Experiments were conducted to investigated the change of primary dormancy and viability of Chinese milk vetch(CMV) seed buried in soil both as seed and pod with seeds under CMV-rice cropping system during the period of 2007～2009. The freshly harvested CMV seed alone and pods with seeds were buried in rice field at 0, 5 and 10cm depths and determined change of seed dormancy and viability at one to three month intervals for 10 months. The CMV seed had high dormancy of 95%, showing only 4～5% germination at the beginning in June but the seed dormancy was gradually broken at rice harvest time in autumn, showing 25 to 35% for seed and 55 to 61% for pod with seeds. The viability loss was faster in the seed than in the pod with seeds regardless of depths of placement in the soil base on decayed seeds. Also the seed placed on the soil surface lost viability faster than the 5～10 burial depths. However, appreciable number of CMV seeds still remained at even 4 months after burial in soil. These results indicate that seed dormancy was enable CMV plant to regenerate naturally from the remained soil seed bank at rice harvest time in autumn.

Field experiments were conducted to investigate persistence of Chinese milk vetch(CMV) seed under naturally reseeded CMV-rice cropping systems during the period of 2007～2009. Persistence of the CMV seeds were evaluated in the naturally reseeded CMV-rice field on different tillage methods and soil depths based on the seed number recovered and the seed longevity in soil. Field observation in the naturally reseeded CMV rice field showed that as many as 917～2,185 CMV seeds m-2 were found from 0～15cm soil depth in the rotary tillage and 250～10,105 CMV seeds in minimum tillage rice cultivation in autumn. The recovered seed germinated 25～33%, 23～43% but still had high percentage of hard seed having 64～72% and 51～77%. Field experiment showed that the CMV seedling still emerged even after 2 years of continuous destructive killing of emerged CMV plant by rotary tillage in naturally reseeded CMV-rice field, indicating that CMV seeds persistent at least two years in rice field.