What happens to the nitrogen a farmer applies as fertilizer each spring?
First, let us consider the forms of nitrogen normally applied, and then attempt to trace what happens to the nitrogen once it is added to the soil. The average complete fertilizer contains approximately 70 percent of its nitrogen in the ammonium nitrogen form (NH4), about 10 percent in the urea form (this is quickly converted to ammonium nitrogen), and the remaining 20 percent in the nitrate nitrogen form (NO3) .
Atkinson, W. O. and Ragland, John L., "What Happens to Fertilizer Nitrogen in the Soil?" (1968). Agronomy Notes. 186.