Methods of Application

Content

Historical Information
  Determination of Essentiality
  Function in Plants
    - Nitrogenase
    - Nitrate Reductase
    - Xanthine Dehydrogenase
    - Aldehyde Oxidase
    - Sulfite Oxidase
Diagnosis of Molybdenum Status of Plants
  Deficiency
  Excess
  Molybdenum Concentration and Distribution in Plants
  Analytical Techniques for the Determination of Molybdenum in Plants
Assessment of Molybdenum Status of Soils
  Soil Molybdenum Content
  Forms of Molybdenum in Soils
  Interactions with Phosphorus and Sulfur
  Soil Analysis
    - Determination of Total Molybdenum in Soil
    - Determination of Available Molybdenum in Soil
Molybdenum Fertilizers
  Methods of Application
    - Soil Applications
    - Foliar Fertilization
    - Seed Treatment
  Crop Response to Applied Molybdenum
References


Soil Applications


Molybdenum fertilizers can be incorporated into the soil by banding or by broadcast applications. Soluble sources of molybdenum such as sodium molybdate and ammonium molybdate may be sprayed onto the soil surface before tilling to obtain a more uniform coverage, but this practice is seldom used (89). Because the molybdenum requirement of plants is low, the quantities of molybdenum fertilizers needed for crop growth are less than for most other nutrients. Rates of 50 to 100 g Mo ha-1 are generally required for soil treatments of agronomic crops, but as much as 400 g Mo ha-1 may be needed for vegetable crops such as cauliflower (12). The uniform application of such small quantities of molybdenum is often achieved by combining molybdenum with phosphorus fertilizers or in mixed, complete (N-P-K) fertilizers, to increase the volume of applied material (89).


Chemical Formulas of Various Molybdenum Sources and Percentage of Molybdenum in Them



Foliar Fertilization


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 Treatment


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).