Abstract: The total amount of winter fallow areas have increased in south China in recent years. It not only causes enormous waste of resources and energies, but also affects paddy soil qualities and farming environment. Winter ryegrass was essential to improve soil productivity and carbon and nitrogen fixation. The purposes of this study were to investigate the effects of winter ryegrass on carbon and nitrogen fixation and the change of soil microbial biomass carbon and soil microbial biomass nitrogen in six different types of paddy soils in south China. The experiment designed winter ryegrass and winter fallow respectively in six different types of paddy soils. The result showed that, winter ryegrass dry matter was significant in different types of paddy soils. Ryegrass biomass was the highest in alluvial sandy soil with 11 324.8 and 8 227.3 kg ha^-1 respectively in aboveground and root. The carbon uptake in aboveground and root of ryegrass was 4 495.3 and 2 799.6 kg ha^-1 respectively in alluvial sandy soil. The nitrogen uptake in aboveground and root of ryegrass was 238.1 and 60.1 kg ha^-1 respectively. The change of soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN) was significant between winter ryegrass and winter fallow treatments in six different types of paddy soils. Winter ryegrass increased soil microbial activities, especially in alluvial sandy soil.

Key words: Ryegrass, Carbon fixation, Nitrogen fixation, Soil microbial