Abstract: To investigate the dynamic distribution patterns of nitrous oxide (N₂O) in the soil profiles in paddy fields with different rice-upland crop rotation systems, a special soil gas collection device was adopted to monitor the dynamics of N₂O at the soil depths 7, 15, 30, and 50 cm in the paddy fields under both flooding and drainage conditions. Two rotation systems were installed, i.e., wheat-single rice and oilseed rape-double rice, each with or without nitrogen (N)application. Comparing with the control, N application promoted the N₂O production in the soil profiles significantly (P<0.01), and there existed significant correlations in the N₂O concentration among the four soil depths during the whole observation period (P<0.01). In the growth seasons of winter wheat and oilseed rape under drainage condition and with or without N application, the N₂O concentrations at the soil depths 30 cm and 50 cm were significantly higher than those at the soil depths 7 cm and 15 cm; whereas in the early rice growth season under flooding condition and without N application, the N₂O concentrations at the soil depth 7 cm and 15 cm were significantly higher than those at the soil depths 30 cm and 50 cm (P<0.05). No significant differences were observed in the N₂O concentrations at the test soil depths among the other rice cropping treatments. The soil N₂O concentrations in the treatments without N application peaked in the transitional period from the upland crops cropping to rice planting, while those in the treatments with N application peaked right after the second topdressing N of upland crops. Relatively high soil N₂O concentrations were observed at the transitional period from the upland crops cropping to rice planting.

Key words: N₂O, soil profile, paddy field, oilseed rape, wheat, cropping system