In this lesson, you’ll learn about denitrification, its relationship to the nitrogen cycle, what’s responsible for it, why it happens and what it means for humans and the environment.

Denitrification

All life on the planet relies on nitrogen. Nitrogen, a chemical element, is used by microbes, plants and animals to live. However, nitrogen is recycled in a process called the nitrogen cycle. This process has many steps, but perhaps the most important step is denitrification. Denitrification is the last step in the nitrogen cycle where the reduction of soil nitrate to nitrogen-containing gases, such as nitric oxide, nitrous oxide, and nitrogen gas, takes place.Denitrification relies on microbial activity to break apart nitrogen-containing elements.

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Microbes consume nitrate to produce energy, but in the process, denitrification occurs and nitrogen is reduced. Specifically, soil microbes utilize nitrate as the terminal electron acceptor to form nitrite in a process called reduction. Nitrite is further reduced to nitric oxide then to nitrous oxide and then nitrogen gas.

Soil and Denitrification

As previously explained, microbes are responsible for denitrification. More specifically, soil bacteria that can live in a variety of environments and withstand great heat, large amounts of salt in the soil and generally can survive when oxygen is present or when it’s not present.

This is the main reason why these soil microbes use nitrate as an electron acceptor because oxygen is not always accessible.In the soil environment, where denitrification takes place, sometimes oxygen is depleted. This is due to the addition of large amounts of water to the soil, causing the soil to be saturated and making oxygen unable to diffuse. This can be a result of rainfall causing flooding, increased irrigation, or rapid snow melt. A great of rule of thumb is if water is ponded, denitrification in the soil is likely to occur.

Negative Aspects of Denitrification

Denitrification typically requires a lack of oxygen, microbes, and a source of nitrate to be used to create energy for the microbes. As the microbes reduce various nitrogen-containing compounds, starting with nitrate, other gases can diffuse to the atmosphere causing negative impacts. Typically, this occurs when there’s an excess of a particular gas, which cannot be reduced before diffusing to the atmosphere.One of the nitrogen-containing gases is nitrous oxide. This chemical is very important in global warming and holds 310 times more heat than carbon dioxide. This gas has been identified as altering long-term patterns of climate and weather, which could drastically impact food production, soil health, and land management.

Nitrous oxide is important to worry about and is of concern when denitrification occurs in wet soil environments, as well. When soil is saturated with water and denitrification is not occurring quickly, nitrate can be lost through leaching. This isn’t beneficial for the environment or food production, as nitrate is a very expensive soil fertilizer.

Lesson Summary

Denitrification is the process by which nitrate is reduced to nitrogen gas by soil microbes when oxygen is not present. This process is vital to the recycling of nitrogen for soil health, microbial and plant growth, and animal health. Denitrification can negatively impact global warming through losses of nitrous oxide.

When nitrate is in excess in the soil, denitrification can prevent loss of nitrate through leaching by reducing it to nitrite, then nitric oxide, then nitrous oxide and, finally, to nitrogen gas.

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