Abstract: By the methods of field experiment, laboratory analysis, and in situ investigation, this paper studied the effects of different tillage conversion on the carbon sequestration capability of farmland soil doubled cropped with wheat and corn. Compared with conventional tillage (CTA), conservation tillage practices benefited the accumulation of soil organic carbon, among which, notillage plus straw returning (NTS) increased the organic carbon accumulation in 0-5 cm soil layer by 18.0%, rotary tillage plus straw returning (RTS) increased this accumulation in 0-5 and 5-10 cm soil layers by 17.6% and 25;0%, respectively, and conventional tillage plus straw returning (CTS) increased the organic carbon in 10-30 cm soil layer by 31.8%. After the conversion from CTA to NTS, the carbon emission from farm operations decreased by 54.3 kg·hm^-2·a^-1; while the conversion from CTA to CTS and RTS resulted in an increase of this emission by 46.9 kg·hm^-2·a^-1 and 34.4 kg·hm^-2·a^-1, respectively. Considering of the accumulation of soil organic carbon and the carbon emission from farm operations, it could be concluded that the conversion from CTA to conservation tillage changed this farmland soil from carbon source to carbon sink, and the RTS among the three conservation tillage modes resulted in the highest soil carbon sequestration (1011.1 kg·hm^-2·a^-1).

Key words: tillage mode, wheat/corn double cropping, cropland ecosystem, carbon sequestration capability, potato, continuous monoculture, biological soil disinfestation, cultural microorganisms, Fusarium sp., soil enzyme.