Zinc is an essential nutrient for plant growth. Zinc is categorized as a micronutrient because the amount required for plant growth is very small, in fact most crops remove less than .5 lb/a zinc. Zinc is required in the formation of plant enzymes and is also associated with the formation of hormones such as Indole Acetic Acid (IAA). In general, a lack of zinc will reduce leaf and plant size, delay maturity and reduce seed formation and total yield.
Common Zinc Deficiency Situations: Zinc deficiencies are common on soils with a pH greater that 7.5. In soils with a high pH, zinc may be precipitated with carbonates and made unavailable. Most of the available zinc in the soil is located close to the soil surface in the organic matter. If fields are leveled and top soil is buried or removed, a zinc deficiency can result due to little organic matter at the surface. Soil temperature and moisture content can also contribute to zinc deficiencies. Cool wet conditions can result in increased incidence and severity of zinc deficiencies. As the weather becomes warmer and dryer the deficiency symptoms will generally disappear.
Zinc Deficiency Symptoms: Zinc deficiency symptoms appear first on the younger leaves of plants because zinc is not translocated from older to younger plant tissue. In grass crops, such as corn, a mild zinc deficiency appears as interveinal striping on younger leaves. Later in the season a severe deficiency will result in broad white bands starting at the base of the leaf. In broadleaf crops, zinc deficiency results in shortening of internodes (rosetting) and a decrease in leaf size (little leaf). In edible beans, symptoms usually appear on the second set of trifoliate leaves. When a severe zinc deficiency occurs, the older leaves may eventually turn gray or brown and die. A zinc deficiency will delay edible bean maturity and decrease yield. In potatoes, a zinc deficiency will result in stunted plants with the young leaves curled upward (fern leaf). Gray or brown irregular spots may appear on older leaves.
Zinc Fertilization and Strategies: Several zinc fertilizer materials are available to prevent or correct deficiencies. Zinc sulfate is the most common dry fertilizer and zinc chelates are the most common liquid material. Common rates of zinc sulfate range from 2-10 lb/a elemental zinc. Soil application of zinc sulfate is the most common and most successful long-term strategy for eliminating zinc deficiencies. Zinc sulfate can be applied as a broadcast treatment and tilled into the soil or applied in a band near the seed. Band application is most effective when placed to the side and below the seed. Zinc chelates are generally used as a rescue treatment and do not result in any benefits to following crops. Common rates of foliar zinc are .25-1.0 lb/a elemental zinc. Multiple applications of foliar zinc are usually required to achieve the same affect as 10 lbs/a zinc applied to the soil before planting.
Changing Crop Rotations: Crop rotations in many areas are beginning to include more zinc sensitive crops, such as edible beans, corn, flax and potatoes. This requires more attention be paid to the zinc level in the soil. If a current soil test shows that zinc levels are low, zinc fertilizer is required. This can be accomplished by applying granular zinc sulfate or foliar zinc chelate. The major concern when rotations are changed is that producers may not know these crops are more sensitive to zinc than crops such as wheat and barley. Once the growers are aware of this concern and they get a soil test to evaluate the zinc status of his fields, you can help them come up with a strategy for zinc fertilization that fits their operation.