A field experiment on nitrogen dynamics and cycling in integrated rice-duck and rice-fish ecosystems in subtropical region of China was conducted from May to September in 2007. The experiment field was equally divided into nine plots for three different treatments: conventional rice field (CK), integrated rice-duck ecosystem (RD) and rice-fish ecosystem (RF).

Results show that the N input from precipitation was 42.83 kg N·ha^-2.The N input from irrigation water in CK, RD and RF were estimated to be 34.36, 32.72 and 41.72 kg N·ha^-2, respectively. N losses via N₂O emission in CK, RD and RF were 4.04, 4.31 and 3.76 kg N·ha^-2, respectively, which showed that RD enhanced N losses via N₂O emission while RF decreased N losses through that pathway. N losses via NH₃ volatilization in RD and RF were 43.09 and 44.89 kg N·ha^-2, respectively, lower than 46.30 kg N·ha^-2 in CK. This was because the presence of ducks and fish resulted in marked decrease in floodwater pH. N outputs via leaching in CK, RD and RF were 6.73, 6.11 and 5.81 kg N·ha^-2, respectively. N outputs via ducks and fish removal were 0.60 and 0.18 kg N·ha^-2, respectively. N uptake by rice was the major N output at 219.95±20.61, 273.65±53.49 and 279.22±17.47 kg N·ha^-2 in CK, RD and RF, respectively. The N balance analysis showed that fertilization and N uptake of rice were the main factors to affect N balance while N output via NH₃ volatilization and N input from precipitation and irrigation were also significant. Moreover, due to the presence of ducks and fish, the apparent N balance in RD and RF was positive in contrast to CK, suggesting that the presence of ducks and fish accelerated the turnover of soil organically bound nutrients and thus significantly increased N output via rice uptake.