Nitrification and Denitrification in Conventional and No‐Tillage Soils

Nitrification and denitrification were studied over the course of a year in conventional and no‐tillage agroecosystems. Soils were sampled monthly at three depths (0–5 cm, 5–13 cm, 13–21 cm). Nitrification was quantified by measuring nitrite (NO − 2 ‐N) production from soils amended with ammonium (NH + 4 ‐N) and chlorate. Denitrification was quantified by measuring nitrous oxide production, in the presence of acetylene, from unaltered soil cores and from soils amended with nitrate (NO − 3 ‐N) glucose and chloramphenicol. Nitrification and denitrification exhibited marked pulses of activity in response to residue input in both conventional and no‐tillage systems. Nitrification and denitrification activities were consistently higher in the top 5 cm of no‐tillage soils than in conventional tillage soil and a reverse pattern was observed at lower depths. Total amounts of nitrification and dentrification activity over 0 to 21 cm were not significantly different between treatments on an annual basis.