nitrogen cycle

The continuous process by which nitrogen is exchanged between organisms and the environment. Some of the atmosphere's free nitrogen combines with other elements to form compounds that are deposited in the soil. These are then converted by bacteria, in a process called nitrification, into nutrients that are absorbed by the roots of green plants. Nitrogen is then passed into the food chain and returned to the soil by the metabolism and decay of plants and animals.

"nitrogen cycle." The American Heritage® Dictionary of Student Science, Second Edition. 2014. Houghton Mifflin Harcourt Publishing Company 21 Sep. 2016

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