February 2017

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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Page 16 of 51 February 2017 | SportsTurf 17 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 defi ciency 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 fi rst application. As more and more is added, a point is quickly reached at the top of the curve where no additional response will occur. So, does Ca work? The answer is yes, if you have the conditions in which Ca is truly defi cient. But the answer is no if you already have enough Ca. It is also possible to apply too much of anything and cause a negative response. Boron for instance has a very narrow range from enough to too much, and excessive B can kill the plant. This is also true of some of the other nutrients to varying degrees. One of the most obvious is N. Grass defi cient in N will be chlorotic and grow slowly, just enough and the plant is at peak performance, but apply too much and you can kill the grass. Other elements, such as P have a very wide range of suffi ciency and negative responses occur only at extremely high levels. This same concept holds true for your body. Does vitamin D work? Yes it does if you have a true defi ciency of this vitamin. But if you already have enough, more is not going to improve your heath, and excessively high doses may be dangerous. We also mentioned economics. Economists fi nd that if an economy is underinvested in certain areas, the application of additional capital will provide a large improvement in economic conditions, but the return on investment diminishes with each addition of capital, until the point of leveling off is reached. Keep this concept in mind when dealing with each of the following elements. Is each of these needed in a fertility program for sports fi elds? Clearly the answer is yes, if they are defi cient, but if there is enough, more and more will not help. MICRONUTRIENT ELEMENTS Iron is often the most common defi cient micronutrient because it can easily become unavailable to the plant in high-pH soil. Tissue tests can reveal needed applications of Fe. Suffi cient levels of Fe in plant tissue are 150 to 500 mg kg-1. Iron is a critical element in the formation of chlorophyll, and turfgrass will demonstrate a yellow or chlorotic color when Fe is lacking. Applications of Fe will make the turfgrass a darker green color within 24-48 hours. Iron and other metal elements such as Mn and Mg will often be applied as a chelated form to hold solubility in high-pH soils. Common forms of Fe used in turf are iron sulfate (FeSO4), and two commonly used chelated forms: iron diethylene triamine pentaacetic acid (DTPA) and iron ethylenediamine-N,N'-bis(2- hydroxyphenylacetic acid) (EDDHA). Chelated forms are more expensive, but should have a positive response that lasts longer than FeSO4. New research also indicates 93% of iron applied as iron glucoheptonate (a form of chelated iron) or iron sulfate were deemed insoluble to the plant within an hour when applied to soil. Applicators need to be sure to not drive across fresh Fe foliar applications to avoid tire marks on the fi eld. Manganese defi ciency can look similar to magnesium defi ciency with the leaves demonstrating a chlorotic appearance. This is due to the role manganese plays in photosynthesis, enzyme activation, and root growth. A healthy turfgrass should contain between 20 to 500 mg kg-1 of Mn on a dry weight basis. Defi ciencies can happen in low- to high-pH soils. Manganese defi ciency will show up in younger growth fi rst since it is immobile in the plant. Soil applications of Mn from either the sulfate or glucoheptonate forms remained at least 30% soluble for 21 days after application; however, a rapid reduction in solubility took place to get to that 30% solubility. Figure 2. The effect of soil pH on nutrient availability. The wider the line, the greater the availability. (Christians et al, 2016). Picture is based on Troug, 1946.

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