Most gardeners apply urea fertilizer directly to the soil in small pellets, known as prills. The fertilizer dissolves quickly in water, and the slightest soil moisture begins a reaction that converts urea into a compound called ammonium bicarbonate within a few days. It happens fastest at high temperatures or high pH and in sandy soil or soil with low organic matter. In a nod to urea's beginnings, the ammonium converts back to ammonia gas. Unless the gas is conserved, urea can lose 50 percent to 90 percent of its nitrogen to the air.