Urea, also called Carbamide, the diamide of carbonic acid. Its formula is H₂NCONH₂. Urea has important uses as a fertilizer and feed supplement, as well as a starting material for the manufacture of plastics and drugs. It is a colourless, crystalline substance that melts at 132.7° C (271° F) and decomposes before boiling.

In general, urea will provide the most nitrogen at the lowest cost. It is easy to store and does not pose as a fire risk for long-term storage. Urea may be mixed with other fertilizers or may be applied on its own. For plants that love acidic soils, urea is one of the top fertilizers for acidifying soils. For gardeners who grow crops like corn, strawberries, blueberries and other heavy nitrogen feeders, urea will supply immediate and powerful applications of nitrogen.

As a result of the chemical reaction that takes place when urea is applied to the soil, special care must be taken to ensure that the nitrogen is not lost when the ammonium evaporates. This can make urea impractical for gardeners dealing with large plots of land. The high solubility of urea also makes dry storage conditions imperative.