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 ranges
1200 in the south east and 1800 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 undulation 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.