EFFECT OF ELEVATED CONCENTRATIONS OF CD AND ZN IN SOIL ON SPRING WHEAT YIELD AND THE METAL CONTENTS OF THE PLANTS

The effect of increasing concentrations of Cd and Zn in a sandy soil o n spring wheat (Triticum vulgare L.) yields and the metal contents of the plants was examined in a pot experiment to establish critical leve ls of these metals in soil. The metals were added (individually and jo intly) to the soil as sulfates in the following doses (in mug g-1, dry wt.): Cd - 2, 3, 5, 10, 15, 25, and 50; Zn - 200, 300, 500, 1000, 150 0, 2500, and 5000. Cadmium added to soil did not affect yields of whea t. The Zn dose of 1000 mug g-1 strongly reduced crop yields; at 1500 m ug g-1 Zn dose wheat did not produce grain. The metal contents of whea t increased with increasing concentrations of Cd and Zn in soil up to 10.3 and 1587 mu g-1 of Cd and Zn in straw, respectively. The concentr ations of both metals were higher in straw than in grain by factors of 3-7 and 1.5-2 for Zn and Cd, respectively. The relationships between Cd and Zn contents of the plants and soils were best expressed by expo nential equations. High concentrations of Zn in soils (1042 and 1542 m ug g-1) enhanced uptake of Cd by plants. The tested threshold concentr ations of the metals in soils (3 mug g-1 for Cd and 200-300 mug g-1 fo r Zn) are safe for Zn but are too high for Cd in terms of protecting p lants from excessive metal uptake. The critical Cd content of sandy so il should not exceed 1.5 mug g-1.