bluuebunny/crossref_metadata_2025 huggingface dataset:
PEDOTUBULES: THEIR DEFINITION, CLASSIFICATION, AND INTERPRETATION
Authors: BREWER R. , SLEEMAN J. R.
Published: July 2006

The term pedotubules is proposed for a group of pedological features which have a tubular external form and which are distinguished from cutans (Brewer, 1960a) by their complex internal composition and fabric. Pedotubules are classified according to their internal fabric and composition, details of external form, distinctness, and by a comparison of their fabric and composition with that of the horizons of the soil profile. Their general morphology suggests their origin as voids caused by faunal and floral (root) activity which have been filled, or partially filled, with soil material. Since little is known of the details of the effects of faunal activity on soil materials, such interpretations are tentative.
THE INFLUENCE OF SOIL TYPE ON THE RESPONSE OF MAIZE TO UREA IN GLASSHOUSE EXPERIMENTS
Authors: COURT M. N. , DICKINS J. C. , STEPHEN R. C. , WAID J. S.
Published: July 2006

A greenhouse experiment compared the effects of ammonium nitrate and urea (1 per cent biuret), applied to forty‐two soils, on the growth and yield of maize foliage.

Dry‐matter yields of maize in most soils were similar when both sources supplied 0·15 g or 0·30 g N per pot. At 0·45 and 0·60 g N per pot plants in soils with urea yielded less than with ammonium nitrate in sixteen and nineteen soils respectively. Urea adversely affected plant development to a greater extent in light soils than in heavy soils and peats. A partial correlation analysis indicated that responses to urea at the two higher rates of application were positively correlated with ammonia absorption capacity and a correlation with clay content was indicated. No significant partial correlations were obtained with organic matter content, pH, exchangeable‐hydrogen, cation‐exchange capacity, and moisture content.
SOIL PROFILES FOR DISPLAY PURPOSES
Authors: BEATER B. E.
Published: July 2006

A technique for the preparation and preservation of soil profiles is described. Constructional details of the metal frame, methods for procuring the monolith in the field and the subsequent facing of it are presented in some detail. The preservation or hardening of the soil monolith in its frame with plasticized poly‐vinyl acetate emulsion, stabilized with poly‐vinyl alcohol, was found to be extremely effective.
CUTANS (CLAY FILMS) AND POTASSIUM AVAILABILITY TO PLANTS1
Authors: SOILEAU J. M. , JACKSON W. A. , McCRACKEN R. J.
Published: July 2006

The influences of iron‐kaolinite cutans enveloping soil aggregates on the availability of K within these aggregates were studied. Synthetic iron‐kaolinite clay coatings on illite aggregates were prepared. Macroscopic and microscopic observations of the synthetically prepared aggregates indicated the formation of almost continuous, partially orientated crystalline iron‐kaolinite cutans around the perimeter. There were indications that the presence of the coating tended to stabilize the aggregates. Photomicrographs of wheat root‐aggregate associations revealed intimate surface contact between the two with some penetration and disruption by the wheat roots, both in the coated and uncoated aggregates.

Plant growth and potassium uptake were restricted in the presence of iron‐kaolinite coatings on K‐rich illite aggregates compared with plants grown on aggregates without coatings. Moreover, the presence of the coatings resulted in appreciable increases in Ca and Mg accumulation by the plants.

Results of this investigation suggest that cutans may modify significantly ion availability and accumulation by plants growing in highly weathered, iron‐rich soils.
THE MOBILIZATION OF IRON BY AQUEOUS EXTRACTS OF PLANTS
Authors: MUIR J. W. , LOGAN J. , BOWN C. J.
Published: July 2006

The organic‐acid fraction maintains iron in solution from pH 4 to at least pH 9.5, with a maximum of 15 mg iron per gram of dried pine needles at pH 8; the amino‐acid fraction is inactive above pH 4.5. The constituents of the organic‐acid fraction are examined individually and their effectiveness com‐pared. Of the active acids, all except phosphoric acid are α‐hydroxy carboxylic acids. A synthetic solution, with a composition that corresponds to the analysis of the organic‐acid fraction, is used to demonstrate that all the major active constituents have been identified. The activity of the individual acids and the organic‐acid fraction is due to their ability to form water‐soluble complexes with iron and to stabilize ferric hydroxide sols. The water‐soluble complexes are formed over a wide range of pH and in the presence of calcium ions. The formation of ferric hydroxide sols, however, is greatly influenced by pH and by the presence of calcium ions. These findings are related to soil processes and to the morphological character of the soils on which Scots Pine trees normally grow.
SOME FACTORS AFFECTING LOSSES OF AMMONIA FROM UREA AND AMMONIUM SULPHATE APPLIED TO SOILS
Authors: GASSER J. K. R.
Published: July 2006

Urea supplying 100 1b of N/acre was either broadcast on the surface or mixed with four soils (two clay‐loams, two sandy‐loams) and losses of ammonia were measured when the soils were maintained at 40, 50, or 60 per cent water‐holding capacity (WHC) and incubated at 5°or 25°C. Urea and ammonium sulphate were similarly applied to two calcareous soils at 40 per cent WHC and 5°or 25°C. Losses varied most among soils, from 2 per cent of the N applied from an unmanured clay‐loam to 13 per cent from an unmanured sandy‐loam. Changing temperature and water content affected losses little on average, but their effects differed with different soils. Losses of ammonia were similar from urea and from ammonium sulphate applied to the calcareous soils. Analyses at the end of the experiments showed that: (i) nitrite tended to accumulate in the sandy and calcareous soils, accumulation being favoured by lower temperature and wetter soil; (ii) ammonia was lost at 25° C from calcareous soils until all the ammonium‐ N had been nitrified, from the slightly alkaline clay soils until nine‐tenths had been nitrified, and from the neutral sandy soils until half had been nitrified.
CATION EXCHANGE REACTIONS
Authors: SALMON R. C.
Published: July 2006

Wyoming bentonite, Blisworth illite, and a fen peat were saturated with different proportions of calcium, magnesium, and potassium, and exchange between these cations was studied by measuring their activity ratios in dilute equilibrium solutions. With both clays the activity ratio aMg/aCa in solution was linearly related to the ratio of adsorbed Mg/Ca, the former being 1.22 times larger than the latter ratio. Peat held magnesium much less strongly than calcium, and the difference increased with increasing magnesium saturation. With all three materials the activity ratio aMg/aCa+Mg in solution was curvilinearly related to the percentage magnesium saturation. Peat adsorbed potassium less strongly relative to the divalent cations than did the clays, and bentonite adsorbed potassium less strongly than illite. Decreasing the Ca:Mg ratio increased the strength with which peat adsorbed potassium, but had no effect on potassium adsorption by the clays. Exchange between magnesium and calcium in forty British soils was studied by measuring the concentration ratio [Mg]/[Ca+Mg] in equilibrium soil solutions. The relation between [Mg]/[Ca+Mg] in solution and the ratio of exchangeable Mg/(Ca+Mg) in different soils varied within the range covered by peat and bentonite or illite, suggesting that differences between soils might be due to different organic‐matter contents. The extent to which [Mg]/[Ca + Mg] in solution was altered by changes in the exchangeable magnesium content differed considerably between soils. These differences were not all explained by variations in exchange capacity, showing that different soils adsorb magnesium with differing strengths relative to calcium.
STUDIES OF FUNGI IN A PODZOL
Authors: WILLIAMS S. T. , PARKINSON D.
Published: July 2006

A study of fungal populations in the mineral horizons of a podzol was conducted using a soil‐washing technique. The mycoflora of various microhabitats was studied and compared. Results indicated that the position of the substrates in the profile largely determined which species were able to colonize them. Investigation of seasonal fluctuations of the fungal populations revealed no significant qualitative or quantitative changes throughout the year, variations observed reflecting the heterogenous spatial distribution of fungi in the soil.
A CLASSIFICATION OF HUMUS FORMS AND MICRO‐FABRICS OF TEMPERATE GRASSLANDS
Authors: BARRATT BERYL C.
Published: July 2006

The humus form is recognized in a soil profile as the group of A horizons in which organic matter is concentrated, and it is thus the upper part only of the genetic humus type, the true measure of which is the complete organic profile extending into B and C horizons. Grassland humus forms are subdivided on a basis of field morphology into two groups: mull, in which the organic residues are largely incorporated as an intimate clay‐humus mixture, and mor, in which organic residues in varying stages of decomposition overlie the mineral soil with a sharp boundary but may show weak mechanical admixture of mineral grains. A mor‐like mull intergrade is recognized where the mull is very high in intimately incorporated organic matter.

According to variation in horizon thickness, structure, and consistence, sixteen humus forms are recognized: strongly granular, weakly granular, massive or blocky, fine, matted, laminated, and lenticular mulls, strongly granular, weakly granular, and laminated mor‐like mulls, and granular, massive, matted, laminated, banded, and mullized mors. Where mineral grains are very abundant in mor a sandy phase is recognized.

Each layer or horizon of a humus form may have one or more distinct micro‐structures or fabrics. Twelve fabrics have so far been recognized under grassland: weak mull humus, strong mull humus, mull‐like moder, mull‐like rendzina moder, leached mull‐like rendzina moder, silica moder, swollen moder, rendzina moder, leached rendzina moder, raw soil humus, sclerotial humus, and raw humus.
A SEASONAL STUDY OF OXYGEN UPTAKE OF SOME PASTURE SOILS AND ACTIVITIES OF ENZYMES HYDROLYSING SUCROSE AND STARCH
Authors: ROSS D. J.
Published: July 2006

Rates of oxygen uptake and activities of enzymes hydrolysing sucrose and starch were determined in soils under pastures of grasses and clovers at bimonthly intervals at eight sites in New Zealand with different climates. Differences between sampling periods were significant in most soils. Values of oxygen uptake and enzyme activities were not generally significantly correlated between themselves nor with the moisture contents of the soils nor their prior rainfall history. It has not been possible to suggest an optimal sampling period for different soils. The oxygen uptakes of all soils increased two‐ to threefold in the presence of glucose. Mean annual values of oxygen uptake of the eight soils were significantly correlated with their contents of organic carbon, reducing sugars produced on incubation in buffer, and rates of hydrolysis of starch, but not of sucrose. Climatic factors and the composition of the pastures probably influence the activities of carbohydrase enzymes in soil. The ratios of the activities of enzymes hydrolysing sucrose to those hydrolysing starch were greatest in the driest soils under predominantly grass pastures at sites with the lowest mean annual temperatures.
STUDIES ON THE DECOMPOSITION OF CONIFEROUS LEAF LITTER1
Authors: HAYES A. J.
Published: July 2006

An investigation of some aspects of the rate and type of decomposition of leaf litter of Abies grandis Lindley, Picea sitchensis (Bongard) Carrière, and Pinus sylvestris L. in a mixed coniferous plantation near Bangor was carried out. Leaf litter was exposed on the surface of the litter layer and at the humus/mineral soil interface, at different distances from the base of selected trees, each type of litter being laid out only under its own tree species. Seasonal changes in the rate and type of decomposition were investigated by exposing litter in June 1959, October 1959, and April 1960. The moisture content of the experimental litter showed a good correlation with rainfall. In all three tree species there was a high positive correlation between leaf length and dry weight, and this was used to determine the progressive losses in dry weight of the litter. There was a rapid initial loss in dry weight, and thereafter Abies continued to lose weight most rapidly, and Pinus more slowly, whereas Picea showed little change. There was usually little change in N content, although in one case this decreased by about 50 per cent in the first two months after exposure. The C content either decreased for the first six months after exposure or showed little change. The C/N ratio generally showed either a consistent slow decrease or little variation, although in the June 1959 exposure there was a very rapid decrease in C/N ratio during the first two months. The quantity of extractable polyphenols decreased very rapidly after the litter had been exposed, and thereafter there was usually little change. There was some evidence that addition of polyphenol from external sources could occur.
A SOIL CATENA ON GRANITE IN SOUTHERN RHODESIA1
Authors: WATSON J. P.
Published: July 2006

Summaries

The profiles and some analytical data were described in I and II (Watson, 1964).
STUDIES ON THE DECOMPOSITION OF CONIFEROUS LEAF LITTER
Authors: HAYES A. J.
Published: July 2006

In a study of some aspects of the rate and type of decomposition of leaf litter of Abies grandis Lindley, Picea sitchensis (Bongard) Carrière, and Pinus sylvestris L., the external features of the needles at different stages of decay have been recorded, together with the micro‐fungi appearing on the needles and cultured from them. A regular sequence of colour changes was demonstrated, from the original green to grey‐green, brown, grey to black. Unless conditions were very favourable, the litter of Picea sitchensis changed colour much more slowly than that of the other species. The proportion of collapsed leaves increased progressively with time, although in the earlier stages of decay reversion to the non‐sunken condition could occur by water uptake. A definite succession of fungi was recorded as the litter decomposed. Needles remaining affixed to the tree were commonly colonized by Fusicoccum bacillare, accompanied on needles of Pinus by Lophodermium pinastri. On freshly fallen needles, Haplographium penicilloides, Aspergillus fumigatus, and Penicillium frequentans occurred frequently, together with white hyphal ‘cushions’ in the stomatal apertures, and a sterile net‐forming surface mycelium. Older litter was colonized by Trichoderma viride, Oidiodendron fuscum, and Verticicladium trifidum. Mucor hiemalis and Aposphaeria sp. were present throughout the period of decay, together with a number of less common species.
BLOCKED CHARGES ON CLAY MINERALS IN SUB‐TROPICAL SOILS
Authors: DAVIDTZ J. C. , SUMNER M. E.
Published: July 2006

Hypothetical mechanisms for charge blocking on the surfaces of kaolinitic minerals are presented to account for the anomalous behaviour of ferrallitic soils on deferrification. On iron oxide removal, the following situations can arise where positive and negative charges (i) both increase, or (ii) both decrease, or (iii) increase and decrease concomitantly. These variations in charge after deferrification can adequately be explained on the basis of blocking which affects both the basal planes and edges of the clay minerals.
CHARACTERISTICS OF SOME SOLONETZIC SOILS IN THE GLACIAL LAKE EDMONTON BASIN OF ALBERTA
Authors: ARSHAD M. A. , PAWLUK S.
Published: July 2006

Physical and chemical analyses of five geographically associated Solonetzic and Chernozemic Black soil profiles from the glacial Lake Edmonton basin were conducted to investigate the mechanisms operative in their genesis. Soils, classified as Black Solonetz and Black Solodized Solonetz, satisfied both morphological and chemical criteria as set forth by the National Soil Survey Committee of Canada for soils of the Solonetzic Order. The lack of pronounced solodization in the Bnt horizons of these soils was attributable to the proximity of bedrock to the surface which prevented the removal of Na salts from the profile. A high content of exchangeable Na in the Bnt horizons appeared to have assisted the comminution of coarse clay particles to fine clay particles. The soil, classified as Saline Black, had the chemical properties but lacked the morphology of Solonetzic soils. Two Eluviated Black profiles were genetically different from each other. While the Eluviated Black profile in one case was completely solodized and appeared to be regrading towards the normal soil type, the soil at the other site had features that reflected the influence of weak solonetzic processes.
THE SOLUBILITY OF PHOSPHATE IN A CALCAREOUS SOIL
Authors: LARSEN SIGURD
Published: July 2006

The concept of chemical potentials was used to study the solubility of phosphate in a calcareous soil when equilibrium was approached by precipitation.

By comparison with results obtained by dissolution of soil phosphate it was demonstrated that precipitation resulted in a considerably greater solubility than did dissolution.

The relationship between the monocalcium phosphate potential and lime potential could be reconciled with the presence of hydroxyapatite in the soil. Ion activity products near to those of pure hydroxyapatite in the presence of calcium carbonate were also obtained.
BROWN PODZOLIC SOILS AND THEIR STATUS IN BRITAIN
Authors: BALL D. F.
Published: July 2006

The characteristics are outlined of freely drained soils, transitional in location, morphology and chemistry between modal Brown Earths and Peaty Podzols, which occur widely in western and upland Britain. They have been classified in a number of ways, which are discussed with reference to a review of American and European treatment of Brown Podzolic Soils. Although precise definition in terms of chemistry is not possible, evidence supports the continued distinction of such soils as Brown Podzolic Soils (or Sols Bruns Podzoliques) considered as a sub‐group of Podzolized Soils.
THE MECHANISM OF PHOSPHATE ADSORPTION BY KAOLINITE, GIBBSITE, AND PSEUDOBOEHMITE
Authors: MULJADI D. , POSNER A. M. , QUIRK J. P.
Published: July 2006

The adsorption isotherms of phosphate have been determined at pH 5 on acid‐washed K‐kaolinite and gibbsite, Na‐ and Al‐kaolinites, and K‐kaolinite in the presence of KCl at 20°C.

An isotherm obtained for K‐halloysite did not support the suggestion made in Part I that any part of the adsorption was due to gross inter‐lamellar penetration in the kaolinite.

It is concluded from the relative behaviour of these systems that adsorption occurs on an edge—Al(OH)2 and in some amorphous region of the clay surface.
THE EFFECT OF IRON OXIDE IMPURITIES ON THE POSITIVE AND NEGATIVE ADSORPTION OF CHLORIDE BY KAOLINITES1
Authors: SUMNER M. E. , REEVE N. G.
Published: July 2006

In the past, the effect of iron‐oxide impurities in kaolinites has been ignored when studying properties such as edge‐charge and Cl− adsorption. In this investigation, iron oxides were found to have a marked effect on the adsorption of Cl− by kaolinite. Cl− was positively adsorbed by some kaolinites at high pH values indicating that positive charges were present under alkaline conditions. A large part of this positive adsorption of Cl− was due to the iron oxide in the samples. The presence of small amounts of iron oxides gave rise to large errors in the measurement of edge‐charge on kaolinite. After deferrification, reasonable results were obtained.
THE RELATIONSHIP BETWEEN OXIDATION‐REDUCTION POTENTIALS AND OXYGEN‐DIFFUSION LEVELS IN SOME WATERLOGGED ORGANIC SOILS
Authors: ARMSTRONG W.
Published: July 2006

In valley and blanket‐bog peat, oxygen‐diffusion rates and corresponding oxidation‐reduction potentials have been measured, and the relationship between them expressed graphically.

Oxygen‐diffusion rates were obtained ‘polarographically’, and the Pt cathode also served as the redox indicator‐electrode.

Plateau‐shifts towards more positive potentials made it necessary to use the reduced voltage setting of −0.48 v for oxygen determinations. These plateaushifts correlate with a lowering of the oxygen content, and an increase in acidity, or, perhaps, with the type of buffer systems found in peat.

The ratio redox potential/oxygen diffusion is not constant. At very low oxygen values there is a relatively large increase in redox potential per unit of oxygen, but, as oxygen approaches 2 × 10−8 g O2cm−2min−1, the ratio becomes much lower, while variations become more obvious.

rH values calculated according to Jeffery (1961), show that, in peat of high iron content at pH 6, the first traces of oxygen correspond to an rH 1.10–1.20 (E6, 50–120; reduced and oxidized iron probably present), while above 2 × 10−8 g O2 cm−2min−1 the rH is greater than 1.20 and oxidized iron probably predominates. Thus oxidized soil, as defined by Jeffery, may be maintained at very low oxygen levels.

It is suggested that oxygen diffusing from plant roots into these peats will oxidize reduced soil products, and thereby protect the plant.
POSITIVE ADSORPTION FROM MIXTURES OF THREE ELECTROLYTE SOLUTIONS
Authors: HELMY A. K.
Published: July 2006

The double layer theory was used for estimating the relative amounts of positively adsorbed cations when a mixture of three salts with mono‐, di‐, and trivalent cations is present in clay electrolyte systems. It is shown that the adsorbed cations are dominated by the trivalent cation when the salts are present at equal concentrations.
A SIMPLE AND INEXPENSIVE APPARATUS FOR AUTOMATICALLY CONTROLLING SOLUTION FLOW RATES THROUGH SOIL COLUMNS
Authors: GRAHAM‐BRYCE I. J. , DAVIES R. I. , AL‐RAWI A. A. H.
Published: July 2006

Accurate control of rate of flow of solution through soil columns is important in laboratory studies of leaching, but is difficult to achieve because of fluctuations in permeability. A simple and inexpensive method of automatically maintaining a constant flow‐rate through several columns simultaneously is described. The apparatus comprises (i) a rotating delivery system which distributes the leaching solution equally to eight compartments, (ii) a system for automatically regulating the flow through each column to keep pace with the solution delivered, and (iii) an automatic fraction‐collector to collect the effluent from the columns. Using this apparatus the standard deviation of the volumes delivered to the eight individual columns was less than 2 per cent of the mean, provided the flow rate was faster than 10 ml/h.
STONE PAVEMENTS IN SOILS OF CAERNARVONSHIRE, NORTH WALES
Authors: BALL D. F.
Published: July 2006

In Caernarvonshire, North Wales, some soil profiles contain a concentration of stones as a layer, a single stone thick, which separates lower horizons of glacial drift from upper colluvial horizons. These layers, stone pavements, are believed to have formed as lag deposits (erosion pavements) on eroded drift surfaces which were then covered by colluvium. The formation and burial of the pavements may be attributed to periglacial and solifluction processes in the Late Glacial period. Local preservation of stone pavements suggests more widespread distribution of soils in which horizon differentiation results in part from depositional rather than pedological processes.
STUDIES ON SOIL POTASSIUM
Authors: BECKETT P. H. T. , NAFADY M. H. M.
Published: July 2006

The immediate Q/I relation of K in a soil relates the amount of labile K present to its chemical potential, measured relative to the chemical potential of (Ca+Mg) in the same soil.

The present work shows that the form of the Q/I relation is almost unchanged either by large additions of K, up to 3750 kg K2O/ha, and the fixation of up to 1900 kg K2O/ha or by the depletion of the soil of both labile and some fixed K, equivalent to 5–20 years cropping.

Release is shown to occur from a pool of non‐labile K, at a rate which decreases as the non‐labile pool is exhausted. The resulting increase in cation exchange capacity is greater than the amount of K released. Not all the K which is exchangeable to M NH4OAc solution is in exchange equilibrium with the soil solution.
A POLAROGRAPHIC TECHNIQUE FOR THE MEASUREMENT OF DISSOLVED SULPHIDE IN WATERLOGGED SOILS
Authors: ARMSTRONG W.
Published: July 2006

The polarographic oxidation of sulphide at the dropping mercury electrode reported by Revenda (1934), forms the basis of this technique for the assay of dissolved sulphide in soil solutions.

Soil solution is expressed from cores removed from the soil in a Hiller‐type borer, and transferred to tubes containing pyrogallol and NaOH. A current‐voltage curve for each sample is then obtained using the dropping mercury electrode in conjunction with a saturated calomel electrode. The current in the plateau region of a curve is proportional to the sulphide concentration, and after volume and temperature corrections, the sulphide concentration in a sample can be read from a previously prepared calibration curve.

The possibility of sulphide loss from the samples before analysis has been found to be slight.

Details of construction, and calibration of the dropping mercury electrode using standard Na2S solutions, are included in the description of the technique and apparatus. The inclusion of such minor modifications as (a) the insertion of a condenser across the microammeter terminals to dampen the large current oscillations produced by the dropping mercury electrode, and (b) the inclusion of a switch to allow reversal of polarity at the microammeter, enabled a circuit of the type currently used for soil oxygen diffusion measurements to be used also for sulphide estimation.
THE EFFECT OF FARMYARD MANURE ON MATRIC SUCTIONS PREVAILING IN A SANDY LOAM SOIL
Authors: SALTER P. J. , BERRY G. , WILLIAMS J. B.
Published: July 2006

Soil matric suctions under a crop of ryegrass on farmyard manure‐treated and untreated plots were determined over a total period of 24 weeks from March to November. The soil moisture characteristic of each plot was determined five times throughout this period, and for each plot and on every occasion a linear relationship was found between moisture content and log matric suction. A formula was derived to account for the seasonal changes in moisture characteristic and it was then possible to obtain matric suction values from the soil moisture contents obtained from twice‐weekly sampling of each plot. Although differences between available‐water capacity of the manured and unmanured plots were small throughout the 6‐month period of sampling, the soil matric suctions of the manured plots were almost always lower than those of the unmanured plots. The lower suctions prevailing in the manured soil could be a factor contributing to the higher yields of ryegrass obtained from the manured plots as compared with those obtained from the unmanured plots.
THE MOISTURE RÉGIMES OF SOILS DEVELOPED ON KEUPER MARL
Authors: THOMASSON A. J. , ROBSON J. D.
Published: July 2006

The moisture régimes of several representative profiles of the Worcester series developed on Keuper Marl are described and interpreted using a simple field technique supplemented by determinations of pore space, moisture content, and moisture release characteristics. It is suggested that the textural B horizon of coarse blocky structure is the cause of waterlogging which occurs seasonally in the upper 61 cm of these soils. The C horizon, which has a fine blocky structure and a lower clay content, is more permeable, and determinations of pore space and moisture content showed an appreciable volume of air voids in it when the overlying horizons were fully saturated with water.

After subsoiling to a depth of 76 cm at one site, the soil was waterlogged less often and then only for shorter periods than formerly.
THE INFLUENCE OF IONIC ENVIRONMENT ON THE NATURE OF IRON OXIDES IN SOILS
Authors: TAYLOR R. M. , GRALEY A. M.
Published: July 2006

The colour in a sequence of soils formed on basalt in the Burnie area of Tasmania changes from red to red‐brown near sea level to a yellow‐brown in the more elevated areas. This colour change reflects the variations in the goethite/haematite ratio which in turn has been positively correlated to the proportions of Ca plus Mg on the exchange complex. The results support the laboratory observations of Schellmann that the adsorption of Ca and Mg ions by freshly precipitated iron oxide gel directs the ageing towards haematite.
THE MEASUREMENT AND MECHANISM OF ION DIFFUSION IN SOILS
Authors: VAIDYANATHAN L. V. , DREW M. C. , NYE P. H.
Published: July 2006

Integral diffusion coefficients for K in two contrasting soils, containing different levels of exchangeable K, are calculated from measurements of diffusive flux to a hydrogen resin paper. The diffusion coefficients are larger, the higher the exchangeable K level or moisture content.

Diffusive flux of K in these soils can be accounted for entirely by diffusion through the soil solution in the pores.

Impedance factors calculated compare satisfactorily with values for similar soils reported by other workers.

The concentration dependence of the diffusion coefficient is shown to be causally related to the nature of the sorption isotherm.

A method for estimating the differential diffusion coefficient at any concentration is described. It can also be calculated from the slope of the sorption isotherm at the chosen concentration, if the value of the impedance factor at the relevant moisture content is known and if diffusion other than through solution only is negligible.
PEDOGENIC GRADIENTS OF THE POLAR REGIONS
Authors: TEDROW J. C. F.
Published: July 2006

Soils of the polar regions are divided into three zones—Arctic Brown, Polar Desert, and Cold Desert. The Arctic Brown soil coincides approximately with the arctic tundra belt, the Polar Desert zone is penecontiguous with the high arctic, and the Cold Desert zone is represented by the ice‐free sectors of Antarctica. The zones are broad and diffuse. Well‐drained soils of the southern sectors of the Arctic Brown soil zone have embryonic podzolic affinities whereas soils of the northern portions of this same zone exhibit a low temperature calcification process akin to a cold steppe condition. Vascular plants form a continuous mat in the Arctic Brown soil zone but within the Polar Desert soil zone they are patchy or at times completely lacking. In the Polar Desert soils algae and diatoms appear to be the main contributors of soil organic matter. The Cold Desert soils of Antarctica are virtually void of organic matter. The above three soil zones, in effect, are sectors of a pedogenic gradient. Progressing from the northern fringes of the forested land, to colder climates, precipitation decreases, organic matter content of the soil decreases, and soil pH values tend to increase. In the Polar Desert soils, alkaline reactions are common whereas the Cold Desert soils of Antarctica are usually saline. Polar Desert soils and Cold Desert soils have many morphologic affinities. Tundra and Bog soils dominate areally in the main tundra belt but are confined to the local swales and depressions in the high arctic. Both Tundra and Bog soils tend to have higher pH values as one progresses to colder, drier climates. Neither Tundra nor Bog soils have, as yet, been recorded in Antarctica.
A STUDY ON SOIL SERIES: THEIR CORRELATION WITH THE INTENSITY AND CAPACITY PROPERTIES OF SOIL POTASSIUM
Authors: BECKETT P. H. T. , NAFADY M. H. M.
Published: July 2006

The Intensity (I) or availability of soil K exhibits considerable variations within a Soil Series, presumably as a result of local differences in management and fertilization. The contrast is most marked between woodland and cultivated examples of the same Series. Earlier work had shown similar variations in the Quantities (Q) of labile K. Those Capacity properties (dQ/dI) of soils for labile K which derive from the planar surfaces of the clay crystals in the mineral skeleton of the soil show rather less variability. The Capacity properties of different samples of soil from one Series are not equal, but become increasingly so as the non‐clay fractions, the amphoteric oxides, and the organic matter held in the < 2μ fraction, are successively removed.

It is inferred that the active surfaces available for K–(Ca + Mg) exchange in the soils studied are fundamentally similar for the soils in any one Series, but that they may be reversibly blocked by organic and amphoteric cations, to varying extents according to their previous management. The differences are greater than the differences commonly observed between different experimental plots in the same field. Duplicate samples of three Series out of the four examined showed close or moderate agreement in their K‐fixation properties.

While soil organic matter has some influence on dQ/dI, the fraction with most effect is not that which makes the most substantial contribution to the CEC of the soil.
USE OF RADIOACTIVE59Fe FOR TRACING SOIL PARTICLE MOVEMENT
Authors: COUTTS J. R. H. , KANDIL M. F. , TINSLEY J.
Published: July 2006

The field studies reported in Part 1 were complemented by laboratory investigations on the labelling of soils and the movement of soil particles by simulated rainfall splash.

Of various labelling techniques tested the most uniform absorption of59Fe, as shown by autoradiographs, was secured by adding DTPA chelating reagent to the FeCl3solution used for wetting soil peds under vacuum. Studies on the specific radioactivity of the Atterberg textural fractions, separated from clayloam, sandy loam, loam and peat soils before and after labelling, showed in all cases that the clay fraction was dominant in retention of59Fe.

The radioactivity was so firmly absorbed that its movement could be used to trace both the horizontal and vertical displacements of labelled soil particles by scintillation counting or autoradiographic techniques. Tests with a rainfall simulator showed a close correlation between the weights and radioactivities of splashed soil particles.

Gravimetric data obtained from unlabelled clay loam and sandy loam soils subjected to ‘rainfall’ of differing intensity, drop size and height of fall gave a linear relationship on a logarithmic scale between mass of particles and distance of splash. Calculation of the kinetic energy lost by water drops on impact with the soil and that imparted to the splashed soil particles show that the relationship depends principally on the rainfall intensity and the texture of the soil.
RATE‐CONTROLLING PROCESSES IN THE RELEASE OF SOIL PHOSPHATE
Authors: VAIDYANATHAN L. V. , TALIBUDEEN O.
Published: July 2006

The isotopic exchange of phosphate ions in a deep river gravel soil, maintained at different pHs from 3.5 to 6.7 in a field experiment, established by the N.A.A.S. at Shardlow, was governed initially (<20 h) by simultaneous ‘first‐order’ and ‘bulk diffusion’ kinetics, but later by ‘bulk‐diffusion’ kinetics only. The ‘bulk‐’ or ‘intracrumb‐’ diffusion coefficient was independent of phosphate manuring, was least at pH 5.5 and increased on either side of this critical pH. The rate constant for the phosphate component exchanging initially with ‘first‐order’ kinetics increased significantly with phosphate manuring at pH 3.5, 4.4, and 5.5, although the constants for unmanured and manured soils did not change with soil pH. But at pH 6.7, the rate constants for the unmanured and phosphate‐treated soils were greater than those in the more acid soils, although the constant for the manured soil was just significantly greater than that of the unmanured soil.

Residual phosphate (i.e. the difference between manured and unmanured soils) adsorbed on the soil was greatest in the more acid soils but water‐soluble residual phosphate increased with soil pH to a maximum at pH 5.5. Residual phosphate, exchanging initially, decreased to nothing above pH 6.5.
FUNDAMENTAL OBJECTIONS TO THE 7TH APPROXIMATION
Authors: WEBSTER R.
Published: July 2006

The 7th Approximation suffers from three fundamental ills. It demands an unattainable degree of precision and its exactly defined, mutually exclusive classes lead to inconsistency or absurdity when the system is used. Logical division is used out of context to construct a hierarchical structure, while the dispersed nature of soil distribution does not lend itself to hierarchical arrangement in any form. Its search for genetically significant properties on which to define classes involves circular reasoning, since the genetic significance of a property can usually be discovered only after the soils have been classified.

Mutual exclusion and rigid adherence to the hierarchy result in the system failing to serve adequately the requirements of soil survey. The 7th Approximation explores to the limit the potential of logical division for soil classification yet remains unsatisfactory. The nature of soil distribution and the requirements demanded of soil classification suggest that a co‐ordinate system would be more profitable, and a study of such systems is urged.
THE EFFECT OF HYSTERESIS OF PORE‐WATER ON THE HYDRAULIC CONDUCTIVITY
Authors: POULOVASSILIS A.
Published: July 2006

It is pointed out with the help of the Independent Domain Theory, that a fraction of the pore‐water constituting a volume ΔV is contained in pores not common to both the wetting and drying states and that this volume in a wetting state is contained in pores whose draining radii are greater than those of the pores containing the water volume ΔV in the drying state.

On the above basis it is suggested that hysteresis may affect the hydraulic conductivity: firstly, through differences of the radii of the pores containing the water volume ΔV, which tend to endow a wetting state with a conductivity greater than that of an equally wet but drying state; secondly, through differences of the coordinates of the above‐mentioned pores, which may influence the paths of flow and consequently the hydraulic conductivity, and will have either a similar or opposite effect. It is concluded, therefore, that the conductivity in the wetting state can be greater, equal, or even less than that in the drying state, depending on the particular porous body.
RETENTION OF LOW LEVELS OF COPPER BY HUMIC ACID
Authors: DAVIES R. I. , CHESHIRE M. V. , GRAHAM‐BRYCE I. J.
Published: July 2006

Most of the Cu previously added to humic acid derived from a sedge fen peat was easily removed by washing with acid, but the strength of binding increased as the Cu content decreased. The capacity to retain firmly bound Cu was reduced to about half by treating the humic acid to block either carboxyl or hydroxyl groups alone or to block both groups together. The retaining sites blocked therefore probably involve both carboxyl and hydroxyl groups acting together, but alternatively could be groups such as hydroxy‐quinone, affected by both types of treatment. Retention of Cu by peat differs from retention by the extracted humic acid.
LIMITATIONS IN ISOTOPIC MEASUREMENTS OF LABILE PHOSPHATE IN SOILS
Authors: AMER F. , MAHDI S. , ALRADI A.
Published: July 2006

Methods used for measuring labile P and assessing the phosphate‐fertility status of soils by isotopic dilution as well as assumptions involved in applying the isotope dilution technique were critically evaluated.

In the presence of high phosphate‐fixing compounds, e.g. reactive iron oxide, labile P may be erroneously overestimated; especially when carrier‐free 32P is used. At the end of the isotopic‐exchange reaction period, high phosphate‐fixing soils may have a higher specific activity in the solid phase than in the solution phase. Methods involving the use of a 0·2 ppm P carrier solution or the addition of an unlabelled carrier to a labelled soil may give satisfactory labile P measurements in low and in medium phosphate‐fixing soil. All the methods tried (carrier‐free, carrier, and inverse dilution), however, failed to give satisfactory results for the high phosphate‐fixing soils.
SULPHATE REDUCTION IN WATERLOGGED SOILS
Authors: BLOOMFIELD C.
Published: July 2006

To study the factors that influence the release of free H2S, flooded soils were incubated with plant material and either sodium sulphate or elemental sulphur. Residual sulphate, FeS and H2S were measured throughout the reaction.

Less free H2S was evolved from a periodically waterlogged soil than from a well‐drained soil of comparable HC1‐ and dithionite‐soluble Fe content. With a readily soluble synthetic Fe2O3 as the source of Fe, a slight excess of Fe over the SO42– equivalent sufficed to prevent loss of H2S.

The native organic matter in the well‐drained Rothamsted top‐soil seemed to have no effect in promoting loss of H2S, but the FeS:H2S ratio was strongly influenced by the nature of the plant material used as the source of energy. With either Na2SO4 or S, considerably more free H2S was evolved with lucerne than with rice blade. With S, the pH of the incubated mixtures was close to that of the nominally S‐free system, whereas with Na2SO4 the mixture became quite alkaline. More free H2S was evolved under the more alkaline conditions obtained with Na2SO4, which suggests that it is the initial mobilization of Fe that governs the distribution of the reduced S, rather than the pH‐solubility relations of FeS.

An oxidized surface layer is very effective in retaining sulphur in the soil.
THE FATE OF APPLIED MOLYBDATE IN ACIDIC SOILS
Authors: SMITH B. H. , LEEPER G. W.
Published: July 2006

Sodium molybdate, at the rate of 10 ppm Mo, was added to the surface of seven acidic soils which were then stored moist for 3 to 10 months. After storage, less than 4 per cent of the added Mo was leached through any of the soils by the equivalent of a 250 mm rain. Between 36 and 91 per cent of the added Mo could be extracted with 0·1M NaOH, this proportion decreasing with longer incubation. Up to 40 per cent resisted treatment with both H2O2 and NaOH, and most of this was extracted with dithionite plus citrate. It is concluded that Mo is not lost by leaching from acidic soils other than sands, but is adsorbed on sesquioxide surfaces and slowly changed into less soluble forms.
EFFECTS OF ADSORBED CATIONS ON PHYSICAL PROPERTIES OF TROPICAL RED EARTHS AND TROPICAL BLACK EARTHS
Authors: AHMED S. , SWINDALE L. D. , EL‐SWAIFY S. A.
Published: July 2006

Similar relative effects were obtained for plastic limits, percentage stable aggregates, and hydraulic conductivities when a tropical red earth, consisting predominantly of kaolin and iron oxide, and a tropical black earth consisting predominantly of montmorillonite, were saturated with Ca, Mg, K, or Na ions or combinations of these. Plastic limits were independent of the nature of the saturation cations, but were significantly dependent upon clay type. Percentage stable aggregates of artificially prepared aggregates and hydraulic conductivity were affected by the four cations in the order Ca = Mg > K Na and were also significantly affected by clay type. Combinations of the four cations generally gave intermediate effects with Ca‐saturated soils more susceptible to deterioration by K or Na than Mg‐saturated soils. The results confirm the generally deleterious effect of Na ions and show that K ions have effects similar to Na on the properties investigated. They suggest that heavy potash fertilization without liming may lead to structural deterioration of these soils.
A COMPARISON OF POTASSIUM‐ACTIVITY RATIOS DERIVED FROM EQUILIBRATION PROCEDURES AND FROM MEASUREMENTS ON DISPLACED SOIL SOLUTION
Authors: MOSS P.
Published: July 2006

Direct and indirect methods of determining cation ratios of natural soil solutions are reviewed. The problems of comparing their results are discussed. K activity ratios derived from measurements on ethyl alcohol‐displaced soil solutions and values determined for the same soils by the Q/I equilibration procedure were in excellent agreement. An approximate rapid Q/I procedure using two K‐Ca solutions whilst less precise in its determination of activity ratio would be useful for routine purposes. The use of a proportionality constant to calculate activity ratios is acceptable.
DETERMINATION OF pH, LIME POTENTIAL, AND ALUMINIUM HYDROXIDE POTENTIAL OF ACID SOILS
Authors: BACHE B. W.
Published: July 2006

pH values in CaCl2 suspensions of some acid Scottish soils increase with time, in some cases by 0·4 units in 24 h. This is attributed to proton uptake by a complex ion displaced into solution, and to obtain unambiguous values, pH in CaCl2 suspensions should be measured within an hour of making up the suspensions.

In moderately to strongly acid soils, lime potential (LP) and aluminium hydroxide potential (AHP) vary with salt concentration and soil: solution ratio. Unique values for these ion‐activity ratios can be obtained by equilibration with a single solution only when the reference cations, i.e. (Ca2++Mg2+) for LP, and Al3+ for AHP, are the dominant exchangeable cations. Otherwise, equilibrium values should be obtained by interpolation from an exchange isotherm at the point where no exchange occurs, i.e. where Δ(Ca+Mg) = o for LP values and ΔA1 = o for AHP values.
A NEW ADSORPTION ISOTHERM FOR PHOSPHATE IN SOIL
Authors: GUNARY D.
Published: July 2006

Phosphate adsorption data for 24 soils showed that although the Langmuir equation gave a good fit, there was significant curvature. Of the alternative equations examined, that of Freundlich provided a better description than that of Langmuir in 22 soils, but the best fit, accounting for more than 99·8 per cent of the variation in phosphate adsorption, was given by introducing a square‐root term:
image

where y= adsorbed phosphate, c= equilibrium concentration of phosphate in solution, B, A, and D are constants. The phosphate adsorption maximum, obtained from I/B, gave values in the range 325 to 1427 μg P/g soil which were 1·39 to 2·40 times those obtained from the Langmuir equation.

The inclusion of a square‐root term in the Langmuir equation could be taken to imply that the soil will adsorb a little phosphate firmly, a slightly greater amount of phosphate less firmly, and so on until a limiting value is reached when all the components of the phosphate adsorption system are saturated.
DISTRIBUTION OF APATITE AND OTHER MINERAL INCLUSIONS IN A RHYOLITIC PUMICE ASH AND BEACH SANDS FROM NEW ZEALAND: AN ELECTRON‐MICROPROBE STUDY
Authors: CESCAS M. P. , TYNER E. H. , SYERS J. K.
Published: July 2006

Apatite, magnetite, ilmenite, and magnetite‐ulvöspinel inclusions were identified in certain primary minerals in a rhyolitic pumice ash and beach sands from New Zealand using an electron microprobe. In addition to being present in apatite inclusions, P was uniformly distributed throughout the matrix of plagioclase feldspars. Included apatite was particularly common in hypersthene and also occurred within Fe and Fe‐Ti rich phases in hypersthene. Quantitative data for Ca and P and the presence of Cl and F indicate the similarity in composition between the apatite inclusions and a chlorofluorapatite from Kola (U.S.S.R.). The coexistence of various mineral inclusions in hypersthene reflects magma composition, oxygen fugacity, and temperature conditions at the time of crystallization.

The presence of included apatite and lattice‐P within certain primary minerals adequately explains the low results reported previously for total P in these samples, obtained by HClO4 digestion as compared to Na2O3 fusion. Apatite and lattice‐P present within magnetite, ilmenite, and magnetite‐ulvöspinel inclusions are expected to be pedogenically inert in weakly and moderately weathered soils.