Short-life cycle, high seed oil content winter-annual species like camelina (Camelina sativa L.), grow exceptionally well in the North Central US. Recent findings indicate that winter camelina, matures early enough to allow double- or relay-cropping with forage or food crops. Additionally, double-cropping reduces the pressure on food production resulting from the introduction of energy crops while providing many environmental benefits. Forage sorghum (Sorghum bicolor L.) is an energy-efficient annual forage crop candidate that can produce high yield under droughty conditions and has low production inputs. The objective was to determine the biomass-oil yield of double- and relay-cropping sequences and compare their energy balance. Winter camelina, cv. Joelle, was planted at Prosper and Carrington, ND, on 29 August, and 1 September, 2011, respectively. The experiment was a RCBD with a split-plot arrangement, where the main plot was winter camelina or fallow, and the sub-plot, forage sorghum, soybean (Glycine max L.), and maize (Zea mays L.). Relay-seeding was performed in late April/early May with corn and soybean and by 15 May with forage sorghum. Double-cropping with sorghum or soybean followed camelina harvest at the end of June. All inputs were recorded in each sequence and converted to energy values. Outputs were calculated for biomass, seed, or crop residue. In Prosper, the energy efficiency in the 11 cropping systems fluctuated from 2.4 to 41.0 GJ ha(-1), in Carrington, 1.6 to 21.6 GJ ha(-1), and in Morris 0.9 to 42.6 GJ ha(-1). Energy efficiency was higher for soybean, corn, and sorghum in monoculture. Although, camelina double- and relay-cropping systems showed significantly lower energy efficiency than the monocultures, the most efficient system within the compound systems was the camelina-relay sorghum cropping system. More research is needed to estimate the contribution of other ecosystem services to the energy balance of novel systems.
