If the C:N ratio is less than 20:1, what happens to nitrogen (N)?

When the carbon to nitrogen (C:N) ratio is less than 20:1, the nitrogen present in organic matter becomes mineralized. This process involves the breakdown of organic material by microbes, which consume carbon as an energy source and release nitrogen in a form that plants can use (such as ammonium or nitrate).

In environments where the C:N ratio is low, there is generally enough nitrogen available in relation to the carbon, allowing microbial populations to efficiently access and convert nitrogen into mineral forms. This mineralization process is crucial for providing plants with the nitrogen they need for growth, as it transforms organic nitrogen into inorganic forms that are readily available to plant roots.

The other options describe different interactions or states of nitrogen: immobilization occurs when there is insufficient nitrogen, and microbes take up nitrogen from the soil, which can occur when the C:N ratio is high; nitrogen fixation specifically refers to the conversion of atmospheric nitrogen into forms usable by plants, primarily by certain bacteria, not directly related to the C:N ratio; and leaching is a process where nitrogen can be lost from the soil, typically associated with excess water, rather than directly linked to the ratio itself.