Inversion of High-Arsenic Soil for Improved Rice Yield in Bangladesh.

ABSTRACT

Rice is the primary crop in Bangladesh, and rice yield is diminished due to the buildup of arsenic (As) in soil from irrigation with high-As groundwater. Implementing a soil inversion, where deeper low-As soil is exchanged with the surface high-As soil in contact with rice roots, may mitigate the negative impacts of As on yield. We compared soil As, soil nutrients, and rice yield in control plots with those in adjacent soil inversion plots. We also estimated the quantity of soil As deposited on a yearly basis via irrigation water, to explore the longevity of a soil inversion to reduce surface As. Soil As, organic carbon, nitrogen, and phosphorus concentrations decreased by about 40% in response to the inversion and remained lowered over four seasons of monitoring. Inversion plot yields increased above control plot yields by 15-30% after a one-season lag despite the recovering but still reduced nutrient levels. Farmers have started conducting soil inversions of their own volition, typically close to where irrigation water enters the field. However, the yield gain will be limited to a few decades at most due to deposition of As via well water, unless the field is irrigated with low-As river or pond water.