Abstract: In order to explore the rules of nutrient release and organic decomposition of green manures in soil,the decomposition dynamics of smooth vetch(Vicia villosa Roth var.),common vetch(Vicia sativa L.),milk vetch(Astragalus sinicus L.),perennial ryegrass(Lolium perenne) in tobacco fields were studied via burying these green manures packed in nylon string bags into the plow layer of tobacco fields.The results showed that the organic matter in green manures decomposed rapidly in the first 2 weeks after burying,and moderately from the third to seventh weeks,slowly after seven weeks.In the first 2 weeks,the average decomposition rate of organic matters was 12.50%-19.18% per week and the average release rates of C,N,P,K were 13.05%-19.56%,20.08%-26.59%,17.86%-26.08%,16.97%-26.08% per week,respectively;from the third to seventh weeks,which were 6.16%-8.58% and 6.23%-8.62%,5.71%-7.83%,4.47%-5.29%,7.01%-8.49%,respectively;after seven weeks,which were 0.65%-0.96% and 0.65%-1.48%,0.50%-1.09%,0.65%-1.36%,0.51%-1.14%,respectively.In seven weeks,the total decomposition rate of organic matters was 60.64%-70.57%,the total release rates of C,N,P,K were 62.17%-71.32%,75.68%-83.03%,70.61%-84.78%,73.88%-80.12%,respectively,and the amount of N release were the highest.Comparatively,the rates of nutrient release and organic matter decomposition were slower for perennial ryegrass in the first 2 weeks;for common vetch were slower from the third to seventh weeks.The C/N ratio increased after green manure burying,it did not reach 24 until the seventh week after burying.