Landscape
And
Nursery
Dialog
Mary Ann Rose
Commercial Landscape
& Nursery Specialist
The Ohio State UniversityJune, 1995
Slow release fertilizers for container nursery production
Keywords: fertilizer, nutrition, nursery, container production
M any types of slow release fertilizers are available to the commercial nursery industry. Slow release fertilizers are a great advantage over soluble fertilizers in that they can offer a complete nutritional package for a season or longer. Release rates vary from weeks to years; in Ohio the 3-4 month and 8-9 formulations are the most popular. Some of these are slow release nitrogen only, and some contain slow release N-P-K. All of these products can be used to grow a successful crop, and may be incorporated or topdressed. It's up to the grower to decide which product fits into the production plan best.
Urea formaldehyde (e.g., Blue Chip 38-0-0) is a polymeric form of nitrogen that is a condensation product of urea and formaldehyde. About one third of the total N in urea formaldehyde (UF) is available in the first few weeks, another third in a few months, and the remaining portion in 1 to 2 years. Growers report that UF sustains a crop about 6-8 weeks. The remainder of nitrogen that releases very slowly over time can help even out the nutritional program, or provide an added benefit to the consumer who buys the plant. UF nitrogen is released primarily by microbial action; increasing temperature and low pH values in the medium increase the release rate.
Isobutylidene-diurea (IBDU) is a condensation product of urea and isobutyraldehyde. The nitrogen in IBDU is released by a chemical hydrolysis reaction, and in contrast to UF nitrogen, the microbial degradation is minimal. Particle size, hardness, and the amount of water passing through the media have the biggest effect on the fertilizer release. Low pH increases hydrolysis, but temperature is not a critical factor. Commercial IBDU fertilizers contain multiple particle sizes to achieve an even release rate. The maximum duration of release for IBDU particles is about 5-6 months. In the Woodace brand of fertilizers, IBDU nitrogen is combined with a plastic coating technology to produce fertilizers that release over periods longer than 5-6 months.
Magnesium-ammonium phosphate (Mag-Amp, e.g., 7-40-6). Nutrients from Mag-Amp are released as the compound solubilizes; release is controlled much as described for IBDU. Compared to other nursery fertilizers, Mag-Amp is low in nitrogen content, and very high in phosphorus. Perhaps it is more properly considered a slow-release phosphorus.
Coated fertilizers. Most container growers are using one or more slow-release fertilizers with either a sulfur or synthetic plastic coating. Below I'll discuss the products that are prevalent in Ohio.
Sulfur-coated ureas (SCU). Sulfur-coated urea (e.g., SREF, LESCO) has long been popular and economical for incorporation and top-dressing of containers. The release rate is controlled primarily by the thickness of the coating and medium temperature. The sulfur in the coating is often an advantage because it lowers the pH of the medium. A disadvantage of the traditional SCU products is that a significant portion of the total nitrogen is released early and rapidly due to cracks and imperfections in the coating. This early release feature has been eliminated and a much more even release pattern has been achieved in the next generation in sulfur coatings, the polymer-coated SCUs. An example of this product is Scott's Poly-S (17-3-6 Topdress). The polymer-coated SCUs are but one type of plastic-coated fertilizer.
Plastic-coated fertilizers. Plastic coating technologies allow manufacturers to carefully manipulate release characteristics and to provide fertilizers that release over periods up to two years in duration. Really only cost limits the manufacturer's creativity. To initiate release from plastic-coated materials, moisture must first diffuse through the coating and solubilizes the fertilizer inside. Temperature is the key factor in the nutrient release from all of these products.
Osmocote 18-6-12 (Scotts), an 8-9 month formulation, has been an industry standard for years. Osmocote is a resin-coated prill containing N, P, and K. Release rates are controlled by coating thickness and temperature. As water diffuses into the prill, the coating swells and the membrane becomes thinner. Coating imperfections in Osmocote contribute to an initial flush of nutrients in the first week after application.
The newer coating technologies do not swell to the degree that Osmocote does. Polyon fertilizers (Pursell Industries) contain polyurethane-coated urea. Like Osmocote, coating thickness and medium temperature control release. This is a new product and we still have much to learn about it.
In contrast to Osmocote and Polyon, The release of nutrients from polyolefin-coated fertilizers is affected by temperature, but not coating thickness. The amount of a surfactant added to the coating determines how rapidly the nutrients are released; more surfactant produces a faster release. Polyolefin resin chemistry is proprietary to a Japanese company, which tends to make these fertilizers somewhat costly. Nutricote (Plantco) and ProKote (Scotts) and are examples of fertilizers with this coating technology. Polyolefin-coated fertilizers do not provide an initial flush
of nutrients that some slow-release fertilizers have. For this reason, the ProKote product also incorporates some readily available methylene urea to provide a higher level of fertility early on.
Well, hope I haven't impossibly clouded your picture of slow-release fertilizers! Truly there are an impressive number available and apparently fertilizer companies are still busy developing new blends and coating technologies. Even, measured release rates and competitive pricing are the goals for the new products. Stay tuned for more about release patterns in a future article.
