Nitrogen Cycle

Put on your science caps, dear readers! Today we are learning about the nitrogen cycle!
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In its most basic terms, the nitrogen cycle is a process by which bacteria convert atmospheric nitrogen into a form available to plants. Plants use the nitrogen to grow. The plants are then eaten and turned into organic waste. This waste enters the soil where it is again taken up by plants. And so it goes!

Nitrogen (N2) makes up 78% of our atmosphere and it is a necessary component of every living thing. Nitrogen, in the form of nitrates (N03), nitrites (NO2), and ammonium (NH4) help create amino acids and nucleic acids, which turn into proteins and DNA.

The nitrogen cycle consists of:

• fixation - bacteria convert atmospheric nitrogen (N2) into ammonium (NH4)
• nitrification - bacteria convert ammonium (NH4) into nitrates (N03)
• assimilation - plants absorb the nitrates (N03)
• ammonification - decaying matter is converted back into ammonium (NH4)
• denitrification - bacteria convert fixed nitrogen back into atmospheric nitrogen (N2)

Nitrogen Cycle (EPA)

Atmospheric nitrogen is generally unavailable to plants, but they really need it. For nitrogen to be absorbed by plants it must be “fixed”. When lightning strikes the Earth, nitrogen is fixed, but the majority of fixation occurs via microorganisms called diazotrophs.

Diazotroph bacteria carry an enzyme that converts atmospheric nitrogen into ammonia, which is then converted into other organic compounds by the bacteria in a process called nitrification. Other microorganisms, such as mycorrhizae, carry similar enzymes that can also fix nitrogen into the soil. In exchange for their efforts, plants provide these bacteria with carbohydrates and sugars. The most effective nitrogen fixing bacteria are from the Rhizobium family. These nitrogen fixing bacteria are found in the root nodules of legumes, such as beans and peas. If your soil is low on nitrogen, it is a good idea to plant members of the legume family and let their microscopic nitrogen fixing factories get to work! 

Industrially, a method called the Haber-Bosch process uses heat and pressure to convert atmospheric nitrogen (N2) into 30% of the ammonium (NH4) used in agriculture. Since the agricultural revolution started 10,000 years ago, humans have been responsible for doubling the amount of nitrogen available to plants. The level of ammonia (NH3) has tripled and nitrous oxide (N20) has begun to break down our protective ozone layer. Rather than applying chemical fertilizers, there are other ways to improve the nitrogen cycle in your garden.

Adding nitrogen naturally

An excellent way to add valuable nitrogen to your soil is to raise or encourage worms in the garden. When worms poop, or die, the nitrogen released is available to plants through ammonification. Worms have the added advantage of improving soil structure, aeration and percolation. Without good soil structure, heavy rains can saturate the soil, creating a bog. In a bog environment, other bacteria step in and convert fixed nitrogen back into the unavailable atmospheric variety in a process called denitrification. Blood meal is an excellent source of nitrogen.

Applying mulch and compost can also improve soil health and soil structure. Nature has evolved effective, sustainable mechanisms for all living things. We can best continue by following those examples.