Judy Greenlee, age 15 of Cleveland, Ohio for her question..
What is the nitrogen cycle?
A cycle is something which goes around and around. The sun evaporates up water and it falls down again as rain to be evaporated again, The‑nitrogen cycle is another of these non‑stop operations that keep the world going along. Nitrogen is a lazy gas. It makes up about four‑fifths of the air, It refuses to help the burning activities of oxygen and even slows down fires. It has no effect on our bodies as we inhale it with every breath. It has no effect on leaves and branches though it surrounds them like an ocean.
In spite of all this laziness, nitrogen is absolutely necessary to all plants and animals. It prefers to stay a lazys filmy gas. But nature has a couple of tricks to make. it db useful work. Nitrogen gas is forced to become various chemical nitrates. We call this nitrogen fixation: Some of this fixation is done by lightning and some by tiny bacteria.
A charge of lightning unites nitrogen with oxygen in the air to form nitric oxide. This cools into nitrogen peroxide and unites with mist and rain to form nitric acid. This tumbles down with every thunderstorm and reacts with various minerals in the ground to form potassiums saltpeter and other nitrates. These are the nitrates necessary for plants to make proteins and protoplasm.
Maybe 80 million tons of nitric acid is fixed by lightning each year. This is not enough for all the plants. The rest is made by‑attain soil‑dwelling bacteria. Some grow free in the dirt. Others team up with the roots of the legume plants ‑ the peas, beans and alfalfa. These bacteria specialists fix nitrogen from the air into nitrates for the. soil.
Nitrates dissolve easily in soil moisture and travel with the sap up into the plants and trees. There they are made into body‑building proteins and ‑protoplasm, the magic fluid present in the cells of all living plants and animals.
The nitrogen cycle next moves over into the animal kingdom. Some animals get their nitrates by eating plants. Others get them by eating the animals that eat the plants. Nitrates are used to make proteins and protoplasm in animals as in plants. Once fixed into nitrates, the nitrogen cycle goes from job to job.
Nevertheless, even as chemical nitrates, the nitrogen is always trying to escape back into a lazy gas. Nitrates are lost with all the waste body material: Some nitrogen always escapes. Leaves‑fall and flowers fade. Old nitrate‑bearing tissues are broken up by decay. Some nitrogen always escapes in this process. Though most stays fixed as nitrates and returns to the soil for re‑use by new growing plants. Every day, some nitrogen escapes from the cycle treadmill. But every day, new nitrogen is fixed into nitrates by lightning and by busy bacteria. .
We remove a great deal of nitrates from the soil with every crop we harvest. We eat these chemicals along with the plants to build our bodies, The soil is poorer because we have taken out next yearts plant food. For this reason we enrich the ground with fertilizers. Better still, the farmer grows a legume crop next year and lets the little bacteria enrich his soil with nitrates fixed from the air.