nitrify

transitive verb nitrified -·fied′, nitrifying -·fy′·ing

1. to combine with nitrogen or nitrogen compounds
2. to impregnate (soil, etc.) with nitrates
3. to cause the oxidation of (ammonium salts, atmospheric nitrogen, etc.) to nitrites and nitrates, as by the action of soil bacteria, etc.

Etymology: Fr nitrifier: see niter & -fy