Nitrogen is an essential fertilizer for all plants. It can be found in the molecules needed for photosynthesis and it is the basis for plant proteins. Nitrogen can be found in decaying organisms and is also in commercially made fertilizers, in the form of nitrates. Too much nitrogen can make plants weak and stunt growth. Too little nitrogen can lower the number of chloroplasts, which affects photosynthesis.
Anhydrous ammonia contains 82 percent nitrogen and takes the longest to completely convert to nitrates, according to Ohio State University Extension. It must be injected into the soil, which makes it difficult to be lost through wind. It is in liquid form, but it can still be lost to erosion when it is applied on steep slopes. Anhydrous ammonia is hazardous to handle.
Urea is a white, crystallized solid that contains 46 percent nitrogen. When used as a fertilizer, urea converts to nitrates in approximately two weeks in the spring when temperatures begin to get warm, provided the soil has received enough moisture. If left on the soil's surface for too long in the summer, it can evaporate into ammonium and carbon dioxide if the soil is moist and temperatures are high, according to University of Minnesota Extension.
Ammonium sulfate is an inorganic salt that contains 21 percent nitrogen and 24 percent sulfur. Sulfur is the primary ingredient used to in soil to lower the pH. According to Michigan State University Extension, ammonium sulfate is highly acidic and requires two to three times more lime to neutralize the acidity as other nitrogen fertilizers.
Ammonium Nitrate is a white, crystallized solid at room temperature but converts to liquid at 300 degrees F. It is 34 percent nitrogen. When applied to the soil it is 50 percent ammonium nitrate and 50 percent nitrates. The ammonium converts to nitrates and the fertilizer is quickly absorbed into the soil. It is best used in surface applications.