Origin and Mineralogy of Nano Clays of Indian Vertisols and Their Implications in Selected Soil Properties

The mineralogical composition of nano-clays (NCs), and their potential implications in soil bulk properties of Indian Vertisols are unexplored. In this study, we have isolated NCs (<100 nm) from Deccan basalt (DB) alluvium derived Vertisols (Typic Haplusterts) of central India and characterized them for their mineralogy and crystalline behavior. The soils are clayey (>60%) in texture, rich in smectite mineral (60–80% in <2 μm fraction), alkaline (pH 7.8–8.5), calcareous, and contain <1.0% organic carbon. The clay fraction (<2 μm) is dominated by smectitic NC (40–60%) followed by hydroxy-interlayered vermiculite (HIV), pedogenic chlorite (PCh), kaolinite, and mica. The smectite is little hydroxy-interlayered (HIS), and hydroxy-interlayering is less pronounced in NC smectites than in the coarser clay smectites. The NC smectites are of smaller crystallite size (3.5–5.5 nm) and higher in crystal strain (15–22%) than coarser size clays because of its low lattice charge. The abundance of smectitic NCs considerably reduces the saturated hydraulic conductivity (<1 cm hr–1) of the soils due to high dispersion and swelling (COLE ≥ 0.20) of smectite clays even at the low level of exchangeable sodium percentage (ESP ≤ 5) and a moderate amount of exchangeable magnesium. The report on nano clays (<0.1 μm) highlights the unique role of nano smectites in some selected soil properties, as well as in the origin of SAT Vertisols of the Indian subcontinent.