A Study of Soils with Redoximorphic Features in Lowland-Upland Transition Zone of Khorat Basin

Abstract

A study of soils with redoximorphic features in lowland-upland transition zone of Khorat Basin
was carried out on six representative areas for their morphology, physicochemical properties,
micromorphological and mineralogical characteristics to assess fertility level, fertility capability soil
classification and land suitability for economic crops. Results revealed that Khorat Basin has undulating
surface on an elevation range of 100-200 m MSL. All soils are highly developed having low fertility. They
developed on wash over residuum from sandstone, wash, alluvium, alluvium over residuum. Pedon 1 does
not have redoximorphic features. Pedons 2 and 3 show the features at a depth of 90 and 72 cm,

respectively. Pedons 4-6 show redoximorphic features starting from the soil surface. The soils are
Kandiustults, Kandiustalfs, Plinthaquults, Plinthaqualfs and Endoaqualfs. Bulk density of the soils ranges
from moderately low to moderately high (1.34-1.71 Mg m-3), field capacity at 41-72% by weight., permanent
wilting point at 40-61% by weight moisture content, available water capacity 3-10% by weight.
The soils pH are extremely acid to neutral (pH 4.04-6.76) and they have very low to moderately low
organic matter (0.67-13.46 g kg-1), very low total nitrogen (0-0.49 g kg-1), very low to high available
phosphorus (0.70-32.67 mg kg-1), very low available potassium (2.36-28.45 mg kg-1), moderately low to
moderate cation exchange capacity (1-11 cmol kg-1), very low to low total extractable bases (0.14-6.72
cmol kg-1), very low to moderate extractable acidity (0.25-4.99 cmol kg-1) and low to high base saturation
percentages (4-97 %). In clay fraction, all soils have mixed mineralogy. Micromorphologically, the features
indicative of redoximorphic feature are intrusive and impregnative in Pedons 2-6. The soils fertility
capability units include Ldakme, SLdakme, Lgakme, Lgkme. Pedons 1-2 are not suitable (N) for paddy
rice but marginally to moderately suitable (S3-sn to S2-sn) for growing upland crops and para rubber.
Pedons 3-6 that have aquic condition which are marginally to moderately suitable (S3-sn to S2-sn)
for paddy rice.