INFLUENCE OF POTASSIUM-MAGNESIUM ANTAGONISM ON TOMATO PLANT GROWTH

The influence of low and high levels of substrate potassium on the uptake and distribution of magnesium was studied in tomato plants. Magnesium content of the stems and leaves increased with increases in substrate magnesium, regardless of the level of potassium. However, high substrate potassium (12 meq/liter) significantly reduced magnesium uptake (content of aerial portions of the plants) at the high substrate magnesium level (3 meq/liter). Under this potassium-induced antagonism, leaf content of magnesium remained constant at the expense of the stem. Greater quantities of magnesium were required in the plant tissues to prevent deficiency under conditions of high substrate potassium. However, under these conditions essentially the same level of magnesium is needed in the indicator tissue of tomato plants (fifth leaf from the top) as is normally believed adequate for optimal growth and yield.