Abstract
Biological dry matter yield, and in vitro-digestibility and its relating plant factors were investigated for the leaf blades and the stems ot napiergrasses (Pennisetum purpureum Schumach) grown at Naha, Miyazaki and Tokyo under two cutting regimes. Digestibilities of the leaf blade and the stem were highly correlated with the lignin concentrations. The regressions of lignin concentrations to biological yield in both leaf blade and stem were positive hyperbolic regressions, whereas regressions of digestibility to yield were negative hyperbolic regressions. The leaf blade was more digestible than the stem and the lower parts of the stem were less digestible than its higher parts. High temperatures, long cutting intervals and maturing of plants appeared to lessen the digestibility of the stem. However, the variations of digestibilities mentioned above, were not so large, and the digestible dry matter yields were regressed linearly to the biological dry matter yields with a significant correlation coefficient at 5% level, irrespective of the differences in the regional site, season and cutting interval. An increase of biological dry matter yield from 10 t/ha to 30 t/ha was followed by a decrease of in vitro-dry matter digestibility of the whole harvested material from 74.3% to 60.0%. The average digestibility was about 65% and this value was estimated to be intermediate among the tropical grasses.
