Energy and Biomass Yield of Industrial Hemp (Cannabis sativa L.) as Influenced by Seeding Rate and Harvest Time in Polish Agro-Climatic Conditions

Energy produced directly from biomass represents an important part of available alternative energy sources. Industrial hemp has potential energy yields that are higher than those of many other energy crops and, as an annual herbaceous crop, hemp fits into existing crop rotations. The total biomass of hemp per hectare is similar to other energy crops, including mostly grown giant miscanthus, poplar, or willow. Industrial hemp is characterized by a short growing cycle, a decreased need for pesticides, and low plant maintenance. The energetic value of hemp depending on agrotechnical factors, such as sowing density and time of harvest, has been assessed in this study. A three-year field experiment was carried out to prove the possibility of using whole plants and separately hemp straw and panicles for energy purposes. C. sativa was sown at eight sowing rates − 5, 10, 15, 20, 30, 40, 50, and 60 kg · ha−1 and harvested at three developmental stages: at the beginning of panicle formation, at full flowering and at the end of seed setting. The optimal harvest time of hemp grown for energetic purposes was demonstrated to be at full flowering and the optimal sowing rate at 30 kg · ha−1 when hemp yielded 14.65 t · ha−1 equals 275.56 GJ · ha−1.