The objective of this study was to evaluate the effect of the mixture of different ratios of kikuyu grass (Pennisetum clandestinum) (K) – potato (Solanum tuberosum) (P) on methane production in vitro, during the second semester of 2012 in the University Research Center (Medellín, Colombia). The treatments consisted of mixtures K/P in ratios of 100/0 (T1), 75/25 (T2) and 50/50% (T3). The results were processed through a repeated measures analysis over time and nonlinear regression. At the end of incubation period (between 0 and 48 hours), the cumulative gas production (ml/g MSi), the cumulative methane production (ml/g MSi) and the dry matter digestibility were statistically differents (p<0.05) among all treatments, increasing with higher levels of potato in the mixture. In the same time interval, the relationship between dry matter digestibility and cumulative production of gas and methane (mg/ml) was statistically equivalent (p>0.05) among all treatments. The final volume of gas and methane (Vf) and its rate of production throughout the fermentation process (k), estimated from the Gompertz model, were also higher (p<0.05) for treatments including potato. Increased methane production is the result of higher dry matter digestibility according CNE level increases in the mixture. Under the in vitro model and in contrast to literature reports, the greater inclusion of CNE did not reduce methane production.
Keywords: non-structural carbohydrates, methanogenesis, in vitro gas production technique.