Agricultural Impact on Nitrogen Cycle

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Nitrogen cycle 7

Nitrogen is present as the most abundant element in our atmosphere. It is crucial for life. Nitrogen is found in the water we drink, soils and plants, and the air we breathe. It is also essential to life. It is one of the fundamental building blocks of DNA, which determines our genetics, is vital to plant growth, and is necessary for the food we grow. But like everything, balance is critical. If there is too little nitrogen, then the plants cannot thrive, which leads to low crop yields. Understanding the Nitrogen Cycle can help us and protect our environment and grow healthy crops.

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On the other hand, excess nitrogen can be toxic to plants and is harmful to our environment. In the absence of adequate nitrogen, the plants become yellowish and do not grow well. Consequently, they bear smaller flowers and fruits. Farmers can add nitrogen in fertilizer to produce better crops, but the excess of nitrogen is harmful to animals and plants and pollute our aquatic systems. 

Why is Nitrogen Cycle Important?

The critical balance of substances that is important for maintaining life is an essential area of research. The balance of nitrogen content in the environment is no different. When plants lack nitrogen, they become yellow and have stunted growth, and they produce smaller flowers and fruits. Farmers can add organic fertilizer containing nitrogen to their crops to increase crop growth.

Without nitrogen fertilizers, experts have estimated that you can lose up to one-third of the crops. It is important to know how much amount of nitrogen is necessary for plant growth because excess of it can pollute waterways and hurt aquatic life.

Nitrogen Cycle is Key To Life

Nitrogen is a critical element of the nucleic acids DNA and RNA. Deoxyribonucleic acid or DNA is a self-replicating compound present in all living beings. It is the main component of chromosomes and carrier of genetic information. Ribonucleic acid or RNA is present in all living cells and it acts as a messenger carrying instructions from DNA.

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DNA and RNA are the most important of all biological molecules and crucial for all living things. DNA carries genetic information. In simple words, it carries the instructions on how to make up a life form. When plants do not get adequate nitrogen, they cannot produce amino acids (containing nitrogen and hydrogen and making up many living cells, muscles, and tissue).

Without amino acids, plants cannot make the particular proteins which the plant cells need to grow. The plant growth get negatively affected in the absence of adequate nitrogen. With excess nitrogen, plants produce excess biomass or organic matter. In extreme cases, plants that have absorbed very high levels of nitrogen from soils can lead to poisoning farm animals that eat them.

What is Eutrophication ?

Excess amount of nitrogen can drain from the soil into underground water sources or enter aquatic systems as above-ground runoff. This excess amount of nitrogen can build up and lead to eutrophication. Eutrophication occurs when large amount of nitrogen enriches the water, leading to excessive growth of plants and algae. An excess amount of nitrogen can even cause a lake to turn bright green or other colors, with a “bloom” of smelly algae known as phytoplankton.

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When the phytoplankton dies, microbes present in the water decompose them. The decomposition process reduces the amount of dissolved oxygen in the water. Consequently, it can lead to a dead zone that does not have sufficient oxygen to support most life forms. The organisms in the dead zone die Due to the lack of oxygen in the dead zone, the organisms in it die. These dead zone formation can happen in freshwater lakes and coastal environments where rivers are full of nutrients from agricultural runoff flow into oceans.

How to Prevent Eutrophication? 

People managing water resources use different methods to reduce the harmful effects of algal blooms and eutrophication of water bodies. One of the methods is to re-reroute excess nutrients away from vulnerable costal zones and lakes. They can also use herbicides or algaecides to prevent the algal blooms, and reduce the quantities. However, it can be hard to identify the origin of the excess nitrogen.

Once a lake has gone through eutrophication, it becomes even harder to do a damage control. Algaecides are expensive, and moreover, they do not correct the source of the problem i.e the excess nitrogen that caused the algae bloom in the first place. 

What Exactly is the Nitrogen Cycle?

Nitrogen moves from atmosphere to the earth, through soils, and back to the atmosphere in a cyclic manner. This cyclic processes is known as the nitrogen cycle. Nitrogen must change forms to move through the different parts of the cycle. In atmosphere, nitrogen exists as a gas, but in the soil, it exists as nitrogen oxide, and nitrogen dioxide. When it used as a fertilizer, it can be found as ammonia which can be processed into ammonium nitrate.

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There are five stages in the nitrogen cycle namely; fixation or volatilization, mineralization, nitrification, immobilization, and denitrification.

Stage 1: Nitrogen Fixation

In the first stage, nitrogen moves from the atmosphere into the soil. Earth’s atmosphere contains a huge amount of nitrogen gas. However, this nitrogen in gaseous form cannot be used directly by plants. Nitrogen needs transformation through the nitrogen fixation process. Nitrogen fixation process converts nitrogen in the atmosphere into forms which the plants can absorb through their roots.

Lightning provides the energy needed for Nitrogen to react with Oxygen, producing nitrogen oxide, and nitrogen dioxide. These forms of nitrogen then enters the soil through snow or rain. Nitrogen can be fixed through the industrial process which creates fertilizer Ammonia. Ammonia is further processed, to produce ammonium nitrate that can be added to soil and used by plants.

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The bacteria in the soil does most of the nitrogen fixation. Some bacteria attach to the roots of plant and have a symbiotic relationship with it. The bacteria get energy through photosynthesis and, they fix nitrogen into a form as per the needs of the plant. 

Stage 2: Mineralization

This stage of mineralization takes place in the soil. Nitrogen moves from organic materials to an inorganic form of nitrogen which can be used by the plants. Eventually, the nutrients of plants gets used up completely. Finally, the plant dies and decomposes. Mineralization occurs when microbes act on organic material. 

All plants under cultivation, except legumes get the nitrogen they require through the soil. Subsequently, legumes get nitrogen through fixation that occurs in their root nodules. The first form of nitrogen produced by the process of mineralization is ammonia.

The ammonia in the soil reacts with water to form ammonium which gets retained in the soil. Ammonium is available for use by plants that do not get nitrogen through the symbiotic nitrogen fixing relationship.

Stage 3: Nitrification

The third stage, nitrification, also occurs in soils. During nitrification, the conversion of ammonia in the soils  into  nitrites, and nitrates takes place. Plants and animals that consume the plants use the nitrates. Some bacteria in the soil can turn ammonia into nitrites.

Although nitrite is not usable by plants and animals directly, other bacteria can change nitrites into nitrates—a form that is usable by plants and animals. This reaction provides energy for the bacteria engaged in this process.

Nitrobacter turns nitrites into nitrates while nitrosomonas transform ammonia to nitrites. Both kinds of bacteria can act only in the presence of oxygen. The process of nitrification produces an extra stash of available nitrogen. 

Stage 4: Immobilization

The fourth stage of the nitrogen cycle is immobilization, sometimes described as the reverse of mineralization. These two processes together control the amount of nitrogen in soils. Just like plants, microorganisms living in the soil require nitrogen as an energy source. These soil microorganisms pull nitrogen from the soil when the residues of decomposing plants do not contain enough nitrogen.

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When microorganisms take in ammonium (NH4+) and nitrate (NO3−), these forms of nitrogen are no longer available to the plants and may cause nitrogen deficiency, or a lack of nitrogen. Immobilization, therefore, ties up nitrogen in microorganisms. However, immobilization is important because it helps control and balance the amount of nitrogen in the soils by tying it up, or immobilizing the nitrogen, in microorganisms.

STAGE 5: Denitrification

In the final stage of nitrogen cycle, nitrogen returns to the air. Bacteria converts the nitrates to atmospheric nitrogen. This process is called denitrification. Due to this , an overall loss of nitrogen from soils occurs. The gaseous form of nitrogen moves into the atmosphere.

Final Takeaway

The cycling of nitrogen through the ecosystem is crucial for maintaining productive and healthy ecosystems with neither too much nor too little nitrogen.  Understanding how the plant-soil nitrogen cycle works can help us make better decisions about what crops to grow and where to grow them, so we have an adequate supply of food. Knowledge of the nitrogen cycle can also help us reduce pollution caused by adding too much fertilizer to soils. Certain plants can uptake more nitrogen or other nutrients, such as phosphorous. 

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