Methane production from biofuel crops grown in New Zealand

On-farm biomethane production from biofuel crops is well established at a large scale in Europe, but there is limited data available in New Zealand. A research trial was established to test components of a biofuel system under New Zealand conditions within a closed-loop nitrogen bioenergy production system (CLN). Forage sorghum yields of 25 t DM/ha were achieved with 100 kg N/ha applied on a moderately low N soil (66 kg mineralisable N/ha) and there was no increase in yield from applying additional N. Sorghum grown with digestate from an anaerobic digester yielded the same as sorghum grown with ammonium sulphate applied at the same rates of total N. Jerusalem artichoke was identified as a promising perennial biogas crop with trial methane yields of 3672 m3 CH4/ha, while forage sorghum showed particular potential for summer dry land. Methane yields of 6559 m3 CH4/ha and 8091 m3 CH4/ha were recorded for the sorghum cultivars Sugargraze and Jumbo respectively. These methane yields are similar to those from biomass crops grown and tested under more intensive conditions in Europe. Crimson clover is superior to white clover as a winter legume (mid-May to mid-November) for DM production in a CLN system, yielding 9.6 t DM/ha compared with 5.3 t DM/ha for white clover.