Stabilized nitrogen products, sometimes called “inhibitors,” are often misunderstood. Their use extends the time that nitrogen remains in the form of urea or ammonium in the soil, but they’re not the same as slow or controlled-release fertilizers. While they do have an impact on nitrogen availability, they work differently than some of the more familiar products like sulfur-coated urea, methylene urea, or polymer coated urea.
“The stabilizer additives actually don’t affect the fertilizer itself,” says Eric Miltner, Ph.D., research agronomist for Koch Turf & Ornamental. “They’re basically urea that’s treated with an amendment. The amendment doesn’t change the fertilizer; instead, it affects soil enzymes and how the urea-based nitrogen is transformed in the soil. The use of stabilized nitrogen products can extend the amount of time that nutrients are available for plant uptake.”
Before plants can take up nitrogen from urea fertilizer, that urea must be converted via two processes, the first of which is called hydrolysis. Urea is broken down into ammonium, and the urease enzyme is an important element of that process. There’s also a potential loss mechanism called “volatilization” where the ammonium is converted to ammonia gas and releases into the atmosphere.
“The degree of volatilization that may happen depends on the amount of urea that’s supplied in a single fertilizer application and how quickly hydrolysis occurs,” Miltner explains. “The more hydrolysis that takes place at once, the greater the potential for ammonium loss due to volatilization. Hydrolysis is a necessary process, because urea has to transform into ammonium, but there’s potential for inefficiency at the same time. A urease inhibitor slows down the rate of hydrolysis, reducing N loss via volatilization, while still making N available to the plant.”
The second step in the process is called “nitrification,” where ammonium is converted to nitrate. Both ammonium and nitrate can be taken up by the plant, but because ammonium is positively charged, it can be attracted to and held by negatively charged soil particles. Nitrate is negatively charged, so it’s not attracted to soil particles and can therefore leach from the system with excess water.
“It’s better to try and hold this nitrogen in the soil as ammonium because it will stay around longer to feed the turf,” Miltner says. “And that’s exactly what a nitrification inhibitor does. It prevents the conversion of ammonium to nitrate.”
Volatilization is more likely to take place in certain scenarios than in others, including in soils with higher pH levels. While volatilization can also occur in low-pH soils, it happens more slowly. Irrigation and rainfall also play key roles. When urea is applied to soil and watered in, volatilization risk diminishes. However, if you have no control over when the fertilizer will be watered in, having a urease inhibitor present keeps the nitrogen in the turf canopy and reduces the risk of losing it to the atmosphere. Conversely, if a site gets a lot of rain or is over-irrigated, a nitrification inhibitor is key to keeping nitrate in ammonium form so that it’s less likely to leach away in overly wet soil.
®, Koch’s stabilized nitrogen product for the professional lawn care and landscape markets, features dual-inhibitor technology. In other words, UFLEXX contains both the urease inhibitor NBPT and the nitrification inhibitor DCD, effectively slowing down the transformations in this process. NBPT gets in the way of the urease enzyme and causes the urea’s conversion to ammonium to happen more slowly, which results in less volatilization. With DCD, ammonium doesn’t rapidly convert to nitrate; it stays in its ammonium form and remains readily available to the plant.
“If you’re considering the use of stabilized nitrogen or nitrification inhibitors, having both NBPT and DCD available is a huge advantage,” Miltner says. “You’re both delaying volatilization and keeping that nitrogen in the ammonium form where plants can use it. The DCD also increases the time that the N remains available, since it is held on exchange site rather than potentially leaching through the profile.”
Because UFLEXX allows more time for nitrogen to move into the turf’s root zone and stay there longer, it produces immediate green-up, followed by sustained turfgrass color for up to eight weeks. While it’s formulated as a granular product, it’s completely soluble and maintains its effectiveness when applied with a sprayer.
“UFLEXX offers dependable performance across varying soil conditions,” Miltner adds. “It performs equally well as a granular nitrogen component in blends or as a soluble nitrogen source in spray tanks. It can also be tank-mixed with many turfgrass protection chemicals, which can help lawn care professionals save time and free up crews for other revenue-generating tasks.”
To learn more about UFLEXX or Koch Turf & Ornamental’s other turf nutrition products for the lawn and landscape market, visit or .