Optimal harvest time for high biogas and biomass yield of Typha latifolia, Typha angustifolia and Phalaris arundinacea

Rewetting of peatland is commonly accepted as a useful measure for counteracting climate change. To increase the acceptance, an agricultural use of fen plants is needed. In this study, the optimal harvest date of Typha latifolia, Typha angustifolia and Phalaris arundinacea regarding their biogas potential and biogas yield per hectare was identified. Furthermore, the influence of the chemical composition of Typha spp. and P. arundinacea on the biogas and biochemical methane potential was determined. Finally, the predictability of the biochemical methane potential (BMP) of Typha spp. and P. arundinacea by their composition with published regression models was examined. The three fen plant species were harvested on five different dates in 2018 and/or 2020. For each harvest, the biomass yield, biogas potential and BMP were determined, the chemical composition of the biomass was analyzed, and the biogas yield per hectare was calculated. The biogas potential of T. latifolia, T. angustifolia and P. arundinacea decreased with increasing plant maturity and ranged between 315 and 647 L_N kg⁻¹ VS, 405 and 596 L_N kg⁻¹ VS and 361 and 597 L_N kg⁻¹ VS, respectively. The biogas and BMP of all three plant species investigated were negatively correlated with the lignin content and could be predicted with published regression models, which included the lignin content as main regressor. The derived optimal harvest dates, which were a compromise between biomass yield and biogas potential, for all three fen plants ranged between the development stages of full flowering and shortly after the seed heads turned brown.