Yields, Calorific Value and Chemical Properties of Cup Plant <i>Silphium perfoliatum</i> L. Biomass, Depending on the Method of Establishing the Plantation

<i>Silphium perfoliatum</i> L. (<i>Silphium</i>) is one of the most promising perennial herbaceous plants, mainly due to its high biomass yield and multiple uses. It can be grown as a fodder, ornamentally, for energy (mainly as a biogas source), and as a honey crop (source of nectar and pollen for pollinators). Despite the considerable qualities of this crop, the <i>Silphium</i> cultivation area in Europe is small. The main limiting factors are the significant costs of plantation establishment and the lack of biomass yield in the first year of cultivation. Considering these aspects, research was undertaken at the Agricultural Experimental Station Lipnik of West Pomeranian University of Technology Szczecin, to assess two methods of establishing a plantation: generative, by sowing seeds (seeds); and vegetative, by transplanting seedlings grown from seeds (planting), on the yield and quality of <i>Silphium</i> biomass attended for combustion and its heating value and chemical composition. In 2016–2019, annual aboveground biomass was harvested after the end of vegetation to obtain the raw material for combustion. The collected dry mass yield (DMY) of <i>Silphium</i> significantly differed between the years and methods of establishing the plantation. The biomass yields increased in the first two years of full vegetation from 9.3 to 18.1 Mg∙ha⁻¹·yr⁻¹, and then decreased in the third year of vegetation to ca. 13 Mg∙ha⁻¹·yr⁻¹ because of drought. Significantly higher DMY was obtained by sowing seeds (ca. 13.9 Mg∙ha⁻¹·yr⁻¹) compared to the planting method (ca. 13.0 Mg∙ha⁻¹·yr⁻¹), due to the higher plant density obtained after the sowing method compared to the planting method. The calorific value in the third year was the highest and amounted to ca. 17.8 MJ·kg⁻¹ DM. The paper also presents changes in soil chemical properties before and after four years of <i>Silphium</i> cultivation.