IMPACT OF SOIL ARSENIC ON RICE YIELD IN BANGLADESH

Rice comprises more than 70% of caloric consumption in Bangladesh, and the majority of this rice is grown during the boro (dry) season. Boro rice is irrigated with groundwater that often contains high concentrations of naturally-occurring arsenic, which can build up in the soil and reduce rice yield. To investigate the impacts of soil arsenic on rice yield, we exchanged high- and low-arsenic soils in thirteen rice fields in Faridpur district, Bangladesh. Soil arsenic and rice yield were measured for soil replacement plots where the soil was exchanged and adjacent control plots where the soil was not exchanged during the 2015 and 2016 boro (dry) and aman (monsoon) seasons. Yield averaged 5.9 t/ha (2015 boro) and 3.9 t/ha (2016 boro) while soil arsenic averaged 20.6 mg/kg (2015 boro). Comparison of replacement and control plots indicates that replacing high-arsenic soil with low-arsenic soil improves rice yield. During the boro seasons, the difference in yield (ranging from +2.3 to -1.9 t/ha) was strongly negatively correlated to the difference in soil arsenic (ranging from -8.8 to +19.1 mg/kg) between adjacent replacement and control plots. In contrast, during the aman seasons, the dominant rice variety was not sensitive to soil arsenic. The relationship between arsenic and yield suggests a boro rice yield loss of 2.8 million tons annually, or 15% of the annual boro harvest, due to the build-up of arsenic in soil over the past 25 years. Given that the buildup of irrigation water arsenic in soils may already have substantially reduced rice yield and that the trend is set to continue unless farmers find a source of low-arsenic irrigation water, it will be important to explore options to address this problem, including soil removal or replacement, soil amendments, improved water management or treatment, or growing alternative crops.