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  • 1
    Language: English
    In: Journal of Plant Nutrition and Soil Science, August 2018, Vol.181(4), pp.586-599
    Description: The presence and mutual interactions of soil organic matter (SOM) and clay particles are major factors determining soil structural stability. In the scope of agricultural management and environmental sustainability, it remains unclear how various mineral and organic matter (OM) fractions, OM–clay interactions and swelling processes in the interparticle space determine soil–water interactions and thus soil structural stability. To investigate this issue, we isolated the mineral and OM fractions of an agriculturally cultivated silty loam soil by soil density fractionation and assessed their hydration characteristics and effects on soil structural stability combining H‐NMR relaxometry, soil rheology and single wet‐sieving of soil aggregates. The results showed that agricultural management practices, in particular compost and ploughing, as well as various OM–clay interactions significantly affected soil–water interactions and soil structural stability. On the one hand, ploughing reduced soil structural stability by promoting clay swelling as a result of disrupted soil structures and reduced SOM content. On the other hand, compost treatment and reduced tillage increased soil structural stability. In all cases, soil density fractionation showed that compost‐derived particulate organic matter (POM) and mineral‐associated organic matter (MAOM) restricted clay swelling and resulted in a highly porous and mechanically stable soil matrix. In particular, POM increased soil structural stability by acting as nucleus for soil aggregation and by restricting clay swelling its presence as solid, granular interparticulate material. In contrast, MAOM seemed to restrict clay swelling clay surface covering and the formation of viscous interparticulate hydrogel structures.
    Keywords: Density Fractionation ; Gel Effect ; Nmr Relaxometry ; Rheology ; Wet‐Sieving
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 2
    Language: German
    In: CHEMKON, July 2014, Vol.21(3), pp.135-137
    Description: To purchase or authenticate to the full-text of this article, please visit this link: http://onlinelibrary.wiley.com/doi/10.1002/ckon.201410228/abstract Byline: Christopher Jahnel, Gabriele E. Schaumann, Bjorn Risch Keywords: Modellexperiment; Tenside; Umwelt ***** No abstract is available for this article. ***** Author Affiliation: Universitat Koblenz-Landau, Campus Landau, Institut fur Umweltwissenschaften, AG Umwelt- und Bodenchemie, Fortstr. 7, 76829 Landau Universitat Koblenz-Landau, Campus Landau, Institut fur naturwissenschaftliche Bildung, AG Chemiedidaktik, Fortstra[sz]e 7, 76829 Landau
    Keywords: Modellexperiment ; Tenside ; Umwelt
    ISSN: 0944-5846
    E-ISSN: 1521-3730
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  • 3
    Language: English
    In: Journal of Plant Nutrition and Soil Science, June 2018, Vol.181(3), pp.441-452
    Description: A soil's cation exchange capacity (CEC) is expected to be relatively inert against changes in cation loading. In this study, we treated a soil sample originating from the organic layer of a forest soil with various bivalent cations after removing the native cations. Sorption isotherms and cation exchange capacity were determined, the latter using the BaCl method. Sorption showed Langmuir characteristics, with the maximum coverage () increasing in the order Ba 〈 Ca 〈 Mg, but being clearly smaller than the initial load of native exchangeable cations. The Langmuir coefficient, , depended oppositely to the order obtained for . CEC increased upon cation treatment and it varied by a factor of almost two. The unexpected variation of CEC was explained by the low cation exchange capacity of the organic matter such that not all functional groups are close enough to be bridged and the second charge of a bivalent cation is not neutralized by the organic functional group. The Langmuir sorption type, and being smaller than the content of sorption sites and being largest for Mg, suggested that only a part of the sites can be cross‐linked and at least part of the cross‐links are formed by hydrated cations. Thermodynamic considerations allowed reconstruction of two contrasting processes during CEC determination by Ba: : the disruption of cross‐links, which increases with the cationic strength and the cation load before CEC determination, but does not require structural re‐orientation in the SOM matrix, and the formation of new cross‐links during CEC determination, depending only on the content of unoccupied sites before CEC determination and requiring structural re‐organization of the matrix and thus a minimum matrix flexibility. The use of bivalent cations for CEC determination may thus result in an overestimation of CEC for organic matter with low CEC. This has, however, promising potential when comparing CEC determined with monovalent cations and bivalent cations. Using a set of bivalent cations, may allow probing distribution of distances between functional groups in the organic matter and even characterize the matrix rigidity of the cation‐cross‐linked network.
    Keywords: Bivalent Cations ; Cation Exchange Capacity ; Cross‐Linking ; Langmuir ; Soil Organic Matter ; Sorption
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 4
    Language: English
    In: Journal of Plant Nutrition and Soil Science, June 2018, Vol.181(3), pp.453-461
    Description: Two previous studies suggested that part of the cation sorption sites in soil organic matter with low exchange capacity have to be considered as “lonely”, ., too far from each other to allow direct cross‐linking by bivalent cations. The objective of this contribution was to understand the mechanisms controlling structural rigidity and physicochemical aging of the SOM (soil organic matter) and the role of water molecule bridges (WaMB) therein. For this, we evaluated the matrix rigidity of an organic surface layer of a Haplic Podzol on a quantitative basis, by assessing WaMB transition temperature () directly after treatment with bivalent cations (Mg, Ca, or Ba) and after eight weeks of aging. Cation loading as well as cation type influenced matrix rigidity. Ba induced the most rigid matrix and Mg the weakest, which is in line with their binding strength in terms of Langmuir coefficient. The matrix rigidity increased with the cross‐linking activity, which is the product of loading and Langmuir constant of the respective cation. The aging process, however, was slowed down by the initial matrix rigidity, and the rigidity of the aged matrix decreased with increasing Langmuir constant. The degree of aging increased with increasing hydration enthalpy of the cation and decreased with increasing cation loading. Thus, directly after cation treatment, direct cross‐links by multivalent cations were most relevant, but WaMB increasingly gained influence on the matrix rigidity during aging. The untreated sample revealed a considerable number of WaMB, resulting in a fairly rigid and strongly cross‐linked matrix which, however, flexibly reacts on external influences like change in cation concentration or relative humidity. With these findings, the ideas on the relevance of indirect CaB‐WaMB associations between distant sorption sites for the rigidity and flexibility of the OM matrix as proposed in previous studies were confirmed on a mechanistic basis in this study.
    Keywords: Aging ; Cation Bridges ; Cross‐Linking ; Soil Organic Matter ; Water Molecule Bridges
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 5
    Language: German
    Description: Techn. Universiẗat, Habil.-Schr., 2006--Berlin.
    Source: Networked Digital Library of Theses and Dissertations
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