Answer:
Nitrification.
Step-by-step explanation:
Nitrification is the second step of nitrogen cycle in which the ammonia is converted into nitrates with the help of bacteria is called nitrifying bacteria. In the first step, biological nitrogen fixing bacteria fixes atmospheric nitrogen into ammonia. This process is known as ammonification. Due to this fixation, the plants is able to use the nitrogen for making amino acids in the body. So the first step is ammonification and the second step is nitrification.