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.
Issue link: http://read.dmtmag.com/i/628092
www.stma.org February 2016 | SportsTurf 13 tent turf quality and fewer deficiency symptoms. These sources also minimize losses due to volatilization, leaching and excessive shoot growth. The terms slow release and controlled release are frequently used interchangeably. Here, slow release refers to uncoated prod- ucts and controlled release refers to coated products. Uncoated products are homogenous, meaning that the compo- sition is the same throughout particles. Examples of uncoated products include ureaform (UF) and methylene urea (MU). These uncoated products contain about 40% nitrogen and rely on micro- organisms to mineralize the nitrogen. Because of this reliance on micro- organisms the nitrogen release rate can be quite variable, usually between 8 and 12 weeks, depending upon pH, soil temperature and soil moisture. During cool or cold seasons UF and MU may not be the products of choice, as micro- organism inactivity will prevent the nitrogen from being released. Another example of an uncoated product is isobutylidene diurea (IBDU), contain- ing 32% nitrogen. IBDU is soluble and releases nitrogen by hydrolysis, like the fast release nitrogen sources, except that it has low solubility and therefore releases nitrogen very gradually over time depending upon soil moisture. Because of the reliance on soil moisture, dry or drought conditions will delay nitrogen release. Additionally, low pH and high temperature will accelerate the release of nitrogen. Since IBDU is not dependent on microorganism activity it is a preferred product for cool season application. Coated products include sulfur- coated urea (SCU), polymer-coated fertilizers (PCF) and hybrid polymer- coated sulfur-coated fertilizers (PCSCU). SCU is 30 to 40% urea nitrogen coated with sulfur and sealed with, typically, wax. Imperfections, micro pores and cracks in the coating allow water to enter and dissolve the urea rapidly. Once water enters, the urea can release very quickly and is sometimes referred to as cata- strophic release. Coating thickness and imperfections control the release rate, so particles release at different rates, usually between 6 to 16 weeks. Microorganism activity is needed to break the sealant to expose the sulfur coating. During cool seasons microorganism inactivity and coating variability can cause a mottling effect on turf. When the sulfur coating is too thick, the nitro- gen does not release, and is referred to as lock-off. These particles may rely on some physical disturbance, such as mow- ing, to break the particle and eventually release the nitrogen. Polymer-coated fertilizers release nitrogen by diffusion through a polymer coating. These products may contain other nitrogen sources such as ammo- nium nitrate, or other nutrients such as phosphorous and potassium. There are a variety of methods and chemistries used to produce the coating. Regardless, manufacturers are able to produce quite predictable release rates depending upon the number of layers and thickness. Water diffuses through the coating to dis- solve fertilizer inside. The fertilizer then