Investigation of effect of particle size and rumen fluid addition on specific methane yields of high lignocellulose grass silage

This work examines the digestion of advanced growth stage grass silage. Two variables were investigated: particle size (greater than 3 cm and less than 1 cm) and rumen fluid addition. Batch studies indicated particle size and rumen fluid addition had little effect on specific methane yields (SMYs). In continuous digestion of 3 cm silage the SMY was 342 and 343 L CH4 kg−1 VS, respectively, with and without rumen fluid addition. However, digester operation was significantly affected through silage floating on the liquor surface and its entanglement in the mixing system. Digestion of 1 cm silage with no rumen fluid addition struggled; volatile fatty acid concentrations rose and SMYs dropped. The best case was 1 cm silage with rumen fluid addition, offering higher SMYs of 371 L CH4 kg−1 VS and stable operation throughout. Thus, physical and biological treatments benefited continuous digestion of high fibre grass silage.