Nitrogen Cycle | Lucent for GK - UPSC PDF Download

The nitrogen cycle is the biogeochemical process that describes the movement of nitrogen and its various forms through the environment. It is essential for maintaining the balance of nitrogen in ecosystems. The cycle consists of several key steps:

• Ammonification: This is the first step in the nitrogen cycle and involves the decomposition of organic nitrogen compounds into ammonia (NH₃) by bacteria and fungi. Ammonification occurs when plants and animals die, and their organic matter is broken down by decomposers. The decomposers release ammonia as a byproduct.
• Nitrification: Nitrification is the conversion of ammonia (NH₃) into nitrate ions (NO₃⁻) by nitrifying bacteria. Nitrifying bacteria perform two sequential processes: ammonia is first oxidized to nitrite (NO₂⁻) by Nitrosomonas bacteria, and then nitrite is further oxidized to nitrate by Nitrobacter bacteria. Nitrates are essential nutrients for plants and can be easily taken up by their roots for growth.
• Denitrification: Denitrification is the final step in the nitrogen cycle and involves the conversion of nitrates (NO₃⁻) back into atmospheric nitrogen (N₂) by denitrifying bacteria. Denitrifying bacteria live in oxygen-depleted environments, such as wetlands and waterlogged soils. They break down nitrates and release nitrogen gas into the atmosphere. This process reduces the amount of available nitrogen in the ecosystem, completing the cycle.

Additional Points

• Nitrogen fixation is another significant process in the nitrogen cycle. It involves the conversion of atmospheric nitrogen (N₂) into forms usable by living organisms.
• Nitrogen-fixing bacteria, found in soil and root nodules of leguminous plants, convert atmospheric nitrogen into ammonia, which can then be used by plants.
• Human activities, such as the excessive use of synthetic fertilizers and the burning of fossil fuels, have disrupted the natural balance of the nitrogen cycle, leading to environmental issues like eutrophication and air pollution.