The processes of nitrogen and ammonia conversion that make nitrogen absorbable by plants are:
nitrogen fixation, ammonification, and nitrification.
- Nitrogen fixation is the process of converting atmospheric nitrogen (N₂) into ammonia (NH₃), making it available for plants.
- Ammonification is the process of converting organic nitrogen (from dead organisms and waste) into ammonia.
- Nitrification is the process where ammonia is converted into nitrites (NO₂⁻) and then to nitrates (NO₃⁻), which are the forms of nitrogen that plants can readily absorb and utilize.
Therefore, the correct answer is: nitrogen fixation, ammonification, and nitrification.