Nitrogen fixation is the process by which atmospheric nitrogen is converted by either a natural or an industrial means to a form of nitrogen such as ammonia. In nature, most nitrogen is harvested from the atmosphere by microorganisms to form ammonia, nitrites, and nitrates that can be used by plants.

In general, the nitrogen cycle has five steps:

• Nitrogen fixation (N2 to NH3/ NH4+ or NO3-)
• Nitrification (NH3 to NO3-)
• Assimilation (Incorporation of NH3 and NO3- into biological tissues)
• Ammonification (organic nitrogen compounds to NH3)
• Denitrification(NO3- to N2)

The five processes in the nitrogen cycle – fixation, uptake, mineralization, nitrification, and denitrification – are all driven by microorganisms.

Examples of this type of nitrogen-fixing bacteria include species of Azotobacter, Bacillus, Clostridium, and Klebsiella. As previously noted, these organisms must find their own source of energy, typically by oxidizing organic molecules released by other organisms or from decomposition.

Each bolt of lightning carries electrical energy that is powerful enough to break the strong bonds of the nitrogen molecule in the atmosphere. Lightning does add nitrogen to the soil, as nitrates dissolve in precipitation. This helps plants, but microorganisms in the soil do the vast majority of nitrogen fixation.

Like carbon, nitrogen has its own biogeochemical cycle, circulating through the atmosphere, lithosphere, and hydrosphere (Figure 5). Unlike carbon, which is stored primarily in sedimentary rock, most nitrogen occurs in the atmosphere as an inorganic compound (N2).

Plants absorb nitrates from the soil to make proteins. Animals consume plants and use it to form animal protein. Humans contribute to the cycle by adding nitrogen rich fertilisers to the soil and by using manure (The Physics Teacher, 2018).

This reaction provides energy for the bacteria engaged in this process. The bacteria that we are talking about are called nitrosomonas and nitrobacter. Nitrobacter turns nitrites into nitrates; nitrosomonas transform ammonia to nitrites.

Nitrogen fixation is the process by which nitrogen gas from the atmosphere is converted into different compounds that can be used by plants and animals. There are three major ways in which this happens: first, by lightning; second, by industrial methods; finally, by bacteria living in the soil.

Fixation

• Biologically: Nitrogen gas (N2) diffuses into the soil from the atmosphere, and species of bacteria convert this nitrogen to ammonium ions (NH4+), which can be used by plants.
• Through lightning: Lightning converts atmospheric nitrogen into ammonia and nitrate (NO3) that enter soil with rainfall.

Compared to O, N is 4 times as abundant in the atmosphere. This is one reason why nitrogen is so enriched in the atmosphere relative to oxygen. The other primary reason is that, unlike oxygen, nitrogen is very stable in the atmosphere and is not involved to a great extent in chemical reactions that occur there.

Excessive N causes “luxuriant” growth, resulting in the plant being attractive to insects and/or diseases/pathogens. The excessive growth can also reduce stem strength resulting in lodging during flowering and grain filling. Excessive use of N also has negative implications for the environment and lowers farm profits.

Place your piece of moistened red litmus paper in a test tube. Fill the test tube with the gas you want to test and stopper it. Wait a few minutes. If the red litmus paper turns blue, it means that the test tube contains a basic gas.