Comparison of nitrogen transformation dynamics in non-irradiated and irradiated alfalfa and red clover during...

To study the contribution of plant enzyme and microbial activities on protein degradation in silage, this study evaluated the nitrogen transformation dynamics during ensiling of non- and irradiated alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.).

Alfalfa and red clover silages were prepared and equally divided into two groups. One group was exposed to γ-irradiation at a recommended dosage (25Gky). Therefore, four types of silages were produced: (1) non-irradiated alfalfa silage; (2) irradiated alfalfa silage; (3) non-irradiated red clover silage; and (4) irradiated red clover silage. These silages were opened for fermentation quality and nitrogen components analyses after 1, 4, 8 and 30 days, respectively.

The γ-irradiation successfully suppressed microbial activity, indicated by high pH and no apparent increases in fermentation end products in irradiated silages. All nitrogen components, except for peptide-N, increased throughout the ensiling process. Proteolysis less occurred in red clover silages compared with alfalfa silages, indicated by smaller (P<0.05) increment in peptide-N and free amino acid N (FAA-N) during early stage of ensiling. The γ-irradiation treatment increased (P<0.05) peptide-N and FAA-N in alfalfa silage at day 1, whereas not in red clover silage; these two nitrogen components were higher (P<0.05) between day 4 and day 30 in non-irradiated silages than the irradiated silages. The ammonia nitrogen (NH3-N) and non-protein nitrogen (NPN) were highest in non-irradiated alfalfa silage and lowest in irradiated red clover silage after ensiling.

The result of this study indicate that red clover and alfalfa are two forages varying in their nitrogen transformation patterns, especially during early stages of ensiling. Microbial activity plays a certain role in the proteolysis and seems little affected by the presence of PPO in red clover compared with alfalfa.