SEASONAL DENITRIFICATION RATES UNDER CORN (ZEA-MAYS L) IN 2 QUEBEC SOILS

Nitrogen losses in soil through denitrification are important due to r educed agronomic effectiveness and environmental concerns with nitrous oxide emissions. Knowledge of denitrification may allow for managemen t procedures to reduce these losses. Field experiments were conducted in 1991 and 1992 to investigate N fertilizer effects on denitrificatio n under corn (Zea mays L.) on two soils of contrasting texture in sout hwestern Quebec. Soil core incubation with C2H2 was used to assess den itrification rates. Total calculated denitrification rate from April t o November in 1991 and 1992 varied from 4 to 41 kg N ha(-1) on a Chico t sandy clay loam and from 29 to 53 kg N ha(-1) on a Ste. Rosalie clay . Denitrification rates increased linearly with increasing fertilizer N rates only in the Ste. Rosalie clay in 1991. Denitrification in the Ste. Rosalie soil was positively related to temperature and NO3- level s in April and May, moisture content from August to November, and temp erature in October and November. Denitrification in the Chicot soil wa s positively related to soil moisture content and NO3- levels in April and May, and soil moisture content in June. Reducing soil NO3- concen trations in April and May could decrease denitrification rate in both Chicot and Ste. Rosalie soils.