Biomass of annual forage crops for biogas production

In Merelbeke (Flanders) a monoculture of maize (+ rye as a catch crop) and a 3 year crop rotation of maize, Italian ryegrass (IR, Lolium multiflorum), 1 cut IR + sorghum (+ rye as a catch crop) were compared in terms of biomass production (organic matter yield) (OM) for methane production. Two N- fertilizer regimes were conducted for the annual crops: a moderate and extensive N-regime (i.e. moderate x 0.6). During a period of 3 years there was no significant difference in OM yield between maize in rotation, maize in monoculture and the combination of 1 cut IR + sorghum at the two N-fertilisation levels. The average yield of 3 years of a monoculture maize (16.6 t OM per ha) was considerably higher than the average yield of a 3 year rotation maize - Italian ryegrass- sorghum (15.2 t OM per ha). The ranking of the individual energy crops in terms of OM production per ha was the same for the moderate and the extensive N fertilization level: maize in rotation> 1 cut IR + sorghum> maize in monoculture >> Italian ryegrass. The substrate specific methane yield of the crops, involved in this experiment, are comparable and have less influence on the methane yield per ha than the area- specific methane yield.