SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.
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FieldScience | By Dr. Tom Samples, Dr. John Sorochan, Adam Thoms, and Brad Jakubowski Nothing minor about micronutrients ALTHOUGH TURFGRASSES CONTAIN ONLY TRACE AMOUNTS OF BORON B, chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni) and zinc (Zn), these eight micronutrients are essential for plant growth and survival. When it comes to turfgrass nutrition, essential micronutrients deserve attention and should not be overlooked. In order for a nutrient to be considered 'essential', it must 1) be required for a turfgrass plant to complete its growth cycle; 2) perform a plant function that cannot take place without it; or 3) be directly involved in photosynthesis, respiration, or the production or breakdown of organic materials within the plant, or necessary for a critical chemical reaction. Of the essential nutrients, carbon, hydrogen and oxygen are supplied to turfgrasses by carbon dioxide and water. The majority of carbon dioxide is taken up through minute pores, or stomates, on the surface of leaves and stems. In addition to Figure 1. Soil pH chart. 8 SportsTurf | February 2013 moving nutrients from one plant part to another, water also provides turfgrasses with hydrogen and oxygen. Turfgrasses primarily absorb the remaining essential nutrients from soil. The fibrous nature of the root system and the massive number of root hairs contribute to a turfgrass plants ability to extract these mineral nutrients from a soil solution. Due to the amount turfgrasses require, nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S) are categorized as macronutrients. The macronutrients are often further sub-divided according to the amount re- quired by turfgrasses. Nitrogen, P and K are primary macronutrients, while Ca, Mg and S are secondary macronutrients. Results of analyses of macronutrients in tissue are often reported as percent on a dry-weight-basis. For example, bermudagrass turf is often considered nutrient deficient if shoot tissue contains less than 2% N, 0.3% P, 1% K, 0.5% Ca, 0.3% Mg and 0.2 % S on a dry-weight-basis. EFFECT OF SOIL PH ON UPTAKE OF MICRONUTRIENTS Micronutrients, also referred to as trace or minor nutrients, are usually found in dry turfgrass shoot tissue at levels less than 1,000 ppm. Micronutrient applications are seldom beneficial to turfgrasses growing in fertile, mineral soils with a slightly acid pH (for example, 6.0 to 6.9). However, when turfgrasses are managed in high-sand-content soils, organic soils or soils with high- or low pH, the application of a micronutrient may be very beneficial. The availability of micronutrients in soil for uptake by turfgrasses is influenced by the level of soil acidity or alkalinity. Plant availability of Fe, Mn, Cu and Zn decreases as the soil pH rises above neutral (7.0), while that of Mo increases with increasing soil pH (Figure 1). ROLE OF MICRONUTRIENTS IN TURFGRASSES Boron affects the formation of plant cell walls and the transport of sugars. Chlorine influences photosynthesis, the division and length of plant cells, and the opening and closing of stomates. Copper is necessary for photosynthesis and influences the lignin content and strength of cell walls. Iron is involved in the production of chlorophyll. Several enzymes associated with the transfer of energy, N fixation and the production of lignin contain Fe. Manganese is necessary for photosynthesis and is involved in the formation and breakdown of N-containing compounds. Plants deficient in Mn for an extended period of time are, most often, very low in chlorophyll. Molybdenum is involved in the formation of proteins and the use of N and S by turfgrasses. Molybdenum also affects the production of pollen. Nickel, recently classified as an essential micronutrient, is a component of an enzyme. www.sportsturfonline.com