Influence of harvest time and frequency on light interception and biomass yield of festulolium and tall fescue cultivated on a peatland

• Biomass yield up to 18.8 Mg ha−1 was recorded on temporarily flooded peatland.
• High yield was obtained with three cuts and two cuts with first cut after flowering.
• Festulolium was more sensitive to timing of the first cut than tall fescue.
• Total intercepted radiation deviated less than biomass yield among the managements.
• This indicates that harvest management affected relative root/shoot partitioning.

In this study, we report efficiencies of light capture and biomass yield of festulolium and tall fescue cultivated on a riparian fen in Denmark under different harvesting managements. Green biomass targeted for biogas production was harvested either as two cuts (2C) or three cuts (3C) in a year. Three different timings of the first cut in the 2C systems were included as early (2C-early), middle (2C-mid) and late (2C-late) cuts corresponding to pre-heading, inflorescence emergence and flowering stages, respectively. The fraction of intercepted photosynthetically active radiation (fPAR) was derived from the canopy reflectance measured on 61 dates throughout a year, and cumulative interception of PAR (IPAR) and radiation use efficiency (RUE) was calculated. The dynamics of fPAR and biomass accumulations was similar for both crops before the first cuts in all managements. Festulolium fPAR in 2C-early and 2C-mid managements declined faster than in 2C-late and 3C managements in the second growth period and thus growing period IPAR of 2C-early and 2C-mid declined by 8% as compared to 3C management where IPAR was 925 MJ m−2. Annual festulolium dry matter (DM) yield in 2C-early and 2C-mid managements (average 14.1 Mg DM ha−1) decreased by 22% compared to 3C management (18.2 Mg DM ha−1). The highest and the lowest RUE of festulolium were observed in 3C and 2C-mid managements as 1.97 and 1.59 g MJ−1, respectively. For tall fescue fPAR declined rather slowly in the second growing period in all 2C managements, which contributed to similar IPAR (908–919 MJ m−2), total biomass yield (16.4–18.8 Mg DM ha−1 yr−1) and RUE (1.80–2.07 g MJ−1) for all managements. Whereas both crops were highly productive under both 3C management and 2C management with first harvest after flowering (i.e., 2C-late), the 2C-late strategy is recommended as the least intensive of the two management systems.