A rice–chicory rotation pattern ensures safe grain production and phytoremediation of cadmium-contaminated paddy fields: A four-year field experiment in southern China

Cadmium (Cd) contamination in paddy systems is a serious problem, and a strategy must be devised that ensures safe grain production and rapid remediation of soil Cd contamination. To investigate the remediation potential of crop rotation and its effect on Cd accumulation in rice, a four-year (seven-season) rice–chicory rotation field trial was conducted on a moderately acidic Cd-contaminated paddy soil. Rice was planted in summers, followed by straw removal, and chicory, a Cd-enrichment plant, was planted during winter fallows. Rotation effects were compared with those with rice only (control). Rice yields between the rotation and control were not significantly different, whereas Cd concentrations in rice tissues decreased in the rotation. Cd concentration in brown rice of the low-Cd variety decreased to less than 0.2 mg/kg (national food safety standard) from the third season onward, whereas in the high-Cd variety, it decreased from 0.43 mg/kg in the first season to 0.24 mg/kg in the fourth season. The highest Cd concentration in chicory aboveground parts was 24.47 mg/kg, with an enrichment factor of 27.81. Chicory had high regenerative capacity and was repeatedly harvested for biomass in multiple mowings, with average aboveground biomass over 2000 kg/ha in a single mowing. Theoretical phytoextraction efficiency (TPE) of one rice season with straw removal was 0.84%–2.44%, whereas the highest TPE of one chicory season reached 8.07%. The seven seasons of rice–chicory rotation extracted up to 407 g/ha Cd from soil with a TPE exceeding 20%. Therefore, rice–chicory rotation and straw removal can effectively reduce Cd accumulation in subsequent rice crops, without interrupting production and simultaneously rapidly remediating Cd-contaminated soil. Thus, the production potential of light to moderately Cd-contaminated paddy fields can be realized with crop rotation.