摘要:

SUMMARYThe Kubelka–Munk theory, which is commonly applied to ‘pigment mixtures’, adequately predicted the colour of mixtures of synthetic haematite, synthetic goethite and deferrated soil powders. The theory illustrated the higher pigmenting effect of haematite compared with goethite. In mixtures containing haematite the calculated colour coordinates could be combined into simple ‘redness’ indices that were highly correlated with haematite content and were not appreciably influenced by goethite.The theory was also applied to the study of the chromatic characteristics of 98 soils, differing widely in their origin but having an organic matter content<2% in which haematite or goethite was the dominant Fe oxide. The theory showed that the average ‘soil’ haematite and ‘soil’ goethite had colours similar to those of their synthetic counter‐parts, whereas the rest of the soil components could be considered as an essentially ‘grey’ matrix. It was also useful in predicting the haematite and goethite contents of soils either from several reflectance measurements of soil‐white standard mixtures or from the indices of redness developed f

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00382.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYThe model developed in part I to describe the dissolution of a planar source of DCPD in soil is extended to deal with the dissolution of particles, allowing for diminution of the particles as they dissolve and the interaction of neighbouring particles. The model has nine input parameters: concentrations of calcium and phosphate in the unamended soil solution, unamended soil pH, phosphate and lime potential buffer capacities of the soil, volumetric moisture content, diffusion impedance factor, and rate of application and particle size of the DCPD. A sensitivity analysis of the model showed that the rate is particularly dependent on particle size, rate of application, and the pH and concentration of calcium in the soil solution. If the particles are so far apart that they do not influence each other, after the very early stages the rate of dissolution is independent of the soil buffer terms. But for typical rates and methods of application, neighbouring particles will influence each other, and the consequent interactions between the rate‐determining variables are comple

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00383.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYThe model of the dissolution of particles of DCPD in soil, presented in part III, was tested against experimentally determined rates of dissolution in soil at two pHs, 4.6 and 6.0. To measure the rates,45Ca dissolved from labelled DCPD was recovered from the soil by shaking the mixture of soil and undissolved DCPD in a CaCl2, extractant. There was good agreement between the observed and predicted rates of dissolution.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00384.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYA simple model is developed for predicting the rates of dissolution of particles of sparingly soluble calcium phosphates in acid soils. The model comprises analytical solutions to equations describing the steady‐state diffusion of phosphate and hydrogen ions in soil. The concentrations of the ions in solution at the boundary between soil and mineral are found from the solubility product of the calcium phosphate and by equating the fluxes of the ions across the boundary. The diminution of the mineral particles as they dissolve, and the effect of neighbouring particles on each other, are allowed for. The model's predictions for dicalcium phosphate agreed very well with those of the more complex model, tested experimentally (Kirk&Nye, 1986a), but only one‐thousandth of the computer time was necessary to simulate equivalent conditions. he extension of the model to predict the rates of dissolution of the apatites in rock phosphates is described, and examples of the predicted rates of dissolution are gi

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00385.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYThe effect of non‐uniform distribution of particles in the soil on the rate of dissolution of calcium phosphate particles was investigated, using a negative binomial distribution to describe the degree of clumping of the particles. A randomly distributed sample dissolved about 10% more slowly than a regularly distributed one. For a degree of clumping in which the sum of the spherical volumes influenced by particles was about 10% of the whole soil volume, the predicted rate of dissolution was reduced by about 85%. The effect of a range of particle sizes in the applied material was also investigated. Typical grades of commercial rock phosphate contain a high proportion of fine particles, resulting in a rapid initial rate of dissolution of the applied material, but the rate trails off as the small particles are exhausted.The effect of the presence of plant roots was also considered, using average root characteristics and assuming the root effects to be spread over the whole soil volume. The rate of calcium phosphate dissolution was increased by root uptake of dissolved phosphate ions, by an amount depending on the rooting density and the rate of calcium phosphate application, and by secretion of acid by the roots. In many circumstances where rock phosphates are applied as fertilizers, plants are likely to be rhizosphere acidifiers; sufficient acid may be secreted to render rock phosphates soluble where they would other‐wise be insoluble. Generally, calcium uptake will not greatly affect the rate of calcium phosphate dissolut

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00386.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYPotassium was extracted from samples of 21 surface soils and nine subsoils using a calcium‐saturated cation exchange resin and concentrated HCI under reflux. Most of the important arable soils of England and Wales were represented in the samples. The two methods permitted determination of the amounts and rates of release of exchangeable K, K fixed in the weathered periphery of vermiculitic and illitic minerals, and K in the unweathered core of mica minerals. Potassium reserves in the soils were classified as High, Medium or Low according to the rate of release of fixed K and the amount and rate of release of mica K. The K reserves of soils in England and Wales could be mapped by soil series using this method of classification. Such mapping would provide data on the extent and availability of reserves in both the short term (i.e. to a crop over a growing season) and long ter

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00387.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYSoil polysaccharide isolated from alkali extracts of Countesswells and Insch series soils has been submitted to electrofocusing with ampholyte in dextran gel. To aid detection, polysaccharide which had been dyed with either Procion Red or fluorescein or labelled14C by prior incubation of the soil with 14C‐labelled substrates, was also used.After electrofocusing, polysaccharide was distributed in the gel over the entire range of pH used, 1.9–10, with the greatest concentration occurring within the pH 1.9–4 region. The distribution was partly the result of adsorption and diffusion. Re‐electrofocusing of material isolated from particular regions of the bed located most of it in the original position, although considerable dispersion occurred, particularly with the less strongly charged material and there was evidence for association/dissociation reactions. This was also observed in a medium containing 8 M urea.The proportion of uronic acid was greatest in the polysaccharides fractions from the pH 3.0–4.0 region of the bed. The increased acidity of the fraction nearest to the anode appeared to relate to the presence of other organic acids, such as succinic, fumaric and levulinic acids. No difference could be detected between the separation of polysaccharide from the two different soils or between the labelled polysaccharides derived from an incubation of14C‐glucose with soil and those from an incubation of14C‐p

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00388.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYA simple three step method is described for isolation of soil fulvic acids in high yield. The complexing agent H2P2O72−(at pH 2) is used to release soil‐bound fulvic acids. Extraction of humic acids is minimal. Selective separation of the protonated fulvic acids from the ionic extractant is achieved on a non‐ionic polyacrylate resin (Amberlite XAD‐7); after washing the resin, fulvic acids were retrieved in>98% yield by adjusting the pH to 6.5. Two problems associated with the classical alkali extraction method are avoided: possible alkaline oxidation of phenolic components, and their oxidation by Fe3+under the acidic conditions employed to precipitate humic acids. The product typically has an ash weight of<0.6% after one XAD treatment. The method has been applied to three soils and one IHSS peat

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00389.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00390.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYTen naturally acidic Scottish soils have been limed with CaCO3at 0,0.25, 0.50, 0.75, 1.00 and 1.25 times the recommended lime requirement, and then subjected to three cycles of alternate wetting to field capacity at 20°C for 1 month and drying for 1 month. The Zn, Cu, Fe and Mn extracted by DTPA solution, both at pH 7.3 and also after adjustment to match the final soil pH, were measured by flame AAS. The same elements were determined in ammonium acetate extracts, for extractants buffered at pH 4.8, pH 7.0 or at the final soil pH. The effect of extractant pH upon the amounts of trace elements removed is discussed for the two extractants, with particular reference to Zn. The influence of soil pH upon the amounts of trace elements extracted is also considered. There appears to be a distinct relationship between rate of decrease of DTPA‐extractable Fe with increasing soil pH and the effect of pH upon DTPA‐extractable Zn, high rates of decrease of extractable Fe being associated with a more continuous decline in extractable Zn with increasing soil pH. Possible reasons for this relationship are discussed, in the light of an experiment conducted to examine the effect of Fe and A1 on loss of Zn from solution at high pH. DTPA‐extractable Cu varied little with increasing s

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00391.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY