European Grassland Federation Conference 2018

1. 0
500
1000
1500
2000
2500
3000
3500
0 N + D 100N +
(D+50N)
0 N + D 100N +
(D+50N)
m3CH4ha-1
Cut 2
Cut 1
Grass Grass - Clover
Results
 Grass clover produced 38% higher annual DM
yields than grass (10.4 Mg ha-1 vs 7.5 Mg ha-1).
 Grass benefitted more from increasing the
intensity of fertilization than grass-clover.
 Grass-clover and grass had similar BMP,
average 297 m3 CH4 Mg-1 volatile solids.
 The methane yield per hectare was highly
correlated to the DM yield.
 Average clover content when using digestate
was 45% in both cuts and 21% when using
digestate + mineral N.
The aim of the study was to compare production strategies with different nutrient
sources when producing grass for biogas production.
Effect of digestate application,
N fertilization and forage
species on biomass and
biogas production
EGF 2018, Cork, Ireland, 17-21 June 2018
Corresponding author: perttu.virkajarvi@luke.fi
Virkajärvi, P.1, Hyrkäs, M.1, Kykkänen, S.1, Pyykkönen, V.1, Laakso, J.1, Kekkonen, P.2,
Ervasti, S.1 and Luostarinen, S.1
1Natural Resources Institute Finland (Luke), 2Savonia University of Applied Sciences
© M. Hyrkäs
Conclusions
 The addition of red clover to a grass-based forage mixture increased the methane yield per
hectare markedly. Using mineral N for the grass increased the methane yield of grass twice as
much as grass clover.
 The clover content of the DM yield was relatively high when digestate was used, but it
decreased when additional mineral N was applied.
D = digestate
Average methane yields 2013-2015
Materials and methods
 Split-plot design with four replicates, years 2013–2015, Maaninka, Finland
 Main plot: the type of species:
1) grass = timothy-meadow fescue,
2) grass-clover = timothy-meadow fescue-red clover,
 Subplot: the fertilization strategy:
1) 0N: no nitrogen,
2) 0N + D: digestate (D from anaerobic (AD) biogas process at 31 Mg ha-1 for 2nd cut,)
3) 50N + (D+50N): 50 kg ha-1 mineral N for 1st cut and D + 50 kg ha-1 mineral N for 2nd cut
4) 100N + (D+50N): 100 kg ha-1 mineral N for 1st cut and D + 50 kg ha-1 mineral N for 2nd cut
 Two harvests per year, grass-clover were harvested 6–11 days later than grass
 Digestate was injected into the soil to a depth of 5–7 cm
 Biochemical methane potential (BMP) was determined with 30 d runs for fertilization
strategies 0N + D and 100N + (D+50N) in three replicates