Salt Tolerance of Green Soybeans as Affected by Various Salinities in Sand Culture

Green soybeans (Glycine max. Merr.) were grown in sand to determine the salt tolerance affected by salinization of sea water, NaCl, Na2SO4, MgCl2 and MgSO4 at osmotic potentials of -1.20, -1.70 and -2.70 bars as compared to a control of -0.70 bars of base nutrient solution. Dry weight of the whole plant, fresh weight of seeds and pods, and number of pole were greatest in the control and decreased in each salinity with decreasing osmotic potentials. Growth was greatest in the MgSO4 series, less in the sea water and Na2SO4 series, and least in the NaCl and MgCl2 series. There was a marked suppression of growth in the NaCl and MgCl2 series at -2.70 bars. Chloride-salinity caused markedly different symptoms from those caused bysulfate-salinity. In chloride-salinity treatments chlorosis and necrosis were observed on margins of leaves, and developed acropetally at the middle and late stages of growth. The lower the osmotic potentials the more pronounced the symptoms. In sulfate-salinity treatments at only -1.70 bars interveinal chlorosis was found. Na, Mg, Cl and SO4 content of leaves and sand solution (SS) tended to increase with decreasing osmotic potentials of treatment solutions in sodium-, magnesium-, chlo ride- and sulfate-salinities, respectively. EC values of SS increased and osmotic potentials of SS decreased as osmotic potentials of treatmentsolutions decreased. The values were similar at the isosmotic potential in each salinity.