REPLACEMENT OF ARSENIC-CONTAMINATED SOIL FOR IMPROVED RICE YIELDS IN BANGLADESH

Rice comprises 71% of caloric consumption in Bangladesh, and winter season (boro) rice is irrigated with groundwater that may contain high levels of naturally-occurring arsenic. This arsenic builds up in agricultural soils over time and is taken up by rice, which can lead to decreased rice yields and increased human intake of arsenic via food. We investigated replacement of localized regions of high-arsenic soils, which are often found near irrigation inlets, as a potential intervention to improve rice yields. In order to help farmers identify arsenic-contaminated soil, we investigated the use of the ITS Econo-Quick field kit based on the Gutzeit method. We compared arsenic in rice field soils measured with an X-ray fluorescence (XRF) spectrometer with visual measurements based on 10-min extractions of 0.5 g of soil in 50 mL of water using the field kit and found a strong correlation (R² = 0.49) across the 2-150 mg/kg range of concentrations. This suggests that the field kit can serve as a rapid and affordable tool for measuring As in rice paddy soil. Using this method, we identified high-arsenic wells used to irrigate rice fields in Faridpur district, Bangladesh, and exchanged the top fifteen centimeters of soil between a 5 × 5 m high-arsenic (near the irrigation inlet) and low-arsenic (far from the irrigation inlet) plot within the command area of each well. We measured soil arsenic and rice yield for thirteen plots where the soil was exchanged (“intervention plots”) and thirteen adjacent plots where the soil was not exchanged (“control plots”), which were cultivated by farmers according to normal practice. We observed a strong negative correlation between difference in rice yield and difference in soil As between the intervention and adjacent control plots (R² = 0.84), with the difference in rice yield ranging from +1.6 to -1.6 t/ha (average yield of 6.6 t/ha) and the difference in soil arsenic ranging from -3.8 to +19.1 mg/kg (average soil As of 19.1 mg/kg). This indicates that replacing high As soil with low As soil has the potential to substantially increase rice yields.