Sodium molybdate and ammonium molybdate are the most commonly used molybdenum sources for foliar fertilization because of their high solubility in water. Foliar applications of molybdenum are most effective if applied at early stages of plant development, and generally a 0.025 to 0.1% solution of sodium or ammonium molybdate (~200 g Mo ha-1), is recommended (85). Wetting agents may also be required in the spray solution to ensure adequate coverage on the foliage of crops such as onion and cauliflower (12). Foliar applications of molybdenum are often more effective than soil applications, particularly for acid soils (9) or under dry conditions (115).
Seed pelleting, or coating, is the most common method for supplying molybdenum to crops (89) and is an effective means of preventing deficiency in crops grown on soils having low concentration of available molybdenum (9). This method ensures a more uniform application in the field, and the amounts of molybdenum that can be coated onto seeds are sufficient to provide adequate molybdenum for plant growth (89). Sparingly soluble sources of molybdenum, such as molybdenum trioxide, are most often used to treat seeds of leguminous crops because soluble molybdenum sources can decrease the effectiveness of applied bacteria inoculum (85). Recommended rates for seed treatment are 7 to 100 g Mo ha-1 (9,85), and higher rates (>117 g Mo ha-1) have been found to cause toxic effects in plants such as cauliflower (116).
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