Nitrogen (N) is a colorless and odorless element. Nitrogen can be found in the soil beneath our feet and the water we drink, and the air we breathe. Nitrogen is an essential component of the bodies of all living things. 

The delicate balance of elements required for life is a hot topic in science, and Nitrogen in the environment is no exception. The most significant of all biological molecules and essential for all living organisms are nucleic acids (DNA and RNA), include Nitrogen. The genetic information, or instructions for building a life form, is carried by DNA. 

Nitrogen is everywhere; about 78% of the Earth’s atmosphere is made up of N2 gas. You may believe that this means we always have lots of Nitrogen available, but that is not the case. Nitrogen in its gaseous state cannot be absorbed and used as a nutrient by plants and animals; nitrifying bacteria must first transform it before entering food chains as part of the nitrogen cycle.

Table of Contents

Why do plants Need Nitrogen?

Plants Need Nitrogen
Plants Need Nitrogen | Image Credit – Freepik

Plants can’t generate amino acids if they don’t get adequate Nitrogen (substances containing Nitrogen and hydrogen and make up many living cells, muscles, and tissue). This inadequacy affects the formation of unique proteins their cells need to thrive. A lack of Nitrogen negatively impacts plant growth. 

Plants with low nitrogen levels turn yellow, have stunted growth, and produce smaller fruits and flowers. Farmers may apply nitrogen-based fertilizers to their crops to increase crop growth. 

Plants create too much biomass, or organic stuff, such as stalks and leaves, when they have too much Nitrogen but not enough root structure. Those plants which absorb a lot of Nitrogen from the soil might damage farm animals that consume them in extreme circumstances.

According to scientists, we would lose up to one-third of the crops we rely on for food and other types of agriculture if nitrogen fertilizers were not used. However, we need to know how much Nitrogen is needed for plant growth, as too much can pollute streams and kill aquatic life.

Nitrogen cycle 

Nitrogen Cycle
Nitrogen Cycle | Image Credit – Wikimedia Commons

1. Nitrogen fixation 

The nitrogen cycle begins with this phase. Atmospheric nitrogen (N2), predominantly available in an inert form, is transformed into the helpful form -ammonia- in this process (NH3).

During the nitrogen fixation process, the inert form of nitrogen gas is deposited into soils from the atmosphere and surface waters, primarily by precipitation. Later, the Nitrogen undergoes a series of changes, separating two nitrogen atoms, which combine with hydrogen to form ammonia.

Symbiotic bacteria, also known as Diazotrophs, help to finish the entire nitrogen fixation process. Azotobacter and Rhizobium are other essential players in this process. The nitrogenase enzyme in these bacteria can combine with Nitrogen and hydrogen gas to form ammonia.

Nitrogen fixation takes place in two ways: through atmospheric fixation, which includes lightening, or through industrial fixation, which requires the production of ammonia at high temperatures and pressures. Manufacturing operations, especially industrial ones that produce ammonia and nitrogen-rich fertilizers, can also help.

2. Nitrification 

The presence of microorganisms in the soil converts ammonia to nitrate in this process. Nitrosomonas bacteria are the key species for the oxidation of ammonia to produce nitrates. Nitrobacter then converts the nitrites generated into nitrates. Because ammonia gas is poisonous to plants, this conversion is critical.

3. Denitrification 

Denitrification is turning nitrate (NO3-) into gaseous Nitrogen and releasing nitrogen compounds back into the atmosphere (N). It is the penultimate stage of the nitrogen cycle, and it happens in the absence of oxygen. The denitrifying bacterial species Clostridium and Pseudomonas metabolize nitrate to produce oxygen and free nitrogen gas as a byproduct.

4. Assimilation 

Plants use their roots to absorb nitrogen molecules from the soil, which are available in ammonia, nitrate ions, or ammonium ions and are employed to produce plant and animal proteins. When the primary consumers eat the plants, it enters the food web.

5. Ammonification 

The Nitrogen in organic matter is released back into the soil when plants or animals die. The organic waste is converted back into ammonium by decomposers, bacteria, or fungus found in the soil. Ammonia is produced during decomposition and then employed in other biological processes.

Importance of nitrogen cycle 

  • Helps in the synthesis of chlorophyll by plants from nitrogen molecules.
  • A metabolic mechanism aids in converting inert nitrogen gas into a valuable form for plants.
  • The bacteria contribute to the decomposition of animal and plant materials during the ammonification process, which helps to clean up the environment indirectly.
  • Nitrates and nitrites are released into the soil, assisting in the enrichment of the soil with the nutrients essential for agriculture.
  • Nitrogen is an essential component of the cell, and it is used to make a variety of critical chemicals and proteins.

Human actions such as the combustion of fuels and nitrogen fertilizers also contribute to the nitrogen cycle. As a result of these activities, the amount of nitrogen-containing molecules in the atmosphere rises. Eutrophication occurs when nitrogen-containing fertilizers are washed away in lakes and rivers.

Nitrogen is key to life

Nitrogen is key to life
Nitrogen is key to life | Image Credit – Flickr

The nitrogen cycle is essential because Nitrogen is a necessary nutrient for the survival of life on Earth. Nitrogen is an essential component of amino acids, which serve as the building blocks of proteins, and nucleic acids, which are the building blocks of genetic material (RNA and DNA). However, it is found in DNA and RNA, proteins, ATP, and chlorophyll in plants.

Plants cannot synthesize amino acids (substances that contain Nitrogen and hydrogen that are found in many living cells, muscles, and tissue) when they do not receive adequate Nitrogen. Also, plants cannot produce the specific proteins required by plant cells if amino acids are absent.

Similarly, animals, including humans, obtain the Nitrogen they require by consuming nitrogen-containing plants or by preying on other animals that consume plants. Animals need Nitrogen to produce the proteins that keep their bodies strong and healthy. Plants and animals disintegrate or break down after they die.

What will happen if there is too much Nitrogen in the soil?

Excessive fertilizer application promotes fertility loss
Excessive fertilizer application promotes fertility loss | Image Credit – O’AHU resource conservation and development council

When a plant absorbs excessive Nitrogen, it accumulates in plant tissue. Toxicity is exacerbated when the plant’s nitrogen supply is primarily NH4+ (ammonium). Too much ammonium reduces ATP levels, allowing energy to be released from photosynthesis. Fertilization is widely used all over the world. Excessive fertilizer application promotes soil organic matter and fertility loss while also promoting soil acidity.


Though Nitrogen is abundant in the atmosphere, plants and animals cannot use it until it is transformed into nitrogen molecules. Nitrogen-fixing bacteria are essential for converting atmospheric Nitrogen into nitrogen molecules that plants can utilize. Creatures absorb Nitrogen by eating these plants or other nitrogen-containing animals. The nitrogenous molecules in the soil are then converted to nitrogen gas by microorganisms. These cycles recur indefinitely, ensuring that the amount of Nitrogen in the atmosphere remains constant.

(Last Updated on May 4, 2022 by Sadrish Dabadi)

Ranjana Regmi is a highly energetic and responsible graduate with a master’s degree in Environment Science. She has a sound academic and professional record of exploring the world of climate change and its dynamics related to vegetation and wildlife. She has developed analytical skills during a few years of work exposure and scientific coherence. She is undoubtedly a bright star for ecosystem preservation with an immense empathy towards biodiversity.