In situ management with a secure cropping system for moderately lead contaminated allotment gardens

International audienceThe maintenance of the agronomic quality of soils in case of allotment garden rehabilitation is of great concern. Considered as a “gentle” solution, phytoextraction may be adapted to this issue. Nonetheless this method requires sometimes many years to achieve the cleaning-up of soils. For this reason phytoremediation hardly develops. To circumvent this problem, this study aimed at developing a secured cropping system in allotment gardens including the authorization to cultivate vegetables unable to accumulate lead (Pb) and phytoextracting crops simultaneously. To achieve this goal , an in situ and participative 3-year experiment has been launched since July 2015 on an allotment garden soil (Nantes, France) naturally contaminated by Pb . Pb in topsoil is 170 mg/kg on average. Vegetables (tomato, winter cabbage or potatoes) and Indian mustard (Brassica juncea), used for phtoextraction, were cultivated in rotation or as crop co-cultures and were compared to a control (without phytoextraction process) The two first seasons of culture showed that Pb concentrations in edible parts of tomatoes and winter cabbages were under the EEC regulatory threshold set at 0.1 and 0.3 mg/kg Fresh Matter. For the “Co-culture”, Pb in Indian mustard shoots was around 0.9 mg/kg dry matter (DM) with a translocation factor (TF) of 1.5 in average and 0.2 mg/kg DM with a mean TF of 0.03, respectively for the season 1 (Tomato) and the season 2 (Cabbage). Then, phytoextraction efficiency was very low. But, compared to previous experiment realized in laboratory, in situ phytoextraction associated with tomato and cabbage is respectively 83 and 18 times more efficient than phytoextraction by itself. For the “Rotation” growing method, lead concentration in Brassica juncea shoots, ca. 0.5 mg/kg DM with a mean TF of 0.2, was significantly lower than what was recorded with co-culture. Analysis of Pb in potatoes are in progress. After three growing crops, the culture of tomatoes and cabbages could be maintained on this site in association with phytoextraction, expecting nevertheless higher performances for this latter. In such a prospect, the regulation could pay attention to this secure cropping syste