Influence of nitrogen fertilization on tropical-grass silage assessed by ensiling process monitoring using chemical and microbial community analyses

Utilization of silage in livestock farming is expected to increase in developing countries in the tropical and subtropical parts of the world. The aim of this study was to investigate the influence of nitrogen fertilization on the chemical composition of herbage, ensiling process and silage quality, and to contribute to the improvement of tropical-grass silage preparation. Guinea grass grown under two different nitrogen-fertilizer application conditions [1·5 kg N a⁻¹ (high-N) and 0·5 kg N a⁻¹ (low-N)] was packed in plastic bags, and its ensiling process was investigated by chemical and microbial-community analyses. Relatively well-preserved silage was obtained from high-N herbage, which accumulated a high nitrate concentration. Denaturing gradient gel electrophoresis analysis revealed that Lactobacillus plantarum dominated throughout the ensiling of high-N herbage and in the early phase of that of low-N herbage. In low-N silages prepared from ammonium sulfate- and urea-fertilized herbage, Lact. plantarum was replaced by clostridia after 40 and 15 days of ensiling, respectively. Nitrate content of herbage is an important factor that influences silage quality, and careful fertilization management can facilitate stable and successful fermentation of tropical-grass silage without any pretreatment. The positive effect of nitrate on the ensiling process of tropical-grass was proved by microbial-community analysis.