- By federal law all commercial fertilizer must list the amount, by percentage, of nitrogen (N), phosphorus (P) and potassium (K). This is written prominently on the package as, for example, 5-10-5 or 10-12-05. The first number is the percentage amount of N, followed by P and K.
Anhydrous Ammonium Nitrate
- Material often is sold as a standalone nitrogen fertilizer. In farming country, it is common to see large tanks for the storage of anhydrous ammonium nitrate, a potent fertilizer that contains up to 82 percent nitrogen.
- Compost is used as a substitute for fertilizer, and in many ways is much better for the soil. The actual amount of nitrogen available depends upon the type of compost and its processing, but at best the percentage normally is much lower than commercial fertilizer. One advantage of compost, though, is that the nitrogen is available over a much longer period and begins to build in the soil for future use.