Page 80 - E-BOOK English

The representatives of Gleysols in Thailand

Thionic Gleysols

Thionic Gleysols have a thionic horizon
starting ≤ 100 cm from the surface soil.

Rangsit series (Rs) is a representative of
Thionic Gleysols. Rangsit soils are formed from
marine sediments mixed with riverine alluvium under
brackish water influence. They occur in former tidal
flats or alluvial plain which grade down to marine

deposits and now free of tidal flooding which has
been in cultivation for some time. Most of soils
are found in southeast of Central plain. Relief is

flat. Slope is about 0-1 percent. They are deep,
extremely acidic soils, and characterized by a black or
very dark gray clay A horizon overlying a brown, grayish
brown or dark grayish brown clay B horizon, which
in turn overlies a dark gray reduced clay C horizon

with an upper boundary approximately 150 cm from
the surface soil. These soils are mottled throughout
with yellowish brown mottles as coatings along root

channels in the A horizon and red, yellowish
red mottles in the B horizon. The yellow jarosite
mottles occur approximately between 50-100 cm of the
surface soil and also are the diagnostic criteria for the
soil series. Slickensides and pressure faces occur in the

B horizon and the soil cracks at the surface when dry.
Soil constraints include acidity, Al and Fe toxicity, as
well as, acute P deficiency deficient. So that should

be groundwater control for the oxidation of pyrite.
For rice cultivation, the suitable soil pH is at 5.5-6.0.
To create favorable soil condition, applications of 2
-1
tons rai of marl with chemical fertilizer (in case of
pH <4.5) or phosphate rock with chemical fertilizer

(in case of pH >4.5) are needed.

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