Nitrogen Cycle

Introduction

The nitrogen cycle consists of biological and abiotic processes that allow the supply and transit of nitrogen on the planet. These processes comprise several stages: fixation, nitrification, assimilation, ammonification and denitrification. Organic compounds are formed in one of these processes necessary for human life, such as proteins. It is important to remember that nitrogen (N) is a chemical element found in the atmosphere at 78%, thus being one of the most abundant elements on earth. Here, we will try to explain the nitrogen cycle in easy-to-understand words along with an easy nitrogen cycle easy diagram.

What is the Nitrogen Cycle?

The biogeochemical nitrogen cycle is so named as compounds that are part of both the human being and the ecosystem. This cycle undergoes a series of repeated chemical processes. You can understand this cycle better with a nitrogen cycle diagram.

This cycle ensures the movement of nitrogen via living organisms and nonliving things like water, soil and air. All along this movement, nitrogen changes its form as it moves from one phase of the cycle to another. 

The nitrogen cycle is a biogeochemical cycle on which the biosphere and all organisms depend for growth. It refers to a set of chemical and biological processes that allow living beings to develop.

Loss of soil nitrogen:

Loss of soil nitrogen is mainly due to the following reasons:

•     Plant removal
•     Destruction of the upper layers of the soil by fire or other phenomena
•     The ions’ mechanical drag by the water filtered through the soil

On the other hand, recovery occurs owing to:

•     Fixation by microorganisms
•     Fixation due to natural events and phenomena
•     Industrial type fixing

Phases of the Nitrogen Cycle

There are five phases of this cycle that you can understand with the help of a nitrogen cycle easy diagram. We can summarise these phases as follows:

Fixation:

During this stage, nitrogen passes from its natural gaseous form to a compatible organic form. The animal and plant cells assimilate since they cannot use the compound in its gaseous form. The result is the formation of ammonia. We can mention fixation in three ways:

•     Biological fixation: It occurs with the microorganism’s participation, specifically bacteria (such as the Rhizobium genus). Together with some plant species such as legumes, it allows the compound’s reduction in ammonia. Organisms capable of binding are called diazotrophs.
•     Fixation by natural events: Based on certain natural phenomena that allow transformation to ammonia in smaller quantities. These events can be lightning during a thunderstorm or lava flow after an eruption.
•     Anthropogenic fixation: There is currently an increase in the amount of fixation of this element through activities carried out by human beings, such as fossil fuels, synthetic fertilisers and planting legumes with nitrogen-fixing capacity.

Ammonification:

The bacteria and fungi degrade the nitrogen to get ammonia or the ammonium ion. It helps get organic compounds such as proteins, amino acids and soil nucleotides.

Nitrification:

Microorganisms capture the ammonia formed during the nitrogen cycle, oxidising and converting it into ammonia. Specifically, genus Nitrosomonas and Nitrobacter bacteria handle this task. This compound will later be taken up and oxidised by other bacteria that inhabit the soil and finally transform into nitrate.

Denitrification:

Through this process, the element returns to the atmosphere in the form of dinitrogen or nitrous oxide gas after being deoxidised by bacterial action.

Assimilative nitrate reduction:

It is carried out by bacteria of the heterotrophic type, such as Pseudomonas fluorescens, during which the nitrate ion returns to its configuration of dinitrogen present in the air. Without this step, the cycle will end with the total elimination of atmospheric nitrogen.

Dissimilatory nitrate reduction:

It occurs through bacteria belonging to the genus Citrobacter, during which nitrate and nitrite pass to their gaseous form of nitrous oxide.

Nitrogen Uptake or Assimilation:

It consists of incorporating the products formed during the cycle (such as ammonium) by plants, bacteria, and other organisms in the soil to be used as nutrients.

A relevant example of this phase is when the plants again take the formed nitrate and convert it into compounds (nutrients) suitable for assimilating by the living organisms that consume it through them.

Role of the Nitrogen Cycle

Understanding the role of the nitrogen cycle is an essential aspect of Biology. The nitrogen cycle is significant for living organisms and is biologically usable by them. It is crucial for the manufacture of nucleic acids, amino acids and DNA. This cycle is also essential for ensuring the fertility of the soil.

Thus, nitrogen is recycled and passes through biological, geological, and chemical processes from one compartment to another. It is a constant cycle that balances the living being’s biological needs, the environment’s ecological needs and planet earth.

Human Intervention 

Human beings actively participate in this cycle in the fixation phase, mainly because economic activities ease the fixation of more nitrogen molecules per day.

Humans are part of the living beings for which nitrogen is essential for the proper functioning of the body. They get it mainly through the consumption of vegetables and animals.

Yet, industrialisation and excessive fertiliser use in agricultural areas have drastically increased nitrogen processing. Even though it is a fundamental element of life, its excess contributes to environmental pollution, mainly in water.

The control of human activities is of utmost importance to maintain the ecosystem balance. It will help us develop stably. In the particular case of fertilisers, their use is excessive and unnecessary, as plants do not use most or a high percentage of their compounds.

Conclusion

The nitrogen cycle consists of biological and abiotic processes that assist in the nitrogen supply and transit. These processes take place through several stages. During this cycle, nitrogen moves via animals, plants and non-living things like air, water and soil. You must also study the reasons for the loss and recovery of nitrogen in the soil. The various phases of the Nitrogen Cycle must be learnt by heart. Finally, you should study the role of this cycle and human intervention’s effect on it.