Soil–landform Relationship and Pedogenesis of Flood Plain Soils of Mahananda Sub-basin, Bihar

Abstract

Alluvial flood plain soils are one of the major soil groups in northern Bihar and are highly heterogeneous
as a result of the hydromorphic environment in which they are formed. Hence, the present investigation
was carried out to understand the soil-landform relationship in Katihar district of Bihar. Five major landforms
like old alluvial plains (1.97%), young alluvial plains (35.64%), meander plains (30.85%), flood plains
(25.35%) and, char land and point (4.5%) were identified after visual interpretation of Sentinel-2 data in
conjunction with survey of India toposheet and digital elevation model (SRT DEM). The detailed soil
survey was carried out to understand the variability in the study area and 200 soil profiles were studied in
different identified landforms. The soils of active alluvial plain (flood plain, char land and point bar)
showed wide range of soil morphological properties with lithological discontinuities. Low chroma and
value in soils of meander plain due to poor drainage conditions and high groundwater table showed gleying
characteristics. The soils of young alluvial plain and active alluvial plain showed irregular distribution of
clay content, cation exchange capacity (CEC) and organic carbon (OC). This study indicates that the soillandform
relationship in alluvial floodplains of Mahananda sub-basin partially followed due to mass
movement of sediments from Himalayas, periodic flooding and deposition of alluvium during different
fluvial cycles of Mahananda river and its tributaries. This was further confirmed by study on pedogenic
indices of different landforms. The study on pedogenic indices in two selected sites (window area) away
from the Mahananda river like fine sand/total sand, very fine sand/total sand, sand/silt, silt/clay, index of
weathering and CEC/clay in the study area doesn’t follow the trend in the flood plain as compared to nearly
stable land. This may be due to the effect of shifting of river course and their tributaries in the selected two
window areas across the different landforms. To overcome the above mentioned problems in soil-landform
relationship in the study area, the identified landforms were further sub-divided based on the local factors
like percentage of crop cover and moisture content. In revised landforms soil types present in each landform
showed soil-landform relationship. Thus, the knowledge on soils in relation to landforms vis-à-vis soil
properties and their pedogenesis is useful in understanding their potentials and problems for sustainable
land use planning.