Phosphorus cycling in rice-duck mutual ecosystem in double cropping rice growth seasons

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.