Abstract: To investigate the effects of field returning of Chinese milk vetch coupled with rice-fish symbiosis on the population growth and yield of rice, we carried out an experiment with four treatments, including winter fallow-double cropping rice (CK) as a control, Chinese milk vetch-double cropping rice (ZD), winter fallow-double cropping rice combined with fish (YD), and Chinese milk vetchdouble cropping rice combined with fish (ZY). We measured leaf areaindex, amount of dry matter accumulation and translocation, rice yield, and yield compositionindex. The results showed that: (1) During the cultivation of double cropping rice, leaf area index at heading stage of the ZY treatment increased by 11.33% and 50.26%, respectively. The photosynthetic potential of ZY increased from 12.30% to 28.96% and 24.00% to 48.46% respectively from tillering stage to heading stage. The net assimilation rate from panicle primordium differentiation stage to heading stage increased by 25.46% and 11.62%. (2) YD, ZD and ZY improved aboveground biomass of double cropping rice. Aboveground biomass of ZY was the highest with 1607.70 and 1526.60 g·m^-2, which respectively increased by 11.22%, 8.81%, and0.90% during the early rice season and 14.34%, 5.42% and 5.78% during the late rice season compared with CK, YD, and ZD. ZY increased aboveground biomass and material transfer to panicle. The double cropping rice harvest index was the highest in ZY, which was 0.58 and 0.59 respectively. (3) The yield of double cropping rice in ZY was 6.68 and 7.15 t·hm^-2 respectively, which increased by 12.79%-17.99%, 2.23%-11.72% and 0.44%-14.95% compared with CK, YD and ZD. Grain number per panicle was the main factor affecting yield formation. Ourresults showed that YD, ZD, and ZY could effectively improve and optimize population growth of double cropping rice, thereby increase rice yield. Further, ZY is better than YD and ZD, and thus is a green and efficient farming method.

Key words: Chinese milk vetch returning to the field, rice-fish symbiosis, double cropping rice, leaf area index, aboveground biomass, yield.