Biomass production and potential ethanol yields of shrub willow hybrids and native willow accessions after a single 3-year harvest cycle on marginal lands in central Minnesota, USA

Short rotation woody crops are being developed as a sustainable source of biomass for the production of bioenergy, biofuels, and bioproducts. With the potential increase in demand of biomass for energy in the future, there is a need to diversify and expand its source. In the present study, we evaluated the growth performance, biomass production, energy content, and potential ethanol yields of shrub willow hybrids and native willow accessions. Shrub willow hybrids cuttings were obtained from the State University of New York through its controlled breeding program while cuttings used for native willow accessions were collected naturally. At the end of one rotation, consisting of three growing seasons, we found that shrub willow hybrids outperformed native willow accession species (P = 0.0004), with an average survival rate of 80 and 39 %, respectively. Biomass production of shrub willow hybrids and native willow accessions ranged from 7.42 to 16.0 and from 0.69 to 1.83 Mg ha^-1 oven dry weight, respectively. The chemical composition (mass fraction % on dry basis) of willow hybrids and native willow accessions generally contained 39 % cellulose, 19 % hemicellulose, 25 % lignin, 1.4 % ash content, 17,500-18,500 kJ kg wood^-1, and 385 L Mg^-1 of theoretical ethanol yield. Energy content and potential ethanol yields on a dry weight basis did not vary between shrub willow hybrids and native willow accessions; however, the amount of biomass produced per unit land area is known to influence potential ethanol yields. Thus, we suggest that shrub willow hybrids offer promising potential as an alternative source of biomass. The results of our study suggest that four of the shrub willow hybrids evaluated have a greater potential for use as biomass energy crops on marginal lands in central Minnesota than the native willow accessions; hence, there is a need to test their potential at a larger scale.