Studies on the salt tolerance of vegetable crops with special reference to osmotic effects and specific ion effects

Abstract

In order to investigate the mechanism of salt injury of vegetable crops, spinach, turnip, celery, welsh onion, kidney bean, and chard were grown in sand culture under glass. HOAGLAND'S solution (about 0.6 atmosphere osmotic concentration) was used as the base nutrient solution, to which the mixture of NaCl, MgCl2, Na2SO4, CaCl2, and KCl at the same ratio in sea water, or each of NaCl, Na2SO4, CaCl2, or MgCl2, was added at 2 and 4 atmospheres osmotic concentration (4 and 8 atm. only for chard). Further, the osmotic concentration of HOAGLAND's solution was raised as high as that of these solutions containing excess salts.1. In most cases, growth reduction was almost linear with the increasing osmotic concentration of the substrate, and the reduction was independent of the kind of salts on an equal osmotic basis. Therefore, the inhibitory effect of excess salts on the plant growth is considered to be primarily due to the osmotic effects in general. However, MgCl2, was generally more toxic than the other salts, and chloride salts were definitely toxic for chard. Sodium salts had favourable effects on the fresh weight yield of spinach and celery, but in the latter crop severe blackheart, a calcium deficiency symptom, developed.2. Effects of excess salts on the calcium absorption by plants were recognized as follows: The increase of the osmotic concentration of nutrient solution markedly inhibited the calcium absorption in celery which easily developed calcium deficiency symptom. In most of the other crops, however, such osmotic inhibition of calcium absorption was not or only slightly observed. In NaCl, Na2SO"4 or MgCl2, treatments, antagonistic relation was observed between Ca and any other cations added; and on an equal osmotic basis, MgCl2, had most marked inhibitory effect on the calcium absorption. The inhibitory effect of excess NaCl on the Ca absorption by plants was recognized to be due to the interaction between Na and Ca in most crops except for celery. In general, sea water salts resulted in slightly lower Ca content in leaves than NaCl, which fact seems to be due to the effect of Mg++ ion in sea water salts.3. Direct toxic effects of Na or Cl were not observed in most crops except for the chloride toxicity in chard.4. On an equal osmotic basis, sea water salts and NaCl produced similar results as to the plant growth, visual symptoms and inorganic composition of leaves except for the Mg content. This fact shows that the ion effects of sea water salts are principally due to N+ and Cl- ions. This point was discussed further on the basis of the composition of real sea water.