Northeast Thailand, the selected study site covering an area of
approximately 170,000 sq km. lies between 14° 14´ to 18° 27´ North
latitude and 101° 0´ and 105° 35´ East longitude (Figure 1.).
Geologically, the most extensive area are formed by a thick sequence of
Mesozoic sediment, the Korat group ranging in age from upper Triassic
to Tertiary. The region is bound by the prominent topography or low
hill on the west and the south. The flat to gently undulating alluvial
plains are formed in the north and south of the region and is divided by
the Phu Phan Range into 2 basins, Sakon Nakhon in the North and
Korat basin in the south. These two basins are underlain by the Maha
Sarakham geologic Formation. Mean annual rainfall averages 1200
mm. in the south east and 1800 mm. in the Northeast of the region.
Land use is restricted to rice, field crops (cassava & sugar cane) and
forest. The scattered trees and isolated patches of remnant forest can be found on the gently
undulating topography of the alluvial plains. The dense forest, mainly Dipterocarp sp and Evergreen
sp covers extensively on the mountainous area and sloping land mostly the National Parks and
Wildlife Sanctuaries. Soils are inherently low in fertility and have light texture with low cation
exchange capacity.