Micronutrient Fertilizer Programs

Micronutrients play an essential role in vegetable crop production.  However, planning a fertilizer strategy involving micronutrients can be difficult.  Micronutrient fertilizers are often expensive and, depending on the element, the actual return on your investment is not always obvious. The fear of a shortfall often outweighs the actual potential for deficiencies.

The roles of micronutrients in vegetables crops are varied.  They range from:

• Photosynthesis and chlorophyll production (copper, iron, manganese, zinc.)
• Fruit set and seed development (boron, molybdenum, zinc)
• Protein and carbohydrate formation (boron, iron, zinc)

With major elements such as phosphorus, potassium and magnesium, a soil test is the primary tool for fertility planning.  However, we still lack a reliable method of soil testing for many of the micronutrients.  Foliar analysis can help to identify deficiencies and plan an application strategy.  Take care to sample at the appropriate crop stage and keep detailed records of each field for future planning purposes.  Knowledge of crop and soil characteristics can also help to target applications where they will provide the most benefit.

Micronutrients in Soil and Plants

Boron

• Vegetables at Risk of Developing a Deficiency: Beets, Brassica Crops, Celery, Rutabagas.
• Deficiency Symptoms: New growth is stunted and discoloured, flower abortion, hollow stems.
• Soil Conditions Most Often Deficient: Sandy soils and dry soil conditions
• Effect of Excessive Amount: Necrosis of leaf margins, pale or whitish new growth.
• Soil Analysis: No
• Foliar Analysis: Yes

Copper

• Vegetables at Risk of Developing a Deficiency: Beets, Lettuce, Onions, Spinach, Tomatoes.
• Deficiency Symptoms: Limp or discoloured leaves, Twisted leaf tips, Thin pale scales in onions, poor colour in carrots.
•  Soil Conditions Most Often Deficient: Muck soils, Coarse sandy soils.
• Effect of Excessive Amount: Foliar sprays that are too concentrated will damage the leaf tissue.
• Soil Analysis: No.
• Foliar Analysis: Yes.

Iron

• Vegetables at Risk of Developing a Deficiency: Rarely seen in Ontario.
• Deficiency Symptoms: Leaves become yellow between the veins.
• Soil Conditions Most Often Deficient: Rarely seen in Ontario.
• Effect of Excessive Amount: N/A
• Soil Analysis: No.
• Foliar Analysis: Yes.

Manganese

• Vegetables at Risk of Developing a Deficiency: Beans, Beets, Cucurbit crops, Lettuce, Onions, Peas, Spinach, Sweet Corn.
• Deficiency Symptoms: Young leaves become yellow between the leaf veins (veins stay dark green.)
• Soil Conditions Most Often Deficient: Soils that were previously poorly drained and eroded, acidic, sandy soils.
• Effect of Excess Amount: On acid soils, excess manganese may reduce root growth.
• Soil Analysis: Yes.
• Foliar Analysis: Yes.

Molybdenum

• Vegetables at Risk of Developing a Deficiency: Beets, Brassica crops, Lettuce, Onions, Spinach.
• Deficiency Symptoms: Stunted plants lack vigour, leaves twist and become whip-like, edges of the leaves become scorched.
• Soil Conditions Most Often Deficient: Muck soils and acidic, sandy soils.
• Effect of Excess Amount: Excess symptoms are similar to iron deficiency.
• Soil Analysis: No.
• Foliar Analysis: Yes.

Zinc 

• Vegetables at Risk of Developing a Deficiency: Beans, Onions, Spinach, and Sweet Corn.
• Deficiency Symptoms: White stripes or patches near the base of young leaves.
• Soil Conditions Most Often Deficient: Eroded, high pH soils and soils high in phosphorus.
• Effect of Excess Amount: Excess zinc may interfere with the uptake of other micronutrients.
• Soil Analysis: Yes.
• Foliar Analysis: No.

Adapted from Managing Crop Nutrients – Best Management Practices.  Agriculture and AgrifoodCanada,OntarioFederation of Agriculture and Ontario Ministry of Agriculture, Food and Rural Affairs.