Effects of urea-fertilization rates on the environmental performance of giant reed lignocellulosic feedstock produced for biorefinery purpose

A life cycle assessment (LCA) was carried out to investigate the environmental constrains of Arundo donax L. (common name giant reed) feedstock cultivation, for biorefinery purpose, treated with different amount of nitrogen fertilizations: 50 and 100 kg ha⁻¹ of N as urea (low input- LI and high input- HI, respectively). The analysis was addressed for a cultivation of giant reed (GR) under Mediterranean conditions, considering primary data for the first eight years of cultivation and further modeled for the whole life cycle (15 years). The goals were, to ascertain and compare the environmental profile as well as to identify the hotspots for both investigated N- management techniques.Results highlighted a potential higher environmental performance for the LI giant reed cultivation, due to the reduced up-stream and direct field emissions linked to urea application. LI impacts resulted to be 24% lower than HI impacts, as averaged values for all impact categories. Crop yield represented a driving parameter and the lower biomass productivity under N low input management partially counteracted the entailed benefits of the lower fertilization rates. Through the inclusion of soil carbon storage, after seven years of harvesting, the whole crop phase revealed a net greenhouse gases sink and also differences between LI (−0.21 kg CO₂ eq) and HI (−0.09 kg CO₂ eq) appeared amplified. This was due to the enhanced C accumulation rate in LI trials (about 7.7 ton C ha⁻¹ at the end of the seventh harvest year of GR cultivation), likely promoted by reduced soil organic matter mineralization at lower nitrogen availability. Nevertheless, in order to provide a full and comprehensive picture of the environmental performance of GR feedstock under different N-fertilization, further studies are needed encompassing the whole production chain: from the cultivation, through selected efficient conversion processes towards the co-production of added value products in the framework of the BioPoliS project.