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Issue link: http://read.dmtmag.com/i/792045
22 March 2017 Landscape and Irrigation www.landscapeirrigation.com LANDSCAPE AND TURF MAINTENANCE response will occur. So, does Ca work? The answer is yes, if you have the conditions in which Ca is truly deficient. 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 deficient 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 sufficiency 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 deficiency 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 find 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? Clearly the answer is yes, if they are deficient, but if there is enough, more and more will not help. MICRONUTRIENT ELEMENTS Iron is often the most common deficient micronutrient because it can easily become unavailable to the plant in high-pH soil. Tissue tests can reveal needed applications of Fe (sufficient 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 (FeSO 4 ), 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 FeSO 4 . 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 turf. Manganese deficiency can look similar to magnesium deficiency 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. Deficiencies can happen in low- to high-pH soils. Manganese deficiency will show up in younger growth first 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. 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 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. If you have enough of a particular element, more is not going to help.