Plant biomass for energy and phytoremediation purposes: three-year analysis of Phalaris arundinacea production on contaminated lands in central Italy

Energy production is one of the main challenges that continues to unsettle nations. The cultivation of plant species as biomass for energy purposes is an option but raises the issue of taking land away from food production. A solution to this controversy has been identified by exploiting those soils that cannot be used for food production, namely contaminated soils. The present study focuses on the evaluation of the biomass productivity of Phalaris arundinacea (Reed Canary Grass) in three different fields in Central Italy, which present potentially toxic element (PTE) contamination. The experiment was conducted over three consecutive years. This study is part of the CERESiS (ContaminatEd land Remediation through Energy crops for Soil improvement to liquid biofuels Strategies) Project which has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 101006717, which started in November 2020 and is set to end in 2024. P. arundinacea is a species that lends itself to biomass production and to the phytoremediation and phytostabilisation of contaminated soils. The three cultivated areas with different textures (EA: sandy loam, B1: clay loam and B2: clay) were prepared with a minimum tillage system in late winter 2021 and sown in spring 2021. Annually, the crop received urea-based nitrogen fertilisation (100 kg ha^-1) in late spring and sprinkler irrigation in dry periods. In the “EA” area, additional tests were conducted with different amounts of nitrogen fertiliser (0 - 50 - 100 kg ha^-1) and seed treatment with biostimulant based on Trichoderma spp.  Production was estimated by sampling the biomass at different annual times. In areas B1 and B2 through two annual mowings (August and November). In EA, on the other hand, the sampling method allowed for the estimation of a single and/or double mowing at different times (August, mid-September and November). This experimental design allowed assessment of biomass growth, regrowth, and bioaccumulation capacity. At harvest time, a chemical-physical characterisation of the biomass was carried out.

The sandy loam texture did not favour the development of P. arundinacea. Dry biomass production over the three years averaged between 4.0 t ha^-1 and 5.1 t ha^-1. Generally, the second mowing did not provide enough yield to justify harvesting. P. arundinacea showed limited phyto-extraction of heavy metals. This is compensated by the positive result of the low concentration of PTE in the plant with abundant biomass production. As a fuel, the biomass showed good qualities, with average HHV and LHV values of over 18.8 and 16.1 MJ kg^-1 respectively. One aspect that could have a negative impact is the exceptionally high ash content, which over the years has averaged around 14.5 %.

This experiment highlights the manifold benefits of using this plant species. The simultaneous capacity for phytoremediation and energy use of the derived biomass are environmental, economic, and social winning points.