Effect of ensiling density on fermentation quality of napiergrass (Pennisetum purpureum Schumach.) silage

The poor quality of silage of tropical grasses may related to the difficulty of excluding air at ensiling due to their high fiber content. The processes of respiration and proteolysis by plant enzymes during the early stages of ensiling are very important keys to make good quality silage. The aim of this experiment is to clarify whether the exclusion of air from the silage mass affects the quality of the napiergrass silage. Two plots of napiergrass were cultivated: one was applied with nitrogen (N) at 50 kg/ha in April and the other was not applied with N. The first growth was harvested in July and immediately chopped into about 1 cm length. The treatments were high (77 g/100 ml), medium (63 g/100 ml) and low (49 g/100 ml) densities of ensiling. Napiergrass was ensiled into a laboratory silo and incubated for 6, 15 and 30 days at 25°C. After opening the silo, pH, total nitrogen (TN), volatile basic nitrogen (VBN) and organic acids were determined. No significant effects of N application were observed in all parameters tested except for N content of silage. The pH value, acetic acid, butyric acid, VBN/TN significantly (P<0.01) decreased in the high density silage, while lactic acid increased. The pH value was increased by low density ensiling due to higher VBN/TN. In conclusion, high density ensiling into the silo could improve the fermentation and nutritive qualities of napiergrass silage irrespective of application.