Application of inorganic passivators reduced Cd contents in brown rice in oilseed rape-rice rotation under Cd contaminated soil

Immobilization of heavy metals by the application of chemical amendments is an eco-friendly, economical and effective method to remediate cadmium (Cd) -contaminated soils. Field experiments were conducted during 2016-2018 following oilseed rape-rice rotation with the application of inorganic passivators i.e., slaked lime (CaOH2>95%) and sepiolite (SiO2>50%, MgO>20%). The experimental treatments were comprised of: rice planting in winter fallow and without passivator (F-PA0); fallow with slaked lime (F-PA1); fallow with sepiolite (F-PA2); oilseed rape-rice rotation without passivator (R-PA0); rotation with slaked lime (R-PA1); and rotation with sepiolite (R-PA2). The slaked lime and sepiolite were applied after the harvest of rape at 2000 and 5000 kg ha-1, respectively. Results revealed that the Cd contents were reduced by 47.44-49.03% in brown rice for F-PA2 and 9.54-42.66% in soil for R-PA2. The superoxide dismutase (SOD) activity was decreased by 10.65-17.98%, the malondialdehyde (MDA) contents were reduced by 28.57% whereas the proline content was decreased by 32.61% under R-PA2. In addition, the filled grain percentage was improved by 6.87% (F-PA2) and 3.70% (R-PA1), respectively. Overall, rice sown after oilseed rape gave better yields than sown after fallow fields while application of slaked lime and sepiolite as passivator could be a potential management option to grow crops in metal polluted soils.