Abstract: Raising duck in paddy rice field is an evolution of Chinese traditional agriculture.In May-October 2010, a field experiment was conducted in a double cropping rice region of Hunan Province, South-central China to study the nitrogen (N) cycling in rice-duck mutual ecosystem during early rice and late rice growth periods, taking a conventional paddy rice field as the control. Input-output analysis method was adopted. The N output in the early rice-duck mutual ecosystem was 239.5 kg·hm^-2, in which, 12.77 kg·hm^-2 were from ducks, and the N output in the late rice-duck mutual ecosystem was 338.7 kg·hm^-2, in which, 23.35 kg·hm^-2 were from ducks. At the present N input level, there existed soil N deficit during the growth seasons of both early rice and late rice. The N input from duck sub-system was mainly from the feed N, and the cycling rate of the duck feces N recycled within the system was 2.5% during early rice growth season and 3.5% during late rice growth season. After late rice harvested, the soil N sequestration was 178.6 kg·hm^-2.

Key words: rice-duck mutual ecosystem, duck sub-system, soil sub-system, N cycling