Where Do Nutrients Come From?

While nitrogen gas makes up 78% of the atmosphere, very little is in a form that plants can use. As shown in the diagram of the nitrogen cycle, organisms in the soil break down materials and convert them into nitrogen-containing molecules that can be used by plants to grow. The nitrogen cycle describes how nitrogen moves through the Earth system.

The phosphorus cycle describes how phosphorus moves between different parts of the Earth system. When phosphorus combines with oxygen to make phosphate, it can be used by plants to grow. The amount of phosphorus naturally occurring in soil is usually very low. Therefore, adding fertilizers that contain phosphorus can help plants grow.