bluuebunny/crossref_metadata_2025_split huggingface dataset:
ADSORPTION OF CADMIUM AND ITS EXCHANGE CHARACTERISTICS IN SOME ISRAELI SOILS
Authors: NAVROT J. , SINGER A. , BANIN A. 
Published: July 2006

SummaryCd adsorption isotherms were measured on five Israeli soils ranging in specific surface area from 65 to 315m2/g. Retention capacity of Cd ranged from 4.7 × 103 to 10 × 103μg/g soil (8.4 to 17.9 mequiv/100 g soil) and was correlated with the specific surface area. Almost all the adsorbed Cd was exchangeable with 0.5 M CaCl2 and the remaining fraction was extractable in 0.5 M HCl. Plots of Kd, the distribution coefficient of Cd between the solid and solution phases, vs. Γ, the surface density of adsorbed Cd, showed that all soils behave similarly, Kd sharply diminishing with Γ. It was suggested, based on comparison with literature data on Cd adsorption on montmorillonite, that below γ s 0. 5 × 1017 ions/m2, specific adsorption mechanisms prevail whereas above it the adsorption is mainly due to electrostatic interactions and ion exchange.
THE STRUCTURE OF BEDS OF SPHERICAL PARTICLES
Authors: DEXTER A. R. , HEWITT J. S. 
Published: July 2006

SummaryThe statistical distributions of intercepted void and particle lengths along lines through beds of random close packed equal spheres are analysed. The structures are described by sets of sixteen conditional porosities. Data are presented for 21 different sphere diameters.The intercepted void and particle lengths are given for two sizes of spheres having diameters in the ratio 1:0.8. The results are not very different from those for equal spheres.The effect of data length on the accuracy of the conditional porosities is measured for four representative particle diameters. A method for calculating pore size distributions from the conditional porosities is presented.
EFFECTS OF IONIC STRENGTH AND NATURE OF THE CATION ON DESORPTION OF PHOSPHATE FROM SOIL
Authors: BARROW N. J. , SHAW T. C. 
Published: July 2006

SummaryThe effects of cations on desorption of phosphate previously added to soil were studied by mixing phosphated soil with solutions of chloride salts at a range of solutionitoil ratios and for periods which ranged from 1 to 96 h. Phosphate desorbed was then related to the experimental variables by a pair of simultaneous equations. In calcium chloride, the rate of desorption of phosphate was inversely proportional to the calcium concentration. Desorption was faster in 0.01 M magnesium chloride than in 0:01 M calcium chloride, and faster in 0.03 M sodium chloride than in either magnesium or calcium chloride. Addition of a further supply of the cation on an exchange resin increased the rate for both sodium and magnesium but decreased it for calcium. A range of monovalent cations formed a sequence from fastest to slowest of: Li+ > Na+ > NH4−> K +, Rb + > Cs +. The identity and concentration of the cations had a large effect on the concentration of phosphate when the solution: soil ratio was small. There were also large effects in the amount of phosphate desorbed when the solution: soil ratio was large and the concentration of phosphate approached zero. This suggested that the escaping tendency of the phosphate was decreased when the cations which balanced the negative charge on the adsorbed phosphate were close to the surface.
THE DESCRIPTION OF DESORPTION OF PHOSPHATE FROM SOIL
Authors: BARROW N. J. 
Published: July 2006

SummaryAfter incubation with soil, phosphate was desorbed in dilute calcium chloride solutions. After short periods of incubation, the amount of phosphate desorbed increased rapidly at first but then net re‐adsorption occurred. After long periods of incubation, desorption was slower and there was no net re‐adsorption with prolonged desorption.Desorption was described in terms of two limiting values: the amount of phosphate (K) which would be desorbed as the concentration of phosphate approached zero, and the solution concentration of phosphate (Co) at which no desorption occurred. Both values decreased as the period of incubation increased. The value of K increased during the desorption phase, but the value of Co decreased. The decrease in Co during desorption was most marked after short periods of incubation and was important in describing the trend for re‐adsorption of phosphate.
POTASSIUM FIXATION IN SOME KENYAN SOILS
Authors: BARBER R. G. 
Published: July 2006

SummaryPotassium fixation was measured for 13 Kenyan soils with a range of applied potassium (0 to 1000 mg kg−1). The fixed potassium was measured, and hence is defined in this study, by the difference between the amount of applied K and the increase in the extractable K after equilibration, using a single ‘equilibrium’ extraction procedure with 0. 25 M Cad, as the extractant. At application rates of 50 and 1000 mg kg−1 the fixed potassium varied from −52% to 64% and 7% to 39% respectively. A correlation was found between the K fixation and % clay content at the 1000 mg kg1 application rate. Estimates of the % fixation by the clay fractions gave 53 to 80% for montmorillonites, 48 to 66% for amorphous clays and 19 to 32% for kaolinites. It is suggested that the amorphous clays may fix potassium by a ‘sieve’ mechanism.
INFLUENCE OF THE SPATIAL DISTRIBUTION OF NITRATE ON THE UPTAKE OF N BY PLANTS: A REVIEW AND A MODEL FOR ROOTING DEPTH
Authors: BURNS I. G. 
Published: July 2006

SummaryPublished literature is re‐examined in an attempt to understand the influence of the spatial distribution of soil nitrate on N uptake in order to devise a simple method for estimating the depth to which nitrate must be leached before it becomes unavailable to the crop. The evidence suggests that most crops can continue normal growth with less than 15% of their roots exposed to nitrate.A simple model of nitrate uptake is constructed in which nitrate is assumed to be totally available above a set depth and totally unavailable below it. This effective rooting depth is assumed to coincide with the depth at which uptake per unit length of root declines to half of the maximum rate. Estimates of effective rooting depth have been made from root distribution data for various vegetable crops grown at Wellesbourne and cereal crops at Rothamsted. The results were found to fit a simple regression equation which can be used to calculate effective rooting depths at any stage of growth from the dry weight and population density of the crop and the mean cross‐sectional area of its roots. This equation is used in the succeeding papers to estimate the effects of leaching on the N fertilizer needs of crops.
THE WATER BALANCE OF AN AGRICULTURAL CATCHMENT. I. ESTIMATION OF EVAPORATION FROM SOIL WATER RECORDS
Authors: McGOWAN M. , WILLIAMS J. B. 
Published: July 2006

SummaryErrors of measurement of soil water content with the neutron probe can be made small enough for most water balance studies; and apart from the possible damage resulting from access tube implacement, they can be readily specified. A more important problem is estimating how much water is lost from soil by drainage.A simple, graphical method is described to distinguish between drainage and evaporation from soil, based upon identification of the maximum depth at which measurable quantities of water are extracted by roots. As a result of errors in soil water measurements and uncertainties in the distinction between drainage and evaporation, estimates of soil water deficit and hence evaporation for a single profile are likely to have a precision of about ±5 mm. Larger variability is commonly found in soil water storage changes measured in replicate profiles partly because of uneven wetting of the soil during rain and partly because of non‐uniform losses by drainage and root extraction. This variability requires careful attention to replication and location of access tubes when assessing the evaporation for a particular site.
DESORPTION OF PHOSPHATE FROM SOILS USING ANION EXCHANGE RESINS
Authors: BACHE B. W. , IRELAND CHRISTINA 
Published: July 2006

SummaryAfter 100h reaction with Cl‐resin and 300h reaction with HCO3‐resin (approaching equilibrium), the concentration of anions complementary to phosphate was the critical variable affecting the transfer of P from soil to resin. Solution concentrations of H30+, Ca2+ and phosphate indicated that desorption of P by OH‐, and dissolution of Ca phosphates, controlled P release from soils. P extracted by HCO3‐resin was much greater than by Cl‐resin from an acid soil, due to lower total anion and higher desorbing anion concentrations, but there was little difference between the two resins with a calcareous soil. HCO3‐resin extracted a constant proportion of isotopically‐exchangeable P from different soils whereas Cl‐resin did not. Anion exchange resins provide a convenient means for producing P desorption curves for soils.
THE INTERACTION OF PHOSPHATE WITH AN ANION EXCHANGE RESIN
Authors: CHRISTENSEN HANS HENRIK , POSNER ALAN M. 
Published: July 2006

SummaryPhosphate adsorbed on an anion exchange resin was titrated with sodium hydroxide. The inflection point which corresponds to the second pK value of phosphoric acid in solution, was lowered 0.9 pH‐unit when the acid was absorbed on the resin. This shift was fully explained by the exclusion of H+ from the resin due to a Donnan equilibrium.The adsorption characteristic of the single and double charged phosphate ion on an anion exchange resin was examined at different pH values and phosphate:resin ratios. A model was suggested for the observed adsorption pattern.
IMOGOLITE AND PROTO‐IMOGOLITE ALLOPHANE IN SPODIC HORIZONS: EVIDENCE FOR A MOBILE ALUMINIUM SILICATE COMPLEX IN PODZOL FORMATION
Authors: FARMER V. C. , RUSSELL J. D. , BERROW M. L. 
Published: July 2006

SummaryExamination by infrared spectroscopy and electron microscopy of the fine clays (<0.5 μm) dispersed at pH 3.5 from H2O2‐treated soil indicates that imogolite and proto‐imogolite allophanes are concentrated in podzolic B2 and B3 horizons, and make up at least 6 percent of one B2 horizon soil, which contains virtually no layer silicate clays. It is argued here that imogolite‐type components are the principal source of extractable aluminium and silicon in such horizons, that they may act as cementing agents in indurated horizons, and that proto‐imogolite, a soluble aluminium‐silicate complex, is the predominant mobile form in which aluminium is transported to B2 and lower horizons of podzols. Comparison of the amounts of aluminium extracted by acetic acid with those extracted by EDTA indicates that extractable aluminium in Bhg, Bh, and organic‐rich A2 horizons is present principally in organic complexes. It is proposed that the aluminium fulvates concentrated in these horizons are formed in situ.
RAINDROP IMPACT STRESS
Authors: GHADIRI H. , PAYNE D. 
Published: July 2006

SummaryEstimates of rain drop impact stress were made from measurements of the penetration of water drops through nylon meshes, from analysis of cine photographs of splash and from the output of a force transducer.Results indicated maximum stresses of 2–6 MPa acting for about 50 microseconds on the perimeter of a circle corresponding with the shape of the initial rebound corona.
Critical potassium potentials for crops. I. The effect of soil type on the growth of ryegrass and creeping red fescue
Authors: PAGE M. B. , TALIBUDEEN O. 
Published: July 2006

SummaryThe quantity: potential relationships for Ca→K exchange in six soils were evaluated, where potential is defined by ΔGK,Ca+Mg. Using the percentage K saturation of the CEC as the index of quantity, the Worcester Series soil, rich in hydrous micas, was shown to have the highest concentration of K selective sites, and Newport Series soil, with mainly kaolinitic clay, the lowest. The other soils, containing mainly smectites, had intermediate K selectivities.An algebraic transformation of this relationship to separate the effects of exchangeable K and CEC showed that 0.01 m CaCl2 released more K than m ammonium acetate. From the exchangeable K : ΔG relationship, two regions of K buffering were observed for all but the Newport soil, the transition occurring at a mean ΔGK,Ca+Mg value of −20.7 kJ mol−1, signifying the K concentration below which K from ‘perlpheral’ regions of micaceous minerals is released. This may explain why the percentage K saturation of the CEC of a soil cropped exhaustively (without K manuring) in the field does not drop below a minimum value.Based on pot experiments, exhaustion and optimum K potentials (ΔGexh and ΔGopt) were derived from second‐degree polynomials fitted to the response curves of plant dry matter yield against ΔGK,Ca+Mg for five soils, the Worcester soil showing little response. ΔGexh was inversely related to the 2 : 1 layer silicate content of the soil (r2=0.98 and 0.94 for ryegrass and fescue respectively), and similarly, ΔGopt, to their CEC values (r2=0.74 and 0.77). Potassium uptake was more closely correlated with exchangeable K than with ΔGopt.
The polarographic study of the equilibrium between humic acid and aluminium in solution
Authors: RITCHIE GERALDINE S. P. , POSNER A. M. , RITCHIE I. M. 
Published: July 2006

SummaryDifferential pulse polarography (d.p.p.) was used to investigate the equilibria between humic acids and aluminium in solution. A reduction potential for humic acids was observed at −1.5 V but only at pH < 3.4. No reduction potential was evident for the metal humate complex. Determination of the free aluminium in solution showed that very little free aluminium (<0.1 percent of total concentration) is in equilibrium in solution with the complex before precipitation.
Chemical and mineralogical properties of sandy and loamy‐sandy ochreous brown earths in relation to incipient podzolization in a brown earth—podzol evolutive sequence
Authors: HERBAUTS J. 
Published: July 2006

SummaryChemical and mineralogical properties of ochreous brown earths have been studied with particular reference to: (1) the distribution within the profiles of Fe and Al compounds; (2) the occurrence of smectite‐like clay minerals in surface horizons.Ochreous brown earths studied belong to a developmental sequence of forest soils, from acid brown earths to ferric podzols, developed on sandy or loamy‐sandy acid parent materials. In such a soil sequence, both selective chemical and mineralogical data show clearly that podzolization is already active in ochreous brown earths, whereas such an incipient podzolization is quite undetectable by direct morphological observations.The distribution patterns of amorphous Fe and Al hydrous oxides and organic associations, clearly show the intergrade character of ochreous brown earths, when compared with the vertical distribution of Fe and Al forms in acid brown earths and podzolized soils. The Fe/Al ratio of both an NH4‐oxalate extract and an NaOH/Na‐tetraborate extract buffered at pH 9.7, measured in the A1B diagnostic horizon of ochreous brown earths, is a particularly appropriate and useful genetic criterion for the detection of incipient podzolization.Moreover, the presence of expansible clay minerals (degradation smectites) in the clay‐sized fraction of the surface horizons of ochreous brown earths (A1 and A1B) can be considered as supplementary evidence of incipient podzolization.
Adsorbed ion activities and other thermodynamic parameters of ion exchange defined by mole or equivalent fractions
Authors: GOULDING K. W. T. 
Published: July 2006

SummaryThe ‘Gaines and Thomas’ method for calculating the thermodynamic parameters of a cation exchange process has been criticized because equivalent rather than mole fractions were used in the definition of adsorbed ion activity coefficients. Although such coefficients are thus not theoretically correct, comparison with directly measured enthalpies of exchange shows that they indicate heterogeneity in the exchange process correctly. They also differ little from coefficients defined in terms of mole fractions. Such a re‐definition alters values of the thermodynamic equilibrium constant, and free energy and entropy of exchange by a constant factor, independent of cations and exchanger. Comparisons of series of cations, soils or clays using these parameters are therefore not affected.
Chemical properties of upland peats influencing the retention of phosphate and potassium ions
Authors: CUTTLE S. P. 
Published: July 2006

SummaryPeat samples representing depths of 0–15 cm and 15–30 cm were obtained from 11 upland sites in southern Scotland. Their pH, ash content, cation exchange capacity, phosphate sorption index and contents of 0.1 m hydrochloric acid‐extractable iron and aluminium were determined as indicators of the extent to which phosphate and potassium ions would be retained following afforestation and application of fertilizers to these sites.In all soils cation exchange capacities were considerably larger than the quantity of potassium normally applied as fertilizer. Phosphate sorption indices were closely related to the content of extractable iron and aluminium in the peat samples. When expressed on a volume basis, the indices were low compared with those published for mineral soils, and some peats appeared to have almost no capacity to sorb phosphate ions from solution.
1H‐nuclear magnetic resonance study of a soil humic acid
Authors: WILSON M. A. , COLLIN P. J. , TATE K. R. 
Published: July 2006

SummaryThe structure of a humic acid from a New Zealand pasture topsoil has been investigated by 1H‐n.m.r. spectroscopy. The work complements a recent 13C‐n.m.r. study on the same humic acid. Irradiating the water peak in the spectrum greatly improves spectral quality. The results show that the proton aromaticity of the humic acid (excluding exchangeable protons) is 17%. Considerable amounts of protons in the humic acid are associated with carbohydrates (35%). Useful structural parameters describing the average molecular structure of the humic acid were derived by combining both 1H and 13C data. Further work is needed to determine both the percentage exchange of protons in alkali and the percentage of inorganic hydrogen in humic acids, before the condensation and the degree of substitution of aromatic rings can be quantitatively estimated.
The calibration of a high resolution gamma‐ray transmission system for measuring soil bulk density and an assessment of its field performance
Authors: HENSHALL J. K. , CAMPBELL D. J. 
Published: July 2006

SummaryThe calibration of a high resolution gamma‐ray density probe and a simple experiment comparing the probe with an earlier, lower resolution version are described. An assessment is made of the performance of the probe in three experiments investigating compaction by tractor wheels, two of which were in the field and the third in an indoor soil tank. A linear calibration relationship was obtained, although the addition of a quadratic term improved the fit of the curve slightly. The probe was found to be much more accurate than the earlier version within 100 mm of the soil surface where treatment effects were largest and most numerous in the field experiments, and thin layers of high density could be detected. Over the 15 month period of the experiments, the stability of the system was found to be satisfactory.
A comparison of the structural characteristics of polymaleic acid and a soil fulvic acid
Authors: SPITELLER M. , SCHNITZER M. 
Published: July 2006

SummaryThe purpose of this investigation was to compare structural characteristics of PMA with those of FA in order to assess the suitability of PMA to serve as a model for FA. Chemical (elemental analyses, CO2H group determinations, increases in OCH3 after methylation, oxidative degradation) and spectroscopic (visible, UV, fluorescence, IR, 13CNMR, and ESR) methods were used for this purpose. While PMA was found to resemble FA in a number of characteristics (water solubility, rich in CO2H groups, dark brown colour), it significantly differed from FA in a number of respects (UV, fluorescence, 13CNMR spectra as well in oxidation products). Compared to FA, PMA appeared to be better organized and more homogeneous at the molecular level, richer in olefinic structures and less aromatic. But the chemical structures of both PMA and FA remain largely unknown.
The extraction and characterization of soil polysaccharide by whole soil methylation
Authors: CHESHIRE M. V. , MUNDIE C. M. , BRACEWELL J. M. , ROBERTSON G. W. , RUSSELL J. D. , FRASER A. R. 
Published: July 2006

SummaryA soil of the Countesswells series was repeatedly methylated by the Hakomori procedure and a chloroform‐soluble product isolated after each methylation. Ninety‐two per cent of the material engendered by seven methylations was released during the first four methylations. This had a methoxyl content of about 20% and contained 2% N. Later fractions had lower methoxyl and N contents.Residual carbohydrate in the soil had reducing sugar content on hydrolysis, equivalent to about 3% of the original value.The extracted material had the infrared spectrum of a methylated soil polysaccharide and, on hydrolysis by 2 m trifluoracetic acid, released methylated sugar derivatives of which 68 were characterised by GC‐MS.Derivatives corresponding to (1→4) linked sugars predominated for both hexose and pentose sugars but there was also a large proportion of (1→3) linkages, (1→3) linkages predominated for the deoxyhexose sugars. There were more sugars with only one or two methylated hydroxyl groups than could be accounted for as branching points because of the relatively small numbers of end groups.Prior reduction of the soil with sodium borohydride had no measurable effect on the nature or yield of the methylated product. This indicates that amino acid sugar linkages susceptible to β‐elimination reactions can have only a very small influence on the reaction.The isolated sugar derivatives accounted for 70% of the total soil sugars. The methylated material before hydrolysis had a low nominal molecular weight on diafiltration, with 68% < 10000. Some of the sugars unaccounted for were probably lost during the dialysis stage necessary to remove dimethyl sulphoxide.
Removal of ferrous iron from field drainage waters by conifer bark
Authors: VAUGHAN D. , WHEATLEY R. E. , ORD B. G. 
Published: July 2006

SUMMARYIron ochre deposition in field drainage systems is produced as a result of chemical and microbiological oxidation of ferrous iron in soil solution to the insoluble ferric form. Conifer bark, from several plant species, will absorb ferrous iron from solution quickly and irreversibly, the bark changing colour from brown to blue in the process. This bark, unlike that from deciduous trees, contains only small quantities of soluble phenolic components so it does not create an environmental problem under field conditions. Trials carried out at a test farm, where bark was placed within nylon mesh sacks and incorporated into the drainage system, were very successful, and drainage pipes which had previously blocked twice yearly remained relatively free of ochre. The use of bark from conifers can offer an inexpensive method of ameliorating the problem of ochre formation without producing environmental pollution.