Nitrogen cycle
- 1. Nitrogen fixation-Atmospheric nitrogen is converted into nitrates by nitrogen-fixing bacteria attached to the root nodules of leguminous plants. A small amount of nitrogen is ‘fixed’ by lightning because it provides temperatures high enough for atmospheric nitrogen and oxygen to react.
- 2. The nitrates are taken up by plants and are used to make plant proteins, animals then eat the plants as their source of nitrates. When plants and animals die or excrete, the remaining organic matter is broken down by decomposition and decay, releasing ammonia.
- 3. Nitrification-Nitrifying bacteria in the soil convert ammonium compounds from decomposed matter back into nitrates.
- 4. Denitrification-In some conditions (usually in waterlogged soil), denitrifying bacteria break down nitrates in the soil and convert them back into nitrogen gas.
NB: Exposure to heavy rain may deplete the soil of nitrates by washing them into nearby rivers and lakes.
NB: Fast-growing crops reduce the levels of nitrates in the soil because they use them up at a quicker rate.
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