EFFECTS OF MOLYBDENUM AND LIME ON THE YIELD AND MOLYBDENUM CONCENTRATION OF CROPS GROWN ON ACID SPHAGNUM PEAT SOIL

Experiments were conducted on a peat soil in the greenhouse to determine the effects of Mo and lime on the leaf tissue Mo concentration and yield of red clover (Trifolium pratense L.), onions (Allium cepa L.), cauliflower (Brassica oleracea var. botrytis L.), lettuce (Lactuca sativa var. capitata L.), and carrots (Daucus carota L.). Molybdenum treatments were: no added Mo, seed treated with Mo, and 4.5, 9.0, 18.0, 36.0, 72.0, and 144 ppm Mo added to the soil. Increases in soil pH from 4.3 up to 6.9 resulted in yield increases of all crops except lettuce. Seed treatment with Mo or small quantities of Mo added to the soil were necessary for optimum yield of all crops. For onions, cauliflower, and lettuce, the Mo seed treatment alone was sufficient. No visual abnormal leaf symptoms were observed with actual leaf tissue Mo concentrations of 192, 640 and 1,018 ppm in red clover, cauliflower, and onions, respectively. Liming generally increased the Mo concentration of crops, but the increase in concentration to applied Mo depended upon the level of lime. Synergism between Mo and lime was observed in tissue Mo concentration for onions and cauliflower. Antagonism between Mo and lime at high levels was observed in yields for cauliflower and carrots. Molybdenum applications of 4.5 ppm or higher resulted in red clover tissue containing greater than 10 ppm Mo, which when fed to cattle could be toxic.