Page 155 - E-BOOK English

The representatives of Vertisols in Thailand

Chromic Vertisols

Chromic Vertisols have a Munsell colour hue

redder than 7.5YR and a chroma of > 4, both moist,

between 25 and 150 cm of the surface soil a layer,
≥ 30 cm thick, that has, in ≥ 90% of its exposed area,

Chong Khae series (Ck) is a representative

of Chromic Vertisols. Chong Khae soils are formed
from alluvium which high in montmorillonitic clays.

They occur on alluvial plain or along the boundary
between terraces and the recent alluvial plain which

have limestone nearby, mainly in Central plain of
Thailand. Relief is flat, but ‘gilgai’ microrelief occurs

where the soils are not cultivated. Slope is about 0
to 1 percent. Drainage is poorly drained. Runoff and permeability are slow.

They are very deep, strongly to medium acidic soils and characterized by
a dark gray or dark grayish brown clay A horizon, overlying a grayish brown,

light brownish gray or gray clay B horizon. Distinct, very fine reddish mottles
occur throughout the profile. Many pressures face and slickensides occur

in the B horizon. Crack at least 1 cm or more wide at 50 cm depth from
the surface soil occurs during the dry season. Reaction is strongly acid to

moderately acid (pH 5.5-6.0). These soils are flooded by impounded
rainwater or river to depths of 30-40 cm for three to four months during

the wet season. Sometimes this area is flooded by irrigation. However, these
soils also dry out deeply with groundwater level falling below 2 m during

the peak of the dry season when deep wide cracks.

153