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Issue link: http://read.dmtmag.com/i/775572
18 SportsTurf | February 2017 www.sportsturfonline.com FIELD SCIENCE Zinc deficiency is a rare problem. It typically occurs in soils with an excessively high or excessively low pH. Zinc deficiencies are generally associated with tissue levels below 15-20 mg kg-1. In various turfgrass species, the range may be as high as 20 to 55 mg kg-1. Deficiency symptoms of Zn will vary with warm- and cool-season turfgrasses. Copper, again a very rare deficiency in turf, and tissue tests of less than 5 mg kg-1 will demonstrate visual symptoms. These symptoms include: a bluish color on new leaves and necrosis that moves to the base of the leaf. Plants need very low amounts of Mo to function. Plant tissue should contain 0.1 to 1 mg kg-1 and soil tests should be in the range of 0.1 to 1.2 mg kg-1. Molybdenum deficiencies are very rare but may occur on turf grown in acidic, sandy soils in humid regions. One of the solutions to Mo deficiency can be to increase soil pH by liming. Boron is the least understood micronutrient, however it is known that grasses need between 5 to 10 mg kg-1 of B in the tissue. Since these levels are so low, that might explain why deficiencies are so rare. However, symptoms of B deficiencies are discoloration of the shoots and stunting of the growth point. Boron fertilization is generally avoided because the range for toxicity is not much above the range for deficiency. Sewage effluent water can be high in B and if effluent is used for irrigation, this is an element that should be monitored. Chlorine deficiencies again are fairly rare, but when they do happen they appear as chlorosis of new leaves, witling, and in some cases necrosis. Plants should contain around 0.1 to 0.6% Cl by dry weight, and deficiencies would show up when tissue Cl concentrations are less than 200 to 400 mg kg-1. If deficiencies appear, applications of potassium chloride can correct the problem. Cl toxicity can occur when Cl becomes >1% of dry weight. Nickel was most recently added to the list of essential elements. Its role in the plant is poorly understood, and in fact no specific Ni deficiency symptoms exist for turfgrasses. Plants normally contain Ni in a range of 1 to 10 mg kg-1 by dry weight, and repeated applications of sewage and related-industrial byproducts could be the source of Ni toxicity on turfgrass stands. A few other elements have also been considered for the list of essential elements for all plants, but have not been added to date. Silicon is often not classified as an essential mineral nutrient for turfgrasses, but turfgrass tissue concentrations typically contain 1% of their dry weight as Si. No current Si recommendations exist for any specific turfgrass species at this time, and currently deficiency symptoms don't exist for Si. Cobalt (Co) is another one of the elements that is not on the accepted list of essential elements, but plays an important role in some higher plants. It is found in plants in small amounts, it helps with metabolism, and has demonstrated a role in nitrogen fixation in legumes. It can be found in coastal mountain soils of California in high levels, which can make for difficult growing conditions for turfgrasses in these soils. Specific ranges of Co are not known for turfgrasses deficiency or toxicity. Sodium is not considered essential for plant growth, but is easily taken up by the plant and present in many soils. Soils with a pH above 8.2 can have Na on Cation exchange sites, which will lower the soils ability to hold and exchange other elements. Excessive Na will also cause the soil to loose structure. Halophytes, or salt-loving plants, remove Na from the soil and thrive with Na present, in many cases, Na is harmful to most turfgrass species. Seashore paspalum is the one major turfgrass exceptions. Tissue tests and soil tests are two of the best ways to see if micronutrient fertilization applications are needed, and these tests will give you an idea of where you stand on overall fertility. Since micronutrients play important roles in healthy turfgrass, they need to be considered in the development of a sound management program. But don't forget the concept of the "curve of diminishing returns." If you have enough, more is not going to help. In fact it can become toxic. Nick Christians, PhD, is a professor in the department of horticulture at Iowa State. Adam Thoms is assistant professor and Extension turfgrass specialist at Iowa State. References for this article are available on www.sportsturfonline.com. For more information on micronutrients, see the latest edition of "Fundamentals of Turfgrass Management 5th ed." (Christians, Patton, and Law, 2016). Table 1. The 17 Essential Nutrient Elements Required for the Growth of Plants Carbon (C) Sulfur (S) Zinc (Zn) Hydrogen (H) Calcium (Ca) Boron (B) Oxygen (O) Magnesium (Mg) Chlorine (Cl) Nitrogen (N) Iron (Fe) Copper (Cu) Phosphorus (P) Manganese (Mn) Nickel (Ni) Potassium (K) Molybdenum (Mo) If you have enough of a particular element, more is not going to help.