Nitrogen Cycle

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1. NITROGEN FIXATION

Nitrogen gas (in atmosphere) is converted into ammonia by bacteria called Rhizobium.

Ammonia is then used by plants.

Rhizobium found inside root nodules of leguminous plants (e.g. peas, beans and clover).

Rhizobium forms a mutualistic relationship with the plants - it provides plants with nitrogen compounds and plant provides them with carbohydrates.

2. AMMONIFICATION

When nitrogen compounds from dead organisms are turned into ammonium compounds by decomposers.

Animal waste (urine/faeces) also contains nitrogen compounds - these are turned into ammonium compounds by decomposers.

3. NITRIFICATION

When ammonium compounds in the soil are changed into nitrogen compounds that can then be used by plants.

First nitrifying bacteria(e.g. Nitrosomonas) change ammonium compounds into nitrites.

Then other nitrifying bacteria (Nitrobacter) changes nitrites into nitrates.

4. DENTRIFICATION

When nitrates in soil are converted into nitrogen gas by denitrifying bacteria - they use nitrates in the soil to carry out respiration and produce nitrogen gas.

This happens under anaerobic conditions e.g. in waterlogged soils.

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