Life cycle assessment of poplar production: Environmental impact of different soil enrichment methods

Abstract

The bioeconomy is expected to play an important role in the low carbon economy and poplar could be one of the species providing lignocellulosic feedstock for bioindustries. Since mineral fertilizers are expensive, alternative methods of plant fertilisation are currently being sought. Therefore, the aim of this study was to determine the environmental impact of the production of poplar grown on poor mineral soil fertilized with mineral fertilizers (F), lignin (L) and mineral fertilizers plus lignin (LF) and unfertilized (C) using a life cycle assessment. The system boundaries embraced the production and use of fertilizers, agricultural operations and field emissions associated with poplar cultivation (from cradle to farm gate). Negative greenhouse gases (GHG) emission was observed in variants: L (−37.0 kg Mg−1 d.m. CO2 eq.) and LF (−20.6 kg Mg−1 d.m. CO2 eq.). The emission in variant C was 25.2 kg Mg−1 d.m. CO2 eq. In all of the cultivation variants except C, a very high normalized score was determined for freshwater eutrophication, followed by variants L and LF in categories: freshwater and human ecotoxicity. A low impact of poplar cultivation was determined for fossil depletion and terrestrial ecotoxicity. A low normalized score was also calculated for climate change. The analyses indicated that lignin can be recommended as the optimum method of fertilisation. Using only mineral fertilizers is slightly less beneficial for the environment. Variant LF is not recommended due to the high impact on freshwater eutrophication, terrestrial acidification, human and freshwater ecotoxicity and depletion of fossil resources.