This study examined the effects of urea, molasses on fermentation dynamics and structural carbohydrate degradation of Napiergrass (Pennisetum purpureum Schumach), which was ensiled in laboratory silos for 3, 7, 14, and 30 days at the ambient temperature. The treatments were additions (fresh weight basis) of: no molasses or urea (control), no molasses and 0.4% urea (U), 4% molasses and 0% urea (M), 4% molasses and 0.4% urea (MU). The results showed that the control group produced an unstable fermentation. U silage always had smallest amount of lactic acid and highest levels of pH, acetic acid, butyric acid and ammonia nitrogen. Compared with control, both M and MU increased water soluble carbohydrate contents which promoted lactic acid fermentation domination, but MU did not restrain clostridial fermentation. After 30 days of ensiling, compared with the control, both M and MU lowered structural carbohydrate contents, and U lowered crude protein content but MU increased this parameter. It was concluded that the combination of 4% molasses with 0.4% urea could improve the fermentation and nutritive qualities of Napiergrass but was not sufficient to inhibit clostridial fermentation.

Key words: Napiergrass, Urea, Molasses, Fermentation dynamics, Structural carbohydrate