4.1 Sodium absorption ratio (SAR)
The classification of irrigation waters with respect to SAR is based primarily on the effect of
exchangeable sodium on the physical condition of the soil. Sodium absorption ratio (SAR) is
calculated by the relation (Karanth, 1997)
SAR = Na + /[(Ca + +Mg 2+ ) 1/2 /2]
Where, concentrations are reported in meq/l.
SAR concentration ranges from 1.03 to 15.44 with a mean of 6.18 for premonsoon
and from
0.6 to 13.0 with a mean of 5.2 in postmonsoon.
During premonsoon, 26 out of 50 wells show
SAR values greater than 6.0. In the case of postmonsoon,
15 out of 50 wells had shown SAR
value greater than 6.0. Layerwise study of SAR indicates that all the wells belonging to the 1 st
layer (about 500m away from the polluted Noyyal River) is found to be above 6.0 and most
of the samples show more than 10.0 (high SAR value) irrespective of monsoon. Most of the
wells belonging to the 3 rd to 5 th layer (1500 to 2500m away from River Noyyal) show lower
SAR values indicating that the percolation effect is not significant to the water bodies at this
region. Hence, this study clearly demonstrates that the wells belonging to the 1 st and 2 nd layer
are found to be affected with respect to SAR.