Nitrification: Definition, Cycle & Equation

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  • 0:00 What is Nitrification?
  • 0:45 The Chemical Process
  • 2:00 Nitrogen Cycle Continued
  • 3:40 Lesson Summary
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Lesson Transcript
Instructor: Kelly Robson

Kelly has taught High School Science and Applied Communications. She holds an Education Specialist Degree in Ed. Leadership.

Plants and animals need nitrogen. The lesson explains the process of turning nitrogen that is unusable by plants into a form of nitrogen that plants can use.

What Is Nitrification?

All living organisms need nitrogen, a chemical element used to form proteins. Proteins make up the structure of organisms and produce life-sustaining functions, including development, growth, and reproduction.

Ammonia (NH3) is a form of nitrogen found in soil. Nitrogen enters the soil in this organic form from decaying plants, animal waste, and lightning striking the Earth. While in this organic form, nitrogen can't be absorbed by plants. Therefore, it must be converted into a usable inorganic form.

Nitrification is the 2-step process of ammonia found in soil being turned into nitrates (NO3-), which are inorganic forms of nitrogen that plants can use. Let's look at this process in further detail.

The Chemical Process

In nitrification, ammonia is first converted to nitrites (NO2-) and then to nitrates. The initial step of this process, known as nitritation, involves a type of bacteria called nitrosomonas. During nitritation, nitrosomonas convert NH3 (ammonia) into NO2 (nitrogen dioxide). The chemical equation for this process is NH3 + 1.5 O2 --> NO2- + H+ + H20.

The second part of the nitrification process is called nitration. Nitration uses the enzyme nitrite oxidoreductase (NOR) to complete the nitrification process. The chemical equation for this reaction is NO2- + ½ O2 --> NO3.

Once both of these processes are complete, the organic form of nitrogen, ammonia, has been converted into an inorganic form of nitrogen, nitrate, that plants can use. The chemical equation 2NH3 + 3O2 --> 2NO2 + 2H+ + 2H20 summarizes the entire nitrification process.


Nitrogen Cycle Continued

To recap, nitrogen enters soil through decaying plants, animal waste, and lightning. When it enters the soil, it's in an organic unusable form. Bacteria in the soil are able to convert the organic nitrogen into nitrates, which plants are able to use.

Plants will suck up the inorganic nitrates and mix them with other chemicals found in the plants themselves to once again make organic substances. Here's a quick cheat sheet: nitrogen = organic in the ground > converted to inorganic by bacteria > then back to organic inside the plant.

These organic substances inside the plant make up substances such as enzymes, proteins, and chlorophyll. When animals eat the plants, they eliminate the nitrogen in their waste, and it returns to the soil in organic form. When plants die and decay, they, too, return nitrogen back to the soil in organic form.

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