Trace element bioavailability, yield and seed quality of rapeseed (Brassica napus L.) modulated by biochar incorporation into a contaminated technosol

•Biochar incorporation into a contaminated technosol did not promote Cd, Cu and Zn phytoextraction by rapeseed.•It increased the As, Cd, Cu, Mo, Ni, Pb and Zn solubility and their potential leaching.•It did not impact the rapeseed yield, except a slight decrease in seed biomass, nor the seed nutritional quality.•Rapeseed cultivation allowed stripping of the phytoavailable technosol Zn and Cd fractions.

Background and aimsRapeseed (Brassica napus L.) is a Cd/Zn-accumulator whereas soil conditioners such as biochars may immobilize trace elements. These potentially complementary soil remediation options were trialed, singly and in combination, in a pot experiment with a metal(loid)-contaminated technosol.MethodsThe technosol [total content in mg kg−1 Zn 6089, Cd 9.4, Cu 110, and Pb 956] was either amended (2% w/w) or not with a poultry manure-derived biochar. Rapeseed was cultivated for both soil treatments during 24 weeks up to harvest under controlled conditions.ResultsBiochar incorporation into the technosol promoted the As, Cd, Cu, Mo, Ni, Pb and Zn solubility. It decreased foliar B, Cu and Mo concentrations, and Mo concentration in stems, pericarps and seeds. But, it did not impact neither the biomass of aerial rapeseed parts (except a decrease for seeds), nor their C (except a decrease for stems), seed fatty acid, seed starch and soluble sugar contents, and antioxidant capacity in both leaves and seeds. Biochar amendment increased the phytoextraction by aerial plant parts for K, P, and S, reduced it for N, Ca, B, Mo, Ni and Se, whereas it remained steady for Mg, Zn, Fe, Mn, Cu, Cd and Co.ConclusionsThe biochar incorporation into this technosol did not promote Cd, Cu and Zn phytoextraction by rapeseed and its potential oilseed production, but increased the solubility of several metal(loid)s. Here Zn and Cd concentrations in the soil pore water were decreased by rapeseed, showing the feasibility to strip available soil Zn and Cd in combination with seed production.