Abstract: Guangxi is one of the main rice-producing areas in China. Due to the karst geomorphology, paddy field in Guangxi is often contaminated by cadmium (Cd) and arsenic (As), which are generally considered to be mainly of geological origin. Organic silicon (Si) fertilizer, a new type of silicon fertilizer, can effectively reduce the accumulation of heavy metals in plants. As our knowledge about Cd or As mitigation by Si fertilizer was mainly based on results from pot experiments, little is known about the effects of Si fertilizer in plot and field conditions. In this study, both plot experiment and field experiment were carried out to investigate the mediating effects of Si fertilization on Cd and As accumulation in rice in the two growing seasons of one year. The dual effects of water management and organic Si application were also explored in the plot experiment. The results showed that Cd concentration in early rice (0.33±0.04-0.43±0.11 mg·kg^-1) was significantly lower than that in late rice (0.77±0.02-1.27±0.13 mg·kg^-1), while the As concentration in grains (0.44±0.01-0.49±0.06 mg·kg^-1) in early rice was significantly higher than that in late rice (0.10±0.01-0.10±0.02 mg·kg^-1). The application of Si fertilizer substantially reduced Cd accumulation in rice, but did not affect As accumulation. Field drying increased Cd concentration in late rice grains by 22%. Results from the field experiment further confirmed that the application of Si fertilizer reduced Cd concentration in early rice by 56% and late rice by 53%. Therefore, the accumulation of Cd in rice can be effectively controlled by flooding in the whole growing period and by applying Si fertilizer.

Key words: silicon fertilizer, cadmium and arsenic compound pollution, rice, field experiment.