The effect of harvest date and the chemical characteristics of biomass from Molinia meadows on methane yield

Abstract Molinia meadows are seminatural habitats of Natura 2000, and their continued existence is heavily dependent on human activities. The aim of the present study was to determine the effect of the harvest time of meadow biomass originating from Molinia meadows on the methane yield. After 35 days of conducting batch digestion tests, the average methane yield was found to be slightly different over the course of four biomass harvest dates: at the end of May, 221 ± 8 NL CH4 kg−1 VS; at the beginning of July, 211 ± 21 NL CH4 kg−1 VS; at the end of July, 200 ± 8 NL CH4 kg−1 VS and on September 1, 197 ± 2 NL CH4 kg−1 VS. During the initial stages of batch fermentation, a higher methane yield was obtained from the biomass harvested at the end of May. This biomass was characterised by higher contents of N, P and K, as well as a lower C:N ratio and reduced Ca and cellulose content. Relative to the content of elements and cellulose as well as the C:N ratio observed, significant correlations were found for methane yields from biomass obtained between the fourth and eighth days of batch digestion. It was determined that the average methane yield on a per hectare basis for the harvested biomass differed depending on the harvest date under investigation. The use of biomass from Molinia meadows for biogas production has the potential to become an important factor in the environmental protection of this type of habitat.