Slow and Steady WINS THE RACE

Soluble forms of nitrogen are fast-acting. In turf, they produce greening and a growth flush almost immediately, but the nitrogen is quickly used up and growth slows again in a short time. Therefore, applications of soluble products need to occur at short intervals, or the result may be a cycle of growth surges interrupted by periods of slow growth.

The value of a more consistently available source of nitrogen — consistent growth, fewer applications — has long been understood by turf managers. That's why controlled-release fertilizers have been the subject of research for more than 50 years.

Several types of slow-release N fertilizer are available. Uncoated products, both liquid and granular, include such materials as methylene urea (MU), urea formaldehyde (UF), isobutylidenediurea (known by the trademarked term of IBDU) and triazones.

These materials are slow-acting because of their chemical properties and modes of N release. Many of them are “reacted” products, meaning they are the result of a reaction of a soluble N form (usually urea) with some other material (often formaldehyde) to create a more stable, less soluble chemical that releases its N more gradually.

“Natural organic” products (often derived from byproducts, such as sewage sludge) are another category of slow-release fertilizers.

Coated fertilizers are another major category of products designed to deliver extended, consistent supplies of N to turf. These products usually contain soluble nitrogen, the release of which is controlled by an outer coating. Manufacturers may also coat slow-release N sources, however, and perhaps other nutrients as well. Plus, manufacturers commonly mix coated slow-release products with a bit of uncoated soluble fertilizer for a quick green-up in addition to the longer-lasting N release derived from the coated material.

No cut-and-dried formula exists for determining which type of fertilizer is best, and it would not be accurate to say that one type of product is inherently superior to another. Many uncoated products compete well in both performance and price with coated products. Even highly soluble fertilizers have their place.

You will also find that some products boast benefits not directly related to how they release their N. For example, some of the natural organics, though they supply some N, seem to offer other, perhaps more subtle improvements related to soil chemistry and biology. Some manufacturers offer additives to their fertilizers to create unique proprietary products.

Certainly, price is always a factor that must enter your decision-making process; but, as with all things, it would be a mistake to simply look at cost without examining value. And above all, make sure the product fits your particular needs.

Coats of many colors

For turf, sulfur-coated urea (SC) has been a staple for many years. The basic SC product starts with a granule of urea, which is coated with layers of sulfur and finally a sealant (typically wax) for better coating integrity. After application, as the coating breaks down (due to handling, manufacturing imperfections and degradation by water and microbes), water enters and dissolves the urea, which then releases back out to fertilize the turf. Once an opening occurs, the urea can release from a granule quickly. That's why this is often called catastrophic release. However, because coating thicknesses vary, release occurs sooner in some granules and later in others, resulting in an overall gradual release pattern.

SC is widely available and inexpensive. Not surprisingly, it is also widely used. However, there are limits to how long and how consistently SC can release N.

Another slow-release approach is to coat a soluble, quick-release N with polymers rather than sulfur. These coatings supply N more consistently because the nutrient releases via diffusion across the polymer membrane, rather than through catastrophic release. Coating thickness affects release rate, but to the extent that manufacturers can control the coating, they can control release rates (often with great precision).

The first significant commercial fertilizer to utilize a polymer coat was Osmocote. Osmocote has been around for several decades, but the basic concept — soluble fertilizer surrounded by a polymer coat — is still current. Manufacturers are refining materials and processes to improve performance.

A somewhat different approach has been to create “hybrid” products — polymer-coated SCs. With PCSCs, you gain better performance than with SCs. PCSCs — in several variations — are one of the most widely used types of specialty fertilizers today.

Some manufacturers have concentrated on refining the polymer coating itself, using thickness and composition to create “designer” fertilizers tailored to specific needs. Others use additives or new combinations of fertilizer types to create their own unique products. This array of options might leave some turf managers confused. But the good news is that you now can find a fertilizer product to suit just about any turf site.


United Horticultural Supply had been marketing ESN as its primary coated (polymer) product. However, according to UHS's Technical Director Russ Mitchell, UHS has phased out ESN and now is launching its Signature Blue line of fertilizers. These products utilize PCSCs and straight polymer-coated fertilizer and STU (Sequentially Timed Urea), but with a twist. They are sprayed with Prospect Plus, a fertilizer additive that, according to Mitchell, improves nutrient uptake and plant growth.

Prospect is available alone as a liquid formulation (zinc ammonium acetate), explains Mitchell, but UHS felt that adding it to fertilizer granules (in the concentrated form, Prospect Plus) would offer superior value to their fertilizer line. (Many turf managers already are familiar with UHS's Signature Green line of products, which is UHS's top-end fertilizer line. This product line features their exclusive BCMU — balanced chain methylene urea, an uncoated product.)

As the name suggests, Pursell Technologies Inc. portrays itself as not just a fertilizer company but a coatings technology company. There's merit to this distinction because, when you get right down to it, plants all require the same two or three forms of N for uptake. The important product differences relate to how the nutrient is delivered.

Pursell is best known for its Polyon-branded products. These polymer-coated granules use Pursell's reactive layer coating (RLC) process to create a high-integrity coating that can be altered during manufacturing to provide the desired release pattern.

The primary reason this works, according to John Johnson, director of marketing for Pursell Technologies, is that temperature is the only environmental factor that significantly affects release rate. Thus, knowing the average expected temperatures for your location allows you to predict how a Polyon-coated product with a given coating thickness will release its nutrients over time. In fact, Pursell offers software, complete with weather data for many geographic locations, that does just that.

Many products, according to Johnson, are affected by other environmental factors — microbial degradation, pH, moisture levels — that make it more complicated to predict release patterns.

Pursell also offers its TriKote products, which are PCSCs. According to Johnson, one of the advantages of TriKote compared to SC is reduced lock off. During manufacturing, a certain percentage (depending on the manufacturing process) of SC granules are too thick to allow water penetration and nutrient release within the usual range of time (6 to 8 weeks, for example). Pursell adds a polymer coat to provide added protection for the SC granule, and this allows them to reduce the thickness of sulfur coating. Thus, less lock off.

As a result of a newly signed marketing agreement, Simplot Turf and Horticulture and many if its Best-branded products will utilize Polyon fertilizers to enhance their performance.

Nu-Gro Technologies Inc. may be better known for some of its uncoated reacted products such as Nutralene and Nitroform, but actually was the first to produce SCUs for sale in North America (starting in 1975). In fact, NuGro even owns the copyright to “SCU.”

In addition to marketing its own brands, NuGro is the basic manufacturer of coated and uncoated products for several other suppliers. NuGro produces both SCU and PCSCU products which, according to Bob Staib, a consultant for NuGro, sell well in both the golf and landscape markets.

The Andersons, inheritors of the Scotts line of professional products, markets two PCSCs: the traditional Poly-S, as well as NS-52. Poly-S products are formulated with a variety of N sources, and some are available with micronutrients as well. In addition, they offer more extended release in their Extend line of fertilizers, which are polymer-coated products.

Lebanon offers Poly-X, a PCSC. Though Lebanon markets MESA, an (uncoated) oligomer sulfate, the company also formulates Poly-X with various other fertilizers to suit a variety of needs.

ProSource One offers a range of fertilizer products, both coated and uncoated. Aside from SCs and PCSCs, ProSource One markets Gold Cote, a line of fertilizers that includes both coated urea as well as coated potassium nitrate.

Similarly, LESCO offers its Poly Plus line of poly-coated SCs, as well as its Novex line, an uncoated material consisting of amino-ureaformaldehyde. LESCO operates the largest SC plant in the United States, located in Martin's Ferry, Ohio.

Pete Cavallaro, a product manager for LESCO fertilizers, explains that their Poly Plus coated products are used more in lawn care, while in the golf industry, superintendents use both coated and uncoated technologies. This is due to several factors, but boils down to lower cost for a product that still meets the agronomic and practical needs of commercial lawn-care operators.

LESCO usually blends Poly Plus with quick-release fertilizer for a fast initial green-up. However, the coated granules still provide longer N release for sustained quality. Poly Plus (depending on the formulation) can last up to 10 to 12 weeks.

Cavallaro also notes that ease of operation is emerging as an issue. Polymer-coated products tend to flow more smoothly through spreaders, and may leave less residue buildup to clean off of equipment at the end of the day.

The drive for greater operation efficiency has created another advantage for coated products, according to Cavallaro. It has, among other things, driven the use of larger spreaders. These tend to be somewhat rougher on fertilizer granules than smaller equipment. And since polymer coatings are tougher than plain SC granules, they stand up to the wear better. This is a crucial issue with coated products, which will release all their nutrients at once if their coating is broken.

This also relates to the use of uncoated Novex on golf courses. Certain areas — greens and tees, for instance — are intensively maintained and the mechanical damage that frequent mowing could impart to coated products might ruin their slow-release qualities. Uncoated products, by contrast, are homogenous and continue to function as intended, because their release characteristics are inherent in the material and not reliant on any barrier. However, Brian Rowan, LESCO's Novex fertilizer product manager, points out that coated granular products may work in close-cut turf if they're small enough to infiltrate the turf canopy and thereby gain some protection from mowers.

Rowan stresses that it isn't necessarily accurate to characterize fertilizers (coated vs. uncoated) by site use. Users must determine what's best for their operations, and what's best relates less to what the site is, and more to how the site is maintained.

Check with suppliers for details about release patterns — duration and consistency of release, how environmental conditions affect release rates, whether physical form matches your operational needs and how the price fits your strategy. Don't approach purchasing decisions with the mindset of finding the one best product. Focus on finding one that suits your specific needs.

Lebanon Seaboard 190
Nu-Gro Technologies 192
ProSource One 193
Pursell Technologies 194
The Andersons 195
United Horticultural Supply 196

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