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Zinc for crop production

Apurba K. Sutradhar: Research Associate

Daniel E. Kaiser, Carl J. Rosen, and John A. Lamb — Extension Specialists in Nutrient Management


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Zinc (Zn) is an essential micronutrient for plant life. In Minnesota, while some soils are capable of supplying adequate amounts for crop production, addition of zinc fertilizers is needed for others. Zinc is a recommended micronutrient in fertilizer programs for production of corn, sweet corn, and edible beans. Several research projects have focused on the use of this nutrient, and much of the following information is based on the results of that research.

Natural sources of zinc

Zinc exits naturally in rocks. The amount of zinc present in the soil depends on the parent materials of that soil. Sandy and highly leached acid soils generally have low plant available zinc. Mineral soils with low soil organic matter also exhibit zinc deficiency. In contrast, soils originating from igneous rocks are higher in zinc. Plants take up zinc as the divalent ionic form (Zn2+) and chelated-zinc.

The role of zinc in the plant

Zinc is an important component of various enzymes that are responsible for driving many metabolic reactions in all crops. Growth and development would stop if specific enzymes were not present in plant tissue. Carbohydrate, protein, and chlorophyll formation is significantly reduced in zinc-deficient plants. Therefore, a constant and continuous supply of zinc is needed for optimum growth and maximum yield.

Zinc deficiency

Research at the University of Minnesota as well as other universities has identified soil conditions where a response to zinc fertilizers is expected. These conditions are:

Soil Temperature: Cool soil temperatures in early spring can intensify the need for zinc. When soil temperature is low, mineralization of soil organic matter slows down resulting less amount of zinc being released in the soil solution. Root growth is also stunted by cool temperatures and reduces the plant’s ability to find new sources of zinc in the soil profile.

Crops that respond to zinc

Crops vary in Zn required to complete their life cycle. Table 1 shows the response to Zn that might be expected from various crops.

table 1

Deficiency symptoms

figure 1

Figure 1. This young corn plant shows typical zinc deficiency symptoms. Note the broad white stripes on both sides of the midrib of the leaf.

figure 2

Figure 2. Zinc deficiency creates shortened internodes (top) on the corn stalk. A normal plant (bottom) is shown in contrast to the zinc-deficient plant.

figure 3

Figure 3. Zinc deficiency creates interveinal chlorosis on soybean plants (photo credit: IPNI).

Plants fail to develop normally when they are deficient in zinc and certain characteristic deficiency symptoms will appear. With corn, these symptoms usually appear in the first two or three weeks of the growing season. If the deficiency of zinc is severe, these symptoms may last throughout the entire season.

A deficiency of zinc in corn is characterized by the development of broad bands of striped tissue on each side of the midrib of the leaf (Figure 1). These stripes begin on the part of the leaf closest to the stalk and appear first on the upper part of the plant. A zinc-deficient corn plant also appears to be stunted. The lack of normal elongation in a corn plant is shown in Figure 2.

Zinc deficiency in edible beans first appears as a yellowing of the lower leaves. As the season progresses, this yellowing develops into a bronze or brown color. The leaves have a rusty appearance. For this crop, however, care must be taken to avoid confusing sunburned leaves with zinc deficiency.

Zinc deficiency in soybean is not common in Minnesota. Symptoms of zinc deficiency in soybean include interveinal mottling or chlorosis (Figure 3) similar to symptoms in dry edible beans. Zinc deficiency should not be confused with iron deficiency chlorosis which is more common in soybean in Minnesota.

For both corn and edible beans, suspected zinc deficiency symptoms should be confirmed with plant tissue analysis.

Phosphorus-induced zinc deficiency might be a concern when high rates of manure are applied to crop land. The manure, however, also contains zinc that can be used for crop growth. Therefore, phosphorus supplied from manure should not create a zinc deficiency for crop production in Minnesota.

Predicting the need for tissue and soil tests for zinc

The need for zinc in a fertilizer program can be determined through soil tests and plant analyses. Plant analyses can confirm a suspected zinc deficiency during the growing season. However, plant analysis should be used in combination with soil tests before arriving at firm recommendations for using zinc in a fertilizer program.

A guide to sufficient levels of zinc in the tissue of several important agronomic and horticultural crops grown in Minnesota is provided in Table 2. Tissue zinc concentration varies between growth stages. It is important that crops be sampled at the growth stage listed if interpretation of plant analysis information is to be accurate.

table 2

When a soil test indicates the need for zinc, small amounts are needed in a fertilizer program to provide for optimum yield. The zinc status of Minnesota soils can be easily measured by routine soil tests. The DTPA procedure is used by majority of soil testing laboratories and is a reliable indicator of the need for zinc in a fertilizer program. The interpretations of this test, along with corresponding fertilizer recommendations, are summarized in Table 3.

table 3Zinc Experiments in Minnesota

table 6

Fertilizer sources

Several sources can supply zinc when needed. Zinc sulfate (35% zinc) is usually used to supply the needed amount of zinc when dry fertilizer materials are used. This material can be either broadcast and incorporated before planting, or used in a starter fertilizer. It blends well with other dry fertilizer materials. Approximately 3 lb of the zinc sulfate material will supply 1 lb zinc per acre.

A zinc-ammonia complex (10% zinc) can be used to supply zinc when fluid fertilizers are used. This material mixes easily with other fluid fertilizers.

Zinc oxide (78-80% zinc) can correct a zinc deficiency but is slowly soluble and not effective in a granular form. To effectively correct a zinc deficiency, zinc oxide must be finely ground. Spreading any finely ground material is a problem in Minnesota because of the wind. So use of finely ground zinc oxide is limited to situations where suspension fertilizers are used.

Application of poultry manure can add considerable amount of zinc to the soil. For example, broiler litter contains 0.01-0.50 lb zinc/ton and laying hen litter contains an average of 0.15 lb zinc/ton. Because zinc content is variable in manure, it is suggested that manure sources be tested for zinc content before application.

Method of application

The addition of zinc to a starter fertilizer is the most economical approach to zinc fertilization. This method provides the nutrient the year it is needed. This is especially important when corn and edible beans are rotated with other crops. If use of a starter fertilizer is not an option, zinc fertilizers should be broadcast and incorporated before planting of either corn or edible beans.

Foliar applications of zinc have not been consistently effective in correcting deficiencies of this nutrient. This method of application should be used on a trial basis only. For foliar applications, powdered zinc sulfate can be dissolved in water and applied to the leaf tissue. The amount dissolved should supply 0.5 to 1.0 lb zinc per acre when a rate of 20 gallons of water per acre is used.

A zinc chelate can also be mixed with water. The amount of chelate mixed with water should supply 0.15 lb zinc per acre when water is sprayed at a rate of 20 gallons per acre.

Research has shown that all sources of zinc (except granular zinc oxide) have an equal effect on crop production. Consider cost before choosing a source of zinc for the fertilizer program.

Zinc toxicity

Most crops are tolerant to high zinc levels in their tissue without any visible symptoms. Cereals are sensitive to zinc toxicity. Typical toxicity symptoms are iron chlorosis and lack of green color in the leaves.


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