Nitrate-N (NO3-) effluents from agricultural ecosystems contributing to the degradation of water quality has become a serious environmental problem. A field experiment was conducted in 1996 and 1997 at St. Emmanuel, Que., Canada, to investigate the combined effects of water table management (WTM) and N fertilization on soil NO3- level and denitrification rates in the top soil layer (0�0.15 m). The field was planted to corn (Zea mays L.) in both years.

Treatments consisted of a factorial combination of two water table treatments, free drainage (FD) at about 1.0 m and subirrigation (SI) at 0.6 m below the soil surface, and two N fertilizer rates, 200 kg ha-1 (N200) and 120 kg ha-1 (N120). SI reduced NO3- concentration in the top soil layer by 42 and 16% in 1996 and 1997, respectively. Nitrate levels in soil were 50% lower in N120 plots in 1996, and 20% in 1997 compared to the N200 plots. Denitrification was higher in SI compared to FD, but not influenced by N rate. As a consequence, WTM practices have implications for both water quality and greenhouse gas emissions. Climatic conditions played a large role in regulating N dynamics in the soil. Due to drier and cooler conditions in 1997, denitrification rates were lower than in 1996, leaving higher residual NO3- in the soil profile following corn harvest.

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