Si-Rich Amendment Combined with Irrigation Management to Reduce Cd Accumulation in Brown Rice

Combining different technologies to improve remediation efficiency is essential for remediating metal-contaminated farmland soils. In situ immobilization and irrigation management have been widely used in the Cd-polluted paddies. However, the interaction between soil amendment and irrigation management and its influence on Cd transportation in the root-soil system is poorly understood. A pot experiment was conducted to investigate the effects of a novel silicon-rich amendment (SR) on Cd behavior in the soil, the radial oxygen loss (ROL) and formation of Fe/Mn plaque on the root surface, and the accumulation of elements in the rice under continuous flooding (CF) and alternate wetting and drying (AWD) irrigations. SR addition under CF irrigation had the lowest Cd concentration in brown rice (0.18 ± 0.04 mg kg−1) among treatments. The CF + SR treatment induced lower Eh and higher pH and led to more exchangeable Cd converted into Fe/Mn oxides and residual fractions, reducing Cd bioavailability in the soil. Moreover, CF irrigation induced Fe/Mn plaque formation, and SR addition further promoted the Fe/Mn plaque formation by enhancing ROL from the roots, strengthening the barrier effects of plaques for Cd uptaking. Besides, the CF + SR application increased the Fe and Ca concentrations in the rice roots to compete with Cd for uptaking and translocation and suppressed Cd accumulation in rice. The findings suggested that the simultaneous use of Si-rich amendment with continuous flooding irrigation is a potentially highly efficient remediation strategy for safe rice production in Cd-polluted paddies.