摘要:

SummaryThe formation of soluble complexes, frequently coloured, when solid lichen compounds were shaken with water suspensions of biotite, granite, and basalt indicated that chemical weathering had occurred. The formation of colourless complexes and the adsorption of the dissolved lichen compound or complex by the silicate phase complicate the interpretation of the spectrophotometric analysis data. Lichen compounds invariably released greater amounts of Ca than of Mg, Fe, and Al from the silicates and, for each lichen compound, the release of Ca was usually greater from biotite than from granite or basalt. Release of cations from the silicate materials resulted largely from metal‐complex formation rather than from reactions directly involving hydrogen ions. Citric, salicylic, and phydroxy‐benzoic acids and EDTA, used as control organic acids, usually released considerably greater amounts of cations from the silicates than did the lichen compounds, consistent with the higher water solubility of the control organic acids. Similar amounts of Fe, Al, Ca, and Mg were released from the silicates by solutions of the lichen compounds and by solid lichen compounds. Lichen compounds are sufficiently soluble in water to form soluble metal complexes and to effect chemical weathering of minerals and ro

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01658.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummarySoils in regions of arid and semi‐arid climates exhibit only limited pedogenetic profile development, and they might be more usefully described, classified and mapped in terms of their depositional character. The main source of understanding of their origins and practical significance is likely to be the sedimentary geomorphology of the area concerned, rather than the minimal pedogenetic features. The term ‘sedosols’ is proposed for these soils and a method of classification is outlined, based on depositional features and origins.Sub‐orders are based on mode of deposition to give four sedimentary families, viz. fluvial, littoral, aeolian, and anthropic.In lower category classification, series based on pedogenetic features cannot be defined and are replaced by the ‘depositional series’ characterized by the types of sediment (e.g. coarse textured, fine textured; saline, non‐saline).Typical phases are based on soil depth and degree of erosion. Salinity induced by irrigation is also best recognized at phase level as it is essentially an ephemeral feature.The three major differentiating characteristics of sedosols are soil texture, degree of depositional stratification and effecti

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01659.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryIn the arid environment of South Arabia the soils (sedosols, see Part I) are not significantly affected by pedogenetic processes. Classification of these soils is therefore in accordance with the principles outlined in Part I, being based upon a consideration of the mode of deposition rather than on considerations of pedo‐genesis. Sedimentary geomorphology, soil classification, soil mapping are discussed for two areas of South Arabia. Mapping purity was satisfactory and reliability was probably greatest in series that were wholly anthropic or wholly natural in origin. In classifying land for single‐flood irrigation agriculture, the total readily available moisture capacity is the major land classification factor. It is a function of texture and effective depth, modified in places by severe stratificat

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01660.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryFe and Al extractable by 3 per cent oxalic acid and by 0.1M potassium pyrophosphate at pH 10 have been determined in horizon samples of two soil profiles of each of three subgroups (Brown Earth, Brown Podzolic Soil, and Peaty Podzol) developed in North Wales on parent materials derived from Silurian shales. The vertical distribution of Fe and Al together with the relationship between pyrophosphate‐extractable (‘fresh’ hydrous oxides) and oxalic‐extract‐able Fe or Al (‘fresh’+‘aged’ hydrous oxides) can assist classification and interpretation of the course of podzolization in these soils. If podzolization is defined as sesquioxide transport, then its degree of development in the soils studied differs according to whether Al or Fe are used as the index element. The evidence supports continued recognition of soils of Brown Podzolic type as an in

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01661.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

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 (7 per cent by vol.) clay illuviation; (2) the degree of reworking of the illuviated clay, subdivided into 3 classes, ranging from weak (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 (700 per cent cm). A distinction was made between the profile index based on thein situilluviation features only and that based on all the illuviation features.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01662.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

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 aggregate

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01663.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

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 givenNratios 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 indexk, 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 constantCandkvalues (isoparentic and isoluvic lines).All computations can be made by desk calculators provided with an extended memory for storage of data and programme

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01664.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryEquilibrium ultra centrifugation is a superior method to the more conventional sedimentation velocity technique for measuring the molecular weight of poly‐disperse humic acid. The technique can be used to estimate number, weight, and Z‐average molecular weights of humic acid and a measure of the polydispersity of the acid can thus be achie

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01665.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryThree common gel‐chromatography materials have been calibrated for humic acid, using fractionated samples the molecular weights of which were calculated by combining sedimentation coefficients determined on the ultracentrifuge with diffusion coefficients.The gel materials were found to have the following fractionation ranges for humic acid when tris buffer was used: Sephadex G‐100, 2500 to 100000; Bio Gel P‐150, below 1000 to 40000; Sepharose 6B, 1500 to 2500000. Borax buffer appeared to extend the range of Sephadex G‐100 to lower molecular weights.A brief comparison is made of the retention behaviours of humic acid, proteins, and dextrans on the gel ma

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01666.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryThe relation between soil suction, degree of saturation, and the air and water permeabilities is experimentally investigated for two clay soils. Marked hysteresis can exist between saturation and permeability, but does not follow a unique trend. Thus permeability can be greater on a wetting or drying cycle depending on the structure of the clay soil. This behaviour is considered in terms of the cluster concept of soil structure, and it is concluded that any general theory of hysteresis must recognize both the macrostructure and microstructure of a soil.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01667.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY