Plasmic Fabric of Vertisols of the Purna Valley of India III Relation to their Cracking

Eight Vertisol pedons of the Purna valley were examined for their physical, chemical, mineralogical and micromorphological properties. Despite their comparable coefficient of linear extensibility, volumetric shrinkage potential, clay contents and amounts of fine clay smectite, the plasmic fabric (b-fabric) in the slickensided horizons of the soils of NE part of the valley is porostriated whereas in soils of SW part it is stippled-speckled to mosaic-speckled indicating weak plasma separation. The related distribution pattern of the s-matrix in all these soils was open porphyric. Weak plasma separation in soils of SW part of the valley is explained in terms of decrease in swelling of fine smectite. Lack of adequate soil water during the wetting cycles due to the sodicity in the subsoils is thought to be the most likely reason for weak swelling of smectite and also for deepening of cracks.