Nitrogen is a vital element to all living things, as it is found in cellular DNA, RNA, and all amino acids, which are used to make proteins. Nitrogen is of particular importance to plants, and ultimately everything that relies on plants as a part of their food chain, as nitrogen is a component of chlorophyll, which is crucial to photosynthesis. Let’s take a look at the importance of nitrogen to plants in more detail.
The importance of nitrogen to plants
Plants can absorb the CO2 they need directly from the air, but they cannot do this with nitrogen, even though 78% of air is atmospheric nitrogen. So, plants rely on microorganisms to “fix” the nitrogen from the air and build it into compounds that plants can use.
Nitrogen-fixing bacteria that live in soil take nitrogen gas (N2) from the air and turn it into ammonium ions (NH4+) in a process called ammonification. There are also some nitrogen-fixing bacteria that have a symbiotic relationship with certain plants, usually legumes. These bacteria live in nodules attached to the legume roots and also fix nitrogen into ammonium. In both cases, nitrifying bacteria then turn the ammonium into nitrites (NO2–) and nitrates (NO3–) that can be readily used by plants.
Nitrogen is returned to the soil when living things excrete waste onto the ground, and when decomposers break down dead plant and animal matter. Denitrifying bacteria in the soil are also able to turn nitrates back into atmospheric nitrogen.
Farmers often rotate the crops in their fields, alternating crops such as corn, which uses up much of the nitrogen in the soil, with crops such as clover or soybeans. The bacteria in the root nodules fix nitrogen and help the plants grow, and also replenish the nitrogen in the soil. Thus, the next crop planted there can take full advantage of the already-fixed nitrogen in the soil and the farmer can rely less on nitrogen fertilizers.