When nitrogen is absorbed by the soil, different bacteria help it to change states so it can be absorbed by plants. Animals get their nitrogen from the plants. Fixation is the first step in the process of making nitrogen usable by plants. Bacteria then changes nitrogen into ammonium.
Chemical Reactions; Nitrogen Fixation (Nitrogen + Hydrogen = Ammonia) , Ammonification (decomposition releases ammonium), Nitrification (ammonia and ammonium into nitrites, then nitrates), Denitrification (bacteria into nitrates and nitrogen gas).
Organic/Inorganic Components; Nitrogen
Impact of Human Intervention; Humans take nitrogen out of topsoil through agriculture. Agricultural runoff disrupts aquatic ecosystems by adding excess nitrates to bodies of water.