Sodicity is a major factor affects crop growth and productivity at global level. Out of 1.5 billion ha of cultivable land at global level, 23% are affected due to salinity and 37% by sodicity. Fourteen Big onion varieties were screened by employing germination test in an osmatic solution of Na2CO3 (Sodium bicarbonate).Simultaneously, all the varieties were allowed to germinate in distilled water (control).Three Replications of 20 seeds of each variety were counted and distributed over two layers of paper towel (21x21 cm) previously moistened with water equivalent to three times the dry weight of the paper and tied both ends with rubber band and kept in a plastic tray with different concentrations ( 0, 25mM, 50mM, 75mM, 100 M ) of Na2CO3. At the end of the 21st day, final germination percent, root length, shoot length, root dry weight, shoot weight, Relative water content and membrane stability index, were recorded in Na2CO3 solution as against the distilled water was calculated. The experiment was designed as a completely randomized design with two factors.  As a result a decline in all onion growth paramers, with increasing sodicity stress has been recorded. Significant differences were observed between the varieties and different Na2CO3 concentrations. Irrespective of Na2CO3 concentrations, Bhima Safed recorded significantly maximum stress tolerant index compared to other varieties and minimum stress tolerant index value recorded bhima red variety. Based on stress tolerant index, Bhima safed variety tolerant to sodicity stress and Bhima red variety sensitive to sodicity stress.

Sodicity is a major factor affects crop growth and productivity at global level. In the cultivablel and at global level, 23% is affected by salinity and 37% land by sodicity. Two seed propagating aggregatum onion varieties (CO 5, CO 6) and two bulb propagating aggregatum onion varieties (Permbalurlocal, thuraiyurlocal) were screened by employing germination test in an osmatic solution of NaHCO3 (Sodium bicorbanate). Three Replications of 20 seeds of each variety were counted and distributed over two layers of paper towel (21x21 cm) previously moistened with water equivalent to three times the dry weight of the paper and tied both ends with rubber band and kept in a plastic tray with different concentrations (0, 10 mM, 20 mM, 30 mM, 40 mM, 50 mM) of NaHCO3 (sodium bicorbanate). Also another bulb propagated varieties, perambalur and thuraiyur local varieties bulb directly sown in beaker have 1.5 kg sand. Control beaker irrigated with only water and other beakers irrigated with different concentrations (25 mM, 50 mM, 75 mM and 100 mM) of sodium bicarbonate solution. Germination percentage was recorded 7 days after. At the end of the 21th day,in four aggregatumonion varieties where final germination per cent, root length, shootlength, vigourindex, stresstolerant index, relative water content and membrane stability index, were recorded in NaHCO3 solution as against the distilled water was calculated. The experiment was designed as a completely randomized design with two factors. As a result a decline in all onion growth paramers, with increasing sodicity stress has been recorded. Significant differences were observed betweenthe varieties and different NaHCO3 concentrations. Irrespective of NaHCO3 concentrations two seed propagating aggregatum onion varieties, CO 6 recorded significantly maximum stress tolerant indexcompare with CO 5 and two bulb propagating aggregatum onion varieties, Thuraiyur local variety recorded significantly maximum stress tolerant index compare with Perambalur local in all sodicity concentation. Based on stress tolerant index, CO 6 and thuraiyur local variety tolerant to sodicity stress and CO5, perambalurlocal variety susceptible to sodicity stress.