The common nitrogen (N) fertilizers are anhydrous ammonia (82% N), urea (45-46% N), solutions of ammonium nitrates and urea (28-32% N), ammonium sulfate (21% N) and ammonium nitrate (34% N). When applying nitrogen in the summer, keep in mind that some forms are subject to surface volatilization resulting in loss of available nitrogen to the plants. Ammonium nitrate is an excellent form to use because surface volatilization losses are minimized (Johnson, 1995). The disadvantage of anhydrous ammonia is that it is hazardous to handle. Also, it must be injected into the soil, and on steep slopes erosion can be a problem. Injecting nitrogen can increase the roughness of the field. Diammonium phosphate (18-46-0) is typically an inexpensive source of nitrogen if you need the associated phosphorus.