Journal
JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE
Volume 169, Issue 2, Pages 157-167Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/jpln.200521791
Keywords
soil organic matter; macromolecular; supramolecular; structural relaxation; physical aging; glass transition
Categories
Ask authors/readers for more resources
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 T-9* 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.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available