Abstract:
Fourteen soil-geomorphic units have been delineated from the
Gangetic plains between the Ramganga and Rapti rivers. The units
delineated are based on remote sensing studies and field checks.
One additional unit immediately east of the study area, described
earlier by Mohindra et al. (in press), and named here as the
Lower Deoha/Ganga-Ghaghra unit also has been included. On the
basis of degree of soil profile development, these units have
been grouped into five members (QGH1 to QGH5, QGH5 being the
oldest) of a soil chronoassociation. The member QGH1 (age < 500
yrs. B.P.) includes soils of floodplains of the Ghaghra and
Rapti, Kosi-Gola Piedmont, Gholia-Dhobania-Bhambhar Piedmont and
Young Sihali-Mohan-Kandra Piedmont. QGH2 member (age > 500 yrs.
B.P.) comprises soils of the Upper Kosi-Gola Plain, Old Ghaghra
Plain and Old Sihali-Mohan-Kandra Piedmont. Soils of the Lower
Kosi-Gola° Plain, Upper Rapti-Ghaghra Interfluve, Upper
Deoha/Ganga-Ghaghra Interfluve and Old Ghaghra Bar are included
in QGH3 member (age > 2500 yrs. B.P.). The QGH4 member (age >
6500 yrs. B.P.) includes soils of the Lower Deoha/Ganga-Ghaghra
Interfluve. Soils Of the Middle Deoha/Ganga-Ghaghra Interfluve
and Lower Rapti-Ghaghra Interfluve are included in the QGH5
member (age 9000 to 11000 yrs. B.P.).
Pedological studies suggest that conditions favourable for
formation of pedogenic calcrete in the Gangetic Plains prevailed
from 11000 to 6500 yrs. B.P. Amelioration of climate and improved
drainage resulted in large scale to complete removal of calcrete
from soil profile in some areas or its dissolution and
reprecipitation in lower horizons in other areas.
Neotectonics seems to have played a significant role in
evolution of morphology and soils of the study area. It
determined areas of active sedimentation and pedogenesis (in
upland areas). It led to tilting and sagging of large blocks.
Tectonic slopes/faults determined direction of courses of large
rivers.
