bluuebunny/crossref_metadata_2025_split huggingface dataset:
ANION ADSORPTION BY GOETHITE AND GIBBSITE
Authors: HINGSTON F. J. , POSNER A. M. , QUIRK J. P. 
Published: July 2006

SummaryThe 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

SummaryThree 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

SummaryA 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

SummaryClay 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

SummaryHumic 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

SummaryHeats 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

SummaryA 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

SummaryA 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

SummaryMethods 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

SummaryMo, 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

SummaryExperiments 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

SummarySoil 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

SummaryA 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

SummaryMultiple 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

SummaryOver 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

SummaryThe 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

SummaryA 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

SummarySoil 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

SummaryThe 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.