101 Questions answered
Understanding Urea Volatilisation: Timing, Conditions, and Risk Factors
No ammonia volatilisation can occur until the applied urea has dissolved and broken down to ammonium/ammonia. If urea is broadcast onto dry soil and conditions remain dry, the urea will remain intact, sometimes for weeks. However, once it has dissolved it will begin to breakdown to ammonium/ammonia within 24–48 hours. If the ammonium or ammonia is not adsorbed by contact with the soil, some may be lost by volatilisation.
Losses from volatilisation tend to occur mostly during day when the soil surface is heated, causing upward air movement. Losses are also more rapid in windy conditions as the ammonia-dense air at the surface is replaced with low-ammonia air, causing a gradient that promotes ammonia movement out of the soil. Warmer temperatures also increase the rate of some of the sub-processes involved, such as conversion of urea to ammonium, and therefore, the overall rate of nitrogen loss.
The risk of volatilisation is higher on wet soil that is drying, rather than dry soil that gets rained on. Why? Wet soil dissolves the urea but doesn’t distribute the ammonium into the soil where the greater soil volume helps buffer the change in pH.
