EFFECTS OF CALCIUM ON GROWTH AND LEAF ION CONCENTRATIONS OF GOSSYPIUM-HIRSUTUM GROWN IN SALINE HYDROPONIC CULTURE

The optimum Ca2+ concentration for growth of cotton (Gossypium hirsutu m cv. Acala SJ-2) was in the range 1 to 15 mol m(-3) for plants growin g in hydroponic culture with 100-150 mol m(-3) NaCl. Most saline (but not sodic) soils contain higher Ca2+ concentrations. CaCl2 was inhibit ory to the growth of cotton above 20-50 mol m(-3). Increasing concentr ations of Ca2+ in the range 0-2 mol m(-2) drastically reduced Na+ accu mulation in the leaves. As CaCl2 concentrations were increased above t he optimum for growth there was a further reduction in leaf Na+ accumu lation, but this was more than offset by increased leaf Ca2+ and Cl- c oncentrations. Leaf K+ concentrations were not much affected by change s in external CaCl2 concentrations. The response of Mg2+ varied from a n increase to a decrease with increasing external CaCl2 and was influe nced by nutritional status. There was no evidence that high Ca2+ cause d a deficiency of Mg2+ in cotton. Except for Cl-, whose concentrations tended to decrease initially and then increase as the CaCl2 concentra tion increased, the anions were largely unaffected by changes in exter nal CaCl2.