Biomass and energy yield of industrial hemp grown for biogas and solid fuel

This study examined the energy yield of hemp (Cannabis sativa L.) cultivated for energy purposes under cold climate conditions in Northern Europe. Split-plot field trials were carried out over three consecutive years to investigate different nitrogen fertilisation regimes. Dry matter yield per hectare, moisture content, hydrogen content and heating value were determined at roughly monthly intervals from July until the following spring every season. The energy yield was calculated and adjusted for a fair comparison with those of other energy crops commonly grown in the study region.Two harvest periods for optimal energy yield have been determined; harvest in September to October, when the hemp is used for biogas production, yielded 14.4 Mg ha−1 and 296 GJ ha−1; harvest in February to April, when the hemp is used as a solid fuel, yielded 9.9 Mg ha−1 and 246 GJ ha−1. For biogas production, the adjusted biomass energy yield of hemp was similar to that of maize and sugar beet and 24 and 14% greater than that of lucerne and clover-grass ley, respectively. As a solid fuel, the adjusted biomass energy yield of hemp was 120% higher than that of wheat straw and similar to that of reed canary grass. Annual variations in dry matter yield depending on weather conditions and sowing dates exceeded variations due to nitrogen fertilisation.Hemp is suitable as an energy crop in cold climate regions of Northern Europe, as it has similar or often higher energy yields than other common energy crops grown in these regions.

► Field trials: optimal harvesting period of hemp as solid fuel is February to April.
► Optimal harvesting period of hemp as a biogas substrate is September–October.
► Energy yields are 296 GJ ha−1 for biogas and 246 GJ ha−1 for solid fuel application.
► DM yields are 14.4 Mg ha−1 for biogas and 9.9 Mg ha−1 for solid fuel application.
► Hemp yields similar or more energy than most energy crops common in Northern Europe.