Arsenic (As)-based pesticides and defoliants have been extensively used in cotton production throughout the southeastern and south central U.S. Some of these soils are currently being used for rice production, and there is growing concern about uptake and accumulation of As in rice grain. As can undergo several chemical and microbial transformations in soil, which may impact arsenic bioavailability for plant uptake. An experiment is currently being conducted in field plots at Stuttgart, AR to determine if different water management systems (flooded and saturated) will impact (i) the transformation and speciation of soil arsenic, (ii) the uptake of arsenic by rice, and (iii) susceptibility to straighthead. The experiment is being conducted, using the rice variety ‘Wells'. Plots are either: 1) fallow or planted with rice variety “Wells”; 2) saturated or flooded, and 3) native soil or amended with additional monosodium methanearsonate (MSMA). Soil samples will be collected prior to planting, after flooding, after draining, and prior to harvest and analyzed for total arsenic and arsenic speciation. Arsenic species will be determined by HPLC-ICP-MS following arsenic extraction. Microbial diversity will also be enumerated in each treatment to better understand the As transformation processes. These results will help to determine if different water management systems can alter arsenic speciation in soil and ultimately affect plant uptake of arsenic.