Although salt injury in plants is due to both osmotic and specific ion effects, little is known about the reaction of rice plants to salinity under increasing sodium adsorption ratios (SAR) in the growth medium. Therefore, a glasshouse experiment was conducted to study the effect of four levels of salt concentration (20, 40, 60 and 80 m-equiv/1 with respect to the sum of Na+, Ca2+ and Mg2+) and four levels of SAR (2, 25, 50 and 75) on growth and mineral composition of rice cvs IR 2153-26-3 and IR 26. The results show that as salt concentration increased, dry-matter yield and percentage water content of shoots decreased regardless of the variety. The rate of decline with salinity was most pronounced under low SAR and in the salt-sensitive variety IR 26. With increase in SAR, the yield, percentage water content and concentrations of Ca, Mg, and K in shoots and roots decreased, but the effects were more marked at the lowest salt concentration and in IR 26. Variety IR 2153-26-3 showed greater tolerance, maintaining a higher concentration of Ca and higher Ca/Na and K/Na ratios and a lower concentration of Na and Cl in the tops compared with IR 26.
The degree of salt injury in rice seems to depend not only on salt concentration but also on SAR in the growth medium whilst salt tolerance is associated with tolerance for both high salt concentration and high SAR. Therefore, in studies on screening rice varieties for salt and sodium tolerance, the interactive effects of SAR and salinity must be considered so as to ensure greater adaptability by the varieties recommended for salt-affected soils.