Which nitrogen source is most likely to cause a rapid green-up followed by a growth flush and carry a higher leaching risk?

• A. Quick-release nitrogen such as urea
• B. Slow-release polymer-coated nitrogen
• C. Nitrogen from organic compost
• D. Mineral fertilizer with nitrification inhibitor

Answer: (A)

Rapid turf green-up and a subsequent growth flush happen when nitrogen becomes available to the plant almost immediately. Quick-release nitrogen, like urea, is soluble and rapidly converted into forms the grass can take up (ammonium and then nitrate). That instant availability drives a surge in chlorophyll production and new shoot growth, giving a rapid, lush green color and a short burst of growth.

But that same speed makes the nitrogen highly mobile in the soil. Once the plant has taken what it needs, any excess nitrate remains in the soil water and can be leached away by rainfall or irrigation, increasing the leaching risk.

Slow-release nitrogen releases N over time, so the green-up is steadier and the flush is minimized, with less leaching risk. Organic compost N mineralizes more slowly and variably, again reducing the chance of a sharp flush. A fertilizer with a nitrification inhibitor slows the conversion to nitrate, which can reduce leaching but dampens the immediate availability needed for rapid green-up.

So the quick-release source best explains both the rapid green-up with a growth flush and the higher leaching risk.