Dead organic matter Nitrates in soil Nitrates Decomposers (bacteria, fungi, earthworms, etc.) Symbiotic nitrogen fixation
Nitrogen-fixing bacteria
Ammonium
1. Approximately 80 per cent of the air is nitrogen gas. However, most of this nitrogen is not available to animals and plants.
2. Certain bacteria, known as nitrogen-fixing bacteria, can change the nitrogen in the atmosphere into nitrates. These nitrates can then be taken up from the soil by plants.
3. The plant supplies the bacteria with food (sugars) and water.
4. The plant uses nitrogen to form protein. Animals get their protein by eating plants or other animals.
5. Decomposers such as bacteria, fungi and earthworms return nitrogen to the soil as ammonium by breaking down dead organic matter.
6. Denitrifying bacteria in the soil break down nitrates, returning nitrogen to the air.
