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Thailand Land Use and Soils
Roughly two-fifths of Thailand is covered by mountains and
hills, the steepness of which generally precludes cultivation.
Nevertheless, perhaps as much as a tenth of this area might also
be converted to agricultural purposes once detailed information
was obtained through surveys. Estimates in the 1970s of overall
land-use suitability classified roughly 58 percent of mountainous
and hilly regions as cultivable (compared with 24 percent 2
decades earlier), of which about 19 percent was usable for paddy,
28 percent for upland crops, and 11 percent for both paddy and
upland agriculture. Actual holdings of agricultural land--not all
of which was under cultivation at any one time--were estimated in
the mid-1970s to occupy about 43 percent of the total land area.
Soils throughout most of the country are of low fertility,
largely as a result of leaching by heavy rainfall. Differences
between the various soil types are the result of differences in
parent rock material, variations in the amount of rainfall,
length of wet and dry seasons, type of vegetable cover, and other
natural factors. In general, stony and shallow soils characterize
the hill and mountain terrain of the North.
Large portions of this mountainous area were traditionally used
by hill peoples for
shifting cultivation (see Glossary). The Lua
(also called Lawa) and Karen cultivated for short periods, then
permitted the land to lie fallow for long periods, which allowed
forest regrowth and restoration of soil fertility
(see
The Non-Tai Minorities
, ch. 2). As a result of population pressures,
however, other groups sometimes failed to follow this practice.
The principle crop of many hill peoples was upland rice; maize
was an important secondary crop. The Hmong, Lisu, and certain
other hill peoples cultivated the opium poppy as a cash crop ,
but this activity had important implications for internal
stability as well as major international repercussions
(see
Criminal Activity and the Narcotics Trade
, ch. 5). Thai
authorities, with substantial international assistance, increased
efforts in the 1980s to redirect these people to other cash
crops, including tobacco and coffee.
Many inhabitants of the lowlands in the North also practiced
shifting cultivation in hill areas lying not far above the
valleys. The valleys usually had better soils, some of fairly
high or moderate fertility, which were used mainly to grow
irrigated rice. In places where population pressures had
developed, the higher areas were often turned to shifting
cultivation to supplement lowland production. The principal crop
was usually upland rice, although other crops were also grown.
Shallow sandy loams cover a large part of the Khorat Plateau.
Their generally low fertility partly explains the lower economic
level of the region. Soils along the main rivers are more
fertile, and alluvial loams of high fertility are found along the
Mekong River. Lowland soils covering about a fifth of the
Northeast (some 3.5 million hectares) had been converted to rice
paddy.
The central plain rice-growing area and the delta of the Mae
Nam (river) Chao Phraya has clayey soils of high to moderate
fertility. Low-lying and flat, much of the area is flooded during
the rainy season. Higher areas on the edges of the plain are
generally well-drained soils of high to moderate fertility that
are suitable for intensive cultivation. These lands are used
extensively for maize and sugarcane. Among other highly useful
soils are the well-drained clayey and loamy soils in parts of the
peninsula where rubber is grown.
Data as of September 1987
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