STUDY AREA
Udon Thani province (Fig 1) selected as a target area of the study
is situated between latitude 16° 48' - 18º 5' 24" N and longitude 102º 0'
36" - 103º 21' 21" E covering a total area of approximately 11,730,302
sq km.(Office of National Statistics, 2000). General topography is
characterized by gentry undulating terrain with prominent mountain
ranges. Mountainous area of the adjacent province lies in the western
border. The province receives the average annual rainfall of 1,400-1,600
mm. Rainfall intensity in the southwest is lower than the area situated in
the northeast region of the province. It was found that the soils
occupying lowland and upland area were 29.16% and 58.57% of the
study area respectively. Based on Landsat satellite data in 2002, it
appeared that most of the area was used for paddy cultivation followed
by upland crops with the growing areas of 15.37% and 19.02% of the
study area.