Micronutrients
Micronutrients include boron, copper, iron, manganese, molybdenum and zinc. Plants use these elements in smaller amounts than the major nutrients, but they are still very crucial to a plant’s overall nutrition.
Micronutrients are usually found in much lower levels in the soil than macronutrients. Soil pH, organic matter, clay content and mineralogy can influence the micronutrient soil test. This makes estimating micronutrient availability less reliable than macronutrient evaluation.
Response of Crops to Micronutrient Fertilizers
Crops vary in their response to micronutrients. Highly responsive crops will often respond to additional micronutrients if the soil micronutrient concentration is low. Medium-responsive crops are less likely to respond, and low-responsive crops do not usually respond to fertilizer additions even at low soil micronutrient levels. A high rating does not mean the crop always needs additional micronutrients. Response to any given nutrient only occurs when the soil is already low in that nutrient.
| Crop | Mn | B | Cu | Zn | Mo | Fe |
|---|---|---|---|---|---|---|
| Asparagus | Low | Low | Low | Low | Low | Med |
| Beans, snap | High | Low | Low | High | Med | High |
| Beets, table | High | High | High | Med | High | High |
| Broccoli | Med | High | Med | High | High | |
| Cabbages | Med | Med | Med | Low | Med | Med |
| Carrots | Med | Med | Med | Low | Low | |
| Cauliflower | Med | High | Med | High | High | |
| Celery | Med | High | Med | Low | ||
| Cucumbers | High | Low | Med | |||
| Lettuce | High | Med | High | Med | High | |
| Oats | High | Low | High | Low | Low | Med |
| Onions | High | Low | High | High | High | |
| Parsnips | Med | Med | Med | Low | ||
| Peas | High | Low | Low | Low | Med | |
| Peppers | Med | Low | Low | Med | ||
| Potatoes | High | Low | Low | Med | Low | |
| Radishes | High | Med | Med | Med | Med | |
| Rye | Low | Low | Low | Low | Low | Low |
| Spinach | High | Med | High | High | High | High |
| Sugarbeets | High | Med | Med | Med | Med | High |
| Sweet corn | High | Med | Med | High | Low | Med |
| Tomatoes | Med | Med | High | Med | Med | High |
| Turnips | Med | High | Med | Med | ||
| Mn = Manganese, B= Boron, Cu = Copper, Zn = Zinc, Mo = Molybdenum, Fe = Iron | ||||||
| 1 Taken, with permission, from the Michigan State University Cooperative Extension Publication E486 Secondary and Micronutrients for Vegetables and Field Crop (Table 3, Relative response of selected crops to micronutrient fertilizers.) | ||||||