SOIL CRUSTING UNDER MICROSCOPE

• Published in: International Multidisciplinary Scientific GeoConference : SGEM Vol. 2; pp. 311 - 317
• Main Authors: Eftene, Alina, Dumitru, Sorina, Raducu, Daniela
• Format: Conference Proceeding
• Language: English
• Published: Sofia Surveying Geology & Mining Ecology Management (SGEM) 01.01.2016
• Subjects: Aggregates; Biochemistry; Biological activity; Channel pores; Collapse; Concretions; Crusts; Data processing; Ecological succession; Gas exchange; Gases; Grains; Granulometry; Illite; Illites; Leaching; Loam; Loam soils; Loess; Mineralogy; Morphology; Porosity; Rain; Raindrop impact; Rainfall; Rainfall impact; Runoff; Sealing; Smectites; Soil; Soil aggregates; Soil compaction; Soil conditions; Soil crusting; Soil erosion; Soil porosity; Soil remediation; Soil sciences; Soil structure; Soils; Voids; France
• ISSN: 1314-2704

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.