Assessment of Denitrification Gaseous End-Products in the Soil Profile under Two Water Table Management Practices Using Repeated Measures Analysis
2005
Elmi, Abdirashid A. | Astatkie, Tess | Madramootoo, Chandra | Gordon, Robert | Burton, David
The denitrification process and nitrous oxide (N₂O) production in the soil profile are poorly documented because most research into denitrification has concentrated on the upper soil layer (0–0.15 m). This study, undertaken during the 1999 and 2000 growing seasons, was designed to examine the effects of water table management (WTM), nitrogen (N) application rate, and depth (0.15, 0.30, and 0.45 m) on soil denitrification end-products (N₂O and N₂) from a corn (Zea mays L.) field. Water table management treatments were free drainage (FD) with open drains and subirrigation (SI) with a target water table depth of 0.6 m. Fertility treatments (ammonium nitrate) were 120 kg N ha⁻¹ (N120) and 200 kg N ha⁻¹ (N200). During both growing seasons greater denitrification rates were measured in SI than in FD, particularly in the surface soil (0–0.15 m) and at the intermediate (0.15–0.30 m) soil depths under N200 treatment. Greater denitrification rates under the SI treatment, however, were not accompanied with greater N₂O production. The decrease in N₂O production under SI was probably caused by a more complete reduction of N₂O to N₂, which resulted in lower N₂O to (N₂O + N₂) ratios. Denitrification rate, N₂O production and N₂O to (N₂O + N₂) ratios were only minimally affected by N treatments, irrespective of sampling date and soil depth. Overall, half of the denitrification occurred at the 0.15- to 0.30- and 0.30- to 0.45-m soil layers, and under SI, regardless of fertility treatment level. Consequently, sampling of the 0- to 0.15-m soil layer alone may not give an accurate estimation of denitrification losses under SI practice.
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