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Monday, 19 December 2011

BLACK COTTON SOIL


     Vertisols owe their specific properties to the presence of swelling clay minerals,
mainly montmorillonite. As a result of the wetting and drying, massive expansion
and contraction of the clay minerals takes place. Contraction leads to the formation of
the wide and deep cracks. These cracks can be wide enough to make the terrain
treacherous for animals. Surface material accumulates in these cracks during the dry
season and is “swallowed” by the soil in the wet season, creating the ‘self mixing’ or
‘self mulching’ action of the vertisols.
The cracks close after rain when the clay minerals swell. During expansion of the
clay minerals high pressures are developed within these soils, causing a characteristic
soil structure with wedge shaped aggregates in the surface soil and ‘planar’ soil
blocks in the subsoil. The slippage of one soil block over the other leads to the
formation of typical polished surfaces known as “slickensides’ on the blocks’



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