From an ecological point of view, nitrogen-fixation is a crucial link in the nitrogen cycle, a worldwide process in which the nutrient is cycled and recycled between the atmosphere, oceans, soil, and living organisms. As long as the cycle continues, nitrogen will always be available for plants and animals. The same does not hold true for the world’s supplies of noncyclable nutrients, such as phosphorus, potassium, magnesium, and iron. As these elements slowly wash out of the land and into the oceans, they become unrecoverable by natural means and, therefore, unavailable to terrestrial plants.
