Ammonium nitrate is, therefore, an excellent nitrogen source in circumstances where nitrogen is required immediately for plant uptake, such as topdressing, because 50 percent of its nitrogen is readily available to the plant. This can be a disadvantage, however, in cases where fertilizer is applied early in the spring, before the crop's need for nitrogen is significant. If heavy rains occur during this period, it can result in a significant portion of the nitrate in the fertilizer being lost. There is a common belief that when ammonium nitrate is used as a topdressing, it vaporizes and is lost in the air if not covered immediately upon application to the soil. This is not so .
Ammonium sulfate contains nitrogen only in the ammonium form.
It will, therefore, require some time after application, particularly when soils are cold in early spring, before it is converted into nitrates. On the other hand, early season nitrate losses are minimized with this product. Because ammonium sulfate has a relatively low nitrogen content, its relative shipping cost per unit of nitrogen is high. Therefore, its cost per unit of nitrogen is often quite high as well, and it is used only occasionally in our region. One other important characteristic in relation to ammonium sulfate is the fact that it produces a strongly acidic reaction in the soil.