Impact of Silicon and Heavy Metals on Hemp ( Cannabis sativa L.) Bast Fibres Properties: An Industrial and Agricultural Perspective

Heavy metal (HM) pollution in agricultural fields reduces crop productivity and quality, and poses a risk for human health. On these areas, the cultivation of crops devoted to biomaterial and bioenergy production thus constitutes an attractive alternative to food crop production. To maintain the soil productivity and to obtain a biomass compatible with the requirements of industry, the use of the beneficial metalloid silicon, applied on leaves during plant growth, has been considered. A field study using Cannabis sativa L. (cv. Futura 75) was performed during 2 consecutive years on two sites (one soil parcel contaminated with Cd, Zn and Pb, and one taken as uncontaminated control) in the North of France. One half of the plants received weekly foliar spray of Si (2 mM). Photosynthesis-related parameters were analysed in situ, while mineral concentration and fibre properties were determined after 4 months of culture. Our results suggest that Si application improves and preserves the mechanical properties of fibres when plants are exposed to HM stress. Si was also shown to increase by 27% the Cd concentration in leaves and by 30% the Zn concentration in stems. Contaminated fibres and shives containing immobilized HM could be used for specific purposes such as inclusion in cement aglomerates.