DBPapers
DOI: 10.5593/SGEM2016/B32/S13.041

SOIL CRUSTING UNDER MICROSCOPE

A. Eftene, S. Dumitru, D. Raducu
Wednesday 7 September 2016 by Libadmin2016

References: 16th International Multidisciplinary Scientific GeoConference SGEM 2016, www.sgem.org, SGEM2016 Conference Proceedings, ISBN 978-619-7105-62-9 / ISSN 1314-2704, June 28 - July 6, 2016, Book3 Vol. 2, 311-318 pp

ABSTRACT
One of the processes that seal the soil is crusting. The succession of many rainfall events during a year periodically changes the top structure and seal the soil surface. Soil sealing by crusting induced radical changes in the top soil conditions as the reorganization of soil constituents, collapse and redistribution of pore system that deeply change the gaze content and biochemistry, and consequently the soil life environment.
The paper aimed to the results of a micromorphological study of a sealed clayey-loam Argic Chernozem formed in loess like deposits. The soil was sealed either in June or in July under the rainfall impact, thus crust and sub-crust soil were sampled in both month (June and July) for physical, chemical, mineralogical and micromorphological analysis.
The data of the micromorphological study emphasized that in June a 6 mm crust formed. The degree of the aggregates breakdown (under the raindrop impact) was moderate, whereas the aggregates that kept their integrity appear imbedded in a matrix riche in skeleton grains and vesicular pores (with entrapped air). The rare vughy packing voids (of compaction) are also present. The plasmic material resulted from the aggregate collapse was locally reorganized and illuviated at 1 cm below the crust, generating coatings and concentrations into the poral space. The structure of the crust and its granulometry emphasized that very low material was leached from the crust zone and no runoff occurred. In July, a 6 - 8 mm dens structural crust was formed. The vesicular porosity was lower that in the June crust, while the destruction of aggregates was higher. The sorting degree of the soil material was also higher, thus a succession of the coarser (rich in skeleton grains) and the finer (rich in plasma) layers formed. In the poral space, located under the crust, textural sorted material was leached at the beginning of the rainfall. The crust micromorphology showed an important runoff. The mineralogical data (of both June and July crusts) showed a difference at the colloidal level, between the crust and the underlined soil, due to a lower content of illite and a higher content of smectite (in the crust).
After the soil sealing, two main processes are involved in soil structural auto-remediation, which succeed each other or take place simultaneously: a physico-mechanical process of creaking; a biological activity which generated channels in the crust that favor gas exchange between soil and atmosphere and also coprolites (the alive and high quality soil aggregates) that substitute the collapsed structural aggregates.

Keywords: soil crusting, micromorphology, auto-remediation

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