Denitrification in underground saturated soil in a rice paddy region

During the rice- and wheat-growing seasons we studied denitrification in the underground saturated soil within a rice paddy region. High concentrations of N2O were observed in the samples taken from observation wells of different depth,, with a maximum of 225.4 +/- 12.3 mug N-N2O l(-1) (n = 6) for the rice season and 110.0 +/- 35.7 mug N-N2O l(-1) (n = 6) for wheat at 2.5 in depth, respectively. High delta(15)N values of NO3- were also observed in the samples collected from observation wells from 2.0 to 5.0 m in depth during the rice and wheat seasons, ranging from 38.0 +/- 3.32 (n = 3) to 78.8 +/- 14.5 (n = 3) and from 35.42 +/- 6.38 (n = 3) to 77.18 +/- 2.66 (n = 3), respectively. We also found that water from wells for domestic use, sampled at around 5 in in depth had high concentrations of N2O and high delta(15)NO(3)(-) values. In regions with high N input, denitrification in the underground saturated soil, on the one hand, mitigates NO3- load in the groundwater, and contributes N2O to atmosphere on the other. (C) 2002 Elsevier Science Ltd. All rights reserved.