Landscape & Irrigation

March 2017

Landscape and Irrigation is read by decision makers throughout the landscape and irrigation markets — including contractors, landscape architects, professional grounds managers, and irrigation and water mgmt companies and reaches the entire spetrum.

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Page 20 of 35 Landscape and Irrigation March 2017 21 LANDSCAPE AND TURF MAINTENANCE How About the Micronutrients? ■ BY NICK CHRISTIANS, PH.D., AND ADAM THOMS While nitrogen (N), phosphorus (P), and potassium (K) generally get the most attention when the subject of turfgrass nutrition for sports fields is considered, there are a number of other elements that can also play important roles in a sound management program. There are 17 elements required for the growth of plants (see Table 1 on page 23). Most of the plant tissue is comprised of carbon (C), hydrogen (H), and oxygen (O), but these three elements are obtained from carbon dioxide in the air and from water and are not included in a fertility program. The other 14 are generally obtained from the soil by the root system, or in some situations through the leaf, and are referred to as the mineral nutrient elements. Of these 14 elements, N, P, and K are usually needed in the largest quantities by most plants, but some of the others can also be important in unusual soil conditions, such as in the sand-based media of a sports field. An imbalance in the soil's pH can also result in deficiencies. These 17 essential elements are divided into the macronutrients and the micronutrients. They are all essential for plant growth; the difference lies in the amounts in which they are needed. Macronutrients are used in the greatest quantities and are generally found in plant tissue in amounts of 1,000 parts per million (ppm) or more. Micronutrients are found in plants at levels of 100 ppm or less. By this definition, carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, sulfur (S), calcium (Ca), and magnesium (Mg) are macronutrients and iron (Fe), copper (Cu), zinc (Zn), manganese (Mn), boron (B), molybdenum (Mo), chlorine (Cl), and nickel (Ni) are micronutrients. In this article we would like to concentrate on the elements other than N, P, and K and how they fit into a fertility program for turf. SOIL AND TISSUES TESTS AND SOIL PH Turf grown on a clay-loam soil with a pH slightly below 7 will rarely show deficiencies of the micronutrients. Grass grown on low-fertility sands, or on soils with an excessively high or low pH may show deficiencies of some of these elements, however. The environment may also play a role. For instance, deficiencies may occur in very wet years, or when it is unusually hot. Therefore, the best starting point is to have both a soil and tissue test completed. Make sure to have an independent lab run soil tests, and not one that is sponsored by your fertility supplier. Soil tests should also report the pH of the soil, which can be an important clue in determining the availability of many of the micronutrients. Figure 2 (on page 22) shows the effect of pH on nutrient availability. The wider the line, the more available is the nutrient to plants, and the narrower the line, the less is available. Elements like Ca and Mg are limited in low pH ranges, while elements like Fe and Mn are readily available in low pH ranges and less available in soils with pHs above 7. CURVE OF DIMINISHING RETURNS There is an important concept in plant nutrition that should be considered before dealing with the individual elements. That is the curve of diminishing returns (Fig. 1). The curve of diminishing returns applies to living systems in a number of important ways and is also used by economists to explain the effects of economic input and output. The concept, simply stated, is that where a deficiency exists, the first increments of the deficient material will produce a considerable increase, whereas each additional increment produces a diminishing response until you reach the sufficient level of that material and no further response can be expected. In agronomics, these curves are also known as "yield curves" and studies are constantly underway with a variety of crops and soil types to determine where the leveling-off point occurs. It makes no sense economically to apply more than is needed for maximum yield. In turf management, our goal is usually not yield of tissue, but aesthetics (how the area looks), but the concept still holds true. If you have enough of a particular element, more is not going to help. Let's use calcium (Ca) as an example. If the grass is growing on a media that is very low in Ca, such as a silica-based sand, the grass will likely show a deficiency of Ca. An ounce of Ca/1,000 ft2 would likely elicit a measureable response on the plant. An additional ounce would provide some response, but not as great as the first application. As more and more is added, a point is quickly reached at the top of the curve where no additional Figure 1. Curve of Diminishing Returns

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