Effect of digestate application, N fertilisation and forage species on biomass and biogas production

摘要

Nutrient recycling is integral to environmentally and economically efficient grassland production. Our aim was to compare production strategies with different nutrient sources when growing grass for biogas production. In a three-year field study (2013- 2015), nutrients were applied to grass in the form of digestate from a farm-scale biogas plant, commercial N fertilisers as well as that provided by biological N fixation. The main plots were grass or mixtures of grass and clover with four different combinations of digestate and N fertilisers as sub-plots. As a three-year average, the grass-clover mixture produced 33% higher DM yields, and had similar CH_4 production potential per kg of volatile solids (VS) and 25% higher CH_4 production per hectarethan grass swards. Grass DM production benefitted more from the use of 50 kg ha~(-1) of mineral N for both the first and the second cut (+57%) than from using digestate at 30 t ha~(-1) containing 92 kgN_(total)ha~(-1) (in which 66 N_(soluble)ha~(-1)) forthe second cut (+23%). Grass benefitted more from both types of fertilisation than the grass-clover mix (+93 vs +30%, respectively). Compared to 0 N plots, the use of digestate decreased the mean clover content less than the use of mineral N (by-20% compared to -62%). P and K balances were negative in all plots but less negative when digestate was used.