What are the common nitrogen sources used on turf and how do N rates influence color, growth rate, and mowing requirements?

• A. Quick-release sources (ammonium sulfate, urea, ammonium nitrate) and slow-release forms (polymer/sulfur coatings, urea formaldehyde); higher N increases color and growth, raising mowing frequency; excessive N can promote disease and thatch
• B. Only ammonium sulfate is used; N does not affect mowing
• C. Only slow-release forms are used; N has no effect on color
• D. Urea is the only source; N has no effect on growth rate

Answer: (B)

Nitrogen is the nutrient that most strongly drives turf color and growth, so understanding both sources and rates is key to a smooth, healthy turf program. Common nitrogen sources include quick-release forms (such as ammonium sulfate, urea, and ammonium nitrate) which provide nitrogen rapidly, and slow-release forms (like polymer-coated or sulfur-coated products and urea formaldehyde) that release nitrogen more gradually over time. The method and timing of N delivery affect how the turf looks and grows: higher nitrogen rates tend to produce deeper green color and faster growth, which means you’ll need to mow more often. But pushing nitrogen too high, especially in warm or wet conditions, can encourage disease, create a thatch layer, and lead to weak, lush turf that’s more prone to stress.

Slow-release sources help maintain color with less chance of rapid growth spurts and mowing spikes, while quick-release sources deliver a quick color response and are useful for rapid recovery or spot feeding. In practice, rates are tailored to the turf species, season, and soil fertility, often guided by soil tests, to balance color, growth, mowing needs, and disease risk.