Zinc and Iron Deficiencies
Fact Sheet No. 0.545 Crop Series|Production by D.G. Westfall and T.A. Bauder* Zinc and iron deficiencies affect certain Visual zinc deficiency symptoms differ Quick Facts field crops, vegetables, trees and ornamentals among crops, but characteristic symptoms in Colorado. These micronutrient deficiencies can be recognized. Fields generally are • Zinc and iron deficiencies are recognized by plant symptoms and by not affected uniformly. Deficient areas are may occur in most areas of soil tests. The purpose of this fact sheet is to normally the areas where topsoil has been Colorado. help farmers and other agricultural workers removed. Zinc deficiency shows early in the identify zinc and iron deficiencies by field growth of plants. • Zinc and iron deficiencies observations and soil tests and to make Young corn and sorghum plants exhibit a can be recognized by plant recommendations for correction of these broad band of white to translucent tissue on symptoms. deficiencies. both sides of the leaf midrib starting near the • Confirm visual observations base of the leaf. Generally it does not extend by soil test and/or plant to the tip; the midrib and outer margin analysis. Zinc deficiencies Zinc Problems remain green. Occasionally, a reddish-brown Zinc deficiencies may occur in all areas of cast may develop in the chlorotic (white or can be corrected by the the state and are frequently associated with yellow) leaf tissue. application of zinc fertilizers. the following situations: Plants tend to be stunted due to a • Soil application of iron • Zinc deficiency has been recognized on shortening of the internodes. Pinto beans fertilizers has not been corn, sorghum, sudan, sorghum-sudan exhibit a general stunting of the young plants. economically feasible on a hybrids, pinto beans and potatoes in Leaves show a general yellowing of the field scale, but iron deficiency Colorado. Different susceptibility levels upper foliage with a browning or bronzing among varieties have been recognized. of the older or lower leaves. The leaves of can be controlled by several • No deficiencies have been recognized on zinc-deficient beans typically have a crinkled other means. wheat or alfalfa. appearance. A general downward curl of • Response to zinc is much greater under the leaves also will occur and pod set will be high yield conditions. poor. Confirm visual observations by soil • Zinc deficiencies frequently are associated tests and/or plant analyses. with areas where the topsoil has been removed by leveling for irrigation, erosion or terrace channel construction. Soil Testing for Zinc • Soils deficient in zinc frequently are low in Determine the need for supplemental organic matter, are sandy and/or have an zinc by soil testing. Collect a composite soil alkaline pH (pH greater than 7.0). sample from the area of the field suspected • High available soil phosphorus levels of being low in zinc. In collecting the sample, produced by fertilization or native in avoid using anything galvanized or made the soil may induce a more severe zinc of rubber. deficiency on soils low in available zinc. Several methods for zinc testing have • Zinc deficiency is much more severe in been proposed. These tests are all based years with cold, wet springs than in years on using a solution of an acid, a chelate or of warm, dry springs. combination of reagents to extract from the soil a portion of the total zinc. This is related, through correlation experiments, to the zinc that plants can extract from the © Colorado State University *D.G. Westfall, Colorado State University professor Extension. 12/92. Revised 12/11. emeritus, soil and crop sciences; and T.A. Bauder, soil. The method used by the Soil Testing Extension specialist, water quality. Original author: Hunter Laboratory at Colorado State University is the www.ext.colostate.edu Follett, former Colorado State Univeristy professor, soil ammonium bicarbonate, diethylene triamine and crop sciences, deceased. 12/2011 pentaacetic acid (AB-DTPA) test. Table 1: Zinc recommendations.* of zinc sulfate (36 percent Zn) should • Iron deficiencies are worse in cool, AD-DTPA Irrigated Dryland be sufficient for two or three years of damp springs. Deficiency symptoms extractable zinc Fertilizer zinc-pounds production. However, test the soil again are frequently most severe on young as ppm Zn per acre Zn to adjust the zinc recommendation for seedlings. Sensitive Crops** (corn, sorghum, sudan, following years. • Sorghum, corn, potatoes and pinto sorghum-sudan hybrids, beans, potatoes) In season, zinc deficiency may be beans are the most severely affected 0-0.9 low 10 5 corrected by spraying the crop with a 0.5 crops. Wheat and alfalfa are the 1.0-1.5 marginal 5 0 percent zinc sulfate solution (1 percent least sensitive. Varietal differences in > 1.5 adequate 0 0 for potatoes) at the rate of 20 to 30 susceptibility have been recognized gallons per acre. A 0.5 percent solution within each species. Other Crops is prepared by adding 4½ pounds zinc • Iron deficiency also may be a problem 0-0.5 low-marginal 5 0 sulfate (36 percent Zn) to 100 gallons in certain lawns, shrubs, ornamentals > 0.5 adequate 0 0 of water. Include a surfactant (wetting and orchards (particularly peach trees). *Recommendation is based on the use of zinc agent). Foliar applications are effective in Iron-deficient fields, when viewed from sulfate as source of zinc. greening foliage but are not as effective in a distance, exhibit irregularly-shaped yellow **Following sugar beets, increase soil test categories by 50% (low = 0 - 1.4 and marginal producing yield response. Consider them as areas. Because iron is not translocated in = 1.5 - 2.2). a salvage measure. the plant, deficiency symptoms appear on The most common inorganic source is the new growth first. Iron deficiency on zinc sulfate. It is considered an excellent Correcting Zinc Table 2: Interpretation of the AB-DTPA source of zinc whether applied as a granular extractable iron test. Deficiencies material in a bulk blend or incorporated Irrigated and Test values in ppm1 Zinc deficiency is readily corrected into solid or liquid fertilizers. Zinc oxide dryland is another inorganic source of zinc that is by application of zinc fertilizers (Table 1). 0-3.0 low effective when incorporated into solid or Considerable research with zinc has been 3.1-5.0 marginal liquid fertilizers. Avoid applying granular conducted by Colorado State University, above 5.0 adequate as well as other universities, during the last zinc oxide on calcareous soils due to its low solubility. Zinc fertilizers should be at least 1Values below 10.0 ppm are classified as 20 years. The following recommendations deficient for turf and many ornamentals. for zinc fertilization are based on this 40-50% water soluble to supply adequate research data. plant available zinc. Organic zinc sources individual plants is characterized by yellow Zinc fertilizer applications can be either (chelates) also are available and generally leaves with dark green veins (interveinal banded at planting or broadcast pre-plant are more effective per pound of zinc than chlorosis). On corn and sorghum, this gives with little difference in response when inorganic sources. Some of these materials the plants a definite striped appearance. If applied at an adequate rate. Generally, have been shown to be three to five times as the condition is severe, the whole plant may broadcast-plowdown is the most effective effective as the inorganic sources. Effective be affected and turn a very light yellow or method of application. Banding may zinc chelates may be used at about one- even white. In many cases where moderate be preferred in situations of shallow or third the rate of inorganic products. deficiencies occur early in the season, minimum tillage. One application of 5 to Manure applications are quite effective plants tend to recover later. 10 pounds Zn per acre, 15 to 30 pounds in eliminating zinc deficiency problems when applied at the rate of 15 to 20 tons per acre. Soil Testing for Iron The AB-DTPA extraction procedure Iron Problems used for zinc allows the determination Iron deficiencies may occur in all areas of iron on the same extract. Collect soil of the state and are frequently associated samples for the iron test from the areas with the following situations: of the field that are suspected of being • Iron deficiency appears in irregular deficient. Collecting a composite sample areas of the field associated with areas from the entire field will not reflect the of high soil pH, free calcium carbonate condition in the eroded or leveled areas. and low organic matter. The AB-DTPA extractant brings into • Areas frequently have had the topsoil solution a portion of the iron in the soil removed by erosion or leveling. that is related to that potentially available for plant uptake. The test levels have been Figure 1. Zinc deficiency in corn. Credit: H. Follett interpreted through experiments and observations of plant growth on soils with a range of extractable iron levels (Table 2). The rate of sulphur necessary to accomplish apply spray when leaves will remain this on calcareous soils is not economically moist for a period of time. Use chelates at feasible (1 pound S for every 3 pounds lower concentrations; 7 to 10 pounds per
of CaCO3). Iron oxide fertilizers are highly 100 gallons of water. Some chelates will water insoluble. Fertilizer containing this cause leaf burn if applied in too high a form of iron will not be available to plants concentration. Check the recommendation in Colorado soils. on the label for rate. Iron deficiency can be controlled by Iron fertilization is recommended several means other than soil application. only for those field crops that are sensitive On medium testing soils, selection of a to low soil iron levels: corn, sorghum, crop or crop variety less sensitive to iron sudan, sorghum-sudan hybrids, beans deficiency can be effective. Manure or and potatoes. Since a soil treatment is not Figure 2. Iron deficiency in corn. sewage sludge at the rate of 15 to 20 tons effective, spray the crop with iron when it Credit: International Plant Nutrition Institute per acre on a dry weight basis may be becomes apparent that the crop is actually effective for several seasons. iron efficient. Correcting Iron Deficiency Applying iron as a foliar spray is effective in restoring green color to plants, Soil application of iron-containing but may not restore top yields. Iron sprays For More Information compounds to eliminate iron deficiency are most effective when applied to young has not been economically possible on a plants and when repeated at 10-day to field scale. Iron chelates are available that two-week intervals. Ferrous sulphate or Zinc plant availability as influenced will correct iron deficiency at application iron chelates can be used as a spray. Iron by zinc fertilizer sources and zinc rates of 5 to 10 pounds of metallic iron per deficiency is best corrected by spraying the water-solubility. Amrani, D. Westfall, G. acre, but they are too expensive to use on crop with a 2 percent ferrous (iron) sulfate Peterson field crops. solution (1 percent for potatoes) at the rate Ferric sulphate and ferrous sulphate of 15 to 30 gallons per acre beginning 10 are not effective as soil applications at Making Better Decisions: Zinc Fertilizer to 15 days after crop emergence. Repeat Efficiency Ratios. T. Shaver and D.G. economically feasible rates. Some products application at 10-day intervals if yellowing Westfall under development may be useful for soil of foliage persists. application. Because the problem of iron A 2 percent solution is prepared by deficiency is associated with high pH and adding 16 pounds iron sulfate (20 percent excessive calcium carbonate in the soil, iron) to 100 gallons of water. Include a the possibility of lowering the soil pH to surfactant (wetting agent). For best results, correct the problem has been suggested.
Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating. CSU Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.