycle depending on the structure of the clay soil. This behaviour is considered in terms of the cluster concept of soil structure, and it is concluded that any general theory of hysteresis must recognize both the macrostructure and microstructure of a soil.
DETERMINATION OF 14C IN SOIL BY A GEL SUSPENSION METHOD
Authors: CHESHIRE M. V. , SHEPHERD H. , KNIGHT A. H. , MUNDIE C. M.
Published: July 2006

Radioactivity in soils labelled with 14C was determined by suspending the finely ground soil in a thixotropic gel, dispersing it by ultrasonics and counting the dispersion in a liquid scintillation spectrometer. The relationship between the weight of sample and counting efficiency was found to be almost linear. Using 30 mg soil, the counting efficiency is 50 per cent and 14C may be determined with an average coefficient of variation of 1.5 per cent to within 5 per cent of the value determined by oxidative procedures.
POTASSIUM RESERVES IN A ‘HARWELL’ SERIES SOIL
Authors: TALIBUDEEN O. , WEIR A. H.
Published: July 2006

A sample of Harwell soil containing 36 percent fine clay (< 0.3 μm) and 14 per cent coarse clay plus fine silt (0.3–5μm) was separated into fractions, and the K‐supplying power of soil and fractions measured by cropping with ryegrass, exchange with Ca resin and double‐label isotopic exchange with 42K and 45Ca ions.

Mineralogical examination of the fractions coupled with the cropping experiments showed that the K‐supplying power of the soil to ryegrass can be explained by the presence of a zeolite, clinoptilolite‐heulandite, in addition to the clay minerals, mica, and interstratified illitic smectite, commonly found in a glauconitic clay‐rich soil. The 0.3–5 μm fraction, containing much zeolite, has an exchange diffusion coefficient for K ions to Ca resin of 1.8 × 10−16 cm2sec−1 compared with a value of 5.7 × 10−20 for the < 0.3μm fractions in which interstratified illitic smectite is the dominant mineral. Isotopic exchange shows that all Ca ions in fractions < 50μm are isotopically exchangeable. In fractions coarser than 20μm, some of the K ions in felspar and mica were not exchangeable within the duration of the experiments.
THE MECHANICAL STRENGTH OF UNSATURATED POROUS GRANULAR MATERIAL
Authors: TOWNER G. D. , CHILDS E. C.
Published: July 2006

The influence of pore‐water suction on the strength of a porous material is that it contributes a compressive load which increases the shear strength. When the material is unsaturated, the normal load or effective stress is due, in part to the continuous water at measured suction in unemptied pores, and in part to isolated bodies in nominally emptied pores at suctions approximating to the suction at emptying.

When the material is draining from saturation, the effective stress σ is

image

where S is the fraction of saturation, α is the fraction of the initial water content drained at the maximum suction, Psd is the prevailing pore water suction, and Psd is a suction passed through in reaching pSd at which the reduction of S is dS. When the material is rewetting, the relationship becomes

image

where psw is now the prevailing suction during wetting and f is a distribution function of the degree of saturation such that

image

δS is the fractional saturation removed in the suction range δsd at sd and regained in the suction range δsw at sw. msd is the maximum suction attained.

The effective stress is revealed experimentally by unconfined compression tests on samples with imposed pore water suctions, and the dependence on this suction confirms reasonably that which is predicted by the theoretical formulas.
SOME EFFECTS OF FERTILIZERS AND FARMYARD MANURE ON THE ORGANIC PHOSPHORUS IN SOILS
Authors: ONIANI O. G. , CHATER MARGARET , MATTINGLY G. E. G.
Published: July 2006

The amounts of P applied cumulatively to a neutral arable soil (pH 7.1–7. in 0.01M CaCl2) at Rothamsted, as farmyard manure, alone or with superphosphate, which were converted to organic P in 100 years ranged from 18 to 44 μg P/g of soil (0–23 cm). Superphosphate alone (3300 kg P/ha) slightly lessened the total organic P in the soil. Neither farmyard manure nor super‐phosphate significantly changed the amounts (38 to 42 μg P/g) of inositol penta‐ and hexaphosphate in these soils. In the surface layers (0–7.5 cm) of soils from permanent grassland at Rothamsted, superphosphate (3370kg P/ha) increased organic P by 134 μg P/g at pH 4.5 and 19 μg P/g at pH 6.5, about 6 and 1 per cent respectively of the P remaining from superphosphate applied cumulatively since 1858. In the sub‐surface layers (7.5–23 cm) superphosphate increased organic P by 93 μg P/g at pH 4.5 and 62 μg P/g at pH 6.2, about 18 and 10 per cent respectively of the P remaining from superphosphate. The sum of inositol penta‐ and hexaphosphates accounted for 32 per cent at pH 4.5 and 21 per cent at pH 6.5 of the increases in organic P in the surface layers and 45 per cent and 26 per cent in the sub‐surface layers at pH 4.5 and 6.5 respectively.

Superphosphate (1260–2100 kg P/ha) applied intermittently or cumulatively increased total organic P by 19 to 52 μg P/g and inositol penta‐ and hexaphosphates by 13 to 17 μg P/g in acid tea soils (pH 3.2–3.4) from Georgia, U.S.S.R. Rock phosphate (510–1020kg P/ha) applied cumulatively had no effect on either the total organic P or the inositol P in acid tea soils (PH 3.6–3.7) from Ceylon.
THE EFFECT OF ORGANIC MATTER ON THE BULK AND TRUE DENSITIES OF SOME UNCULTIVATED PODZOLIC SOILS
Authors: ADAMS W. A.
Published: July 2006

Organic matter content was found to have a dominant effect on both the bulk and true densities of soil in the organic and eluvial horizons of the podzolic soils examined. The soils were stone‐free, structureless, and of similar texture. The effects of organic matter on bulk density were described by the equation:
image
A similar equation was devised for true density. Use of these equations indicated that, in the soils examined, total pore space could be predicted from organic matter content measured as per cent loss on ignition.
THE EFFECT OF pH ON THE INCORPORATION OF AMINO ACIDS INTO HUMIC ACID EXTRACTED FROM SOIL
Authors: ADAMS W. A. , PERRY D. R.
Published: July 2006

The effect of pH on the incorporation of six 14C‐labelled amino acids and a dipeptide into humic acid extracted from a podzolic soil was examined. Maximum incorporation was found to occur at a pH which coincided with the apparent dissociation constants of their α‐amino groups. Incorporation took place, into forms which were both acid‐hydrolysable and non‐hydrolysable, the latter accounting for between ten and twenty per cent of the total.
CLAY MINERALS IN SOILS DERIVED FROM LOWER OLD RED SANDSTONE TILL: EFFECTS OF INHERITANCE AND PEDOGENESIS
Authors: WILSON M. J.
Published: July 2006

The clay mineralogy of thirty‐two profiles located mainly in the Vale of Strathmore and developed on glacial till derived from Lower Red Sandstone sediments and lavas has been investigated by X‐ray diffraction. The soils were selected so that the parent material was related predominantly to one of the rock types common in the Lower Old Red Sandstone succession—namely, marl, sandstone, lava, or conglomerate. Comparison of the < 1.4μm fractions separated from fresh rock samples with those separated from the C horizons of the soils clearly established the dominant influence of parent rock on the soil‐clay mineralogy. The clay minerals inherited by the soil often include unusual trioctahedral expansible minerals such as saponite, interstratified vermiculite‐chlorite, and smectite‐vermiculite, as well as more common types like mica, montmorillonite, and chlorite. Kaolinite is also found but it is not certain that it is only of inherited origin. Weathering of the clays during soil formation brings about complete degradation of the expansible trioctahedral minerals, a process usually well advanced in the B or even at the top of the C horizon, and vermiculitization of mica. The latter process occurs mainly in the A horizon, with concomitant precipitation of interlayer aquohydroxy‐aluminium ions thereby forming a vermiculite‐chlorite intergrade. Chlorite and kaolinite appear to be little affected by weathering. The weathering transformations are most pronounced in freely drained acid soils (pH < s) and are at a minimum in poorly drained soils and where the pH remains above 6. The susceptibility to weathering of the trioctahedral expansible minerals results in relatively high values for exchangeable magnesium at the base of the profile.
TACTOID SIZE AND ION EXCLUSION IN FLOCCULATED CLAYS
Authors: MILLS J. G. , ZWARICH M. A.
Published: July 2006

The chloride‐exclusion volume of calcium‐saturated specimens of two bentonites and seven soils were determined over a range of electrolyte concentrations. These systems are believed to approximate the flocculated condition of most Manitoba soils. The montmorillonite was found to be arranged in tactoids or crystallites having an approximate 19Å basal spacing. The assumption of complete chloride exclusion from the interlayer volume over most of the concentration range combined with exclusion according to Gouy theory by the external surfaces provided a reasonable explanation of the experimental data. The number of montmorillonite layers comprising a tactoid, as calculated from the negative absorption determinations, was found to be strongly dependent upon the particle size of the montmorillonite.
A FOSSIL BROWN FOREST SOIL FROM ANGUS
Authors: ROMANS J. C. C. , DURNO S. E. , ROBERTSON L.
Published: July 2006

A soil profile preserved below a barrow of Neolithic age appears to have been a brown forest soil developed under deciduous woodland in which oak was an important component. There is evidence of Neolithic forest clearance.
DETECTION OF CLAY IN SOIL SOLUTION WITH METHYLENE‐BLUE PAPER AND THE ASSESSMENT OF CLAY MOBILITY IN SOILS
Authors: GOMBEER R. , D'HOORE J.
Published: July 2006

The adsorption of methylene blue and the accompanying colour change appears to be a fairly specific and sensitive reaction for colloidal soil clay, especially when used with chromatography paper as a supporting medium. Thus minute amounts of clay in migrating soil solutions can be detected, and stability and electro‐phoretic mobility of very dilute suspensions evaluated.
STUDIES ON SOIL COPPER I. THE FRACTIONATION OF COPPER IN SOILS
Authors: McLAREN R. G. , CRAWFORD D. V.
Published: July 2006

A method for fractionating soil copper was developed and applied to 24 soils representing a range of British soil types.

The scheme distinguishes five fractions:

soil solution and exchangeable copper;

copper weakly bound to specific sites;

organically bound copper;

copper occluded by oxide material; and

residual copper mainly in clay lattice structures.

Correlation and regression analyses confirmed the general validity of the scheme and indicated an association between free manganese oxides and copper which considerably influences the distribution of copper between the main soil constituents. It is suggested that the concentration of copper in the soil solution is controlled by equilibria involving specifically adsorbed copper and that the bulk of the‘available’soil copper reserves reside in the organically bound fraction.
OXIDOREDUCTIVE DEGRADATION OF SOIL MINERALS AND CLAYS D,L‐3(3,4‐DIHYDROXYPHENYL) ALANINE BY SOIL MINERALS AND CLAYS
Authors: MAYAUDON J. , EL HALFAWI M. , BATISTIC L.
Published: July 2006

The effect of the perhydrol (H2O2) treated soils on the decarboxylation rate of d,1‐3(3,4‐dihydroxyphenyl) alanine (DOPA), as examined by radiorespirometry, is highly significant and well‐correlated (r=+0.913) with the clay content.

Among the pure Na clays used, Wyoming bentonite had the strongest effect on the DOPA decarboxylation. The reaction was activated by phosphate buffer and completely inhibited by a dithionite treatment.

Gas phases like carbon monoxide, hydrogen, or nitrogen do not inhibit the DOPA decarboxylation rate.

A chromatographic study of the intermediate products formed during DOPA degradation reveals the presence of 5,6‐dihydroxyindole. These results suggest that DOPA degradation by clays proceeds by a sequence of oxidoreductive reactions following the Raper (1927) scheme. The ferric oxides associated with the clay, and not the dissolved oxygen, are the electron acceptors. DOPA is oxidized to eumelanin which has an elementary percentage composition of C = 62.65; N = 11.05; H = 6.30; 0 = 20.
REAPPRAISAL OF ETHYLENE GLYCOL MONO‐ETHYL ETHER (EGME) METHOD FOR SURFACE AREA ESTIMATIONS OF CLAYS
Authors: ELTANTAWY I. M. , ARNOLD P. W.
Published: July 2006

Using an ethylene glycol mono‐ethyl ether (EGME) retention method, full unimolecular layer coverage of Ca‐montmorillonite surfaces was established in 2 hours in an evacuated system (0.5 mm Hg) containing a free liquid surface of EGME and dry CaCl2, as a separate phase. EGME retention in the presence of CaCl2‐EGME solvate led to incomplete unimolecular layer coverage, the EGME retention being governed by exchangeable Ca‐EGME interaction and not by the real extent of the clay surface. Unlike montmorillonite which has the two layers of EGME molecules between adjacent alumino‐silicate sheets, a vermiculite intercalated only one layer of EGME in the interlamellar space. Relevant X‐ray and differential thermal microanalysis data are provided.
STUDIES ON IODINE IN BRITISH SOILS
Authors: WHITEHEAD D. C.
Published: July 2006

A method for the determination of iodine in soils and other agricultural materials was developed on the basis of an existing Auto‐analyser procedure for iodine in blood.

Using this method, soils from twenty‐three widely separated sites in the U.K. were found to have total iodine contents ranging from 2.7 to 36.9 mg/kg. Total iodine contents were not closely correlated with the distance of the site from the coast or with rainfall, indicating that these factors did not exert major effects on iodine content. When two soils derived from marine alluvium were excluded, total soil iodine contents were positively correlated with aluminium oxide extracted by Tamm's reagent (r= 0.88***), with ferric oxide extracted by citrate‐dithionite (r= 0.64**), and with soil organic matter (r = 0.59**).

Analysis of twenty‐two fertilizer materials, and of the faeces and urine from sheep fed diets containing two levels of iodine, indicated that inputs of iodine to the soil from these sources were small.

From the correlation between total soil iodine contents and other soil properties, together with the proportions of the total iodine extracted by various reagents including sodium hydroxide and oxalic acid, it is concluded that soil iodine is associated, in part, with sesquioxide material and, in part, with soil organic matter.
THE PREPARATION OF CLAY SOILS FOR DETERMINATION OF STRUCTURE
Authors: GREENE‐KELLY R.
Published: July 2006

Most methods for the determination of structure require the soil to be freed of water and yet to retain its original character. The methods of freeze‐drying and critical point‐drying are examined and it is concluded that they are not generally satisfactory. It is possible to preserve the soil fabric whilst water is slowly exchanged with an organic solvent (e.g. methanol or dioxan). The fabric is hardened and the degree of hardening is increased by subsequent exchange with certain water‐immiscible solvents (e.g. diethyl ether). Some shrinkage must be tolerated when it is desired to remove the liquid from the fabric. The best method was found to be infiltration by liquid carbon dioxide and its removal above its critical temperature. Despite some shrinkage the fabric seems unchanged.
THE EFFECT OF DENSITY ON WATER RETENTION PROPERTIES OF FIELD SOILS
Authors: REEVE M. J. , SMITH P. D. , THOMASSON J.
Published: July 2006

The bulk density, available water (Aν), air capacity (Cα), and retained water capacity (θν) were determined for 158 A, B, and C horizons of field soils. Clay (< 2 μm) and silt (2=60 μm) were also determined. Statistical analysis of the results demonstrated that bulk density exerts a profound influence on Aν, Cα, and θν, but the effect varies between texture groups and horizons. Significant negative correlations were obtained between bulk density and Cα for most texture and horizon groups. In B and C horizons Aν and θν also decrease with increasing density, whereas in A horizons Aν and θν tend to increase with bulk density except in silty soils. Within a limited range it is feasible to control these parameters by using field techniques to achieve optimum bulk density for particular soils.
RELATIVE EFFECTS OF TRACTOR WEIGHT AND WHEEL‐SLIP IN CAUSING SOIL COMPACTION
Authors: DAVIES D. B. , FINNEY J. B. , RICHARDSON S. J.
Published: July 2006

The results presented are from field studies in which soil compaction was measured under tractors working with different wheel loads and levels of wheel‐slip. Wheelslip proved to be more important in causing compaction than additional wheel loading, and this effect was more pronounced for more powerful tractors. In most agricultural circumstances the aim is to secure the best compromise between weight and slip as alternative means of achieving greater work output from tractors. The results indicate that in situations where there is a need to avoid compaction, particular attention should be given to providing sufficient wheel loading and the possibility of moving faster to take up more power at lower slip.

For the range of soil moistures encountered sinkage was the most convenient and satisfactory method of assessing total reduction in porosity, and differentiated between treatments better than any of the other methods (see below) apart from water‐entry rates.

Measurement of soil density at three levels to 15 cm depth accounted for less than 50 per cent of the loss of porosity estimated from sinkage and the method did not detect differences due to treatment.

Shear strength measured at one depth (3.5 cm) differentiated between treatments, but penetration resistance at 7.5 cm did not. Water‐entry rates sensitively detected treatment differences but the method was too time‐consuming for comparison of all treatments.

The efficiency of traction of four‐ and two‐wheel‐drive tractors was measured at intervals during the winter on a clay loam and the results related to surface moisture contents. After a steep reduction in efficiency, when the soil returned to field capacity, subsequent changes in efficiency were small.
ANION ADSORPTION BY GOETHITE AND GIBBSITE
Authors: HINGSTON F. J. , POSNER A. M. , QUIRK J. P.
Published: July 2006

The desorption of specifically adsorbed (ligand exchanged) anions, such as phosphate, selenite, and fluoride, from the surface of gibbsite and goethite has been studied by repeatedly washing the adsorption complex with solutions of constant pH and ionic strength but containing no specifically adsorbable anions. The desorption of the anions varies between complete reversibility and almost complete irreversibility. Measurements of surface charge by the uptake of Na+ and Cl‐ revealed that, on washing the adsorption complex, the surface charge returned to its value at the given pH in the absence of specifically adsorbed anions. Thus when the isotherm was irreversible, OH‐ was desorbed (or H+ adsorbed) in preference to the desorption of the specifically adsorbed anion, whereas when the isotherm was reversible the specifically adsorbed anion was desorbed.

Irreversibility appears to involve the nature of the adsorption complex at the surface. Where only monodentate ligands form, for example fluoride adsorption, the isotherm is reversible, whereas bridging or multidentate ligands and the formation of ring structures at the surface favour irreversibility.
A METHOD FOR SOIL PARTICLE‐SIZE ANALYSIS USING ULTRASONIC DISAGGREGATION
Authors: PRITCHARD D. T.
Published: July 2006

A method for routine particle‐size analysis of soils is described which is quicker than methods using peroxide. Organic matter is destroyed by ignition at 400°C and an ultrasonic bath is used for disaggregation.

The efficiency of ultrasonic baths for this purpose is affected by the temperature, aeration status, and depth of water in the tank; the nature, size, and depth of immersion of the sample vessel; and also the ratio of solid to liquid in the sample vessel.

Standardization is preferably based on the effect of treatment on standard materials, rather than the energy output of the apparatus used.

It is difficult to differentiate between aggregates and primary particles, and to choose a method applicable to all soils.
A COMPARISON OF THE SORPTION OF INORGANIC ORTHOPHOSPHATE AND INOSITOL HEXAPHOSPHATE BY SIX ACID SOILS
Authors: ANDERSON G. , WILLIAMS E. G. , MOIR JACQUELINE O.
Published: July 2006

A comparison has been made of the sorption of inorganic orthophosphate and inositol hexaphosphate by six acidic surface soils from arable land in north‐east Scotland. The sorption of inorganic P increased with increasing quantities added and tended towards a maximum, but was never complete. In contrast, the organic P was completely sorbed up to an added quantity which varied with the soil, and above this level the absolute sorption decreased, probably due to the formation of soluble complexes involving iron and aluminium. The sorption sites were apparently the same for the two P forms and, particularly at high levels of addition, the organic P depressed the sorption of inorganic P. Inorganic P did not depress the sorption‐of organic P, which was preferentially adsorbed. The results help to explain the extreme stability of inositol hexaphosphate in these soils.
THE PRESERVATION OF PEAT MONOLITHS FOR PERMANENT DISPLAY
Authors: HAMMOND R. F.
Published: July 2006

Techniques for preparation and preservation of peat soil monoliths for display purposes are described. Impregnation with a low molecular weight polyethylene glycol polymer has been found to be extremely effective in stabilising the natural structural features of peats.
SOME EFFECTS SUB‐SURFACE DRAINAGE AND PLOUGHING ON THE STRUCTURE and COMPACTABILITY A CLAY SOIL
Authors: STEINHARDT REUVEN , TRAFFORD B. D.
Published: July 2006

In a field experiment to determine the direct and indirect effect on soil structure, of sub‐surface piped drainage as compared with natural surface drainage only, in ploughed and unploughed soil, a factorial systematic design with four replicated blocks was used. Structural changes were monitored during 8 months of natural rain and finally irrigation, by measuring surface heights and soil strength (penetration resistance) in relation to moisture content and matric suction, at plough sole depth (27 cm). A compaction test using a tractor with differentially loaded wheels, was applied at various times after irrigation, measuring the resulting wheel sinkage and wet density of the soil.

The effects of the drainage treatments were found to be temporary, except a ‘crusting’ effect during the drying of the unploughed surface drained soil. The ploughed soil with sub‐surface drainage showed greater frost heave than the undrained soil. The soil strength at 7.5‐22.5 cm. depth was linearly related to the matric suction within the range of –3 to 20 cm‐water. The compaction data for the unploughed soil suggested relationships between matric suction, sinkage, and wet density, but complicated interactions prevented any general conclusion. In the ploughed soil, compaction data established the beneficial effects of subsurface drainage in reducing damage from tractor traffic, decreasing wheel sinkage and reducing compaction both below and 16 cm from the track edge. A rise in matric suction of 10 cm‐water, in the range 2‐24 cm‐water was, on the average, as effective in reducing rutting as a wheel load reduction of 670 kg (0.54 kg/cm2 reduction of tyre inflation pressure). It was concluded that for clay soils having a temporary excess moisture, draining the water table to below 50‐60 cm depth should be recommended as a precautionary measure to minimize structural damage.
FIELD STUDIES OF THE SOIL ATMOSPHERE II. OCCURRENCE OF NITROUS OXIDE
Authors: DOWDELL R. J. , SMITH K. A.
Published: July 2006

Studies were made of the seasonal changes in the occurrence of nitrous oxide in the atmosphere of two clay soils. During the winter of 1971‐2 the nitrous oxide concentrations at both sites were in the range 20‐50 ppm. Levels increased with rising soil temperatures in spring, the mean values reaching 50‐170 ppm in May; some individual samples contained 1500‐6500 ppm. The level of nitrous oxide was inversely related to the oxygen content of the soil atmosphere and was also correlated with the nitrate and nitrite concentration of the soil water, but could not be correlated with either the proximity of field drains, soil moisture content or rainfall.
THE NATURE OF ALKALI‐SOLUBLE SOIL ORGANIC PHOSPHATES
Authors: ANDERSON G. , MALCOLM R. E.
Published: July 2006

Fractionation of the phosphates in a sodium hydroxide extract of an arable soil has shown the presence of a number of esters of a type not previously detected in soils. These included several mono‐phosphorylated carboxylic acids with C to P ratios of approximately 7 or 8 to I and two esters each containing glycerol, myoinositol, chiroinositol and an unidentified component. Another ester, probably containing two phosphate groups, was also detected but was not completely separated from other compounds containing no P. These esters constituted only approximately 3 per cent of the total soil organic P but considerable losses of organic P occurred during the extraction and isolation procedures. The amounts of the inositol phosphates, nucleoside phosphates, and inorganic pyrophosphate in the extract were also measured.
A NOTE ON THE PLASTICITY LIMITS OF AGRICULTURAL SOILS
Authors: TOWNER G. D.
Published: July 2006

The plasticity limits of seventeen agricultural soil standards representing contrasting textures, were measured both by the standard methods and by the fall‐cone penetrometer method (Towner, 1973). The results are compared with the Casagrande A‐line in the plasticity chart. The plasticity limits obtained by the fall‐cone method are given for twelve other soils. The plasticity indices for the soils tended to lie about a single curve. They lay above the Casagrande A‐line at low values of liquid limit. There was some suggestion of an order according to texture along this curve.
THE EFFECT OF FREE AND CLAY‐BOUND HUMIC MATTER ON THE UPTAKE OF SULPHATE BY ROOTS
Authors: DELL'AGNOLA G. , FERRARI G.
Published: July 2006

Humic substances stimulate the amount of sulphate actively transported by excised barley roots to an extent depending on the humification pattern of the original soil organic matter. Humic fractions separated on Sephadex differ in their effects on the active transportation of sulphate by roots; both the carboxyl‐to‐phenolic OH ratio and the molecular weight strongly affect the biological activity of the fractions. In contrast, the procedure used to extract the humic material (sodium hydroxide or sodium pyrophosphate) has little influence. When the humic material is complexed with montmorillonite, sulphate uptake is further enhanced.
IDENTIFICATION OF PHOSPHATE‐REACTIVE SITES OF HYDROUS ALUMINA FROM PROTON CONSUMPTION DURING PHOSPHATE ADSORPTION AT CONSTANT pH VALUES
Authors: RAJAN S. S. S. , PERROTT K. W. , SAUNDERS W. M. H.
Published: July 2006

The amounts of hydroxyl ions released from hydrous alumina during phosphate adsorption were measured at constant pH values and at different phosphate concentrations using an automatic titrator. The hydroxyl ions released were plotted against phosphate adsorbed and the equations that gave best fit to the data were differentiated. The variation in the differentials (dOH/dP) with increasing phosphate adsorption was consistent with the theory, proposed below, on the type of sites responsible for phosphate adsorption, by synthetic hydrous alumina containing bayerite and pseudoboehmite, at different concentrations.

At low phosphate adsorption which corresponded to low phosphorus concentration, adsorption took place mainly by displacing aquo groups (Al‐H2O). With increase in phosphorus concentration hydroxo groups (Al‐OH) became the predominant sites of adsorption.

At still higher concentrations, where phosphate adsorption displacing aquo and hydroxo groups was nearly completed, the hydroxyl bridges linking aluminium atoms (Al‐OH‐Al, ol groups) were broken. This created new sites which were responsible for additional adsorption of phosphate at these concentrations.
KINETICS OF ION EXCHANGE IN SOIL ORGANIC MATTER
Authors: BUNZL KURT
Published: July 2006

The rate of ion exchange reactions of humic substances (humic acid and peat) with lead ions was investigated at 25 °C. All experiments were carried out under finite solution‐volume conditions. To the well‐stirred aqueous suspensions of the above samples lead ions were added in such small amounts that, after attainment of the equilibrium, the initial equivalent fraction of lead in the humic substance had increased only by a small amount. The kinetics of such differentially small ion exchange processes were studied as a function of the initial lead content of the samples. The experiments showed that the absolute rates for the uptake of small amounts of lead ions decrease, if the initial lead content of the samples increase. The relative rates of ion exchange, i.e. the rates with respect to the extent of each reaction, showed a more complicated behaviour, as they can exhibit a minimum at a certain initial lead content of the sample. The rate‐determining step of the above ion exchange experiments was shown, by interruption tests, to be diffusion of the ions through the Nernst‐film surrounding the ion exchanger particles.

Theoretical calculations of the rates of film‐diffusion controlled ion exchange processes were carried out and the results revealed that the rates of any differential ion exchange reaction should decrease with increasing initial content of the ion adsorbed, their exact magnitude depending, among other quantities, strongly on the separation factor. The relative rates for the attainment of the equilibrium, on the other hand, depend much less on the initial ionic composition of the ion exchanger. A comparison of the experimental and the calculated results yields satisfactory agreement if the experimentally determined dependence of the separation factor on the lead content of the samples is taken into account.
THE EFFECT OF LIGHT ON THE ESR SPECTRA OF HUMIC ACIDS
Authors: SLAWINSKA D. , SLAWINSKI J. , SARNA T.
Published: July 2006

Photo‐induced Electron Spin Resonance signals have been detected in basic aqueous solutions of humic acids from soil and from synthetic and commercial sources. Parameters of these signals under atmospheres of air, O2 and N2 were the same as or very similar to those of the already known ‘dark’ stable ESR‐signals of humic acids and melanins. The maximum increase of signal amplitude under the influence of 395–780 nm wavelength irradiation was one order of magnitude. The influence of microwave power on ESR‐signal amplitude was examined under different atmospheres. It has been found that oxygen strongly diminishes the saturability of signals. This indicates that oxygen has an influence upon relaxation properties of paramagnetic centres of humic acid. Photoinduced ESR signal is a newly discovered feature of humic acids, similar to that of melanin and may be expected to affect physico‐chemical processes occurring in soils.
MOLECULAR WEIGHT DISTRIBUTION OF SOIL ORGANIC MATTER AS AFFECTED BY ACID PRE‐TREATMENT AND FRACTIONATION INTO HUMIC AND FULVIC ACIDS
Authors: GOH K. M. , REID M. R.
Published: July 2006

Effects of acid pre‐treatment and fractionation on the molecular weight distribution of OIM Na4P2O7 organic matter extracts were investigated in a chronosequence of weakly weathered soils developed on aeolian sand in New Zealand.

Acid pre‐treatment of soils with OIM HCl followed by OIM HCI:03M HF was found to enhance the polydispersion in the nominal molecular weights of the extracts. The same treatment resulted in significant increases in yield and reduction in ash content. However, prolonged standing of extracts in the acids led to acid‐induced polymerization, resulting in a predominance of organic matter in the higher nominal molecular weight ranges.

Fractionation of organic matter extracts by acid precipitation into humic and fulvic acids did not separate them according to molecular weight as commonly believed. Instead, fulvic acids from most soils were found to have similar nominal molecular weight distributions to those of their humic acid counterparts. A large proportion of soil fulvic acid compounds was in the > 100 000 nominal molecular weight range.
THE USE OF THE FREUNDLICH ISOTHERM FOR SOIL PHOSPHATE SORPTION DATA
Authors: FITTER A. H. , SUTTON C. D.
Published: July 2006

Phosphate sorption data for twenty‐nine soils were found to fit the Freundlich adsorption isotherm better if a measure of native labile P was first added to the sorption data, and this sum plotted against intensity. The exponent from the isotherm thus obtained was closely related to exchangeable A1 (in acid soils) and exchangeable Ca (in neutral and calcareous soils), with a mole ratio of one P to 6 A1 or Ca.
DETERMINATION OF THE STRUCTURAL STABILITY CLASS OF ENGLISH AND WELSH SOILS, USING A WATER COHERENCE TEST
Authors: GREENLAND D. J. , RIMMER D. , PAYNE D.
Published: July 2006

The structural stability of samples of 180 soils of known composition was examined by the Emerson test. This test is based on the swelling, slaking, and dispersion behaviour of soil aggregates when immersed in water and under mechanical stress.

In the surface soils investigated there appeared to be a critical level of organic matter, corresponding to 2 per cent organic carbon, below which soils were very liable to structural deterioration especially in the absence of calcium carbonate. Exceptions occurred and are discussed in relation to soil composition.

A very few soils gave variable or indeterminate results and on these the tests were repeated on larger numbers of aggregates. Most soils were readily classified into one or other of the eight classes recognized by Emerson, and the test is a simple and convenient way of distinguishing soils likely to have structural problems in the field.
THE EFFECT OF THE EARTHWORM DENDROBAENA RUBIDA ON THE SOLUBILITY OF LEAD, ZINC, AND CALCIUM IN HEAVY METAL CONTAMINATED SOIL IN WALES
Authors: IRELAND M. P.
Published: July 2006

The quantities of lead, zinc, and calcium dissolved by various extraction techniques from soil, earthworm faeces, and decayed earthworm (Dendrobuena rubida, Savigny) corpses have been studied.

A small proportion of the total metals was water soluble and the amount of lead in faeces was significantly higher than in soil. Putrefied earthworm extracts gave by far the highest concentrations of all three metals.

Acetic acid extractable lead was higher in soil than faeces but putrified earthworm extracts gave the highest concentration of lead. The quantities of zinc and calcium extracted were lowest in soil, higher in faeces, and much higher in decomposed earthworms.

This particular species of earthworm can therefore be considered as a possible source of lead and zinc contamination in heavy metal polluted, acid soil.
FIXED AMMONIUM IN NIGERIAN SOILS
Authors: OPUWARIBOI E. , ODU C. T. I.
Published: July 2006

In soil profiles from Nigeria native fixed ammonium was positively and significantly correlated with per cent silt, per cent clay, per cent silt plus clay, pH, exchangeable potassium and cation exchange capacity but not with exchangeable ammonium or organic matter. The results of multiple and partial regression analyses indicated that native fixed ammonium was most closely correlated with per cent clay, exchangeable potassium, and cation exchange capacity.
FIXED AMMONIUM IN NIGERIAN SOILS
Authors: OPUWARIBOI E. , ODU C. T. I.
Published: July 2006

The ability of the organic and inorganic soil components to fix added ammonium was assessed using 15N as a tracer. In surface soils between 20 and 90 per cent of the ammonium retained after four cycles of alternate wetting and drying was due to organic matter. In subsoils containing little organic matter ammonium was fixed almost exclusively by layer silicate minerals.
THE DETERMINATION OF DESORPTION ISOTHERMS FOR SOIL PHOSPHATE USING LOW VOLUMES OF SOLUTION AND AN ANION EXCHANGE RESIN
Authors: BREWSTER J. L. , GANCHEVA A. N. , NYE P. H.
Published: July 2006

Phosphate desorption isotherms were determined (a) by shaking 1 g soil with 3 ml 0.01M CaCl2 solution plus different amounts of an anion exchange resin, and (b) by diluting soil with different volumes of 0.01M CaCl2 solution. Adsorption isotherms were determined using a soil to solution ratio of 1 g to 3 ml. In soils of intermediate P status adsorption isotherms appeared continuous with desorption by method (a), but not with desorption by method (b), which predicted lower buffer powers than did (a). Method (a) led to increases and (b) to decreases in pH. Additions of dissolved silica had no influence on P desorption by method (b).
RATIONALIZATION OF IONIC STRENGTH AND CATION EFFECTS ON PHOSPHATE SORPTION BY SOILS
Authors: RYDEN J. C. , SYERS J. K.
Published: July 2006

The amounts of inorganic phosphate (P) sorbed by four contrasting unfertilized soils during 40 h were influenced by the ionic strength and cation species of the contacting solution (support medium) used, as indicated by isotherms over the final P concentration range of 0 to 1 μg P/ml and 0 to 10 μg P/ml. An increase in ionic strength enhanced P sorption during 40 h but the species of cation also influenced the amount of P sorbed, as shown by the isotherms obtained in 10−2M Ca and 3 × 10−2M Na systems. Although pH affected the amounts of P sorbed, pH effects alone could not adequately explain the differences in P sorption. Kinetic studies indicated that within the range of P addition used for each soil, the equilibrium P concentration, at infinite time, was independent of ionic strength and cation species. Consequently, the composition of the solution affected only the rate at which equilibrium was attained. The results are attributed to the effects of ionic strength on the surface charge of retaining components and the thickness of the diffuse double layer, and the effects of specilic sorption of a divalent cation on surface charge, as they relate to the rate of P sorption.
THE HIGH‐ AND LOW‐ENERGY PHOSPHATE ADSORBING SURFACES IN CALCAREOUS SOILS
Authors: HOLFORDI I. C. R , MATTINGLY G. E. G.
Published: July 2006

The two‐surface Langmuir equation was used to study P adsorption by 24 calcareous soils (pH 7.2‐7.6; 0.8‐24.2 per cent CaCO3) from the Sherborne soil series, which are derived from Jurassic limestone. High‐energy P adsorption capacities (x″m) ranged from 140–345 μg P/g and were most closely correlated with dithionite‐soluble Fe. Hydrous oxides therefore appear to provide the principal sites, even in calcareous soils, on which P is strongly adsorbed (x″m 6–51 ml/μg P). The low‐energy adsorption capacities (x″m) ranged from 400–663 μg P/g and were correlated with organic matter contents and the total surface areas of CaCO3 but not with per cent CaCO3, pH, or dithionite‐soluble Fe. Total surface areas of CaCO3 in the soils ranged from 4.0 to 8.5 m2/g soil. Low‐energy P adsorption capacities agree reasonably with values (100 pg P/m2) for the sorption of phosphate on Jurassic limestones but phosphate was bonded much less strongly by soil carbonates (k″= 0.08–0.45 ml/μg P) than by limestones (k∼10.0 ml/μg P). Low‐energy P adsorption in these soils is tentatively ascribed to adsorption on sites already occupied by organic anions (and probably also by bicarbonate and silicate ions) which lessen the bonding energy of co‐adsorbed P.
A SIMPLE AND RAPID METHOD OF SOIL WATER DETERMINATION
Authors: AGGARWAL G. C. , TRIPATHI B. R.
Published: July 2006

A wide‐mouthed pycnometer was employed for rapid determination of soil water. The principle involved is to weigh the pycnometer when filled with the soil sample and water. The particle density of soil needs to be known. There is no necessity to add exact volumes of water. For the 7 soils studied, the water content values obtained by the proposed method were similar to those by oven‐drying.
THE USE OF POLYACRYLAMIDE TO REPLACE CARBON IN THE DETERMINATION OF‘OLSEN'S’EXTRACTABLE PHOSPHATE IN SOIL
Authors: BANDERIS A. , BARTER D. H. , HENDERSON K.
Published: July 2006

The addition of 2.5 mg/l of polyacrylamide to 0.5M NaHCO3 used as an extractant for ‘available’ phosphate overcame most of the analytical difficulties associated with the use of activated carbon which was recommended in the original procedure of Olsen et al. (1954). No significant differences in the amount of P extracted were found between polyacrylamide and carbon and with the former, technical problems were greatly reduced. Consequently, the modification of the original method to incorporate polyacrylamide has been adopted in the Agricultural Development and Advisory Service of the Ministry of Agriculture, Fisheries, and Food as a standard method for the determination of available phosphate in soils.
THE ACCUMULATION OF SOIL ORGANIC MATTER AND ITS CARBON ISOTOPE CONTENT IN A CHRONOSEQUENCE OF SOILS DEVELOPED ON AEOLIAN SAND IN NEW ZEALAND
Authors: GOH K. M. , RAFTER T. A. , STOUT J. D. , WALKER T. W.
Published: July 2006

Soil organic matter was extracted by a mixture of O.IM Na4P2O: O.IM NaOH from a chronosequence of weakly weathered soils developed on aeolian sand, and fractionated into humin (non‐extractable), humic acid, and fulvic acid. The mass of total organic carbon in the profiles, the 14C content and the 13C/12C ratios were also determined.

The weight of total carbon increased rapidly at first and then gradually without attaining a steady state. This trend was also shown by the humin and fulvic acid fractions, but the humic acid fraction appeared to have reached a maximum after about 3000 years. The order of total weights of the organic fractions was humin > fulvic acid > humic acid.

The evidence suggests that the proportions of the humic fractions formed by decomposition are related to soil differences but not to vegetation. The greater part of the plant material found in the soils appears in the humin and fulvic acid fractions.