Controlled-Release Ferts Offer Many Advantages

Why these products may make environmental and economic sense for your program

There are many good reasons to include controlled-release fertilizers in your property maintenance or lawn care programs. These reasons are both economic and environmental.

All nitrogen fertilizers, whether quick-release or controlled-release, become part of the soil nitrogen cycle. Controlled-release products, however, release nitrogen over a longer period of time.

For example, research at several universities suggests that later-season fertilization with the newest polymer-coated “enhanced-efficiency” products provide an early spring green-up with less flush growth. A late-season fertilization with these new polymer-coated products, which release controlled amounts of nutrients – but only when they’re needed by plants – may even negate the reduce bagging or double-cutting during your incredibly busy springs.

Because of their extended release, you may find that there’s no need to make an application of a quick-release product every six or seven weeks. Instead, you (or your lawn tech) can use the time you free up to perform other revenue-producing services on clients’ properties.

The newest efficiency-enhanced products can also help landscape and lawn care pros provide more environmentally acceptable services and, in some cases, comply with regulatory issues. Significantly less nitrogen (N) has been shown to leach from controlled-release fertilizers than from soluble N products. For this and other reasons, the extended-release nature of these products, usually dependent upon microbial activity initiated by soil temperature and moisture, would seem to provide a good opportunity to keep clients’ properties green and healthy during seasonal fertilizer bans, such as those in place in New Jersey and many Florida communities.

Most controlled-release fertilizers are nitrogen-based, and most research to this point has evaluated plant responses N responses. These products produce different responses in different turfgrass species, even taking into account different temperature and climatic conditions. In other words, one size does not fit all when it comes to determining which controlled-release product will work best on your properties.

And, of course, there are cost considerations, even among slow-release products. These products (and especially the latest efficiency-enhanced polymer-coated products) cost more per pound of N. And, as we all recognize, landscape and lawn care operations make their product choices balancing both cost and results; if less-expensive products produce results acceptable to clients, that’s where they’ll spend their money.

Efficiency-enhanced, slow-release, controlled-release, delayed-release: Semantics aside, substantial differences exist among the individual specialty fertilizers fitting the general category of controlled-release fertilizers. For example, none of us would confuse natural organic fertilizers processed from animal wastes with today’s technically advanced polymer-coated products. However, both would be considered slow-release fertilizers. For the sake of brevity, let’s leave the topic of the so-called natural organic fertilizers for a future piece. We’ll relay upon the definition offered by the Association of American Plant Food Control Officials (AAPFCO) to guide us.

“Fertilizers in which one or more of the nutrients have limited solubility in the soil solution, so that they become available to the growing plant over a controlled period. The ideal in such a fertilizer would be the release of nutrients at a rate exactly equal to the needs of the plant,” according to AAPFCO. “The limited solubility may be an inherent characteristic of the fertilizer such as in the urea-formaldehyde reaction products … or it may be imparted to a soluble fertilizer by coating the particle with such materials as molten sulfur, waxes and plastics.”

Coated and uncoated products

Controlled-release fertilizers are broadly divided into coated and uncoated products. Coated products typically consist of quick-release N sources surrounded by a barrier that prevents the N from releasing rapidly in into the environment. They consist of a fertilizer core surrounded by a coating, such as sulfur or a polymer. Uncoated products rely on their physical characteristics, such as low solubility, for their slow release.

Slow- and controlled-release fertilizers have been available to the green industry for a long time. Urea-formaldehyde has been available to the trade since 1955, the methylene ureas since the 1960s, Osmocote was released in 1967 and sulfur-coated urea in the early 1970s. And, of course, humans have used animal waste to fertilize crops since before recorded history. In that sense, it’s the synthetically produced fertilizers, whose production and use exploded only in the 20th century, that are the relative newcomers. That said, because of their availability, cost and convenience of use, synthetic quick-release fertilizers (often in combination with the less expensive slow-release products such as SCU) are most widely used by the green industry and, in particular, by the turf care industry.

Here are your choices

Here is a brief recap of some of the controlled-release products available to the green industry:

• Ureaform (UF) and methylene urea (MU) are mostly granular, but there are some liquids. They are about 40 percent N and 28 percent WIN (water insoluble nitrogen). They are formed by reacting urea and formaldehyde. The main difference is chain length resulting in a different mineralization rate. The longer the chain, the less soluble it will be mineralized. They release N for eight to 12 weeks, the rapidity of the activity dependent upon soil temperature and moisture. They are significantly more active at 75 degrees Fahrenheit than at 50 degrees Fahrenheit, for example.
• IBDU (isobutydine dilurea) is urea reacted with isobutyraldehyde. It’s a white crystalline solid available in various particle sizes. Its chemistry is similar to UR and is 30 percent N, 90 percent WIN. The IBDU molecule reacts with water and breaks apart. The rate at which IBDU dissolves in water is dependent upon particle size and the amount of moisture in the soil. Release depends on granule size; smaller granules release N faster than larger granules. Release is not microbe dependent so it can occur at relatively low temperatures and is preferred for cool-season applications. IBDU is relatively insoluble so only small amounts are available at any one time.
• Sulfur-coated urea (SCU) contains a solid urea core coated with sulfur and wax. They’re usually brown to tan or yellow, depending on the urea source. SCU contains 30 to 40 percent N, depending upon coating thickness. The coating is usually not perfect. Some particles usually have cracks and others have thin spots or holes. The release is determined by the thickness of the coating of individual particles and also on the quality of the coating. SCUs can provide N for six to 16 weeks in turfgrass. Again, this is dependent upon the uniformity of coating thickness and soil temperatures, with warmer temperatures needed to allow microbes to break down the wax coating. Included in this category of products are the hybrid polymer-coated sulfur-coated fertilizers (PSCF). Polymers are essentially plastics. The polymers of PSCFs are chosen to provide a continuous membrane through which water and nutrients must diffuse, rather than fill in imperfections. Rate of water diffusion in and out of the particle is dependent upon the permeability characteristics of the polymers.
• Polymer-coated fertilizers (PCF) contain a solid urea coated with a polymer (plastic). The polymer coatings are tough and thin. These are the most technically advanced forms of turfgrass fertilizers in terms of nutrient release and plant-use efficiency. PCFs release nutrients by diffusion, which is fairly constant over time, through a semi-permeable polymer membrane. Nutrient release in these products depends upon the thickness of the polymer coating and soil temperature and moisture. Indeed, the release rate can be controlled by the composition and thickness of the coating.

This graphic from Agrium Advanced Technologies shows the importance of moisture and temperature in releasing nutrients from polymer-coated products.

Always read the fertilizer label or ask your supplier about information about the fertilizer. This should include how the fertilizer is manufactured, the materials used to make the formula, how much initial release you can expect, how long the product will provide nutrients to turfgrass and at what temperature.

Regardless of your fertilizer choice, whether quick-release or one of the several controlled-release products, your responsibility as a green industry professionals is to be stewards of the environment. That means following the “4R’s” concept: the Right fertilizer source at the Right rate at the Right time in the Right place.

Ron Hall is editor-in-chief of Turf magazine. He has been reporting on service industries, including the landscape/lawn service industry, for the past 28 years. Contact him at rhall@mooserivermedia.com.