Abstract: In this study a second cut alfalfa crop harvested at the early flowering stage (10% of plants flowering) was used as raw material for making bagged silage. The research comprised a two-factor evaluation of formic acid as an additive [concentration 3 (A₁), 6 (A₂) or 9 mL·kg^-1 (A₃)], with no addition as the control. Silage bags from the various formic acid treatments were opened for fermentation analysis after 30, 60 and 120 days. Both formic acid addition and ensiling time significantly influenced silage quality. Formic acid addition significantly reduced the pH value, ammonia nitrogen:total nitrogen ratio, and acid detergent fiber (ADF) value of the silage (P<0.05). Except for crude protein (CP), silage time had a significant effect on the silage nutritional quality (P<0.05). Among all the treatments, alfalfa silage with 6 mL·kg^-1 formic acid added (A₂) and 60 days fermentation time gave the best overall result. The interaction effect between formic acid addition and ensiling time was significant for dry matter (DM), neutral detergent fiber (NDF) and crude fat (EE) content (P<0.05), but was not significant for other silage quality parameters (P>0.05).

Key words: alfalfa, formic acid additives, silage time, silage quality