Zinc (Zn) is taken up by plants as the divalent Zn2+ cation. It was one of the first micronutrients recognized as essential for plants and the one most commonly limiting yields. Although Zn is required in small amounts, high yields are impossible without it.
Zinc (Zn) deficiency is growing in the Midwest, and it’s more likely to occur in corn than soybean fields. This is happening in part to earlier planting of corn in cool and moist soil. Also, more residue resulting from conservation tillage and higher grain yields places added stress on seedlings to absorb Zn from soil.
Zinc is heavily involved in enzyme systems that regulate the early growth stages, and is vital for fruit, seed and root system development; photosynthesis; formation of plant growth regulators; and crop stress protection. Further, Zn is a team player with nitrogen (N), phosphorus (P) and potassium (K) in many plant-development processes.
Soils require Zn in very small amounts compared with N or K. Only about a half-pound of Zn is needed per acre for high-yield (180 bushels per acre) corn production. Sixty-bushel wheat needs about 0.28 pound of Zn per acre. Yet, lack of Zn can limit plant growth, just like N or K, if the soil is deficient or crop uptake is restricted.
In addition to being an essential component of various enzyme systems for energy production, Zn is required in protein synthesis and growth regulation. Zinc-deficient plants also exhibit delayed maturity. Since Zn is not mobile in plant, Zn-deficiency symptoms occur mainly in new growth. This lack of mobility in plants suggests the need for a constant supply of available Zn for optimum growth.
The most visible Zn-deficiency symptoms are short internodes (rosetting) and a decrease in leaf size. Chlorotic bands along the midribs of corn, mottled leaves of dry bean and chlorosis of rice are characteristic Zn-deficiency symptoms. Loss of lower bolls of cotton and narrow, yellow leaves in the new growth of citrus also have been identified as symptoms of Zn deficiency. Delayed maturity also indicates Zn-deficient plants.
Zinc loss takes place in many ways. Deficiencies are mainly found on sandy soils low in organic matter and on organic soils. They occur more often during cold, wet spring weather and are related to reduced root growth and activity. Periods of lower microbial activity decrease Zn release from soil organic matter. Zinc uptake by plants decreases with increased soil pH. High levels of available P and iron in soils also adversely affect the uptake of Zn.
Symptoms of deficiency can vary across crop species, but similarities exist for how nutrient insufficiency impacts plant tissue color and appearance. Nutrient deficiencies are commonly associated with the physical location on the plant
(i.e., whether the symptoms are primarily observed on older versus newly formed plant tissue), but these symptoms can spread as the severity of the deficiency progresses.