Speciation of Smectites in two Shrink-swell Soils of Central Peninsular India

Shrink-swell (Vertisols and their intergrades) soils cover an extensive area especially in Peninsular India with smectites as the dominant mineral. It was felt necessary to find out the species of smectites for better management of these soils. Hence, two benchmark Vertisols namely Seloo from Wardha and Saikhindi from Ahmadnagar districts of Maharashtra were chosen for the study. High resolution mineralogical analysis employed through X ray diffraction (XRD) techniques of the silt, total clay and fine clay fractions of both the pedons were carried out along with Greene-Kelly test with only fine clays. Silt (50-2 μm), total clay (<2 μm) and fine clay (<0.2 μm) fractions are dominated by smectite in both the soils; the smectites content increased gradually with decreasing size fraction. The fine clay fractions are mostly composed of smectite with small amounts of vermiculite and traces of chlorite, kaolin and feldspar. Greene-Kelly test indicated that both Seloo and Saikhindi soil fine clays are dominated by beidellite/nontronite over montmorillonite. The Seloo fine clay smectite is composed of 18–26 per cent and 74–82 per cent montmorillonite and beidellite/nontronite, respectively, and for Saikhindi it is composed of 32–41 per cent and 59–68 per cent for montmorillonite and beidellite/nontronite, respectively. However, these fine clay smectites are of low charge dioctahedral nature and therefore may not have any K selectivity. This property appears to have implications in K management of shrink-swell soils of Deccan basalt areas