Turfgrass Fertilization: Elevate Fertilizer Know-How

By Christine Menapace
From the Spring 2019 Issue

Turf fertilization can be a landscaper’s best friend or worst enemy. Get it wrong, and it can cost your business clients and money. Get it right, and you have happy customers and healthy lawns. In fact, dollar for dollar, fertilization can do more to improve poor quality turfgrass, or maintain good quality turfgrass, than any other management practice, according to Dr. Peter Landschoot, professor of turfgrass science at Penn State. But first, you need to do your homework. According to Landschoot, a successful fertilization program requires: 

turfgrass fertilization

(Photo: Getty Images)

  • assessing the turf’s nutritional requirements;
  • understanding fertilizers; and
  • knowing how much to apply and when.

Assessing Nutritional Requirements

The first step in any fertilization program should be soil testing. While this testing won’t provide insight into the amount of nitrogen needed, it will provide insight on phosphorous, potassium, and lime. For some nutrients, it’s the only way to accurately determine how much fertilizer the turf actually needs, yet too often this step is bypassed.

“I know it doesn’t happen a good portion of the time,” says Landschoot. “Golf course and sports turf managers use soil tests, but with landscapers it’s a mixed bag. Though I see an increasing trend of more people using them. In some states, it’s become law that you cannot apply phosphorous to established turf without a soil test.”

Landschoot recommends testing every two or three years, not just when there’s an issue. “Once you see a problem,” he says, “it can take a while to fix it.”

Find a lab, preferably in your region, or at least familiar with the region, that can provide recommendations specifically for turf, not agronomic use. Follow sampling instructions carefully, since they can vary depending on lab, and use the same lab year after year for consistency. “Soil testing is a relatively small investment for the information it provides,” says Landschoot. If you wing it and get it wrong “it can take a lot of time and money to correct.”

Understanding Fertilizer

While most everyone knows to read the fertilizer grade, that trinity of numbers—nitrogen, phosphorous, and potassium—that represents the percentages of ingredients by weight, there’s a lot more to understanding what’s in the bag if you want to get the most bang for your buck. “Learn how to read a fertilizer label,” urges Landschoot. “When I give talks to turfgrass professionals, I always hit on knowing terminology. These terms aren’t fun, it’s just really boring stuff,” he admits. “But it’s just so important.”

Key to understanding a label is knowing the different forms of nitrogen and how these act when applied to the soil. For instance, while the difference between quick release and slow release fertilizers may seem apparent, the label may be a bit misleading. Quick release fertilizers include compounds containing ammonium, nitrate, and/or urea and have 11% to 46% nitrogen. Slow release fertilizers have varying degrees of water insoluble nitrogen, or WIN.

Slow and controlled release nitrogen fertilizers, nitrogen stabilizers, and phosphate management products are all categories of Enhanced Efficiency Fertilizers, or EEFs. The Association of American Plant Food Control Officials (AAPFCO) defines EEFs as fertilizer products that can reduce nutrient losses to the environment while increasing nutrient availability. These fertilizers can slow the release of nutrients for uptake, or abate the conversion of nutrients into loss susceptible forms.

But there’s a difference between slow release and controlled release. In slow release fertilizers, complex compounds release nitrogen by biochemical breakdown, and release time is determined by the compound and biological activity.  In controlled release products, nitrogen is released by diffusion through a polymer coating. The release rate is controlled by soil temperature. (More on this below.)

Landschoot recommends that for a truly slow release fertilizer, look for the term WIN. A bag that claims “slowly available water soluble nitrogen” is likely to act more akin to a quick release fertilizer but may have less potential for burn, he says.

Ultimately, the goal of a nitrogen fertility program is to optimize plant uptake while minimizing leaching, runoff, and gaseous losses. While leaching and runoff can be minimized by not overwatering and turning off spreaders on pavement, gaseous losses (called volatilization) can occur following applications of quick release urea or ammonium in high temperatures on alkaline soil if not watered-in after application. As a result, some quick release products are available that contain additives called “urease inhibitors,” also called “stabilized” fertilizers, that can improve efficiency by reducing gaseous losses. Landschoot says “Certain additives can be good based on the situation.”

As to slow and controlled release, there are many different nitrogen sources. Here’s a summary of how some work:

Ureaform: Urea and formaldehyde with at least 35% nitrogen and 60% WIN. Comprised of three Fractions based on solubility and rate of release with I acting more like quick release and III being the slowest. Dependent on microbial activity and can have low efficiency in first years of use.

Triazones: Liquids made with urea, formaldehyde, and ammonia. Classified as slow release but acting more like urea quick release than other slow release nitrogen sources.

IBDU: Isobutyraldehyde and urea. 90% WIN. Can have three to four week delay in grass response.

Sulfur Coated Urea (SCU): Urea sprayed with molten sulfur and sealant. Releases from microbial action and cracks in the coating. Release varies from granule to granule with variability of coatings.

Polymer Coated Nitrogen: Urea or other nitrogen source coated with a thin layer of plastic resin. Release occurs when water is absorbed by the coating. Can have different coating thicknesses for different rates of release. Release rate increases with higher temperatures but not significantly affected by soil moisture, volume of water applied, soil pH, or microbial activity.

Knowing the difference in nitrogen sources and how they release can aid in efficient timing and application of fertilizers. Know the terminology and talk to reps at trade shows. “Every product has unique characteristics,” says Landschoot. “If you know how to interpret that label, that’s 50% of the game.”

Fertilizer Application: How Much, When, And Frequency

Besides nitrogen sources, spreading the right amount of fertilizer per square foot is key. And yes, you need to do math! A fertilizer calculator developed by Purdue University can be found online. Or, a handy two-step table to make the calculations yourself can be found here.

However, Landschoot recommends knowing how to do the calculations on your own. “We struggle with this with some of our students,” he comments. “But you better know it. You can make one big mistake and you’re losing customers and maybe your job. It’s just what you have to do in this business. It’s why we call ourselves professionals.”

turfgrass fertilization

On small lawns enclosed by sidewalks and driveways, use a drop spreader or a liquid application for greater accuracy. (Photo: Getty Images)

Unfortunately, there is no “one size fits all” optimum number of fertilizer applications. Most programs range from two to four applications a year, depending on amount of fertilizer desired, nutrient release rates, grass species, climate, and costs. “If I were a grounds manager, I’d try to keep applications to about three times a year to save labor,” says Landschoot. However, he points out, “…timing is a more important issue than the number of applications. Think mid to late spring, late summer, and maybe late fall.”

Landschoot also emphasizes that landscapers should keep in mind overall turf health (root growth), not just greening up (leaf growth). Late summer is actually the most effective time of year to fertilize because it helps the grass make carbohydrates (used for root growth and stress tolerance) which leads to healthier, greener grass in spring. (If soil is sandy, use a slow release fertilizer in late summer to minimize leaching.) On the other hand, excess fertilizer in spring can lead to more pronounced leaf growth, but with the possibility of turf stress later in the season. For more detailed information, see Landschoot’s paper.

A Few More Tips

A few more generalized tips to make the most of a fertilizer program include:

  • Returning clippings to lawns can cut nitrogen fertilizer use by up to one-third.
  • Turfgrass species differ in fertilizer requirements. For example, Kentucky bluegrass and perennial ryegrass typically require twice as much nitrogen fertilizer per year as fine fescues.
  • On small lawns enclosed by sidewalks and driveways, use a drop spreader or a liquid application for greater accuracy.
  • With granular fertilizer, consider the SGN, or size guide number, of the granules. It should be between 75 and 250 (75-150 for golf course greens and fairways, and 200-250 for lawns) for optimum spreading efficiency. Buy one bag and check the amount of dust or broken particles (a waste of money) and size uniformity before buying several bags.
  • Don’t apply nitrogen to summer dormant lawns or on frozen winter surfaces.
  • Water-in urea or ammonium fertilizers, especially in warm weather.

To Outsource?

Of course, not every landscaping company wants to take on the responsibility of offering a fertilization program, especially in states with regulations, laws, and licensing requirements. (A helpful list of state fertilizer laws can be found on the AAPFCO website.) In this case, outsourcing is an attractive option.

“It’s definitely more popular than it used to be,” says Landschoot. “It makes sense.” But this shouldn’t mean you’re off the hook. “You still need to know what you’re doing so you don’t pay for what you don’t need. Look at the soil test. Ask questions.”

Menapace is a professional freelance writer and editor with over 25 years of experience in publishing, journalism, copywriting, and marketing.

Share your thoughts in the Comments section below or send an e-mail to the Editor at acos-grove.turf@groupc.com.

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