This long-term field trial aimed at remediating a Cu-contaminated soil to promote crop production and soil functions at a former wood preservation site. Twenty-eight field plots with total topsoil Cu in the 198–1,169 mg kg⁻¹ range were assessed. Twenty-four plots (OMDL) were amended in 2008 with a compost (made of pine bark chips and poultry manure, OM, 5% w/w) and dolomitic limestone (DL, 0.2%), and thereafter annually phytomanaged with a sunflower—tobacco crop rotation. In 2013, one untreated plot (UNT) was amended with a green waste compost (GW, 5%) whereas 12 former OMDL plots received a second compost dressing using this green waste compost (OM2DL, 5%). In 2011, one plot was amended with the Carmeuse basic slag (CAR, 1%) and another plot with a P-spiked Linz-Donawitz basic slag (PLD, 1%). Thus six soil treatments, i.e., UNT, OMDL, OM2DL, GW, CAR, and PLD, were cultivated in 2016 with sunflower (Helianthus annuus L. cv Ethic). Shoots were harvested and their ionome analyzed. At high soil Cu contamination, the 1M NH₄NO₃-extractable vs. total soil Cu ratio ranked in decreasing order: Unt (2.35) > CAR (1.02), PLD (0.83) > GW (0.58), OMDL (0.44), OM2DL (0.37), indicating a lower Cu extractability in the compost-amended plots. All amendments improved the soil nutrient status and the soil pH, which was slightly acidic in the UNT soil. Total organic C and N and extractable P contents peaked in the OM2DL soils. Both OMDL and OM2DL treatments led to higher shoot DW yields and Cu removals than the GW, CAR, and PLD treatments. Shoot DW yields decreased as total topsoil Cu rose in the OMDL plots, on the contrary to the OM2DL plots, demonstrating the benefits to repeat compost application after 5 years. Shoot Cu concentrations notably of OMDL and OM2DL plants fitted into their common range and can be used by biomass processing technologies and oilseeds as well. In overall, there is a net gain in soil physico-chemical properties and underlying soil functions. HIGHLIGHTS - Compost incorporated into Cu-contaminated soils improves the sunflower growth. - Soil organic matter increases in compost-amended soils. - Extractable soil Cu decreases in compost-amended soils. - Shoot Cu removal by sunflower reaches 26–88 g Cu ha⁻¹ year^−1.

A 2-year pot experiment was carried out to examine the aging effect of biochar (B), alone or combined with iron grit (Z), on Cu stabilization and plant growth in a contaminated soil (964 mg Cu kg(-1)) from a wood preservation site. The experiment consisted in 3 soil treatments, either planted with Arundo donax L. (Ad) or Populus nigra L (Pn): (1) untreated Cu-contaminated soil (Ad, Pn); (2) Unt + 1% (w/w) B (AdB, PnB), and (3) Unt + 1% B + 1% Z (AdBZ, PnBZ). After 22 months, the soil pore water (SPW) was sampled and roots and shoots were harvested. The SPW compositions at 3 and 22 months were compared, showing that the SPW Cu2+ concentration increased again in the PnB and PnBZ soils. Cultivation of A. donax enhanced the dissolved organic matter concentration in the SPW, which decreased its Cu2+ concentration but promoted its total Cu concentration in theAd and AdB soils. Adding Z with B reduced both SPW Cu2+ and Cu concentrations in the pots cultivated by A. donax and P. nigra as compared to B alone. The B and BZ treatments did not enhance root and shoot yields of both plant species as compared to the Unt soil but their shoot Cu concentrations were in the range of common values. (C) 2016 Elsevier B.V. All rights reserved.