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Fluid Journal : Summer 2017
12 The Fluid Journal Summer 2017 development and micronutrient uptake resulting in deficiencies and indelible yield damage. Because micronutrients are required in very small amounts for adequate nutrition, the range between “enough” micronutrient and “too much” micronutrient can be a lot more narrow than for macronutrients. Micronutrient toxicities that occur can damage or retard plant growth and affect yield. Toxicities rarely result from over-fertilization. They are more commonly associated with contaminations such as from concentrated wastewater, waste sludge being continually applied, or from excessive application of copper- or zinc-containing fungicides. Contaminated irrigation water can also be a source of micronutrient toxicity. Micronutrient Deficiencies It is beyond the scope of this article to list all the possible types of micronutrient deficiencies and their characteristic symptoms. Information, photos, and tables of deficiency factors are available from multiple online sources. However, some crops and soil types are more prone to certain types of micronutrient deficiency than others. Examples include boron deficiency in alfalfa; copper deficiency in wheat, corn, and soybeans; nickel deficiency in pecans; and molybdenum deficiency in soybeans. Zinc deficiencies frequently occur on calcareous, high-pH, sandy texture, high phosphorus, and eroded soils. Poorly drained soils may also be deficient. Some of the more common symptoms to look for include: • stunted growth • delayed maturation • yellowing, and wilted leaves (particularly younger leaves) • thickened, puckered, curled, or brittle leaves • dead growing points • aborted flowers, heads, or seeds • poor grain filling • fruit deformities • increased root disease. These symptoms often occur in irregular patches within fields and can have a drought-like appearance. Keep in mind that there can sometimes be a “hidden hunger” for micronutrients present, in which crops don’t show any overt symptoms until decreased yields are observed at harvest. Tissue and Soil Testing While visual symptoms and suspect soil conditions can raise the possibility of micro-nutrition deficiency, the best approach to identifying a problem and implementing a viable solution lies in regular tissue and soil testing. Your local lab or extension office can guide you through the process, but be aware of the strengths and limitations of each. Soil testing can only measure the quantity of nutrients identified as present through analytical methods, not their total levels nor their availability to plants. By combining frequent soil testing with regular plant-tissue analysis, you can more accurately diagnose deficiencies that may be present and develop the best prescription for addressing those deficiencies. Timing is also an important element. Testing during early to mid-season plant growth may provide time to correct a problem, whereas tissue samples taken during later stages of growth are good to determine corrective actions for the next crop. If you are dealing with a suspected problem, take plant and soil samples from both the affected areas and the unaffected areas. A comparison of results can help create a much clearer picture of the problem and the actions that should be taken. 4Rs of Nutrient Stewardship Once the need for a micronutrient supplement has been determined, the next steps are clearly identified by the industry standards set out in the 4Rs of Nutrient Stewardship. These include determining the “Right Source” for supplying the target nutrient, applying the “Right Rate” for optimal benefit, at the “Right Time” of application during day, growth stage, or growing season. Detailed discussion of those three Rs is beyond the scope of this article; however, we will further expound on the fourth R, “Right Place,” which addresses the application placement and method. Application Methods Micronutrient application methods affect application rates and nutrient use efficiency. Broadcast preplant applications are usually less effective than banding beside the row or in direct seed contact. Uniform distribution of small amounts of micronutrients is a problem when micronutrients are blended with large amounts of dry micronutrient carriers. Coating dry blend materials with micronized micronutrient materials can improve distribution of small amounts of micronutrients. Seed coating is another effective means of uniformly providing small amounts of micronutrients to overcome early season shortages but may need to be partnered with other applications to provide sufficient amounts. Banding micronutrients in fluid starters beside the seed row or in direct seed contact (pop-up) is an effective application method, but special care must be given to rates of some micronutrients to avoid toxicity when placed in the seed row. Foliar sprays or fertigation can provide micronutrients to ward off potential deficiencies or partially correct deficiencies during the growing season. When deficiency symptoms appear, indelible crop damage has already occurred but such damage can be minimized by immediate applications. Fertigation provides the utility of applying nutrients at critical periods of crop water demand by both leaf and root absorption and avoids compaction effects of ground application (iron blight). Be sure to understand fertilizer compatibility with irrigation systems and water quality. Foliar sprays are also well suited for the application of micronutrients. High quality sources of micronutrients are able to permeate and diffuse through the leaf surface into the plant.