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  • Journal of Plant Nutrition and Soil Science
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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: English
    In: Journal of Plant Nutrition and Soil Science, April 2014, Vol.177(2), pp.141-149
    Description: The objective of this study was to investigate the effects of mono‐ and polyvalent cations on sorption of the two hydrophobic compounds nonylphenol (NP) and phenanthrene (Phe). To this end, exchange sites of a sandy soil were saturated with either Na, Ca, or Al and excess salts were removed by washing. The samples were then sterilized and either stored moist, dried at room temperature, or at 20°C, 60°C, or 105°C in a vented oven. Saturation with Na led to an increase of dissolved organic C (DOC) concentration in the soil water extracts, whereas the polyvalent cations Ca and Al decreased it. The H‐NMR relaxometry analyses showed that Al restricted the mobility of water molecules that are confined within the SOM structure to a higher extent than Ca or Na. According to contact‐angle (CA) analyses, cation treatment did not significantly change the wetting properties of the samples. Batch sorption–desorption experiments showed no clear salt‐treatment effects on the sorption and desorption equilibria or kinetics of NP and Phe. Instead, the sorption coefficients and sorption hysteresis of NP and Phe increased in dry soil. With increasing drying temperature the CA of the soils and the sorption of both xenobiotics increased significantly. We conclude that structural modifications of SOM due to incorporation of polyvalent cations into the interphase structure do not modify the sorption characteristics of the soil for hydrophobic compounds. Instead, increasing hydrophobization of organic soil constituents due to heat treatment significantly increased the accessible sorption sites for nonpolar organic compounds in this soil.
    Keywords: Soil Organic Matter ; Sodium ; Calcium ; Aluminum ; Contact Angle ; Wettability ; Relaxation Time
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 3
    Language: English
    In: Journal of Plant Nutrition and Soil Science, April 2006, Vol.169(2), pp.157-167
    Description: Glassy, rubbery, and crystalline phases are representatives of supramolecular structures which strongly differ in order, density, and other characteristics. In this contribution, the amorphous nature of soil organic matter (SOM) is reviewed with respect to the glassy/rubbery model, glass transition mechanisms, interactions of SOM with water, and physical aging. Glass‐transition behavior and physical aging are inherent properties of amorphous solids, and numerous spectroscopic investigations give insights into different domain mobilities of humic substances (HS). The correlation between sorption nonlinearity and glassiness of polymers and HS supports a relation between sorption and amorphicity in Aldrich humic acid. Further evidence is still required for the transfer to soil HS and SOM. Sorption and differential scanning calorimetry (DSC) data suggest a correlation between aromaticity and glassiness in HS, and the available data do currently not allow to decide unambiguously between specific sorption and hole filling as explanation. This needs to be verified in future research. Although parts of the investigations have up to now only been conducted with humic substances, the collectivity of available data give strong support for the glassy/rubbery conception of SOM. They clearly indicate that amorphous characteristics cannot be excluded in SOM. This is further supported by the observation of different types of glass‐transition behavior in samples of whole humous soil. In addition to classical glass transitions in water‐free soil samples, water surprisingly acts in an antagonistic way as short‐term plasticizer and long‐term antiplasticizer in a second, nonclassical transition type. Latter is closely connected with physico‐chemical interactions with water and suggests water bridges between structural elements of SOM (HBCL‐model). The gradual increase of * in SOM indicates physico‐chemical aging processes, which are not restricted to polymers. They may be responsible for contaminant aging, changes in surface properties and increased soil compaction in agricultural soils.
    Keywords: Soil Organic Matter ; Macromolecular ; Supramolecular ; Structural Relaxation ; Physical Aging ; Glass Transition
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 4
    Language: English
    In: Journal of Plant Nutrition and Soil Science, April 2006, Vol.169(2), pp.145-156
    Description: This contribution reviews and discusses structural aspects of soil organic matter (SOM) and humic substances (HS) with special respect to the macromolecular and the supramolecular view. It can be concluded that (1) dissolved humic acids behave as supramolecular associations of relatively small molecules with an enormous flexibility of reaction of environmental conditions, (2) multivalent cations may increase the apparent molecular weight by the formation of coordinative crosslinks in dissolved and undissolved natural organic matter (NOM), (3) sorption nonlinearity in solid humic acids and SOM may be due to polymer properties of NOM, (4) sorbates affect sorbent characteristics of SOM, and (5) hysteresis and conditioning effects in SOM can up to now best be explained with the polymer analogy. A distinct polydispersivity of SOM over a wide range of molecular masses is to be assumed. The supramolecular and the macromolecular models were derived from humic acids with different composition and on the basis of different sample states. Although the supramolecular model has not explicitely been shown for unfractionated DOM, the combination of all discussed studies suggests supramolecular as well as macromolecular characteristics of NOM. Neither macromolecules nor small molecules can be fully excluded in solid and dissolved SOM. Microregions with different properties provide different types of sorption sites. SOM is suggested to be regarded as amorphous material. This point of view is not restricted to high molecular masses and may supplement our understanding of SOM by the model of physical aging.
    Keywords: Soil Organic Matter ; Macromolecular ; Supramolecular ; Structural Relaxation ; Physical Aging ; Glass Transition
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 5
    Language: English
    In: Journal of Plant Nutrition and Soil Science, October 2000, Vol.163(5), pp.523-529
    Description: The dissolution of organic matter in soil is of fundamental relevance for the fate of organic contaminants associated with organic matter and for the microbial availability of organic matter. In this study, the kinetics of soil organic matter (SOM) dissolution from a sandy forest soil was investigated under different electrolyte conditions, using a continuous extraction method. The mathematical analysis of the concentration signal obtained from extractions with constant flow rates and after sudden flow rate changes showed that the dissolution of SOM is diffusion limited. The dissolution rate was lower during extraction with 0.01 M CaCl. The reaction on sudden flow rate changes was slower when extracting with 0.01 M CaCl as compared to water, and the mechanism was different. These observations were explained by a gel phase developing in the swelling SOM. The lower dissolution rates found for extractions with 0.01 M CaCl could indicate a more stable gel structure in the presence Ca. The development of the gel phase may be influenced by mechanical strain due to increased flow rates. Einfluss von CaCl auf die Freisetzungskinetik von gelösten organischen Substanzen aus einem sandigen Boden Die Auflösung organischer Substanzen im Boden ist von grundlegender Bedeutung für ihre Bioverfügbarkeit und für das Verhalten organischer Schadstoffe, die an die organische Substanz gebunden sind. In dieser Studie wurde die Kinetik der Auflösung organischer Substanzen unter verschiedenen Elektrolytregimen mit Hilfe einer kontinuierlichen Extraktionsmethode untersucht. Die mathematische Analyse der Konzentrations‐Zeit‐Verläufe bei Extraktionen mit konstanter Flussrate und nach plötzlichen Flussänderungen zeigten, dass die Freisetzung der organischen Substanzen diffusionskontrolliert war. Die Freisetzungsrate war geringer, wenn mit 0.01 M CaCl extrahiert wurde. Im Vergleich zu Extraktionen mit Wasser waren die Reaktionen auf plötzliche Flussveränderungen bei Extraktionen mit 0.01 M CaCl deutlich langsamer. Sie unterschieden sich auch im Mechanismus. Diese Beobachtungen wurden durch die Bildung einer Gelphase in der quellenden organischen Bodensubstanz erklärt. Die geringeren Freisetzungsraten bei 0.01 M CaCl könnten auf eine stabilere Gelstruktur in der Anwesenheit von Ca‐Ionen hinweisen. Die Gelbildung könnte durch mechanische Belastungen, wie z.B. hohe Flussraten beeinflusst werden.
    Keywords: Soil Organic Matter ; Dissolved Organic Matter ; Colloids ; Gel ; Kinetics ; Electrolyte Effect
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 6
    Language: English
    In: Journal of Plant Nutrition and Soil Science, 04/2000, Vol.163(2), pp.179-181
    ISSN: 1436-8730
    E-ISSN: 1522-2624
    Source: Wiley (via CrossRef)
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  • 7
    Language: English
    In: Journal of Plant Nutrition and Soil Science, April 2000, Vol.163(2), pp.179-181
    Description: Glass transitions have been reported for purified humic acids only. In this study, a glass transition was detected in a sample of a sandy forest soil by Differential Scanning Calorimetry (DSC). The glass transition temperature was 79°C for air‐dried samples and 77°C for pre‐moistened samples. In addition to the glass transition, an exothermic process around 30°C was detected in pre‐moistened samples. This could be due to water loss of soil organic matter. However, the nature of this process is not yet understood. This study showed that the macromolecular behaviour of SOM, as indicated by DSC, reacts to the moisture state of soil organic matter. Thermische Eigenschaften der organischen Bodensubstanz mittels DSC‐Messung: Ein Hinweis auf einen Glas‐Übergang Glasübergänge konnten bislang nur in gereinigten Huminsäuren nachgewiesen werden. In dieser Studie wurde mittels Differential Scanning Kalorimetrie (DSC) ein Glasübergang in Proben von unterschiedlich vorbehandeltem Boden entdeckt. Die Glasübergangstemperatur betrug 79°C bei der luftgetrockneten und 77°C bei der befeuchteten Probe. Zusätzlich zum Glasübergang wurde in befeuchteten Proben ein exothermer Prozess um 30°C beobachtet. Die Natur dieses Prozesses ist noch ungeklärt. Der Vorgang könnte durch Wasserverlust der Humussubstanzen erklärt werden. Diese Untersuchung zeigt, dass das durch die DSC angezeigte makromolekulare Verhalten der organischen Bodensubstanz auf den Feuchtezustand der organischen Bodensubstanz reagiert.
    Keywords: Soil Organic Matter ; Colloids ; Dsc ; Swelling ; Glass Transition
    ISSN: 1436-8730
    E-ISSN: 1522-2624
    Source: John Wiley & Sons, Inc.
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  • 8
    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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  • 9
    Language: English
    In: Journal of Plant Nutrition and Soil Science, August 2015, Vol.178(4), pp.641-648
    Description: Olive oil production generates large amounts of olive mill wastewater (OMW). OMW has a high nutrient content and could serve as fertilizer, but its fatty and phenolic constituents induce soil water repellency, phytotoxicity, and acidification. An appropriate season of OMW application may mitigate negative consequences while preserving beneficial effects. In order to investigate this, a field study was conducted, in which OMW was applied to an olive orchard in Israel either in winter or summer. Soil–water interactions (water drop penetration time, hydraulic conductivity), soil physicochemical parameters, phenolic compounds, and soil biological activity (bait‐lamina test) were determined 12 to 18 months after OMW application. The results showed elevated K contents in all treatments, but all other soil properties of winter treatments were comparable to the control, which suggested a certain recovery potential of the soil when OMW is applied in winter. By contrast, summer treatments revealed a ten‐fold higher soil water repellency, a three‐times lower biological activity, and a four‐fold higher content of phenolic compounds, independently of whether the soil was kept moist by irrigation or not. Thus, the OMW constituents were neither degraded nor leached by winter rain when applied during the hot season. Further research is needed to distinguish leaching and biodegradation effects, and to understand the development of the composition and degradation kinetics of organic OMW constituents.
    Keywords: Water Re‐Use ; Biodegradation ; Bait‐Lamina Test ; Soil Water Repellency ; Phenolic Compounds ; Waste Water
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 10
    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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