Abstract: Rice-duck mutualism is the development of raising duck in rice field in Chinese traditional agriculture. In this study, a field experiment of raising duck in rice field was conducted in a double cropping rice region of Hunan Province from May to October 2010, and an input-output analysis was made to analyze the phosphorous (P) cycling in the riceduck mutual ecosystem, taking a conventional rice field as the control. Neither pesticides nor herbicides were applied throughout the growth period of rice in the riceduck mutual ecosystem. In the early rice-duck mutual ecosystem, the P output was 52.28 kg·hm^-2, of which, the P output from duck was 1.71 kg·hm^-2; in the late rice-duck mutual ecosystem, the P output was 83.24 kg·hm^-2, of which, the P output from duck was 6.17 kg·hm^-2. During the double cropping rice growth seasons, the P inputs of the rice-duck mutual ecosystem decreased the P deficit in soil subsystem. The P input of duck subsystem mainly came from feed P, and the cycling rate of duck feces P in the mutual ecosystem in early rice and late rice growth seasons was 12.5% and 13.5%, respectively. After late rice harvesting, the P sequestration in soil was 195.41 kg·hm^-2. In contrast with conventional rice, riceduck mutualism decreased the deficit of soil P, while increased the soil P sequestration by 36.9%. This study provided reference for further development and utilization of rice-duck mutualism in this country.

Key words: home-field advantage, microbial biomass carbon, microbial respiration, microbial metabolic quotient.