Does Sodicity in Vertisols Affect the Layer Charge of Smectites?

Abstract

Sodicity in smectite dominant shrink-swell soils (Vertisols and vertic intergrade) is common in the semi-arid region. It is not known whether long-term sodicity in soils changes the layer charge of smectites as layer charge is an important fundamental property of smectitedominated soils and most of the soil properties depends upon the layer charge. Understanding the importance of layer charge of soil clay smectites, two benchmark Vertisols, one Paral soils (sodic) and the other Boripani soils (non-sodic) from Akola and Nagpur districts of Maharashtra were chosen for the study. The study intended to show whether long-term sodicity causes hydroxy-interlayering in smectites which result in an increase in layer charge. The soils had high clay and smectite content and the smectite charge was distributed in both tetrahedral and octahedral layers. The layer charge of both the soil fine clays are the lowest reported till date for Indian smectites and varied from 0.307 to 0.353 and 0.328 to 0.360 mol(-)/((Si, Al)4O10(OH)2) in a soil profile for Paral and Boripani soils respectively. Hydroxy-interlayering in smectites was also negligible. The study discussed that sodicity may not be responsible for the formation of hydroxy-interlayering in smectites and thus not likely to increase the layer charge.