ZINC TOXICITY IN SOYBEAN GROWN AT HIGH IRON CONCENTRATION IN NUTRIENTSOLUTION

Iron (Fe) deficiency in plants may be caused by heavy metal toxicity a nd is expressed mainly by chlorosis in young leaves. Zinc (Zn) is ofte n the heavy metal involved. The growth of soybean (Glycine max [L.] Me rr.) in a 40 mu M Zn nutrient solution was studied using a factorial 2 x2x2 experiment; two Fe (20 and 100 mu M), two S (0.02 and 20 mM), and two Fe foliar fertilization (with and without Fe-DTPA) levels. Lower dry matter yield, chlorosis in young leaves, and change in the periodi c movement (light/dark) of unifoliate leaves were the main symptoms of Zn toxicity. Plants supplied with 100 mu MFe produced more dry matter than those supplied with 20 mu M and did not show leaf chlorosis, but still showed a change in the periodic movement of the leaves. A high Fe supply prevented most of the detrimental effects of toxic Zn. There was no effect of sulfur (S) on plant symptoms, and foliar fertilizati on with Fe-DTPA did not result in regreening of chlorotic leaves.