Environmental consequences of the reintegration of miscanthus into a crop rotation in highly metal contaminated context
(2026) Intersoil 2026 — Location: Barcelone (7.October.2026)
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- Abstract
- When agricultural lands are so contaminated with pollutants that they are no longer suitable for food and feed production due to human exposure risks, growing non-food biomass offers an alternative for farmers. In addition to aiding the phytomanagement strategy of degraded sites, biomass production contributes to the European target of achieving at least 42.5% renewable energy in the energy mix by 2030. Among the candida.tes, Miscanthus × giganteus, a rhizomatous grass, has demonstrated its ability to thrive on contaminated soils while providing low-cost annual biomass for multiple uses (mulch, bedding, energy, building materials, plastics). A crucial characteristic of this plant is its ability to store metallic elements (ME) in its root system, drastically reducing their content in harvested parts during the senescence phase. It is therefore an excellent candidate for phytostabilisation of pollutants. Due to its perennial nature, C4 metabolism, and lack of known pests, miscanthus is typically cultivated in Europe for around twenty years before yields gradually decline. After this production period, the crop is terminated and may be replanted with miscanthus or incorporated into a crop rotation. In the context of contaminated soil, questions arise regarding the fate of pollutants stored in the soil and those concentrated in miscanthus residues (litter, rhizomes, roots) that might be released into soil during their decomposition. Indeed, edaphic changes linked to the incorporation of large quantities of organic matter, alongside the changing speciation of metals released from contaminated residues, could impact their mobility and (phyto)availability of MEs and their subsequent transfer to future crops. Ultimately, the general aim is to assess the sustainability of the benefits provided by phytotechnologies after the phytomanagement phase. In the former mining basin of Northern France, an agricultural area has been particularly affected by past emissions from two lead and zinc smelters, resulting in high soil levels of Cd, Pb, and Zn. A large-scale phytomanagement trial was initiated in 2009 utilizing miscanthus as fuel for local boilers. This successful trial convinced some farmers, who have continued to plant miscanthus in the area. Fifteen years later, as miscanthus yields begin to decline on some plots, farmers are considering crop conversion. An experiment was conducted on a plot established in 2010 (Ti), involving the destruction of part of the field after the final harvest (March 2023, T0), followed by the cultivation of maize (October 2023, T1) and/or wheat (July 2024, T3). Area where miscanthus remained served as a positive control, while a section unplanted since 2010 (i.e., grass cover) served as a negative control, allowing the assessment of the impact of miscanthus residues on soil function and the transfer of MEs studied to conventional crops. This study aims to assess the impact of contaminated residues of miscanthus on soil functioning and on the fate of MEs in soil and their transfer to future crops (i.e., maize and wheat). Soil contents of Cd, Pb, and Zn ranged from 12.7–14.3, 701–807, and 876–1003 mg kg−1, respectively. Despite low soil availability (2–6% for Cd, <0.1% for Pb, and 0.1–0.2% for Zn), likely due to organic complexation, these MEs accumulated in residues sampled before the final harvest (litter > rhizomes >> roots). These residues did not alter soil physical and chemical parameters or Cd transfer to maize grains cultivated after miscanthus removal, which remained compliant for animal feed. However, the residues promoted the Cd transfer to wheat straw and grains (T0/T3). Consequently, both wheat grains and straw were non-compliant for Cd under European food and feed legislation The results also indicate that chemical parameters are influenced more by the active crop than by miscanthus residues. For instance, 13 years of miscanthus cultivation significantly reduced the nutrient pool compared to grass cover (i.e., negative control). Similarly, in T1, maize cultivation increased exchangeable cations and available Fe and Mn compared to treatments without maize. Analysis over time highlighted that miscanthus introduction (Ti/T0) led to soil acidification and variations in nutrient availability (i.e., decrease in Mn and increase in Fe). Furthermore, maize (T1) mobilized the exchangeable cations (Ca2+, Mg2+, K+ and Na+) on the soil’s clay-humic complex. Finally, six to twelve months of residues degradation had no significant effect on soil (bio)availability of Cd, Pb, and Zn. However, wheat appeared more sensitive than maize to the presence of previous crop residues (i.e., miscanthus and/or maize) that increased Cd transfer from soil to plant. Long-term monitoring is essential, as miscanthus residues, particularly the lignin-rich root system, take several years to decompose. Nevertheless, selecting the appropriate crop species following a phytomanagement strategy remains the most critical precaution for ensuring food safety.
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Bidar, G., Agnan, Y., Louvel, B., Pernin, C., Ronceux, A., De Almeida, T., & Leveaux, T. (2026). Environmental consequences of the reintegration of miscanthus into a crop rotation in highly metal contaminated context. Intersoil 2026, Barcelone. https://hdl.handle.net/2078.5/279385