Abstract: Sweet sorghum is recently developed silage. The objective of this study was to determine the effects of sorghum varieties and best harvest time based on the biomass and quality of sweet sorghum. The biomass and nutritional quality of different sweet sorghum varieties were determined and compared at different growth stages. The results showed that the biomass and nutritional quality of sorghum change along the different developmental stages. The biomass of the sorghums was consistent with the S-shaped Logistic growth curve. The whole plant dry matter,brix degree and nitrogen free extract showed an increase trend during the growing stage. In opposite,the content of crude protein,ether extract,crude ash,and cellulose showed a decrease trend during the growing stage. The biomass,brix degree and nitrogen free extract of sweet sorghum cultivars（Keller、ST008 and H310）are significantly higher than grain/sweet sorghum E048. The biomass of sweet sorghum is even higher than that of maize,and some nutrient indexes are better than corn. We found from elongation stage to milk ripe stage would be the better harvesting stage,at which the sorghum have integrated high biomass and good nutritional quality. Taken together,it can be concluded that sweet sorghum can be used as high quality silage to partially replace silage maize,and might be mixed with silage maize to feed cattle and sheep.

Key words: sweet sorghum, biomass, crude protein, crude fat, cellulose, dry matter