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  • Blackwell Science, Ltd  (2)
  • 1
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: We have sought to understand the molecular mechanisms by which dissolved organic matter (DOM) forms and soil organic matter (SOM) degrades in upland peaty gley soil under grass. Pyrolysis mass spectrometry (Py-MS) and pyrolysis gas chromatography mass spectrometry (Py-GC/MS) were applied to characterize the DOM collected from lysimeters and its parent SOM. The macromolecular organic matter in the litter and fermentation (Lf) horizon of the soil consists primarily of little decomposed lignocellulose from grass, whereas the humus (Oh) horizon is characterized by an accumulation of selectively decomposed lignocellulose material, microbial metabolites and bound fatty acids. The mineral horizon produced a relative enrichment of furan structures derived from microbial reworking of plant polysaccharides but virtually no lignin signals. A series of exceptional long chain C43 to C53 fatty acids with odd over even predominance, probably derived from mycobacteria, were also identified in the Oh horizon. Side-chain oxidation and shortening, increase of carboxyl functionality and selective removal of syringyl (S) 〉 guaiacyl (G) 〉 p-hydroxyphenyl (P) lignin units were the main reactions when lignin degraded. Compared with SOM, the DOM shows a large accumulation of more oxidized lignin and aromatic structures, especially those containing carboxylic and dicarboxylic acid functionalities and with shorter side-chain length. The polysaccharide-type compounds in the DOM were more modified (greater abundance of furan structures in pyrolysis products), and had significantly lower molecular weight and more diverse polymeric structures than did those in soils. Increased temperature and rainfall appeared to result in greater relative abundance of lignin degradation products and aromatic compounds in DOM.
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  • 2
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Compaction, tillage, stresses around growing roots and other soil deformation events may be predicted by the critical state model of soil mechanics, but estimating the parameters is time consuming and expensive. We develop a back analysis of the constant cell volume triaxial test, in which the critical state parameters are derived from the results of a single test. This both saves much labour and provides more information than traditional analyses, which require several triaxial compression tests and an isotropic compression test to yield the same information. The method finds, using a minimization algorithm and a quasi-analytical solution to the stress–strain equations, the simulated soil deformation (and hence the properties used in that simulation) that best fits the test data. The minimization is a form of regression analysis.For normally consolidated samples the method provides stable estimates of the slope of the critical state line (M), the slope of the virgin compression line (λ) and elastic modulus (E). The standard errors of the estimates are small in relation to the means of these parameters. The estimates appear to be more reliable than those of more commonly used estimation procedures. The slope of the rebound line (κ) is estimated, but a measure of the accuracy of the estimate cannot be calculated.
    Type of Medium: Electronic Resource
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