1. Living organisms:
* Plants: Nitrogen is a key component of proteins, DNA, and RNA, which are essential for plant growth and development. They obtain organic nitrogen through the absorption of nitrates and ammonium ions from the soil.
* Animals: Animals get their organic nitrogen from consuming plants or other animals.
* Microorganisms: Bacteria and fungi play a critical role in the nitrogen cycle, both in converting inorganic nitrogen into organic forms and vice versa.
2. Dead organic matter:
* Litter: When plants and animals die, their bodies decompose, releasing organic nitrogen into the soil as part of their organic matter.
* Humus: Humus is a stable, decomposed organic matter that forms in the soil and contains organic nitrogen.
3. Waste products:
* Animal waste: Animal excreta (urine and feces) contain organic nitrogen that can be broken down by microorganisms in the soil.
* Sewage: Waste water from human settlements contains organic nitrogen from human waste and other sources.
4. Other sources:
* Fossil fuels: Coal, oil, and natural gas contain some organic nitrogen that is released into the atmosphere during combustion.
In summary, organic nitrogen is present in all living organisms, dead organic matter, waste products, and some fossil fuels.
