of Ban Don Bay and Phangnga Bay, Thailand - WorldFish Center

oxidized layers. The lower part of the profile, the C-horizon, is always saturated with water which
results in bluish color or strong graying condition. The soils are alkaline (ph 7-8) in reaction and
are generally moderately fertile and high in organic matter content. Mudballs are almost always
observed.
Disturbed mangrove soils along Phangnga Estuary occurred as a result of tin mining. But
these soils were colonized by nipah palm after being abandoned as mines.
Soils developed on beach ridges or dunes normally have a predominant sandy texture
and form long narrow strips parallel to existing shoreline. They are classified as Tropohumods
and Quartzipsamments. Most have been used for cultivation of coconuts. However, the former
is less desirable due to severe limitation in root zones.
Lowland soils
Most of the lowland soils are cultivated for paddy rice. They may be developed on
brackish deposits or riverine alluvium. Internal drainage is poor and commonly flooded in the
rainy season.
The acid sufate soils (unit 2.1) form on brackishwater deposits with relatively high sulfur
content. They are extremely acidic in reaction and are classified as Acid Tropaquepts. Rice yield
commonly depends upon the degree of acidification and management level.
Most of the loamy soils (unit 2.2) occupy the lower part of alluvial terraces or transitional
sites between terraces and coastal lowland. These soils are commonly classified into
Plinthaquults and Paleaquults. The former have dark red mottles usually in platy, polygonal or
reticulate pattern; the latter do not have these. Loamy soils are exclusively used for paddy rice.
Average yield under ordinary management ranges from 1,560-2,190 kglha.
The clayey soils (unit 2.3) occupy the basin of large rivers or former tidal flats. They
include Tropaquepts and Paleaquults and most have been cultivated for paddy rice, with yield
somewhat higher than that of loamy soils.
Upland soils
These commonly occur on undulating to rolling topography with slopes ranging from 3%-
35%. Their parent materials vary from old alluvium to transported material derived from various
rocks. Areas where these types of soils occur are generally cleared of natural vegetation and
cultivated primarily for rubber, fruit trees, oil palm and, to a lesser extent, annual upland crops
such as maize, ground nuts and cassava. However, parts of the area are left idle and revert to a
low secondary vegetation consisting of low shrubs, canes, bamboos and grasses, especially
lmperata cylindrica. Upland soils are subdivided into the following units:
The deep to moderately deep loamy soils (unit 3.1) comprise those in groups
Paleudults, Tropudults and Plinthudults which are moderately to well-drained and have rapid to
moderate runoff. The natural fertility is relatively low. Lateritic gravels may occur in the lower
subsoils.
The deep to moderately deep clayey soils (unit 3.2) belong only to Paleudults. Their
characteristics are similar to those described in unit 3.1 except that the former have more clay
content in subsoils.
The shallow soils (unit 3.3) comprise those containing lateritic gravels or rock
fragments throughout the soil profiles. Those containing lateritic gravels can be classified into
Paleudults; otherwise, they can be into Tropudults or Troporthents. In general, these soils are
cultivated for rubber but parts are left idle and commonly revert to a type of low shrubs and
grassy undergrowth.