Zinc fertilization
Zinc, an essential plant nutrient, is involved in many plant growth processes and in the production of tryptophane, a compound needed in some proteins and plant growth hormones.
Zinc is important in early plant development, aiding in vigor and root growth, and later in even crop maturation.
As a micronutrient, zinc is required in much smaller amounts than nutrients like nitrogen, phosphorus or sulphur. Though the amount of zinc required is small, it is no less important. If it is not available to the plant, reduced crop yields can be significant.
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In soil, zinc is usually found in concentrations of 10-300 parts per million. Soils in Saskatchewan generally contain adequate amounts of native zinc. During the 1980s a large number of zinc-fertilized cereal trials conducted by the University of Saskatchewan failed to increase grain yields.
While whole fields don’t usually exhibit zinc deficiency, it sometimes can be observed in some crops in small “pockets” within a field. Zinc deficiencies have also been claimed on irrigated soils.
Zinc is a micronutrient whose normal concentration range is 25 to 150 ppm in plants. Deficiencies are usually associated with concentrations of less than 20 ppm and toxicity will occur when the leaf concentration exceeds 400 ppm.
Flax, corn and beans are particularly sensitive to zinc deficiency. Mildly sensitive crops include barley, alfalfa, clovers and potatoes.
Wheat, oats, peas, mustard and canola are generally considered insensitive.
Zinc deficiency can often be identified by distinctive plant symptoms that appear in the leaves due to a lack of chlorophyll.
Blotches may be seen
Light green or yellow bands or blotches may develop between the veins of leaves, particularly the older, lower ones.
Leaves may also be malformed by continued growth of only part of the leaf tissue. Delayed ripening is a common symptom in field beans.
Zinc deficiencies in flax can result in grayish-brown spots on the younger leaves and the top of the main stem later dies. In wheat and barley, yellowish areas occur on the middle leaves of the plant followed by grayish-brown spots. Plants are short and leaves tend to bunch at the top, creating a fan shape.
Soil conditions most associated with zinc deficiencies are light textured and sandy, high lime or calcareous soils, some organic soils, and subsoils exposed by wind or water erosion or by land leveling.
Classical zinc deficiencies do appear on soils low in available zinc but high in available phosphorus. Single heavy applications of phosphate fertilizer can induce a zinc deficiency. Deficiencies can also appear during cool, wet conditions, often in water-saturated areas. However, these symptoms generally disappear with warmer weather with little or no apparent effect on the plants.
Zinc fertilization can be expensive so it is important to confirm a deficiency before treatment through soil and plant tissue tests.
Zinc fertilizers should be broadcast and thoroughly incorporated. Seed placed zinc fertilizer is not recommended.
It can be banded if band spacings are narrow. Zinc is relatively immobile in soil, so wider band spacings may not be as effective as broadcasting. Banding of zinc fertilizers with acid-forming nitrogen fertilizer can increase efficiency.
Fertilizers are available as zinc oxide, zinc chelates and zinc sulfate, the latter being most common.
If symptoms are detected and confirmed early, a foliar application of 0.5 lb./acre of zinc sulfate can be applied.
A single application will remain available for several years.
– Saskatchewan Wheat Pool
