The Remediation Strategy and Mechanism of Combined Passivation and Foliar Inhibition for Safe Rice Production in Red Paddy Soil Contaminated With Heavy Metals

To solve the problem of Cd in rice over the food-safe standard, the present field study was carried out to explore the combined passivators (a mixture of quicklime (Q), polyacrylamide (A), sepiolite (S)) and Si-/Se- containing foliar inhibitors (Si or Se) at low (1) and high (2) application rates were added into the red paddy soil. After harvest the rice, the soil samples were collected to examine the soil properties, bacterial community, and the availability of heavy metals (Cd, Pb, and Cu) in soil. The rice samples were obtained to investigate the accumulation of heavy metals by rice. All of the treatments increased the soil's pH, but the treatments excluding QSe2 decreased the total P and soil organic matter (SOM), which was favourable for the immobilisation of heavy metals in red paddy soil by decreasing 14.29%-42.86% of available Cd, 10.18%-63.17% of available Pb, and 6.95%-36.81% of available Cu. With the increasing application rates, QAS significantly decreased the heavy metals available because of the enhanced immobilisation, while QSi and QSe significantly increased the heavy metals available because of the inhibited plant uptake. After remediation, QA1, QSi2, and QSe2 most effectively decreased the uptake Cd by rice in the present red paddy soil to solve the problem of Cd exceeding the threshold value according to the National Food Safety Standard of China (GB2762-2017). Additionally, the treatments, with the exception of Q1, QA1, QSi1, and QSi2, did not dramatically change the community structure of bacteria at the genus level in soil. Considering the safety and stability of soil, QSe2 was the primary recommendation for remediating Cd-contaminated red paddy soil.