THE EFFECTS OF ALTERNATE WETTING AND DRYING ON THE CONCENTRATIONS OF ARSENIC AND OTHER TRACE ELEMENTS IN RICE GRAIN

Rice is a staple food for billions of people around the world. However, traditional rice cultivation methods that involve flooding the soil can lead to the accumulation of arsenic (As) in the rice grain. Alternate wetting and drying (AWD) is a water management practice that has been shown to reduce As levels in rice grain, while also saving water and reducing methane emissions. In this study, conducted in Arkansas, USA, in 2017 and 2018, we investigated the effects of AWD on the concentrations of As and other trace elements in rice grain. The results showed that AWD tended to increase the concentrations of cationic trace elements (e.g., zinc, manganese, copper) in the rice grain, while decreasing the concentrations of oxyanionic trace elements (e.g., As, molybdenum). This was likely due to the changes in soil pH and redox conditions that occur under AWD. Linear mixed-effects modeling showed that effects of AWD on grain composition were more pronounced in 2017 than in 2018. This may be because the dry-downs that occur during AWD treatment happen at different times in the rice plant's development, and the timing of these dry-downs can have a significant impact on grain composition. The study also found that there was significant interannual variability in the grain elemental composition of continuously-flooded fields, which may have been due to the weather conditions, such as temperature, which can vary from year to year. The findings of this study suggest that AWD can be a promising water management practice for reducing As levels in rice grain, while also maintaining the concentrations of other essential trace elements. However, further research is needed to optimize the timing of dry-downs to maximize the benefits of AWD.