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Essential micro-nutrients for plants
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This week’s column finishes the discussion of essential plant nutrients with the micro-nutrients. These are necessary for the plant to complete its life cycle but are needed in very small amounts compared to the macro-nutrients. The positively charged micro-nutrients are Copper (Cu), Zinc (Zn), Iron (Fe), Manganese (Mn), and Nickel (Ni). The negatively charged anions are Boron (B), Molybdenum (Mo), and Chlorine (Cl). Nickel was the last essential element identified and other than knowing it is essential, we know very little about it and deficiencies are almost nonexistent. So what do these elements do that makes them essential?
While needed in very minute quantities, these elements perform vital plant functions. They serve as catalysts for enzymes which allow them to perform functions from photosynthesis to cell division. Catalysts are not consumed in the reaction and can be used over and over. Therefore lesser amounts are needed. For a few highlights of functions:
• Chlorine, Cl, aids in disease suppression in grass crops, especially small grains.
• Copper, Cu, enhances the flavor of fruits and vegetables. It also increases sugar content.
• Boron, B, is essential in seed and cell wall formation.
• Molybdenum, Mo, is the catalyst for the enzyme that converts nitrate to ammonium for the production of amino acids.
In contrast to the macro-nutrients, we do not have good soil tests for all the micro-nutrients with the ability to relate the amount in the soil to needed fertilizer and sufficiency in the plant. Plant tissue analysis is often necessary in combination with soil tests. Often by the time tissue analysis indicates a deficiency, it is too late to correct the problem for the current year.
Nutrient availability here is primarily dictated by soil pH with nutrients available in the proper amounts from slightly acid to slightly basic. At high pH, nutrients such as iron are tied up by phosphorus and unavailable. At low pH values, very acid soils, nutrients like manganese can be over available and severely damage the plant. This is a key difference between micro and macro nutrients. For micro-nutrients, the difference between sufficiency for plant growth and toxicity, too high a concentration, is quite small. For example, a corn crop of 150 bushels per acre requires 0.008 lb. of molybdenum, 0.27 lb. of zinc and 1.90 lb. of iron. Contrast that with 150 lb. of nitrogen. Producers really do not have to deal with toxic levels of macro-nutrients.
As yields increase and land is farmed for over a century, some of these nutrients are starting to become deficient in soils. Micro-nutrient fertilization is slowly gaining in use as producers continually seek to increase yields. Here, common micro-nutrient fertilizer applications include zinc on corn and chloride (Cl) on wheat. In certain areas, boron is starting to be applied on alfalfa. For corn, adding a small amount of zinc may be the difference between 200 and 220 bushel corn. Chloride on sensitive wheat varieties can add 20% or more to the yield.
However, care must be taken to insure what is actually needed and to apply it in the proper amount. Finally, there may be certain plants requiring other elements. These elements are common to all plants.

Dr. Victor L. Martin is the agriculture instructor/coordinator for Barton Community College. He can be reached at 620-792-9207, ext. 207.