bluuebunny/crossref_metadata_2025 huggingface dataset:
HETEROGENEITY IN SILICON‐IRON MIXED HYDROXIDES
Authors: HERBILLON A. J. , VINH AN J. TRAN
Published: July 2006

Several mixed hydroxides obtained by co‐precipitation of FeCl2 or FeCl2 with Na2SiO2 followed by ageing and purification were studied by X‐ray diffraction, infra‐red spectroscopy, and surface‐area measurements.

The compounds with molecular ratios SiO2/Fe2O3 ranging from 0·1 to 1·17 are essentially amorphous.

Silica, which is not to be considered as an integral part of the gel, is chemi‐sorbed on the ferric or‘ferrosic’ phase.

The good agreement between IR, DTA, and surface‐area measurements with increasing molecular ratios permits the distinction between two ranges of silica contents. In the first range, MR <·1, silica is directly chemisorbed on the adsorbant. In the MR >0·1 range, silica polymerizes as a separate phase growing upon the‘ferrosic’ or‘ferric’ phase.
CATION EXCHANGE PROPERTIES OF MICAS
Authors: NEWMAN A. C. D.
Published: July 2006

The abilities of 10 trioctahedral and 3 dioctahedral micas to release K by cation exchange were compared by repeatedly extracting the micas with NaCl solutions.

For a chosen solution concentration and pH, the quasi‐equilibrium concentration of K in a solution in contact with a mica is largely independent of the fraction of mica K exchanged. The solution concentration ratio cK/cNa ranges from 1×10‐5 for dioctahedral micas to 1·2×10‐3 for a very reactive biotite and seems to depend on the number of mica structural‐hydroxyl groups orientated so that the OH transition moment is perpendicular to the mica basal plane. In the phlogopite‐biotite series, the most important single constituent of a mica that determines its K release is the F content.

Micas that lose much negative charge when the K is exchanged release K more readily to acidic solutions. The pH of unbuffered solutions increases during the exchange of K from these micas, confirming the view that sorption of protons decreases the negative charge of the aluminosilicate layers.
QUANTITATIVE PEDOLOGICAL STUDIES ON SOILS DERIVED FROM SILURIAN MUDSTONES
Authors: ADAMS W. A. , EVANS L. J. , ABDULLA H. H.
Published: July 2006

The main mineralogical change during soil development on Silurian mudstone in mid‐Wales is the weathering of chlorite. Quantitative assessments of changes occurring during pedogenesis have indicated that the release of Mg, Fe, and Al from the parent rock is coincident with the textural degradation of the mudstone. Acid dissolution suggests that the iron‐rich chlorite, which is probably diagenetic and may act as a rock cement, contains most of the Mg and Fe present in the rock.
CLAY MINERALOGY OF SOME SEASONALLY FLOODED SOILS OF EAST PAKISTAN
Authors: HABIBULLAH A. K. M. , GREENLAND D. J. , BRAMMER H.
Published: July 2006

The clay fractions of four seasonally flooded soils from East Pakistan have been studied using X‐ray, DTA, and infra‐red methods, total chemical analysis, surface area determination, and electron microscopy. The soils represent young alluvium (Borda), a juvenile groundwater laterite (Nunni), a groundwater lateritelatosol intergrade (Noadda), and a surface‐water glei (Chhiata). Mica and kaolinite were present in all the soils, and vermiculite in all except possibly Noadda. Vermiculite, total magnesium content, and SiO2/Al2O3 ratio decreased and kaolinite increased in the sequence Borda–Nunni–Noadda. Electron micrographs indicated that in the Borda soil, which is the youngest and subjected to the longest period of annual flooding, iron hydroxides are present as gels coating the surfaces of the clay mineral particles. Such coatings are less apparent in the Nunni clay, and in the Noadda clay most of the ‘free iron oxides’ appear as small granules. The Chhiata soil has about 12.5 per cent of its clay fraction in the form of an amorphous gel rich in silica, and much of the mica and vermiculite in a randomly interstratified complex.
IRISH PLAGGEN SOILS—THEIR DISTRIBUTION, ORIGIN, AND PROPERTIES
Authors: CONRY M. J.
Published: July 2006

Soils have been described in Ireland which meet the definition of thick manmade surface horizons conforming to Plaggen epipedons (Conry, 1969). Unlike the north‐west European Plaggen soils these Irish Plaggen soils have not been formed by the prolonged addition of Plaggen material (heather sods, forest litter, or grass plaggen) and dung, but were formed by the addition of calcareous sea sand, applied either alone or mixed with stable dung. Although only small quantities of grass sods were used in the formation of the Irish Plaggen soils, they should not be separated genetically from the true Plaggen soils of NW. Europe. They occur in coastal areas, within one mile of the coast approximately, where sources of calcareous sand are readily available.

These Plaggen soils generally have a loamy‐coarse‐sand to coarse‐sandy‐loam texture, a granular to single grain structure and loose to very friable consistence. Colour is directly related to the colour of the original soil. Depth varies from field to field and is related to population density.

The Irish Plaggen soils are always base saturated. Phosphorus, potassium, magnesium, and sodium are very much higher than in the unsanded counterpart.

Trace element deficiencies include boron, magnanese, and cobalt. Like the Plaggen soils of NW. Europe the Plaggen soils in Ireland are superior in productivity to their non‐Plaggen counterparts; not only has man's influence increased crop yield substantially, but the range of crops produced has also been enlarged. The Irish Plaggen soils show symptoms of a moisture deficit only in prolonged dry periods.
LOESS IN THE SOILS OF NORTH NORFOLK
Authors: CATT J. A. , CORBETT W. M. , HODGE C. A. H. , MADGETT P. A. , TATLER W. , WEIR A. H.
Published: July 2006

Thin silty deposits cover large areas of north‐east Norfolk, occurring mainly on gently sloping and flat plateau sites and on the floors of valleys cut in the glacial deposits. Particle size and geographic distribution of the deposits suggest that the silt is windblown. The mineralogical composition of the silt fraction resembles that of the silt of Hunstanton Till, suggesting that most of the deposit was derived as loess from outwash of the Weichselian glacier. However, at some localities the sand and clay components of the deposits were derived, at least partly, from subjacent glacial sediments of pre‐Weichselian age. The distribution of the silty deposits strongly affects the pattern of soil types and sometimes the growth of crops.
QUALITY CONTROL IN SOIL SURVEY
Authors: BIE S. W. , BECKETT P. H. T.
Published: July 2006

The paper examines 66 Australian soil surveys in a variety of terrains (but not close forest), by several survey procedures, and published at a range of map scales. It relates the Survey Effort (E) of professional staff (in man‐days per km2) to (I) survey procedure, (2) the kind of mapping unit, and (3) the intricacy of the soil pattern mapped. Intricacy (I), the average number of mapped soil boundaries crossed by 1 km of random linear traverse, is related to the total length of mapped boundary (km per km2).

When the surveys are grouped according to survey procedure and mapping unit, the survey effort for each group may be described by a regression of the form
image

. B could not be shown to differ significantly between groups. D varied in the ratio 0.5: I, according to whether or not surveys used air photograph interpretation, and in the ratio 0.3:0.7:1.o, according to whether they mapped land systems, other compound mapping units, or simple mapping units.

Since the choice of survey procedure and mapping unit is usually governed by the intricacy of the soil pattern the effect of these factors can be summarized in a single regression for all 66 surveys:
image

There is a significant (P≤ 0.001) log‐log regression between I and map scale.
AGEING OF HYDROLYSED IRON (III) SOLUTIONS1
Authors: HSU PA HO , RAGONE STEPHEN E.
Published: July 2006

Three 0.01m Fe(ClO4)3 Solutions of R= 0, 1, and 2, respectively, were studied over a period of 8 months, where R is referred to the HCO3−/Fe3+ mole ratio in preparation. The R= 0 solution was initially light yellow and clear but rapidly changed to a dense cloudy Suspension after a 9‐day induction period. Hydrolysed species rapidly grew from <10 nm to >650 nm. Particles of intermediate size were not observed during the entire period of study. Settleable FeOOH precipi‐tate was first observed in 5 weeks with 23 per cent of its iron noted as precipitate at the end of 5 months. The R= 1 and R= 2 Solutions were reddish‐brown of low turbidity. Rapid hydrolysis and polymerization were observed immediately after preparation. The hydrolysed species gradually grew in size during ageing and no settleable FeOOH precipitate was observed for at least two years. A hypo‐thesis based on Lamb and Jacques's model of Fe3+ hydrolysis is proposed to interpret the reactions taking place in these three Solutions. In the R= 0 solution, the initial number of nuclei for condensation is low, whereas the poten‐tial supply of Fe(OH)3 is abundant. In the R= 1 and R= 2 Solutions the number of nuclei initially formed is high, whereas a limited amount of mono‐meric Fe(OH)3 is available for condensation. The initial number of nuclei relative to the concentration of monomeric species is the key factor that governs the appearance and properties of these Solutions.
ELECTRON‐SPIN RESONANCE OF HUMIC ACIDS FROM CULTIVATED SOILS
Authors: CHESHIRE M. V. , CRANWELL P. A.
Published: July 2006

An examination has been made of the electron‐spin resonance spectra of humic acids from (i) two groups of cultivated soils from the north‐east of Scotland, and the related natural soils from which the cultivated soils are considered to be derived, and (ii) some Rothamsted soils.

With the Scottish soils the humic acids from the more acid natural soils (pH <4.6) show e.s.r. spectra with a four‐peak structure (class I), and those of the less acid soils (pH >4.6) almost structureless spectra (class II).

The cultivated soils contain humic acids with the same class of spectrum as that of the soils from which they are derived, even though they are now much less acid (PH 5.9 –6.5).

Humic acids from Rothamsted soils, sampled recently, were compared with those from the same site sampled 80 years previously. Where the soil has been allowed to revert towards a natural state but still contains free calcium carbonate the pH remained high (7.8–7.9) and the spectrum of the humic acid remains class II. Where the soil contained no free calcium carbonate the pH has fallen from 7.1 to 4.5 on reversion and the spectrum class of the humic acid has changed from II to I.

The results support the hypothesis that the class of spectrum of the humic acid depends on the pH at which it is formed.
THE RESIDUA SYSTEM OF CHEMICAL WEATHERING: A MODEL FOR THE CHEMICAL BREAKDOWN OF SILICATE ROCKS AT THE SURFACE OF THE EARTH
Authors: CHESWORTH WARD
Published: July 2006

The residua system of chemical weathering is here defined as the chemical sink towards which the bulk of earth's surface materials (i.e. the silicate rocks) trend during weathering. Chemically the system is defined in terms of four major components, SiO2–Al2O3–Fe2O3–H2O, evidence being derived from relative solubilities of components under earth‐surface conditions; from experiments in which weathering environments have been simulated in the laboratory; and from field studies of rocks and their weathered mantle. The residua system can be used as a framework to construct mineral facies diagrams showing assemblages of the commonest earth‐surface minerals that occur within it: quartz, gibbsite, goethite, kaolinite, halloysite. In a qualitative manner the facies diagrams can then be interpreted in terms of the partial pressure of water (PH4O) and the temperature, T. The usefulness of this approach in systematizing studies of soil genesis is illustrated with reference to the weathering of granite.
THE INFLUENCE OF IRON AND ALUMINIUM HYDROXIDES ON THE SWELLING OF Na‐MONTMORILLONITE AND THE PERMEABILITY OF A Na‐SOIL
Authors: EL RAYAH H. M. E. , ROWELL D. L.
Published: July 2006

Hydroxy Fe and A1 interlayers reduce the swelling of Na‐montmorillonite in NaCl solutions. A deposit of sesquioxide round an aggregate or orientated flake of clay restricts swelling until the sesquioxide coating is broken by the swelling pressure of the clay. A1 is more effective than Fe.

The effect of sesquioxides on the permeability to NaCl solutions of an alkali soil depends on the control of clay swelling in a manner expected from the above results. A sesquioxide coating round a soil aggregate stabilizes the structure until the coating is broken by the swelling pressure of the clay in the aggregate.
PLUMBOGUMMITE MINERALS IN A STRONGLY WEATHERED NEW ZEALAND SOIL
Authors: ADAMS J. A. , HOWARTH D. T. , CAMPBELL A. S.
Published: July 2006

Phosphate minerals of the plumbogummite group were tentatively identified in a strongly weathered and leached New Zealand soil formed from granite by comparing changes in inorganic phosphate fractions, after calcination, of a soil sample with those occurring in Christmas Island rock phosphate. This identification was confirmed by X‐ray diffraction. Plumbogurnmite minerals were mainly concentrated in the so‐called residual organic P fraction with a lesser but significant proportion in the residual inorganic P fraction. Phosphate minerals of this group may be quite common in other strongly weathered New Zealand soils.
THE REACTIONS OF SOLUBLE ALUMINIUM WITH MONTMORILLONITE
Authors: BROWN G. , NEWMAN A. C. D.
Published: July 2006

The amount of aluminium sorbed by calcium bentonite from basic aluminium chloride solutions depends on the ratio of OH to A1 in the original solution. Except when OH/A1 = 0, only part of the sorbed A1 is exchanged by dilute solutions of barium or calcium chlorides and the exchange capacity of the clay decreases in proportion to the amount of aluminium retained by the clay. Al‐bentonite appears to contain a mixture of A13+ and a basic cation in which OH/Al is 2.5. Neutralizing Al‐bentonite with calcium acetate of pH 7.2 restores only part of the exchange capacity and some charged interlayer aluminium is thought to remain in the clay at this pH. It seems possible, therefore, that charged interlayer aluminium may be found even in soils with a neutral reaction.
OCHRE FORMATION IN FIELD DRAINS IN PYRITIC SOILS
Authors: TRAFFORD B. D. , BLOOMFIELD C. , KELSO W. I. , PRUDEN G.
Published: July 2006

Two distinct forms of ochre are known to occur in field drains. One form, which is most common in wet peaty areas, is caused by the growth of filamentous iron bacteria. The second form is associated with Thiobacillus ferrooxidans, and occurs where the soil contains pyrite.

Contrary to previous reports, liming decreases the rate at which pyrite is oxidized in soil and, by decreasing the amount of iron entering the drains in a given period, should significantly increase the active life of the drainage system. Regular liming is probably preferable to a single large initial dressing.
GAMMA RADIATION FOR MEASURING WATER CONTENTS IN SOIL COLUMNS WITH CHANGING BULK DENSITY
Authors: OLESEN S. E.
Published: July 2006

Water profiles in soil columns were measured by the single‐source gamma radiation method. Together with the normal attenuation equation, linear or parabolic equations for the relation between bulk density and volumetric water content were used. To compensate for moderate changes in the bulk density during the experiment both initial and final bulk density and the water content were used in the water profile estimations.

For a sandy loam soil, the radiation method without any corrections for bulk density changes resulted in a mean error of the volumetric water content estimation of 0.035 cm3 cm−3, when the water content changed from 0.35 to 0.15 cm3 cm−3. By correction for changing bulk density by means of a linear or a parabolic equation the maximum difference between real and estimated water content was 0.009 and 0.002 cm3 cm−3, respectively. Applying the latter method and a count of 105 the error of a single water content measurement was 0–004 cm3 cm−3.
AN EXAMINATION OF THE FALL‐CONE METHOD FOR THE DETERMINATION OF SOME STRENGTH PROPERTIES OF REMOULDED AGRICULTURAL SOILS
Authors: TOWNER G. D.
Published: July 2006

Measurements of unconfined shear strengths were made over a range of moisture contents on seven remoulded agricultural soils which covered a range of textures, and these were used to calibrate the Swedish fall‐cone device. It was found that the calibration factor, usually regarded as constant in engineering literature, was dependent on soil texture, but constant over a range of moisture contents for a given soil texture.

From the assumption that the liquid and plastic limits correspond to two fixed specified strengths, it is shown that one can use the fall‐cone device to determine these limits by making measurements of cone penetrations over a range of moisture contents. It is suggested that a modified plasticity chart, which can be obtained very simply from measurements of cone penetrations made over a restricted range of moisture contents, may be used for characterizing soil behaviour.
ADSORPTION OF THE HERBICIDE 2,4‐D ON GOETHITE
Authors: WATSON J. R. , POSNER A. M. , QUIRK J. P.
Published: July 2006

Adsorption, of the herbicide 2,4‐Dichlorophenoxyacetic acid (2,4‐D) on an iron oxide, goethite, was studied in aqueous suspensions as a function of solution pH, ionic strength of the medium, and initial 2,4‐D concentration.

The 2,4‐D anion was reversibly adsorbed on positively charged goethite surfaces, maximum adsorption being observed near the pKa of 2,4‐D (2.73) and at low ionic strength. Within certain levels of adsorption (5–22 mg 2,4‐D adsorbed/g goethite) the complex became hydrophobic and floated to the liquid surface. This flotation effect disappeared on further adsorption.

It is suggested that adsorbed 2,4‐D anions are orientated with their hydro‐phobic aromatic ends directed towards the solution, the carboxyl groups being weakly bound to positive sites on the oxide surface. At high levels of adsorption, some of the anions are orientated in the opposite direction by π–π interaction, with the first adsorbed layer and the surface reverts to its hydrophilic nature.
SOLUBLE ALUMINIUM AND CALCIUM‐ALUMINIUM EXCHANGE IN RELATION TO THE pH OF DILUTE CALCIUM CHLORIDE SUSPENSIONS OF ACID SOILS
Authors: BACHE B. W.
Published: July 2006

Measurements of pH and A1 concentration were made on 10‐2 M CaCl2, suspensions of a number of acid soils that had been limed to give 3 range of pH values, and exchangeable A1 and Ca+Mg were determined in 1.0 M NH4Cl extracts. The variation of pH with A1 concentration did not support the theory that pH is controlled by the solubility of Al(OH)3. For some of the soils, proton release on hydrolysis of A13+ions in solution accounted for the pH values, and explained quantitatively the variation of pH with the Ca:Al balance of the exchange complex, taking account of the selectivity coefficient for exchange, Kca→A1 Although Kca→A1 was smaller for soils containing more humus, their pH values were also less than those predicted by the hydrolysis of A13+ in solution, indicating that they contained other sources of protons, presumably the carboxyl groups in humus.
MEASUREMENT OF SOIL MOISTURE NEAR THE SURFACE USING A NEUTRON MOISTURE METER
Authors: GRANT D. R.
Published: July 2006

Correction factors for neutron moisture meter measurements near the soil surface have been established from readings at several depths taken before and after the removal of 10 cm of surface soil. In determining the factors it is assumed initially that a uniform soil moisture profile exists. The factors are then applied to the measurements and, from calibration of the neutron meter, the soil moisture profile is established. If large variations with depth are revealed, the initial assumption of uniformity of moisture profile does not apply. A method of determining corrections to the computed factors to allow for the variations in the soil moisture with depth is described. This requires a knowledge of the variation of the correction factors with moisture content and methods of determining this are discussed.
INTRODUCTION OF GRADATIONAL AND PEDOMORPHIC FEATURES IN DESCRIPTIONS OF SOILS
Authors: BOS R. H. G. , SEVINK J.
Published: July 2006

A soil profile is considered as the result of the interaction of pedogenic and gradational processes. Distinction is made between monopedomorphic, polypedomorphic, and buried soils. Description of these soils often meets with difficulties due to inadequacies in existing profile description systems. A new system is proposed, based on the differentiation between gradational and pedomorphic features. In this system the concept of pedogenetic horizons (A, B, C, etc.) is deliberately abandoned in favour of the recognition or failure to recognize pedomorphic features at a certain depth and over a certain vertical extent. Some examples serve to elucidate the new system.
STUDIES ON THE MINERALIZATION OF UREA, COATED UREA, AND NITRIFICATION INHIBITOR TREATED UREA IN SOIL
Authors: REDDY R. N. S. , PRASAD RAJENDRA
Published: July 2006

A laboratory incubation study was conducted with a sandy clay loam soil (pH 7.8) at New Delhi to study the mineralization of urea, coated urea (sulphur‐coated urea, shellac‐coated urea), and urea treated with nitrification inhibitors (N‐Serve, sulphathiazole) a general purpose microbicide (coal tar), and neem (a non edible oil‐seed) cake. Coated fertilizers mineralized much slower than urea; urea‐N from these materials remaining in soil after z weeks of incubation being two to three times that from untreated urea. However, most N from coated fertilizers was mineralized after 4 weeks. Nitrification inhibitors were quite effective in retarding the nitrification of urea; N‐serve being much more effective than sulphathiazole. Neem cake and coal tar extract were less effective than sulphathiazole in controlling nitrification of urea but they did retard the nitrification of urea for z weeks.
IRON AND ALUMINIUM AS CEMENTING SUBSTANCES OF SOIL AGGREGATES
Authors: GIOVANNINI G. , SEQUI P.
Published: July 2006

Extraction of five soils with acetylacetone in benzene does not change their particle‐size distribution, compared with no pre‐treatment or dispersion, but it decreases the water stability of soil aggregates. The decrease is closely related to the extent of the extraction of iron and aluminium by acetylacetone in benzene from soils.

The metals extracted by acetylacetone are essentially bound to the organic matter. It is suggested they behave as junctions of a net composed of polymeric chains of soil organic matter. The mesh, which exerts a protective action on soil aggregates, is weakened at the junctions of polymeric chains after the removal of metals so that the stability to the disrupting action of water is decreased.
THE POTASSIUM STATUS OF SIX LOESSIAL SOILS OF CANTERBURY, NEW ZEALAND, IN RELATION TO RAINFALL AND RATE OF LOESS ACCUMULATION
Authors: HAY M. J. M. , WALKER T. W. , ADAMS A. F. R. , CAMPBELL A. S.
Published: July 2006

A selection of greywacke‐derived loessial soils in Canterbury, New Zealand, was examined to test the hypothesis that soil K status is a function of soil‐forming factors. Soils were selected such that factors besides loess accumulation and rainfall were relatively constant and the effects of each variable could be isolated. Soil K status was evaluated by plant, chemical, and X‐ray diffraction techniques. With increasing rainfall and decreasing rate of loess accumulation soil K status decreased; there was a concurrent decrease in illite and increase in interstratified mineral content of the clay fraction.
EFFECT OF WATER SUCTIONS ON THE GROWTH IN SOIL OF THE CILIATE COLPODA STEINI, AND THE BACTERIUM AZOTOBACTER CHROOCOCCUM
Authors: DARBYSHIRE J. F.
Published: July 2006

Pure cultures of the bacterium Azotobacter chroococcum, and mixed cultures of A. chroococcum and the ciliate Colpoda steini, were incubated for 35 days in soil samples, which were either saturated or subjected to a constant suction (either pF 1.5, 2.0, or 2.7). Previous to inoculation, the soil samples had been sterilized by y‐irradiation (5 Mrad) and saturated with a solution of glucose and mineral salts.

In the samples maintained at pF 2.7, the Colpoda population decreased after inoculation. In the other samples the ciliate populations increased after inoculation, and the duration of each growth period was related to the degree of suction applied. The longer growth periods were associated with the smaller suctions. Twenty‐eight days after inoculation, saturated soil contained the largest ciliate population.

Large numbers of Azotobacter cells were present in all samples, although there was a decline in numbers with time. Azotobacter populations in the samples at pF 2.7 did not increase after inoculation, and smaller Azotobacter populations were often present in the mixed compared with the pure cultures at the same pF value.
HYDROLYSIS REACTIONS IN SODIUM‐MONTMORILLONITE SUSPENSIONS
Authors: LLORCA R. , CRUZ‐ROMERO G.
Published: July 2006

Explanation of the hydrolysis of Na‐montmorillonite in NaCl solutions if based on Donnan equilibria, the order of the hydrolysis reaction, and CO2–H2O‐NaCl‐NaOH equilibria. Equations describe quantitatively the extent of hydrolysis as a function of per cent clay in suspension, and initial NaCl concentration. Lack of fit between experimental and calculated Na+ and H • activities is attributed predominantly to lack of equilibrium with atmospheric CO2 in the first stages of the reaction, and thereafter to secondary reactions due to chemical instability of protonized clay, when H+ activity continuously decreases. The presence of CaCO3 in natural clay samples leads to pH values 1 to 2 units higher than those due only to hydrolysis.
FLUORIDE ADSORPTION BY ILLINOIS SOILS
Authors: OMUETI J. A. I. , JONES ROBERT L.
Published: July 2006

Fourteen surface and 6 subsurface horizons of Illinois soils adsorbed significant amounts of F− with release of OH−. At low concentrations, adsorption was described by both Langmuir and Freundlich isotherms. The calculated Langmuir adsorption capacities were related to pH, clay, organic carbon, and amorphous aluminum contents.

Two soils with different gross chemical properties behaved in essentially the same manner, with adsorption maxima occuring between pH 5.5 and 6.5. The similarity between adsorption at different pH values for the soils and those for bauxite, allophane and synthesized ‘soil chlorite’, and the lack of adsorption maxima between pH 5.5 and 6.5 for pure kaolinite and montmorillonite, suggest that F− adsorption in the soils is due primarily to the presence of amorphous aluminum oxyhydroxides which are common weathering products in these soils.
DESORPTION AND ISOTOPIC EXCHANGE RELATIONSHIPS OF PHOSPHATE SORBED BY SOILS AND HYDROUS FERRIC OXIDE GEL
Authors: RYDEN J. C. , SYERS J. K.
Published: July 2006

Sorption of added inorganic phosphate (P) was irreversible in four contrasting soils and hydrous ferric oxide gel during 16 h desorption after 40 h sorption at the same (iso)pH. Irreversibility increased with increasing time of desorption above 30 h. When the amount of P which was chemisorbed during the sorption step was subtracted from the amount desorbed, the latter fell on the isotherm describing the more‐physical, potential‐determining sorption. No pH change occurred during desorption and net negative charge decreased by 1 equivalent per mole P desorbed.

These results suggested that only more‐physically sorbed P was desorbed at the iso‐pH. The more‐physically sorbed P was also reversible with respect to changes in the ionic strength and cation species of the desorbing solution. The isotopic exchangeability of the more‐physically sorbed P was at least ten times greater than that of chemisorbed P. With increasing sorption time, both the ease of desorption and exchangeability of sorbed P decreased. Subsequent to desorption, the exchangeability of the remaining sorbed P also decreased. These observations are interpreted in terms of the concurrent changes in the amounts of chemisorbed and more‐physically sorbed P.
THE USE OF MOUNDS OF THE TERMITE MACROTERMES FALCIGER (GERSTÄCKER) AS A SOIL AMENDMENT
Authors: WATSON J. P.
Published: July 2006

Twelve termite mounds and adjacent Ah and Ap horizons were sampled at three sites near Salisbury, Rhodesia. The mass of termite mounds occupied by M. falciger at one site was estimated at 620 t/ha, and contained the following amounts of nutrients expressed as percentages of the amounts in mounds and Ap horizon combined: extractable Ca 95%, mineral N 81% extractable K 69%, and available P 69%.

Pot experiments using perennial ryegrass gave higher dry matter yields from termite mounds than from the Ap and Ah horizons. Crop production could therefore be increased by mixing termite mounds with the soil.
ORIGINS AND STABILITY OF SOIL POLYSACCHARIDE
Authors: CHESHIRE M. V.
Published: July 2006

Recent work on the origin of soil polysaccharide and its biological stability in soil is reviewed. It is concluded that much of the constituent hexose and deoxyhexose sugars are of microbial origin, whereas the pentose sugars are derived from plant residues. The stability of soil polysaccharide in its native state is not related to its chemical composition but to its unavailability. This is caused by inaccessibility within undecomposed biological residues and to insolubility resulting from adsorption on clay, the formation of metal complexes, or tanning by soil humic substances. Complexing by metals and tanning may also inhibit enzymic hydrolysis.
ADSORPTION ON HYDROUS OXIDES: II. OXALATE, BENZOATE AND PHOSPHATE ON GIBBSITE
Authors: PARFITT R. L. , FRASER A. R. , RUSSELL J. D. , FARMER V. C.
Published: July 2006

Adsorption isotherms, the infrared spectra of adsorbed species, and the amount of hydroxyl released when oxalate is adsorbed, all indicate that adsorption of oxalate, benzoate and phosphate at low solution concentrations occurs only on A1(OH)(H2 O) sites exposed on edge faces of the platy gibbsite crystals studied. This is confirmed by the finding that the vibrations of surface hydroxyl groups on the principal plate faces are unaffected when excess oxalate is present, and further supported by the low affinity for oxalate of imogolite, a tubular mineral with a very large gibbsite‐like surface, but with a very low concentration of edge sites.

Infrared spectra indicate that oxalate is adsorbed in bidentate form. Near neutrality and at low solution concentrations, gibbsite adsorbs more oxalate than does goethite of comparable surface area.
THE MICROMORPHOLOGY OF GIBBSITE FORMS IN SOILS
Authors: ESWARAN H. , STOOPS G. , SYS C.
Published: July 2006

Using optical and scanning electron microscopy various forms of gibbsite are described in some tropical soils. In a lateritic soil from Zaire gibbsite occurs on argillans, in randomly oriented crystal sheets, as nodular aggregates infilling vughs and on ped faces. The mineral also surrounds quartz grains and kaolinite pseudomorphs after biotite. In other soils gibbsite occurs as silt‐size particles disseminated through the matrix, as large nodular aggregates, and as anatomizing sheets associated with crystal chambers. It is clear from these observations that alumina must be a mobile constituent and was probably translocated through the soil in solution.
SURFACE CHEMISTRY OF THE HYDRANDEPTS AND ITS RELATION TO NITRATE ADSORPTION AS AFFECTED BY PROFILE DEPTH AND DEHYDRATION1
Authors: BALASUBRAMANIAN V. , KANEHIRO Y.
Published: July 2006

The pH0 and ZPC of two Hydiandepts were determined by potentiomettic titiation in NaCl and by ion adsorption measurements from NH4NO3, respectively. The decrease of pH, pH0, and ZPC due to drying was explained by the hydrolysis reaction. Partial drying, high organic matter content, and low Al2 O3 concentration in the surface soil were responsible for its low pH, pH0 and ZPC. The high pH0 of subsoils was attributed to the presence of amorphous aluminosilicates and mixed polymeric gels of Fe(III) and A1 with high water content. The significant decrease of nitrate adsorption due to dehydration is discussed in relation to the change in pH, pH0, ZPC, and surface area on drying.
ROTHAMSTED STUDIES OF SOIL STRUCTURE II. MEASUREMENT AND CHARACTERISATION OF MACROPOROSITY BY IMAGE ANALYSIS AND COMPARISON WITH DATA FROM WATER RETENTION MEASUREMENTS
Authors: BULLOCK P. , THOMASSON A. J.
Published: July 2006

Macroporosity (>60 μm) in the three pairs of soils described in Part I was measured and characterized by image analyses. There are significant differences in macroporosity between the soils in each pair, particularly in the subsoil horizons. The results show that the Ragdale, Denchworth and Salop soils are more impervious than those of the Hanslope, Evesham and Flint soils.

Comparison of the image analysis results with those derived from air content at 0.05 bar suction shows that in most cases macroporosity by the former is larger. In image analysis the maximum diameter of each pore is measured whereas the water retention method measures the diameter of the smallest exit point of each pore. Differences between the two types of measurement will thus be at a maximum in soils containing many large pores with narrow exit necks.
ROTHAMSTED STUDIES OF SOIL STRUCTURE VI.
Authors: NORTH P. F.
Published: July 2006

An ultrasonic method has been used to measure the stability index, σ, for each horizon of six soils. They provided three soil series comparisons: Hanslope‐Ragdale, Evesham‐Denchworth and Flint‐Salop, in which the first‐named series in each pair is ‘rarely problematic’, and the second ‘commonly problematic’ in management.

The results for the top soils are presented in terms of the relationship between σ and the concentrations of those soil constituents likely to contribute to stability of aggregates: organic matter, clay, iron and aluminium oxides, and calcium carbonate. Regression analysis indicates significant correlations for all except the iron and aluminium oxide components.

For each soil pair, the ultrasonic measures of stability did not reflect soil management experience, either for surface or sub‐soil horizons. In general the commonly problematic soil appeared to have the same if not higher stability than its rarely problematic partner. Ultrasonic measurement of stability to dispersion, whilst indicating possible mechanisms of soil aggregate formation and breakdown, gives little help in identifying soil management potential.
MINERALISABLE ORGANIC NITROGEN IN SOIL FRACTIONATED ACCORDING TO PARTICLE SIZE
Authors: CAMERON R. S. , POSNER A. M.
Published: July 2006

A sandy‐loam under wheat‐pasture‐pasture rotation was sampled both after legumeenriched and legumedepleted pasture leys and then fractionated according to particlesize using mainly sedimentation in water. The C/N ratios decreased from 18 to 7 with decreasing particle‐size and were similar for both pasture types, despite ratios of 13 and 31 respectively for organic material collected at the surface of the soil before sampling. Organic matter was most concentrated in fractions having mineral particle‐sizes between 0.3 and 4.0 μm e.s.d.

Mineralisation of the N of high C/N fractions was much greater in incubations under waterlogged anaerobic conditions than under aerobic conditions, yet for low C/N fractions, there was little difference.

Most of the readily mineralisable soil N resided in fractions of mineral e.s.d. less than 4 μm and much of this was probably recently formed microbial tissue or metabolites. An increasingly greater proportion of the N within size‐fractions was mineralised as the particle size decreased, the increase being greater for aerobic incubations. The proportion of N mineralised in the surface organic material was much greater for legume‐rich than for legume‐poor pasture, but in the soil fractions, a corresponding difference was established only for sand‐sized organic matter.
DESORPTION OF PHOSPHATE FROM GOETHITE
Authors: MADRID L. , POSNER A. M.
Published: July 2006

The reversibility of the adsorption of phosphate on goethite was measured by diluting suspensions of goethite on which phosphate was adsorbed with large volumes of phosphate‐free solution at the same ionic strength. The effect on the reversibility of various adsorption and desorption conditions was studied, particularly pH, temperature, ionic strength and time of reaction.

The apparent irreversibility of the adsorption reaction seems to be due to a slow adsorption reaction of part of the phosphate after a very rapid initial adsorption, with a similar behaviour when the phosphate is desorbed. When the total adsorption plus desorption time is long enough, both adsorption and desorption points tend to lie on a single curve which corresponds to the isotherm calculated according to the Stern double‐layer theory.
ADSORPTION OF SELENITE, PHOSPHATE AND SULPHATE ON HYDROUS ALUMINA
Authors: RAJAN S. S. S.
Published: July 2006

Selenite was adsorbed on a positively charged hydrous alumina at a solution pH of 5.0, and the OH − released and changes in the surface charge were measured. The adsorption isotherm levelled off at high concentrations suggesting a definite adsorption maximum. The OH− released yielded a curvilinear relationship of increasing slope with the selenite adsorbed. The positive charge on the alumina surface was neutralized by the adsorbed selenite and the net charge became close to zero as the adsorption of selenite was near maximum.

The molar ratio of the ligands (OH−+ OH2) displaced over selenite adsorbed was more than one at surface saturations of <0.5, but it was approaching one with increasing adsorption of selenite. The results are explained in terms of preferential adsorption of divalent (SeO23−) and monovalent (HSeO−3 selenite on a highly positively and less positively charged surface respectively, in agreement with the VSC− VSP model of Bowden et al. (1973; 1977). The supply of SeO23− for adsorption is considered to be favoured by an expected lower H activity in solution adjacent to the positively charged surface than that in the bulk solution.

A general discussion is given on the ligand exchange adsorption of selenite, phosphate and sulphate on hydrous alumina.
USE OF THE DROP‐CONE PENETROMETER ON UNDISTURBED AND REMOULDED SOILS AT A RANGE OF SOIL‐WATER TENSIONS
Authors: MULLINS C. E. , FRASER A.
Published: July 2006

Drop‐cone measurements were made on undisturbed and remoulded samples of topand sub‐soil from two sites equilibrated at tensions between zero and 600 kPa (6 bar). All samples remained virtually saturated up to the highest tension. Within a few days after remoulding, cone penetration values had returned to those obtained on undisturbed samples.
THE WATER BALANCE OF AN AGRICULTURAL CATCHMENT III THE WATER BALANCE
Authors: McGOWAN M , WILLIAMS J. B. , MONTEITH J. L.
Published: July 2006

The catchment of the Kingston Brook has an area of 57 km2, mainly under pasture (56%) and arable crops (36%). Changes of soil water content, measured with a neutron probe from April 1969 to March 1973, were analysed to determine evaporation (summer only) and drainage. From measurements of rainfall and runoff, supplemented by Penman estimates of evaporation (in winter), water storage is estimated month by month.

Annual mean values (mm) were: rainfall (559), evaporation (398), runoff (157). During the summer, the measured decrease in soil water storage contributed ca 100 mm to evaporation and drainage and there is evidence of delayed recharge (about 30 mm) during the winter. A linear relation between annual rainfall and annual runoff is interpreted in terms of (i) a fixed catchment storage (125 mm); (ii) a small and nearly constant winter evaporation (ca 49mm); (iii) summer evaporation of 125 mm from storage plus a constant fraction (0.57) of contemporary precipitation.

Summer evaporation was restricted by the supply of rain in every year from 1969 to 1976. By estimation, 500 mm of summer rain is needed to maintain potential evaporation, and the deficit at which actual evaporation falls below the potential rate was about 40 mm. Replacing the pasture by cereals would increase runoff by about 10% because of the shorter growing season.
THE VOLATILISATION, FROM SOILS AND MIXTURES OF SOIL COMPONENTS, OF IODINE ADDED AS POTASSIUM IODIDE
Authors: WHITEHEAD D. C.
Published: July 2006

Iodine, as potassium iodide in solution, was added to samples of 24 surface soils, 15 subsoils and 16 mixtures of sand with other materials representing soil components, at 10 μg iodine/g soil. The extent of volatilisation of the added iodine was measured after 30 days' exposure in a well‐ventilated room. With many of the surface soils volatilisation was negligible although with an acid sandy podsol it amounted to 57 per cent of the iodine added. Eleven of the subsoils induced volatilisation amounting to > 10 per cent of that added. With sand alone, having a pH of 5.7, volatilisation amounted to 100 per cent, and with the mixtures it ranged from nil to 100 per cent. Organic matter reduced volatilisation, probably by retaining the iodine in bound form. Montmorillonite, kaolinite and ferric oxide also reduced volatilisation in comparison with sand alone, but had less effect than did organic matter. Calcium carbonate, although in general reducing volatilisation, probably through its influence on pH and hence on retention by other materials, caused no reduction when added to sand alone.
The effect of pH and metal binding on the transport properties of humic acids
Authors: RITCHIE GERALDINE S. P. , POSNER A. M.
Published: July 2006

The molecular weight, shape and size of fractionated humic acids and their metal complexes were determined from sedimentation and diffusion measurements made at various pH values. For all the species studied, the molecular weight and size decreased as the pH became more alkaline. However, the shape of the molecule (approximately spherical) was unaffected by pH. The molecular weight and size of the metal humates depended not only on the type of cation but also on the degree of dissociation ofthe humic acid and the hydrolysis ofthe metal ion.
Eluvial/illuvial coefficients of major elements and the corresponding losses and gains in three soil profiles
Authors: MUIR J. W. , LOGAN J.
Published: July 2006

The major element compositions of three soil profiles from the north‐east of Scotland have been determined and from them losses and gains of major elements have been calculated. Eluvial/illuvial coefficients are also calculated and used to measure the intensities of soil processes. This information forms the basis of a discussion on the development of the profiles. The main process involves the decomposition of minerals, especially in the upper horizons, the loss of constituents to drainage and the translocation ofa few to the lower horizons.
Some fundamental aspects of the formation, stability and failure of mole drainage channels
Authors: SPOOR G. , LEEDS‐HARRISON P. B. , GODWIN R. J.
Published: July 2006

The various stresses are examined which can arise in the vicinity of a mole channel from its formation to ultimate collapse. Possible failure mechanisms contributing to channel collapse or deterioration are proposed, together with the major soil properties associated with them. Supportive evidence for the proposals, obtained from individual laboratory and field experiments, is presented.
Critical potassium potentials for crops: 2. Potentials for wheat, maize, peas, beans and sugar beet in their early growth on a sandy loam
Authors: PAGE M. B. , TALIBUDEEN O.
Published: July 2006

Wheat, maize, leafless peas, field beans and sugar beet were grown in a constant environment for 4 weeks after germination on a sandy loam containing initially a 70‐fold range of exchangeable K levels. The yield response curves to the mean soil K potential (ΔGK, ca+ Mg) for the growth period for each crop were divided into three linear sections, for positive, zero and negative response, by a numerical iterative method, and from these, exhaustion (Δ Gexh), optimum (ΔGopt) and toxicity (Δ Gtox) K potentials were derived.

Values of ΔGexh were similar for all crops. The Δ Gopt values increased in the order legumes < cereals < sugar beet. High potassium potentials which produced decreases in yield were far greater than any likely to be encountered in a natural system. It is suggested that yield reductions at high K potentials were caused by inhibition of the uptake of other cations rather than by toxic levels of K in the plant tissue.

At this early growth stage, seed K concentrations and K contents of the crops affected ΔGexh and Δ Gopt values in different ways and to different extents. The influence of the K requirements of the crop and the crop's ability to extract K from the soil are briefly discussed.
Studies of litter and acid insoluble soil organic matter fractions using 13C‐cross polarization nuclear magnetic resonance spectroscopy with magic angle spinning
Authors: WILSON M. A. , HENG S. , GOH K. M. , PUGMIRE R. J. , GRANT D.M.
Published: July 2006

Cross polarization carbon‐13 nuclear magnetic resonance spectroscopy with magic angle spinning (CP‐MASS) was used to analyse for various forms of carbon in soils, a moss peat, hydrochloric acid insoluble residues from soils and peat, and litter from beech and pine trees. The chemical composition of the litters was also investigated by conventional techniques.

The results show that hydrolysis with hydrochloric acid extraction removes nearly all oxygenated alkyl carbon from the soils used. It is shown that humification pathways in which carbohydrates are incorporated into humic substances via nonhydrolysable linkages are not important for the soils investigated in this work.

CP‐MASS data suggest that the percentage of aromatic carbon in pine leaves increases with increase in ageing time. The results for the beech leaves are not sharply defined.
Optimal interpolation and isarithmic mapping of soil properties
Authors: McBRATNEY A. B. , WEBSTER R.
Published: July 2006

The principle of optimal estimation using regionalized variable theory is extended from that of a single soil property to situations where there are two or more spatially interdependent ones. Auto and cross semi‐variograms express the spatial relations among the properties concerned. They can be estimated from data and can then be used to interpolate the values of a variable by co‐kriging from measurements of it plus data on one or more other properties that have been more intensively sampled. The technique of co‐kriging is described and illustrated by a case study of the particle size distribution at Woburn experimental farm. There was a strong co‐regionalization with common anisotropy between topsoil silt, subsoil silt and subsoil sand. This allowed topsoil silt to be estimated and mapped by co‐kriging more precisely than by kriging from data on topsoil silt alone.

When the auto and cross semi‐variograms for a set of variables are known in advance or estimated from reconnaissance they can be used to plan an optimal sampling scheme. The main variable is sampled on a rectangular grid with finer grids for subsidiary variables. The maximum kriging variances are calculated for a range of sample spacings and relative sampling intensities. Those that match the maximum tolerable variance are potentially useful. The optimum scheme is the one that achieves the desired precision for least cost. For Woburn it is shown that measuring a main variable would need to cost at least 5 times that of a subsidiary variable to make a design for co‐kriging economically sound. Such differences are unlikely for particle size fractions. Nevertheless there are many other instances in soil research where there are large differences in cost. If there is also a strong co‐regionalization then savings should be possible by designing a sampling scheme that takes advantage of co‐kriging.