bluuebunny/crossref_metadata_2025 huggingface dataset:
THE ISOLATION OF NUCLEOSIDE DIPHOSPHATES FROM ALKALINE EXTRACTS OF SOIL
Authors: ANDERSON G.
Published: July 2006

Two pyrimidine nucleoside diphosphates have been isolated from sodium hydroxide extracts of soils. They were initially detected in fractions which had been separated by ion‐exchange chromatography, and were purified by a combination of ion‐exchange and paper chromatography. Their ultraviolet spectra indicated that one ester contained thymine and the other uracil, and this was confirmed by hydrolysis. The ratio of P to pyrimidine was 2, but their acid stability showed that the esters were not nucleoside‐5’ pyrophosphates. Both gave a positive reaction to a colour test for deoxypentose and comparison with reference samples prepared from calf‐thymus DNA showed that they were thymidine‐3′: 5’ diphosphate and deoxyuridine‐3′:5’ diphosphate.

The nucleoside diphosphates may be artefacts, derived from polynucleotides by acid and alkaline hydrolysis, but their isolation confirms, for the first time, the existence in soil of characteristic structural units of DNA.
OCCURRENCE OF INOSITOL PHOSPHATES AND OTHER ORGANIC PHOSPHATE COMPONENTS IN AN ORGANIC COMPLEX
Authors: OMOTOSO T. I. , WILD A.
Published: July 2006

A calcareous organic soil was extracted by shaking with Na+‐resin suspended in 0·2M acetyl acetone at pH 8·3. Fractionation of the fulvic acid on Sephadex G 25 gave (a) a high molecular‐weight component which contained inositol tetraand hexa‐phosphates and a sugar phosphate; (b) low molecular‐weight components which included the mono‐, di‐, and triphosphate esters of inositol and two sugar phosphates, but no free inositol phosphates. Inositol phosphates and sugar phosphates accounted for 30·2 per cent and 16·6 per cent of the soil organic P respectively. Our evidence indicates that these phosphate esters exist in an organic complex.
THE SPATIAL RESPONSE PATTERN OF GAMMA BACKSCATTER DENSITY GAUGES
Authors: DEVLIN G. , TAYLOR D.
Published: July 2006

This theoretical study shows that the sensitivity of the usual type of gamma backscatter gauge changes markedly for different soil volume elements according to their position with respect to the source and detector locations. There is a maximum in the so‐called detector region and a less important maximum in the source region. Calculation shows that 50 per cent of the total response of the instrument originates from 14 per cent by volume of the soil from a hemisphere of diameter d, d being the source‐detector separation. Since the response pattern of this type of backscatter gauge is far from uniform, it is necessary to consider the response patterns in planning the conditions of experiments involving these gauges to obtain the highest sensitivity. This is of particular importance in studying soils of a heterogeneous nature.
FURTHER STUDIES ON VARIABILITY OF SOIL CHEMICAL PROPERTIES: EFFICIENCY OF SAMPLING PROGRAMMES ON AN UNCULTIVATED BROWN EARTH
Authors: BALL D. F. , WILLIAMS W. M.
Published: July 2006

Assessments of mean and range of variation for pH, loss on ignition, total nitrogen, and exchangeable K, Na, Ca, Mg, and Mn in the surface horizon of a uniform uncultivated soil have been made by nine sampling programmes. The selected soil was known to have spatial chemical variability of magnitudes widely found in other soils and situations. The effort involved in these programmes was, for sampling and analysis time, from 1.2 to 66 man‐days. The most complete sampling programme (275 samples each a composite of 10 cores), was used as a standard against which to compare the efficiency of the other programmes. Mean values for chemical quantities other than loss on ignition differed statistically significantly between programmes but there was no consistent trend with any particular programme. Knowledge of the range of variation is believed to be very important in interpretation of analyses and it is found that a programme using only 6 composite samples measures > 50 per cent of the range for most quantities and that a programme using about 25 composite samples measures at least two‐thirds to three‐quarters of the total range.
THE MEASUREMENT AND MECHANISM OF ION DIFFUSION IN SOILS
Authors: VAIDYANATHAN L. V. , NYE P. H.
Published: July 2006

The counter‐diffusion of phosphate against chloride was measured in a moisture‐saturated block of soil by following the efflux of phosphate into a limited volume of well‐stirred CaCl2 solution, of the same ionic composition as the soil‐pore solution except for a lower initial phosphate concentration. By varying this phosphate concentration effective diffusion coefficients over a wide range of depletion were measured. The fraction of labile phosphate desorbed, and the relation between phosphate desorbed and concentration of phosphate in the equilibrium solution were measured in the same experiments.

Effective diffusion coefficients varied from 0.43 to 1.50 × 10‐4cm2 sec‐1, tending to decrease as depletion increased. Depletions ranged from about 0.3 to 25 per cent of the 32P exchangeable phosphate, which corresponded to a lowering of the solution concentration by about 30 to 65 per cent of the initial concentrations.

Diffusive movement of phosphate in this soil can be accounted for by diffusion through the liquid pathway only. The effective diffusion coefficient can be predicted from phosphate desorbed in response to a change in the concentration of the equilibrium solution, and an impedance factor.
THE SHRINKAGE OF CLAY SOILS DURING IMPREGNATION BY POLYETHYLENE GLYCOLS
Authors: GREENE‐KELLY R.
Published: July 2006

Linear measurements on a remoulded clay soil showed that the replacement of pore water by molten polyethylene glycol 6000 (PEG 6000) was responsible for the main contraction of the sample. Subsequent cooling of the wax resulted in only a small further shrinkage. The volumetric shrinkage of different clay soils on impregnation with PEG 6000 was about one‐half to three‐quarters of that on air‐drying. The contraction increased with increasing average molecular weight of the PEG fraction. Exchange of pore water with digol, O(CH2CH2OH)2, before impregnation with PEG 6000, decreased the total shrinkage by a further one‐third.
MICROMORPHOLOGY OF SOILS DEVELOPED FROM VOLCANIC ASH AND RIVER ALLUVIUM IN THE KOKODA VALLEY, NORTHERN DISTRICT, PAPUA
Authors: PAIN C. F.
Published: July 2006

Soils found on fan surfaces in the Kokoda Valley are derived from both volcanic ash and river alluvium. The alluvium is variable, some of it being mixed with volcanic ash. The main differences in the micromorphology of the soils appear to be related to the relative amounts of volcanic ash present in the soil profile. The plasma of soils formed on volcanic ash is isotropic in thin section. The plasma of alluvial soils exhibits increasing birefringence with decreasing amounts of volcanic ash. It is suggested that random structures in the clay fraction of the volcanic ash may account for its isotropic nature.
DISTRIBUTION OF CARBON DIOXIDE AND OXYGEN IN THE GAS PHASE OF AEROBIC SOILS
Authors: WOOD J. T. , GREENWOOD D. J.
Published: July 2006

It is shown that, under certain conditions, the increase in carbon dioxide partial pressure is proportional to the drop in oxygen partial pressure in the gas phase in fallow soils. The principal assumptions are that respiration is unaffected by lowering of oxygen partial pressure until very low levels are reached, and that the respiration quotient is constant. Previously reported measurements of the composition of gases extracted from soil are consistent with the theory.
AIR AND WATER PERMEABILITY OF COMPACTED UNSATURATED COHESIVE SOIL
Authors: BARDEN LAING , PAVLAKIS GEORGE
Published: July 2006

The air and water permeabilities of unsaturated cohesive soils have been measured in a modified triaxial cell permeameter which maintains separate continuity of both the air and water phases during permeation. Three different cohesive soils have been tested and the results interpreted in terms of the cluster concept of soil structure, which recognizes the existence of both macro‐ and micro‐pores. Both air and water permeability are shown to be dominated by the geometry and degree of saturation of the intercluster macro‐pores. Compression of the soil always reduces the air permeability but can increase the water permeability by increasing the membrane flow around the clusters. The relations between soil suction, occlusion of the air channels, and compaction water content have also been studied.
MOLECULAR SIZES AND FUNCTIONAL GROUPS OF HUMIC SUBSTANCES EXTRACTED BY 0.1M PYROPHOSPHATE FROM SOIL AGGREGATES OF DIFFERENT STABILITY1
Authors: DELL'AGNOLA G. , FERRARI G.
Published: July 2006

Aggregates from non‐cultivated soil and from cultivated soil enriched with mineral fertilizers or farmyard manure were separated into fractions of different diameter and stability. The humic substances extracted from each type of aggregate were subjected to gel‐filtration on Sephadex. The more stable aggregates had a higher content of Na4P2O7‐extractable humus and free iron hydroxides, and a predominance of humic substances of apparent molecular weight >100 000, whereas the less stable aggregates were richer in compounds of low molecular weight.

Structure stability was lower in the cultivated soil than in the non‐cultivated, and in the soil with mineral fertilizers in comparison to that with farmyard manure. Humus of m.w. >100 000 had a COOH content twice as great and a phenolic OH content five times greater per unit of molecular weight than humus with m.w. <100 000. The former is the more suitable stabilizer of soil aggregates.
PROLONGED LEACHING OF ORTHIC BLACK Ah MATERIAL WITH WATER AND AQUEOUS EXTRACTS OF POPULUS TREMULOIDES AND P. BALSAMIFERA LEAVES
Authors: DORMAAR J. F.
Published: July 2006

Cylinders filled with Orthic Black Ah material were leached over a 2‐year period with distilled water or with aqueous extracts of aspen or black poplar leaves that were collected late in the growing season.

Actual losses from the soil and chemical analyses of the leached soil indicated that the aqueous extract of aspen poplar leaves imposed greater changes on the chemical properties of the soil than did the extract of black poplar leaves. These changes were particularly noticeable for pH, total and exchangeable Ca, and 0.1N NaOH‐extractable C. The aqueous extract of aspen poplar leaves acidified the soil more strongly than the extract of black poplar leaves, even though there was little difference between the two extracts in polyphenol and polysaccharide content and the total acidity of the black poplar extract was about twice that of the aspen poplar extract.

Aqueous extract of weathered aspen poplar leaves was no more effective than distilled water.
THE RELATION BETWEEN COST AND UTILITY IN SOIL SURVEY
Authors: BECKETT P. H. T. , BURROUGH P. A.
Published: July 2006

This paper discusses how to compare the utility of soil maps. For three contrasting areas, in Southern England, it compares the utilities of a number of single‐property and general purpose (series) soil maps, produced by free and grid survey, at map scales from 1 :20,000–1:70,000.

The‘purity’of series mapping units increases with survey effort. Where the soil boundaries had fairly clear external expression free survey was superior to grid survey. On average the purity of maps by grid survey was higher than for maps by free survey at comparable survey effort.

The uniformity of soil properties within mapping units was measured by relative variance (RV)= within‐unit variance/total variance, (1–RV) indicates the increased precision achieved by the soil map. It increased with survey effort. For series maps by free or grid survey (1–RV) depended on how closely soil properties were associated with profile classes, and on the extent to which soil boundaries could be mapped on their external expression. Free survey was preferred at scales between 1: 100,000 and 1:30,000, when the soil boundaries could be mapped on their external expression, (1–RV) for the profile classes on which the mapping units are defined puts a ceiling to the utility of series maps (grid or free) which is already nearly achieved at map scales near 1:25,000. Except for properties very poorly associated with profile classes, single property maps do not have great advantage over series maps at medium map scales, but they attain higher values of (1–RV) at scales greater than 1: 25,000.
THE RELATION BETWEEN COST AND UTILITY IN SOIL SURVEY
Authors: BECKETT P. H. T. , BURROUGH P. A.
Published: July 2006

The paper presents the final conclusions of this study. For the three areas surveyed it compares the costs and utilities of different procedures for producing soil maps at scales of 1: 20 000–1:70 000, using the criteria for utility discussed in Part IV. In particular it compares the utilities of different maps produced at the same cost, or the costs of producing different maps of equal utility, and the ratios of utility/cost for different survey procedures at different map scales.

Within the limits of the approximations made and in areas presenting survey problems comparable to the area of lowland Britain surveyed, series maps by grid survey seem likely to give better value for money than series maps by free survey, at map scales greater than 1:50 000 in most landscapes and at all scales in some landscapes. There is a ceiling to the utility of general purpose maps of soil series, which is already nearly achieved at map scales of 1:25 000–1:20 000, and is surpassed only by single property maps by grid survey, at larger scales and at considerably higher cost.
NITROGEN, PHOSPHORUS AND SULPHUR CONTENTS OF HUMIC ACIDS FRACTIONATED WITH RESPECT TO MOLECULAR WEIGHT
Authors: SWIFT R. S. , POSNER A. M.
Published: July 2006

Two humic acids, extracted from widely different soils, have been fractionated with respect to molecular weight by means of gel chromatography. The resulting fractions were assayed for total nitrogen, amino acid nitrogen, phosphorus and sulphur.

Nitrogen and phosphorus contents were greatest in the high molecular weight fractions and decreased considerably with decreasing humic acid molecular weight. The change in nitrogen content was accounted for mainly by the loss of amino acid nitrogen. By contrast, sulphur contents remained constant throughout the molecular weight range. These changes may reflect part of the process whereby nutrient elements, combined organically within humic acid, are made available for plant growth.
THE KINETICS OF HETEROGENEOUS ISOTOPIC EXCHANGE
Authors: PROBERT M. E. , LARSEN S.
Published: July 2006

Isotopic exchange of phosphate ions between soil and solution was examined with particular emphasis on the slower reaction involving the incorporation of the tracer in the solid phase that follows the very fast exchange reaction between the solution and the surface of solid. Experimental data fitted both an equation composed of a sum of exponentials and a much simpler two‐constant equation. The goodness of fit was similar in each case but it was concluded that the exponential type of equation was not useful as a means of elucidating the mechanisms involved. The two‐constant equation may be derived from the kinetics of crystallization and recrystallization processes, and therefore provides an interpretation which is amenable to experimental verification.
THE EFFECT OF SOIL FACTORS ON THE EXTRACTION OF SOIL ORGANIC MATTER BY ANHYDROUS FORMIC ACID
Authors: JONES M. J. , PARSONS J. W.
Published: July 2006

Twenty‐five soils, having a wide range of organic matter contents, were extracted with anhydrous formic acid containing 10 per cent acetylacetone, and the extracted material precipitated in two fractions with diisopropyl ether. Precipitates comprised from 5.1 to 51.1 per cent of the original soil organic matter, the proportion extracted tending to be greatest from acid soils of fairly high organic matter content and least from neutral or slightly alkaline soils of low organic matter content. Soil clay content appeared to have no effect on the efficiency of organic matter extraction, but was the most important soil factor governing the proportion of the total soil‐N extracted. Amounts of N extracted ranged from 10.2 to 57.8 per cent of the original soil N content, extraction efficiency being greatest with soils of low clay content and low pH. There was evidence to suggest that soil clay afforded some protection to N compounds against extraction. The results indicate that formic acid/acetylacetone is most effective with soils in which much of the organic matter is only partly humified.
ANION ADSORPTION BY GOETHITE AND GIBBSITE
Authors: HINGSTON F. J. , POSNER A. M. , QUIRK J. P.
Published: July 2006

The relationship between adsorption and pH, termed the adsorption envelope, varies with the pKa, of the conjugate acid of the anion, for several adsorbents in presence of an excess of specifically adsorbed anions. At pH values where the acid is fully dissociated, specific adsorption occurs only to the extent of the positive charge of the surface and little specific adsorption is found at pH values more alkaline than the zero point of charge (zpc).

With incompletely dissociated acids, anion adsorption can also take place at pH values more alkaline than the zpc providing the pH is somewhere near a pKa value of the acid, where the energy required to abstract a proton from the acid is at a minimum. The proton is required for the removal of a surface OH which provides a site for the anion.

Specific anion adsorption (i) from a fully dissociated acid can reduce the positive charge of the surface to zero and (ii) from a weak acid can make even a negative surface more negative. Thus specific adsorption shifts the zpc to more acid values.

The relationship between anion adsorption and OH release is not necessarily simple.

The ideas proposed for anion adsorption have implications for cation adsorption and incorporation in an oxide surface.
MICROMORPHOLOGICAL QUANTIFICATION OF CLAY ILLUVIATION
Authors: MIEDEMA R. , SLAGER S.
Published: July 2006

Three concepts are introduced to describe the extent of clay illuviation phenomena quantitatively for pedogenic interpretations: (1) the degree of clay illuviation per thin section or (sub)horizon, subdivided into 5 classes, ranging from negligible (< 0.3 per cent by vol.) to very strong (> 7 per cent by vol.) clay illuviation; (2) the degree of reworking of the illuviated clay, subdivided into 3 classes, ranging from weak (< 30 per cent reworking) to strong (> 70 per cent); (3) the profile clay illuviation index: the sum of products of clay illuviation percentage per (sub)horizon and horizon thickness (in cm). The index ranges from very low (< 50 per cent cm) to very high (> 700 per cent cm). A distinction was made between the profile index based on the in situ illuviation features only and that based on all the illuviation features.
NITRATE LEACHING UNDER BARE FALLOW AT A SITE IN NORTHERN NIGERIA
Authors: WILD A.
Published: July 2006

A two‐year study on a site in northern Nigeria under bare fallow showed that nitrate formed from soil organic matter persisted in the top 120 cm of the soil profile throughout most of the rainy season. The rainfall in the two years was 1199 and 973 mm. Slow leaching was attributed to the combined effect of adsorption on to positive charges in the textural B horizon, high rainfall intensities, and the presence of cracks and channels in the soil, down which water will pass quickly without leaching the newly mineralized nitrate. This nitrate diffuses relatively slowly through the aggregates or is carried downwards by water moving in the small pores. Leaching of nitrate added to the surface as fertilizer would be more rapid than that of nitrate formed from soil organic matter within the aggregates.
MATHEMATICAL EXPRESSION OF ELUVIATION‐ILLUVIATION PROCESSES AND THE COMPUTATION OF THE EFFECTS OF CLAY MIGRATION IN HOMOGENEOUS SOIL PARENT MATERIALS
Authors: VAN WAMBEKE A.
Published: July 2006

Clay movement and its effect on the differences in texture between the A and B horizons are expressed by mathematical equations. The factors which are considered are the actual amount of clay which has moved (l), the ratio of the thick nesses of the horizons (N), and the original clay content (C). Parent materials are assumed to be homogeneous.

Knowing the clay contents of the A and B horizons, it is possible to calculate for given N ratios the theoretical amount of clay which has moved in order to achieve the observed textural difference. The theoretical clay content C'of the parent material can also be computed. All computations assume homogeneous parent materials and closed profiles, i.e. materials that do not collapse, shrink, or swell, and consider all other clay transformations non‐operative.

An eluviations index k, which indicates the proportion of the original clay that has been translocated, is proposed for evaluating the intensity of clay migration.

Examples of practical applications are given: i.e. the required difference in clay content between A and B in the definition of the argillic horizon should not be kept constant in soils which have variable initial clay contents; graphs illustrate the effects of clay migration for constant C and k values (isoparentic and isoluvic lines).

All computations can be made by desk calculators provided with an extended memory for storage of data and programmes.
AUTOXIDATION OF HUMIC ACID UNDER ALKALINE CONDITIONS
Authors: SWIFT R. S. , POSNER A. M.
Published: July 2006

Humic acid was treated for 30 days with normal NaOH under either N2 or O2. In both cases some acid‐soluble material resulted which was enriched with free and peptide α‐amino N and also with total N. The molecular weight of the humic acid fell under alkaline conditions, while there was a decrease in total UV and visible absorption due to the production of less‐coloured material which was largely present in the acid soluble fraction. Under O2 these effects were considerably enhanced and simultaneously a significant arnount of O2 was consumed. Other changes produced by O2 were an increase in the cation‐exchange capacity, particularly of the acid‐soluble fraction, the production of carbonate, an increase in the Oxidation state of the acid, and a lessening of the resemblance of the acid to lignin as shown by the infra‐red and UV spectra.

In the main the changes produced by O2 are similar to those observed for humic acids of decreasing molecular weight that can be extracted from a soil, either by differential extraction or by extraction followed by fractionation into different molecular‐weight classes.
REACTIONS OF AMMONIA WITH SOIL. I
Authors: ASHWORTH J.
Published: July 2006

Heats of adsorption and adsorption isotherms of ammonia gas were measured at 300 K (27 °C) on outgassed soil saturated with Na+, K+, NH4+, Ca2+, or Mg2+ ions. The Ca and Mg soils adsorbed apparently one more NH2 molecule per exchangeable ion than the Na and K soils, mostly in the relative pressure range o to 0.005, but not much more than the NH4 soil. The initial heat of adsorption was c. 75 kJ mol‐1 on the Ca and Mg soils and c. 60 kJ mol‐1 on the other soils. The results suggest that most NH, is sorbed on these soils through reactions not involving exchangeable cations.
A METHOD FOR STUDYING SOIL‐WATER PROPERTIES OF SOIL PROFILES
Authors: POULOVASSILIS A.
Published: July 2006

A method for studying the soil‐water properties of soil profiles is described and its development for application in the field is suggested. The method consists of infiltrating water at a constant rate at the surface of the soil and determining the resulting steady‐state suction and moisture profiles down the soil profile. It has been applied for relating the pore‐water suction and hydraulic conductivity to the pore‐water content of a a‐m‐long soil monolith.
RELATIONSHIP OF INORGANIC PHOSPHATE FRACTIONS T O MINERALOGICAL CHANGES IN CALCINED CHRISTMAS ISLAND ROCK PHOSPHATE
Authors: ADAMS J. A. , CAMPBELL A. S.
Published: July 2006

A close relationship exists between inorganic phosphorus fractions and mineralogical changes in ‘C’‐grade Christmas Island rock phosphate calcined at temperatures up to 1100 °C. Amounts of acid‐extractable Ca‐P closely followed the presence and crystallization of calcium phosphates. Amounts of NH4F‐P were related to the presence of simple aluminium phosphates. The ammonium fluoride reagent did not extract more complex aluminium phosphates such as crandallite and millisite. These minerals were considered to be present in the 2nd NaOH‐P and residual‐P fractions. NH4F‐P plus acid‐extractable Ca‐P was closely related to radish growth responses.
TECHNIQUES FOR MEASURING CHANGES IN THE PACKING STATE AND CONE RESISTANCE OF SOIL AFTER THE PASSAGE OF WHEELS AND TRACKS
Authors: SOANE B. D.
Published: July 2006

Methods are described for measuring the changes in the horizontal and vertical distribution of packing state and cone resistance following the passage of wheels and tracks over prepared beds of soil. A gamma‐ray transmission system was employed with automatically controlled scanning in a 2 × 2 cm grid in soil sections of 1.08 m length by 0.3 m depth, using a scintillator/photomultiplier detector assembly with stabilized pulse‐height analysis and magnetic tape recording. Changes in cone resistance were measured in a 2 cm (vertical) by JO cm (horizontal) grid in a section 1.4 m length by 0.5 m depth using an electrically driven penetrometer with load and displacement simultaneously recorded on an XY plotter and magnetic tape. Results were analysed and displayed graphically by computer with packing state expressed by a number of optional properties (dry bulk density, total porosity, air‐filled porosity, void ratio, or specific volume).

Pronounced differences in packing state and soil strength were observed as a result of the passage of a two‐wheel‐drive tractor, with and without cage wheels, and a crawler tractor. Adding a cage wheel decreased slightly the compaction below the rubber tyre, but formed a partially compacted zone below the cage wheel. Increases of dry bulk density and soil strength were recorded below the crawler track but the values for these properties did not reach the maximum values found below the rubber tyre.
THE MOBILIZATION AND FIXATION OF MOLYBDENUM, VANADIUM, AND URANIUM BY DECOMPOSING PLANT MATTER
Authors: BLOOMFIELD C. , KELSO W. I.
Published: July 2006

Mo, V, and U are mobilized as anions by aerobically decomposing plant matter; the behaviour of the dissolved metals differs in several respects from what would be expected in inorganic systems.

With respect to dialysis through cellophane, between pH I and 4 the mobilized Mo is fixed by colloidal organic decomposition products, with maximum retention at pH 1.5; V is retained between pH 1.5 and 7.0, with a maximum at pH 3. The specific fixation of Mo and V by soil organic matter was considerably less, and persisted over wider pH ranges–1.5‐6.5 and 1.0‐9.0 respectively. The fixation of U by both forms of humified organic matter increased sharply to a maximum around pH 4‐5, and thereafter decreased slightly up to pH 8.

The anionic forms of the three elements persisted when MOO:2‐4, VO;‐3 and UO, were incubated with anaerobically decomposing plant matter; under these conditions V(V) was probably reduced to V(IV), and it seems that an anionic V(IV) complex was formed.

Although the molecular size of the colloidal decomposition products of lucerne was somewhat less than that of organic matter extracted from Rothamsted top soil, acid hydrolysates of the two humic acids contained the same twenty‐three amino acids, in much the same relative proportions.
EFFECT OF CULTIVATIONS ON RAISING SPRING SOIL TEMPERATURES FOR GERMINATION WITH PARTICULAR REFERENCE TO MAIZE
Authors: SPOOR G. , GILES D. F. H.
Published: July 2006

Experiments on south‐facing ridges showed significant increases in soil temperature at 5 cm depth on the south slope of the ridge when compared with the ridge top and horizontal surfaces. The average maximum temperature was 2 °C higher halfway down the south‐facing ridge slope than beneath a horizontal surface and on certain individual days differences of up to 7 °C were recorded in maximum temperatures between the two positions. The ridge top temperature was intermediate between those on the slope and horizontal. Minimum temperatures were similar at all positions. The increased maximum temperature on the ridge slope significantly increased the accumulated temperature hours above 10 °C. The moisture status on the slope of a compact ridge followed closely that of a horizontal surface, being slightly lower during droughts. The ridge top dried out rapidly during droughts. The increase in maximum temperature and accumulated temperature hours above 10 °C, together with the acceptable moisture level found in the side of a compact south‐facing ridge should offer advantages either for earlier germination or for a more rapid rate of emergence of maize.
THE RESPONSE OF UNSATURATED SOILS TO ISOTROPIC STRESS
Authors: DEXTER A.R. , TANNER D. W.
Published: July 2006

Soil compression is caused in agriculture by tillage implements, plant roots, treading by animals, and by wheels and tracks of vehicles. Increases in soil density resulting from compression usually reduce crop growth and yield.

Compression and expansion of samples of five remoulded soils, each at several moisture contents, were investigated. Soil samples were subjected to isotropic stress of up to 3.5 MN m−2 in a pressure cell. Volume changes were measured by the volume of pore fluid effused or infused through one of the sample surfaces.

Particle packing densities, D, were well described by the equation

image

where D0 is the maximum limiting value of D, P is the applied isotropic stress, and B, C, K, L are adjustable parameters. One of the exponential terms in this equation describes deformation of soil crumbs and the other describes rearrangement of individual particles.

Two sample sizes gave similar values for the equation parameters. A small increase in moisture content results in a large increase in soil compressibility. It is hypothesized that resistance to compression may be one of the principal influences in the mechanical restriction of root growth.
STUDIES ON SOIL COPPER
Authors: McLAREN R. G. , CRAWFORD D. V.
Published: July 2006

A method based on that used by McAuliffe et al. (1948) for phosphorus was developed for determining isotopically exchangeable copper in soils using the radioisotope 64Cu. The authors are confident that, with a few exceptions, isotopic equilibrium in soil/solution systems is attained rapidly enough to overcome possible difficulties resulting from the short half‐life of this isotope. For the twenty‐four soils examined, amounts of isotopically exchangeable copper were found to be between 0.19 and 12‐24 μg g‐I and represented between 2 and 21 per cent of the total soil copper.

A correlation test and an experiment involving fractionation of labelled soils both demonstrated that the bulk of the isotopically exchangeable copper was located in the organic‐bound fraction. Not all copper specifically adsorbed by organic matter was readily exchangeable with 64Cu : for one sample of organic material examined only 20 per cent of the adsorbed copper was isotopically exchangeable after 24 hours equilibration. The corresponding figures for clay materials and oxide material were found to be between 75 and 60 per cent.
MULTIPLE DISCRIMINANT ANALYSIS IN SOIL SURVEY
Authors: WEBSTER R. , BURROUGH P. A.
Published: July 2006

Multiple discriminant analysis can be used to distinguish to best advantage several multivariate, more or less polythetic, classes of soil. The method allows profiles to be allocated consistently and most appropriately to existing groups for which representatives have already been chosen. The method is described in geometric terms and is applied to the allocation of profiles in both well known and little known areas, South Central England and Sabah. For the areas in England good separation between soil classes was demonstrated; in Sabah the classes of the reconnaissance survey were less distinct. Representative profiles were chosen for all existing classes and the remainder of the profiles allocated using discriminant functions. In all cases a better classification resulted in that there was less dispersion within classes and hence better separation between them. Provided conformant data can be collected in routine survey the method promises to allow a good working combination of man and machine: the soil surveyor to decide the classes desired, and the computer to handle large quantities of data and make routine allocation.
THE MODIFICATION AND APPLICATION OF THE QUANTITATIVE X‐RAY DIFFRACTION METHOD OF SCHULTZ (1964) TO THE MINERALOGICAL STUDY OF LONDON CLAY SAMPLES
Authors: BURNETT A. D.
Published: July 2006

Over 300 samples of London Clay from twenty‐one widely scattered sample locations in the London and Hampshire Basins were to be examined in detail by X‐ray diffraction techniques. The quantitative method of Schultz (1964) was chosen as being most suited for the analysis of the samples. Series of tests designed to investigate the reproducibility characteristics of the method were conducted. These showed that the sampling, sample preparation, and interpretation procedures used all introduced cumulative reproducibility errors of roughly equal magnitude which completely overshadowed errors introduced by machine‐response variation. It was also established that minerals whose contents were below 10 percent of whole sample failed to be consistently quantitatively estimated.

The accuracy of this method of analysis depended heavily on Schultz's quoted ‘intensity factors’ which were involved in the calculation of individual mineral contents. The authenticity of these factors with regard to the London Clay suite of minerals was checked by comparing accurately determined mineral percentages of six standard London Clay samples with the results obtained by use of the Schultz procedure and factors. The method was found to be basically sound although the intensity factors for quartz, total clay minerals, carbonates, and illite had all to be slightly adjusted. The accurate quartz percentages were established by three different X‐ray diffraction techniques and the carbonate percentage checks were accomplished by specially designed wet chemical methods. The total clay mineral and illite contents checks were carried out by back‐calculation of the Al2O3, and K2O percentages as determined from full wet chemical analysis. Using the adjusted factors, quartz percentages are estimated accurate to ±6 percent, total clay minerals to ±7 percent, carbonate percentages to ±1.5 percent, and illite contents to ±4 percent of the whole rock.
EXPERIMENTAL CONDITIONS CONCERNING POTENTIOMETRIC TITRATION OF HUMIC ACID
Authors: BORGGAARD O. K.
Published: July 2006

The humic acids of four soils from Denmark have been extracted by EDTA. The humic acids were separated from EDTA by precipitation with Ba2+. The ash content was lowered by treatment with HF and HC1. The ash content in the four humic acids was less than 0.6 per cent. Chemical analysis of the humic acids supply some evidence for the suggestion that EDTA extracted organic matter is a more definite fraction than humic acid extracted by NaOH.

It was shown that an alkaline humate solution stored in sterile, sealed ampoules under N2 does not change its initial pH, indicating that the protolytic equilibrium is established instantly. It is therefore proposed that the titration of humic acid should be carried out as quickly as a normal acid‐base titration.
FIELD STUDIES OF THE SOIL ATMOSPHERE
Authors: SMITH K. A. , DOWDELL R. J.
Published: July 2006

A study was made of the concentrations of ethylene and oxygen in the soil atmosphere under field conditions at three contrasting sites. The duration of the experiments ranged from 6 weeks to 9 months. A clear relationship between high moisture content and both the production of ethylene and the depression of oxygen levels was found in a sandy loam, although there was great variability between replicate sampling points. Concentrations of oxygen in a heavy clay soil remained below 10 per cent (v/v) throughout the winter and spring, followed by a gradual rise to near‐atmospheric levels. Concentrations of ethylene were not correlated with those of oxygen, except in the winter, but rose logarithmically with soil temperature during the spring, increasing by twenty times over the range 4‐1 I °C. There was no significant difference between plots which had been subjected to different drainage treatments, and again there was great variability from point to point. In a more permeable clay soil, however, the levels of oxygen were higher, and were related to the proximity to drains and the height of the water table, but not to the levels of ethylene. The concentration of ethylene showed a similar logarithmic increase with temperature to that observed in the heavy clay, and exceeded I ppm throughout the period May‐July.

The factors which have the greatest influence on the concentrations of ethylene in the soil were considered to be temperature, depression of oxygen concentration, the availability of substrates for microbial activity and the effect of soil moisture content on the air‐filled porosity of the soil. Concentrations of ethylene greatly in excess of those which, under some circumstances, inhibit root growth, are likely to be of widespread occurrence in heavy soils during the spring and early summer and in light soils when unusually wet.
THE ASSESSMENT OF SOIL TEXTURE FROM SOIL STRENGTH MEASUREMENTS
Authors: TOWNER G. D.
Published: July 2006

Soil texture is usually assessed by either the manipulation of the field soil in the hand or by a particle size analysis of the dispersed soil. These two methods are often regarded uncritically as alternatives, and this paper stresses the point of view that the hand manipulation method is the preferred one, because the particle size analysis method depends on the establishment of relevant correlations. However, the subjective nature of the first method is admitted, and the paper describes an attempt to devise an objective test based on the elements of the hand assessment. From the observation that one senses the reaction of the soil to compressive and shearing forces during an assessment by hand it is suggested that some measure of soil strength might be used as an index of texture.

The strength of twenty‐three soils was measured over a range of water contents using the fall‐cone penetrometer. The curves representing the relationship between the strengths and the water contents were all of a similar shape and tended to form a regular array, with the lighter soils at the low water content end of the scale and the heavier soils at the higher end. They showed that the strength of a given soil was very sensitive to water content.

It was concluded that the separation of the soils into the broad textural classes was made mainly from measurements of the strengths of the wetted soils, but that the more detailed descriptions, including for example, specification of the grade of the sand, required in addition an estimation of the sizes of the particles obtained by feeling them between the fingers. As a corollary, these finer divisions are not related to soil strength, and thus are dubious indications of heaviness or lightness.
THE CALCAREOUS SOILS OF AZERBAIJAN II. PHOSPHATE STATUS
Authors: ABEDI M. J. , TALIBUDEEN O.
Published: July 2006

The phosphate status, before and after P treatment in the laboratory, of surface soils from thirteen profiles of an Iranian catena, described in Part I, was investigated by determining the distribution of labile phosphate in solution and external and internal surfaces, and by examining their calcium phosphate solubility relationships.

The labile P distribution of added P suggests generally that soils with most carbonate in the silt fraction (Part I) hold added P mostly on external surfaces, and those with increasing carbonate in the clay fraction, less so. Recovery of 200 and 400 mg/kg soil of added P in the labile phosphate was related to soil phosphate status directly and to the total carbonate area of the soil inversely. Solubility relationships indicated saturation with CaCO3 and a compound approaching octacalcium phosphate in composition.

The two saline‐alkaline end‐members of the catena from the Low Land area differed somewhat in having more of their P content in soluble and labile forms, and in storing added P uniformly on external and internal surfaces.
EFFECT OF PLOUGHING AND DIRECT DRILLING ON SOIL NITRATE CONTENT
Authors: DOWDELL R. J. , CANNELL R. Q.
Published: July 2006

The concentration of nitrate‐N at 30 cm depth in a clay soil was 2–5 times greater (p<.05) after ploughing than after direct drilling during the winter and spring of 1972–3. However, by early May no significant differences could be detected between cultivation treatments. It is concluded that decreased mineralization of soil nitrogen in the direct‐drilled soil is the main factor responsible for the differences observed.
GRAPHICAL REPRESENTATION OF TRICATIONIC EXCHANGES WHERE ONE OF THE CATIONS IS THE PROTON
Authors: ANDRÉ J. P.
Published: July 2006

Most constituents of the adsorbing complex of the soil are cationic exchangers with variable exchange capacity: it is possible to study graphically exchanges involving the protons and two other cations. The representation developed here uses and generalizes the principle of the bicationic exchange isotherms in a square diagram. This helps to explain some experimental phenomena and enables the final equilibria of the exchange reactions to be forecast. The model seems useful for application in agronomy and physiology.
STORING AND PROCESSING DATA FOR SOIL AND LAND USE CAPABILITY SURVEYS1
Authors: RUDEFORTH C. C.
Published: July 2006

Computer methods currently used at Aberystwyth for handling the many observations of soil and site during survey are described. While complex statistical analysis of the data is possible, the emphasis in this paper is on automatic sorting according to existing classifications and land–use, assessing the contents of map–units, and producing automatic dot distribution maps from grid data.

Changes in class limits are easily made to give alternative maps. This is illustrated by land–use capability maps of Pembrokeshire.

A feedback technique allows identification of sites like those growing particular crops or crop combinations, so that maps of potential crop land are produced. Provisional maps of potential barley and early potato land in Pembrokeshire illustrate the technique. Questions of computing strategy and the relevance of economic conditions are discussed.
REACTIONS RESPONSIBLE FOR HIGH pH OF Na‐SATURATED SOILS AND CLAYS
Authors: CRUZ‐ROMERO G. , COLEMAN N. T.
Published: July 2006

Hydrolysis, defined as double decomposition between Na‐adsorbent and water, occurred to extremely limited extent in suspensions of Na or Na‐Ca smectites, soil, or Dowex‐50. High pH, near 10 or above, occurred only when CaCO3 was present. Concentrations of Na were from 1–5 me/l in systems containing CaCO3, With Na or Na‐Ca Dowex‐5o and CaCO3, in CO2‐free water or NaCl solution, pH and concentrations of Na in solution‐phase were predictable from Na‐Ca exchange coefficients, CaCO3, solubility product, and ionization constants of H2CO3.
PHOSPHATE ADSORPTION AND THE DISPLACEMENT OF STRUCTURAL SILICON IN AN ALLOPHANE CLAY
Authors: RAJAN S. S. S.
Published: July 2006

Phosphate was adsorbed at a constant pH, on allophane clay samples which had been pre‐treated with selenite to remove adsorbed silicate. The concomitant release of selenium, silicon, and hydroxyl ion on phosphate adsorption was also measured. The results are compared with those obtained from a similar experiment conducted using clay which had not been treated and they substantiate the earlier conclusion that phosphate displaces structural silicon of clays. The amount displaced increases parabolically with increasing levels of phosphate adsorbed over the concentration range studied.
PHOSPHATE ADSORPTION BY SYNTHETIC AMORPHOUS ALUMINOSILICATES
Authors: RAJAN S. S. S. , PERROTT K. W.
Published: July 2006

Phosphate adsorption isotherms were determined for four synthetic amorphous aluminosilicate gels with A1: A1 + Si molar ratios of 0.29 to 0.88. The concomitant silicate release and acid consumed to maintain the pH of the suspensions constant were also measured.

The adsorption isotherms were analysed applying a two‐term Langmuir equation–assuming two types of sites. The experimental points fitted the predicted adsorption curves only up to a certain amount of phosphate adsorbed. The deviation at high phosphate adsorption values suggested the presence of more than two types of adsorption site.

A comparison of phosphate adsorbed with the silicate released and acid consumed to maintain the pH constant indicated that, for a 3 h reaction time at concentrations below about 10 μmol cm−3, phosphate exchanges mainly with aquo and hydroxo ligands and with adsorbed silicate. At higher concentrations phosphate is adsorbed (i) on sites arising from the disruption of hydroxy aluminium polymers in the gels and (ii) by the displacement of structural silicate.
PRINCIPAL KINDS OF CHRONOSEQUENCES AND THEIR SIGNIFICANCE IN SOIL HISTORY
Authors: VREEKEN W. J.
Published: July 2006

There are four principal kinds of chronosequences of soils that differ in age. These sequences have different combinations of isochrony and/or time‐transgression of incipience and cessation of development of their encompassed soil members. A further criterion is the presence or absence of partial overlap in the history of these members.

Post‐incisive sequences have been commonly used for inferences on pathways and rates of development of individual soils, but their usual interpretation relies on the assumption that all soils involved developed the same way even while some of them may be polygenetic. Theoretically, pre‐incisive sequences are to be preferred because they should provide time‐lapse information on soil development. But, since they necessarily involve buried soils, problems of post‐burial change may complicate their interpretation. The usefulness of fully time‐transgressive sequences with partially overlapping soil tory depends on their predominant pre‐incisive or post‐incisive character. Fully time‐transgressive chronosequences without overlap of soil history may provide insight into regimes of soil development throughout geologic time, but not into rates of change of individual soils. Functional soil‐landscape units, such as catenas and valley basins may have internal soil age differentiation. This imposes restrictions on the systematic investigation of their evolution.
A NEW METHOD FOR ESTIMATING THE PHOSPHOLIPID CONTENT OF SOILS
Authors: BAKER R. T.
Published: July 2006

A simple and effective procedure for estimating soil phospholipids is described. The method uses Soxhlet extraction with (i) ethanol plus benzene (1:4 by volume) followed by (ii) methanol plus chloroform (1:1 by volume).

The method compared favourably with the standard procedure of Hance and Anderson (1963) with the advantage that no acid pre‐treatment of the soil was required.
CADMIUM ADSORPTION BY SOILS
Authors: LEVI‐MINZI R. , SOLDATINI G. F. , RIFFALDI R.
Published: July 2006

The Langmuir adsorption equation was found to describe Cd adsorption from dilute solutions at 5°C and 25°C for ten soils from Tuscany. The calculated Langmuir adsorption maxima (Q) and bonding energy coefficients (K) were well correlated with CEC and organic matter content.

On the basis of the temperature effect on Q and K, the mechanism of Cd adsorption is discussed.