Nitrification

Nitrification is the microbial oxidation of ammonium to nitrite and then nitrate. It converts reduced nitrogen into forms readily taken up by plants or lost from soils and waters.

Ammonia oxidation: The microbial conversion of ammonia to nitrite, the first step of nitrification. This is the first chemical step, carried out by ammonia-oxidizing archaea or bacteria.
Ammonium: The positively charged nitrogen ion NH₄⁺, common in soils and waters. Ammonium is the reduced nitrogen substrate that enters nitrification.
Soil fertility: The capacity of soil to support plant growth through available nutrients and suitable conditions. Nitrification supplies nitrate that plants can absorb, while also changing nitrogen retention.
Nitrate leaching: The downward movement of dissolved nitrate through soil with percolating water. Nitrate is highly mobile, so nitrification can make nitrogen vulnerable to groundwater loss.
Nitrite oxidation: The microbial conversion of nitrite to nitrate. This second step completes the oxidation sequence.
Ammonia: The nitrogen compound NH₃, which exists in equilibrium with ammonium in water. Microbes generally oxidize ammonia, whose availability depends on pH and temperature.
Nitrification inhibitor: A substance that slows microbial ammonia oxidation in soil or other systems. These compounds delay nitrate formation and can reduce nitrogen losses from fertilized fields.
Denitrification: Microbial reduction of nitrate or nitrite to gaseous nitrogen compounds, often ending in nitrogen gas. It consumes nitrate produced by nitrification and returns nitrogen to the atmosphere.
Ammonia-oxidizing archaea: Archaea that obtain energy by oxidizing ammonia to nitrite. They perform the first step across many soils and aquatic environments.
Nitrite: The nitrogen oxyanion NO₂⁻, an intermediate in nitrification and other nitrogen transformations. Nitrite is produced in the first step and consumed in the second.

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