Characterization of some cracking clay soils of Rajmahal Trap in Sahibganj District, Jharkhand

Abstract

Two cracking clay soils of Rajmahal Trap viz., Jetkumarjari and Jirul Series were studied for their morphological, physical, chemical and mineralogical characteristics. The soils are very deep, somewhat poor to moderately well drained, silty clay in texture with cracking characteristics indicated by occurrence of pressure faces at sub surface horizons. They are weakly acidic (pH 6.0) to slightly alkaline (pH 7.6) in reaction, medium to high CEC (25.8-33.3 (p+ )kg-1 ), high base saturation (74-86%) and low EC (0.07-0.36 dSm-1 ). Clay mineralogical studies indicated the dominant presence of low charge di-octahedral smectitic minerals, followed by small amount mica and kaolinite and very small amount of vermiculite. Similarities in mineral assemblage indicated that both the soils are developed mainly from common source i.e., Rajmahal Trap. The presence of mica indicates their inheritance from granite-gneiss whereas vermiculite is the weathering product of biotite. Clay minerals other than vermiculite formed in humid climate of earlier geological period and are preserved in the present day dry climate along with vermiculite. Land resource managers need to take note of the unique mineralogical make up of the soils for advising the agricultural land use planning to maintain soil health. Cracking clay soils developed in smectite rich alluvium of the Rajmahal Trap are of both young and matured in nature as evidenced by their classification. The soils were classified under the fine, smectitic hyperthermic family of Vertic Endoaquepts and Typic Haplusterts.