The Micronutrients & Plant Growth - Molybdenum's Role
Molybdenum (Mo) is required for symbiotic nitrogen fixation (nodulation) by legumes and reduction of nitrates for protein synthesis. Plants require molybdenum levels of 0.1 to 2.5 ppm in their tissues for normal growth. Applying higher rates can create problems.
Over application of molybdenum on forage crops can cause a disease called "Molybdenosis," heart disease, and scouring in ruminant animals. High molybdenum content in forage crops can also interfere with copper uptake in ruminant animals ultimately causing a copper deficiency. Therefore, caution is needed when applying molybdenum to crops scheduled for grazing or silage. Its availability increases with soil pH, meaning deficiency symptoms occur most frequently under acid soil conditions. Molybdenum availability varies with soil type, being highest on organic soils, less on clays, and least of all on sandy-textured soils.
Molybdenum deficiency symptoms are very similar to those for nitrogen: pale-green to yellow leaves; yellow spots on leaves; marginal chlorosis along side and tip of blade; thick cupped leaves; reddish-brown coloration of stems and petioles; and whiptail leaves (narrow irregular growth). The marginal chlorosis exhibited by some plants looks similar to potassium deficiency. A low rate of foliar sprays can generally correct a deficiency.