At 46 percent nitrogen, urea packs more punch per pound than other nitrogen-only fertilizers. Because nitrogen moves easily through soil -- and plants need it in larger quantities than any other nutrient -- it regularly requires replacement, especially in gardens supporting vegetables or other crops. Urea provides ready nitrogen, but unless handled properly, much of the nitrogen can be lost.

A manufacturing process creates urea fertilizer by combining ammonia gas, known as anhydrous ammonia, with carbon dioxide. High temperatures and pressure aid the chemical reaction that ultimately produces urea. The product is synthetic, but the process imitates the cycle that naturally occurs when mammals metabolize nitrogen in their bodies. The natural process creates ammonia that the liver converts to nitrogen-carrying urea, which the body then excretes. By using similar chemical reactions, manufacturers create the 46-0-0 product that is urea fertilizer.