Page 89 - E-BOOK English

Histosols

Definition

Histosols are developed by the deposition and accumulation of organic materials from
the surface with a depth of at least 10 cm overlying ice shelf, hard rock, or organic matter-rich
coarse fragments within 40 cm If these organic materials are found within 100 cm from the

surface soil, they are expected to have a depth of at least 60 cm of moss and that of at least
40 cm for other organic materials.

Distribution

Histosols cover worldwide approximately 2,031-2,343 million rais in temperate regions
and cold mountainous areas. In the tropics, the areas of these soils are only about 1/10 of the
total.

In Thailand, the estimated total area of Histosols is 481,580 rais, mostly distributing in
the south of Thailand or Peninsular Thailand. Other minor distributions cover on the east coast,
where the largest area of Histosols located in Narathiwat on the east side of the province along
the coast.

Formation

The formation processes are initially deposition and accumulation of organic materials
to create a histic horizon. These organic materials are mostly derived from aquatic plants or

those plants in high humidity areas. The histic horizon is developed from the lower part and
becomes thicker. The degree of decomposition of the organic soil material is various and
controlled by temperature and waterlogging. With various degrees of decomposition, the
organic materials are found with partially complete decomposition or with some parts of slow
decomposition, which together develop an organic complex with higher stability, called humus.

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