Nitrogen Cycle

Nitrogen gas (N₂)

Unfixed; triple bond makes it stable; found in atmosphere.

Ammonium (NH₄⁺)

Fixed form; produced by decomposition and nitrogen fixation.

Nitrite (NO₂⁻)

Intermediate fixed form; produced during nitrification.

Nitrate (NO₃⁻)

Highly mobile fixed form; important plant nutrient.

Nitrous oxide (N₂O)

Greenhouse gas released during denitrification.

Nitrogen fixation

N₂ → NH₄⁺ by bacteria or industrial process.

Ammonification

Organic nitrogen → NH₄⁺ by decomposers.

Nitrification

NH₄⁺ → NO₂⁻ → NO₃⁻ by nitrifying bacteria.

Assimilation

Plants absorb NH₄⁺ or NO₃⁻.

Denitrification

NO₃⁻ → N₂ or N₂O; returns nitrogen to atmosphere.

Major nitrogen pools

Atmosphere, soil, plants, consumers, decomposers.