bluuebunny/crossref_metadata_2025_split huggingface dataset:
TOWARDS A DIRECT, NON‐DESTRUCTIVE METHOD OF CHARACTERISING SOIL HUMIC SUBSTANCES USING 13C N.M.R.
Authors: NEWMAN R. H. , TATE K. R. , BARRON P. F. , WILSON M. A. 
Published: July 2006

SummaryThe structure of a humic acid from a New Zealand pasture topsoil has been investigated by conventional solution 13C n.m.r. spectroscopy and by the cross polarisation technique. Relaxation results showed that a pulse spacing of about 0.2 s was optimum for n.m.r. of the humic acid dissolved in 0.5 M aqueous NaOH. Aromatic rings accounted for 26 per cent of the total carbon. Cross polarisation n.m.r. is a viable method for obtaining 13C spectra of solid humic acids, although aromaticity cannot be estimated as accurately as for coals.
THE USE OF ADSORPTION EQUATIONS TO DESCRIBE COPPER COMPLEXING BY HUMIFIED ORGANIC MATTER
Authors: SANDERS J. R. 
Published: July 2006

SummarySamples of humified organic matter were extracted from several sources by water or alkali, and divided into colloidal and dialysable fractions. The variation of the concentration of complexed copper with that of added copper was determined for these fractions using a cupric ion‐sensitive electrode. A computer program fitted five equations often used to describe adsorption of ions on soil surfaces to the results. The data did not fit Langmuir or Temkin equations very well, probably because of the heterogeneity of adsorption sites of the organic matter; they fitted double Langmuir, Gunary and Freundlich equations almost equally well, leaving very small residual sums of squares. The Freundlich isotherm is preferred as it has only two parameters and the values of these are fairly stable to changes in the range of copper concentrations considered, or to doubling of the complexant concentration.
SOLUBILITY AND SORPTION OF CADMIUM IN SOILS AMENDED WITH SEWAGE SLUDGE
Authors: SOON Y. K. 
Published: July 2006

SummaryThe mechanisms governing the retention and release of Cd in two soils, a loam and a loamy sand, pretreated with anaerobically digested sewage sludges or with chemical fertilizers, were studied using batch equilibration in 0.05 m Ca(NO3)2 solution containing up to 6 μg Cd/ml. Adsorption rather than precipitation as Cd3(PO4)2 limited solution Cd2+ concentration. With the addition of 50 μg Cd/g, however, precipitation as CdCO3 was likely at pH 7.6. Cadmium adsorption increased with increasing soil pH. The differences in Cd adsorption between different soil treatments were attributed mainly to the soil pH (6.9 to 7.9) induced by sludge application. About 82 to 92 per cent of adsorbed Cd was retained by cation exchange and complexing sites. Soils treated with sludge increased the amount of exchangeable Cd but reduced the amount of complexed Cd compared with the fertilized soil. Cadmium retention by cation exchange became more dominant as the amount of Cd in the soil was increased.
STUDIES OF SOIL ORGANIC MATTER USING FORMIC ACID SOLVENTS: FACTORS AFFECTING COMPOSITION AND DEGREE OF FORMYLATION OF ORGANIC ISOLATES
Authors: SINCLAIR A. H. , TINSLEY J. 
Published: July 2006

SummaryTwo soils were extracted under reflux with formic acid/H2O for 0.25 h, followed by formic acid/HF for 0.25 h. In one set of experiments 14C‐labelled formic acid was used in the first extraction and unlabelled formic acid in the second: in a second set this labelling sequence was reversed. After separation from the soil residues, the soil extracts were further refluxed for up to 3.75 h. Organic matter was then precipitated from the various extracts by addition of di‐isopropyl ether. Prolonged boiling of the extracts reduced the recovery of organic matter and nitrogen, and increased the inorganic contamination of the organic isolates.The degree of formylation of the isolates from the first extraction with formic acid/H2O increased with reflux time to 0.50 h and thereafter decreased, but overall it was appreciably greater than that of the isolates from the second extraction with formic acid/HF. Formylation of the latter increased slowly with reflux time up to 4.00 h. In both solvents hydrolysis and formylation of organic solutes occur concurrently during refluxing.Treatment of formic acid/H2O extracts with a TiCl4/HCl/propan‐2‐ol reagent to precipitate organic matter and washing the precipitate in a hydrous HF medium resulted in lower yields than precipitation with di‐isopropyl ether, but the final washed precipitate contained much less formyl groups and inorganic material.
SOIL SEGMENT OVERLAP IN CHARACTER SPACE AND ITS IMPLICATIONS FOR SOIL CLASSIFICATION
Authors: WEBSTER R. , McBRATNEY A. B. 
Published: July 2006

SummaryA major problem in soil classification for soil survey is the lack, or uncertainty, of correspondence between mapping units in different localities. The problem is examined using multivariate soil data recorded at short regular intervals along transects in Oxfordshire and Aberdeenshire. The data for each transect were transformed to canonical variates, the first two of which were then used to locate soil boundaries and to show the relationships among the sampling points in that projection of the character space.With few exceptions, the sampling points in adjacent segments on all three transects lay in different parts of the canonical variate (CV) plane, showing that the boundaries were well defined. On the transect near Witney, Oxfordshire, distant segments either occupied distinct parts of the CV plane, or were superimposed on it. For the other two transects the portions of the CV plane occupied by some segments overlapped only partially the space occupied by one or more other segments that were not contiguous on the transects. The results show that on two of the three examples, lack of correspondence between mapping classes in different localities is already present in small tracts of country.
THE BASIC FACTORS WHICH DETERMINE INHERENT SOIL FERTILITY IN UGANDA
Authors: FOSTER H. L. 
Published: July 2006

SummarySoil samples collected from approximately 1700 fertilizer trials carried out around 62 centres in Uganda were analysed. Mean levels of total N. organic P and cation exchange capacity at the 60 centres which had non‐volcanic soils were very closely related to mean organic matter levels and largely explained the strong correlation of indices of available N, P and base status with organic matter. The indices of available P and base status were additionally related to pH and the indices of available N and P were further negatively correlated with sunshine hours.Soil organic matter itself was closely related to the content of clay, silt and free Fe. with which it is presumed it forms a stable complex, whilst soil pH decreased with rainfall in excess of evaporation. Thus soil texture, rainfall and hours of sunshine are the basic factors which largely determine inherent soil fertility in Uganda.
SOIL FRIABILITY
Authors: UTOMO W. H. , DEXTER A. R. 
Published: July 2006

SummarySoil friability is defined and a method for its measurement is developed from the theory of brittle fracture of soil aggregates. The variation in friability with soil water content is in good agreement with the results of tillage experiments done by earlier workers. It is found that Urrbrae and Strathalbyn sandy loams are most friable at water contents approximately equal to their Casagrande Plastic Limits.The method is applied to study the effects of wetting and drying cycles, freezing and thawing cycles, and phosphoric acid treatment on the friability of the Urrbrae soil. It is found that all of these treatments increase soil friability as defined.
THE DETERMINATION OF IONIC DIFFUSION COEFFICIENTS IN FIELD SOILS. I. DIFFUSION COEFFICIENTS IN SIEVED SOILS IN RELATION TO WATER CONTENT AND BULK DENSITY
Authors: BARRACLOUGH P. B. , TINKER P. B. 
Published: July 2006

SummaryA method for measuring diffusion coefficients in large cores of structured field soils has been developed and tested, in the first instance using sieved soil. Bromide‐chloride and bromide‐nitrate counter diffusion coefficients have been determined using ion exchange membranes as sinks for the diffusing ions. The effects of membrane selectivity, soil surface preparation, solution concentration, water content and bulk density have been investigated. The organic colloid content appears to have a considerable influence on the impedance factor‐water content relationship of a soil. Increasing the bulk density at constant volumetric water content linearly reduced the impedance factor by up to 30 per cent. The relationship between impedance factor and bulk density is discussed.
THE ADSORPTION OF COPPER BY SOIL MATERIALS AT LOW EQUILIBRIUM SOLUTION CONCENTRATIONS
Authors: MCLAREN R. G. , SWIFT R. s. , WILLIAMS J. G. 
Published: July 2006

SummaryThe adsorption of copper by individual soil components (organic matter fractions, oxides and clay minerals) was examined at equilibrium solution concentrations of copper within the range found in natural soils, the distribution of copper between solution and solid phases being measured by means of labelling with radioactive 64Cu. At these low solution concentrations it was found that the copper adsorption isotherms were essentially linear. The oxides and organic materials adsorbed the greatest amounts of copper. The concentration of copper in natural soil solutions will be controlled by these materials to a far greater extent than by the clay minerals, the influence of which may be negligible in some soils. Solution concentrations of copper are relatively unaffected by both the background concentration of major cations and by changes in pH within the ionic strength and pH range found in normal agricultural soils.Copper adsorption studies with humic and fulvic acids showed that total solution copper concentrations could be greatly enhanced above the equilibrium levels for ionic copper by the presence of soluble organic complexes. The importance of taking into account the presence of such copper complexes in soil copper studies is emphasised.
SORPTION OF INORGANIC PHOSPHATE BY IRON‐ AND ALUMINIUM‐ CONTAINING COMPONENTS
Authors: McLAUGHLIN J. R. , RYDEN J. C. , SYERS J. K. 
Published: July 2006

SummaryThe amounts of inorganic P sorbed by a range of Fe‐ and Al‐ containing components varied appreciably and decreased in the order allophane > fresh Al gel > Fe gel pseudoboehmite > aged Al gel > dried Fe gel > Fe‐coated kaolinite > haematite > goethite > akaganeite > gibbsite = ground kaolinite > dispersed kaolinite. Al gel sorbed 30 to 70 times more P than gibbsite, and Fe gel sorbed approximately 10 times more P than its crystalline analogues (haematite, goethite. and akaganeite). Despite large differences in the extent of P sorption, the form of the isotherm was essentially the same for each sorbent. The ability of freshly‐prepared Al gel suspensions to sorb P decreased with ageing, a property not shown by Fe gel. Drying of Fe gel at 80°C, however, caused an approximately 4‐fold decrease in P sorption. Precipitation of Fe gel (2% Fe) on the surface of kaolinite increased P sorption by a factor of 10. The occurrence of Fe gel as a coating apparently presents more sorption sites to solution per unit weight of Fe gel than Fe gel alone. A linear relationship (r= 0.98) was obtained between the amount OH− sorbed per unit increase in pH value (‘hydroxyl buffering’) and the overall P sorption maximum for each sorbent. Hydroxyl buffering provided a better index of P sorption potential than specific surface area. Except for the crystalline Fe sorbents, isotherms obtained by plotting fractional sorption saturation against final solution P concentration for the sorbents were essentially coincident with those for several contrasting soils. For crystalline Fe components a lower relative amount of weaker sorption, as opposed to chemisorption, of the overall sorption maximum was obtained. Differences in the extent of P sorption. however, appear to be primarily related to the number of functional M‐OH groups presented at the solid‐solution interface.
QUANTIFICATION OF WEATHERING, SOIL GEOCHEMISTRY AND SOIL FERTILITY
Authors: KRONBERG B. I. , NESBITT H. W. 
Published: July 2006

SummaryContinental chemical weathering is discussed with reference to a diagram, in which the ratio (CaO + Na2O + K2O)/(Al2O3+ CaO + Na2O + K2O) is plotted against the ratio (SiO2+ CaO + Na2O + K2O)/(Al2O3+ SiO2+ Na2O + K2O). The former ratio is a measure of the degree of feldspar breakdown, which is accompanied by the formation of secondary minerals (illite, smectite, etc.). The second ratio is a measure of the enrichment during weathering of Al, Si oxide phases such as kaolinite, quartz and gibbsite.The application of the diagram to a series of global examples leads to the statement: 1) Chemical weathering is the principal process by which continental surfaces are modified. 2) The extent of chemical weathering is correlated with the age of continental surfaces. 3) Global agricultural productivity is correlated with geologically recent additions of fresh rock debris by processes of volcanism, glaciation or alluviation.
SPECIFIC EFFECT OF MAGNESIUM ON THE HYDRAULIC CONDUCTIVITY OF SODIC SOILS
Authors: ALPEROVITCH N. , SHAINBERG I. , KEREN R. 
Published: July 2006

SummaryExchangeable Mg does not have a specific effect on the hydraulic conductivity (HC) and clay dispersion in calcareous soils. Conversely, in well‐weathered soils, which do not contain CaCO3, a specific effect of exchangeable Mg is evident, on both HC losses and clay dispersion, when the Na/Mg soils are leached with distilled water (simulating rain water). Soil clays, when Mg‐saturated, are chemically more stable and do not release electrolytes into the solutions: they thus disperse more easily when leached with distilled water. The presence of exchangeable Mg enhances the dissolution of CaCO3 in calcareous soils, and the electrolytes prevent the dispersion of the clay and HC losses in the Na/Mg calcareous soils.
TOTAL NITROGEN STATUS OF SOILS UNDER BUSH FALLOW IN THE FOREST ZONE OF SOUTH WESTERN NIGERIA
Authors: AWETO A. O. 
Published: July 2006

SummaryA substantial increase of total nitrogen occurred in the top 10 cm of soil profiles during the first ten years under bush fallow but no significant increase occurred in the 10–30 cm layer. The increase of nitrogen in the topsoils is related to soil organic matter content, increase in tree size and in vegetation cover.
A pulse method for studying effects of dead‐end pores, slow equilibration and soil structure on diffusion of solutes in soil
Authors: PINNER A. , NYE P. H. 
Published: July 2006

SummaryA model is described for solute diffusion in an aggregated medium in which a proportion of the water‐filled pores are connected to a continuous pore network by narrow channels through which the diffusing ion can move only slowly. The experimental conditions for detecting departure from normal diffusion behaviour are discussed. A pulse technique for measuring the selfdiffision coefficient of 36Cl in both undisturbed and repacked soil samples at various moisture contents is described. No evidence of slow exchange between freely and slowly accessible pores was obtained. The self‐diffusion coefficients in large undisturbed peds were somewhat greater than in repacked sieved samples at the same volumetric moisture content.
Simulating diffusion within soil aggregates: a simple model for cubic and other regularly shaped aggregates
Authors: ADDISCOTT T. M. 
Published: July 2006

SummaryDiffusion within a cube was simulated by a model which divides the cube into concentric volumes and computes by Fick's first law the diffusive flux between adjacent volumes and between the outermost volume and the external solution. The model can also be applied directly to a sphere and, with minor modifications, to other regular shapes. It was tested in two forms: (a) with the distances between the interfaces of adjacent concentric volumes made equal, and (b) with the volumes themselves equal, by using it to simulate the uptake of solute by a sphere from a stirred solution of limited volume. The output from the latter form of the model agreed the more closely with values obtained from a solution of the diffusion equations in radial co‐ordinates, and this form was used subsequently. The model was used successfully to simulate the diffusion of bromide from cubes of chalk and chloride‐36 from porous ceramic spheres, and its flexibility was illustrated by its ability to simulate experiments in which aliquots of the external solution were removed for assay.
Seasonal fluctuations in nitrogen fixation (acetylene reduction) by free‐living bacteria in soils contaminated with cadmium, lead and zinc
Authors: ROTHER J. A. , MILLBANK J. W. , THORNTON I. 
Published: July 2006

SummaryAcetylene reduction by non‐symbiotic, heterotrophic micro‐organisms in a range of soils containing different concentrations of heavy metals was determined using intact soil cores. The suitability of this method for the soils used in this investigation was established. Samples were collected seasonally, and were incubated under standard conditions (darkness: 15°). Mean values of metal concentrations in the soil (μg g−1) were: Cd: 1–200; Pb: 60–8000; Zn: 70–26000, Cu: 20–40. Rates of acetylene reduction were generally low, from 2800 to 50000 nmol C2H4, m−2 day−1. Assuming a 3:1 ratio of C2H2 reduction to N2 fixation, this represents a rate of 0.3 to 5.0 g N fixed ha−1 day−1 in the surface 150 mm of soil. No consistent effect of heavy metal concentration was found. The most important factors determining activity were soil moisture content and possibly inorganic nitrogen concentration. It thus appears that the bacteria in polluted soils are capable of adapting to potentially toxic concentrations of heavy metals, or that these metals are present in the soils tested in unavailable or non‐toxic forms.
A reassessment of podzol formation processes
Authors: ANDERSON H. A. , BERROW M. L. , FARMER V. C. , HEPBURN A. , RUSSELL J. D. , WALKER A. D. 
Published: July 2006

SummaryTranslocated (oxalate‐soluble) Al and Fe are present predominantly in inorganic forms in the B2 horizons of the five pcdzol profiles examined: A1 as imogolite and proto‐imogolite allophanes, and Fe as a separate oxide phase. Below the top few cm of the B2 horizon, over 75 per cent of the extractable (acid‐plus alkali‐soluble) organic matter is present as Al‐fulvates, largely sorbed on allophanic material. The Bh horizons of the Iron Humus Podzol and Iron Podzol intergrades are distinguished by very high levels of organically bound Fe (soluble in EDTA solution), five to ten times more than in immediately adjacent A2 or B2 horizons, and also by larger humic acid contents than in comparable B2, levels in typical Iron Podzols. Inorganic forms of translocated Al and Fe are probably absent from two of the three Bh horizons examined, and also from the Bhg horizon overlying the thin iron pan in the Peaty Podzol. The organic matter in this Bhg horizon is saturated with Al rather than Fe. Chemical and physical processes which could lead to evolution of a profile along the genetic sequence, Iron Podzol, Iron Humus Podzol, Peaty Podzol, are postulated. During the formation of an Iron Podzol, positively charged inorganic sols carry aluminium, silicon and iron from the A2 and deposit them in the B2 horizon; subsequently, with the development of an H layer, colloidal humus migrates through the A2 and precipitates on the positive colloids at the top of the B2 horizon to form a Bh horizon, in which remobilized ferric species are trapped by the organic matter. In higher rainfall areas, occasional waterlogging above the oxide‐impregnated B2 leads to a thin iron pan, separating permanently oxidizing conditions below from seasonally waterlogged and reducing conditions above.
A technique for the measurement of gaseous diffusion in porous media
Authors: REIBLE D. D. , SHAIR F. H. 
Published: July 2006

SummaryAn apparatus composed of two well‐mixed vessels connected by a tube was used to measure the effective diffusivity of a gas (sulphur hexafluoride, SF6) in porous beds of sand, steel wool and glass beads. The general solution to Fick's second law for the apparatus was employed in the analysis. The ratio of the measured effective diffusivity of SF6 to SF6‐air diffusivity was found to equal approximately the void fraction of the porous bed raised to the 1.43 power. This relationship agreed well with previously collected data and with the theoretical models of Millington (1959) and Marshall (1959). The effective diffusivity of wet porous materials was also measured and, at higher moisture contents, found to deviate strongly from that measured in dry materials. The effective diffusivity of SF6 in sand with 20 per cent moisture (volume basis) was found to be about one‐fourth as large as the value expected from the dry‐bed experiments. No significant deviation was found for sand of 10 per cent moisture content or lower.
Predicting bare soil temperature. I. Theory and models for the multi‐day mean diurnal variation
Authors: BUCHAN G. D. 
Published: July 2006

SummaryThe energy balance equation for the soil‐air interface is expressed, by suitable approximations, in a form linear in the surface temperature T0. This forms the basis of two predictive models for the diurnal variation of T0, averaged over a many‐day interval, for potentially evaporating bare soil. Input data include total solar radiation, air temperature and vapour pressure, windspeed ua, cloud cover c, and soil radiative, aerodynamic and thermal properties (the latter assumed uniform). In the simpler model, based on harmonic analysis, ua and c are assumed constant. For Nt observations per day, an algebraic solution is found as a set of equations for the parameters of up to the first Nt/2 harmonics. In the second model, dynamic wind‐speed is introduced, and a more complicated linear algebraic method of solution is required. The models have agroclimatic value, since by averaging they predict the thermal ‘climate’ of soil, in contrast to instantaneous models which describe the time‐specific thermal ‘weather’.
Predicting bare soil temperature. II. Experimental testing of multi‐day models
Authors: BUCHAN G. D. 
Published: July 2006

SummaryTwo agroclimatic models described earlier are tested against measurements of temperature at the soil surface, T0, and in bulk soil, T(z,t), at an experimental site near Aberdeen during spring, summer and autumn. Soil temperature is predicted most accurately in spring and autumn, when the constant‐windspeed model ENBL1 predicts the mean within 0.3 K of measurement. Thedynamic‐windspeed model ENBL2 predicts within 0.1 K in all intervals, and with error<0.3 K to depth z=32 cm in spring and autumn. A sensitivity analysis of the output diurnal wave, T0(t), shows that maximum input economy requires only time‐dependent shortwave radiation, Rs(t), and air temperature, Ta(t), other inputs being constant. Two or three harmonics in ENBL1 should suffice, requiring four or six measurements per day, depending mainly on the time‐structure of the primary driving function Rs.