Selected soil water tensions at phenological phases and mineral content of trace elements in rice grains – mitigating arsenic by water management

Abstract

The adoption of water-saving practices in rice cultivation modifies soil water tension regime, then influencing accumulation of chemical elements in rice grains. Some studies report higher concentrations of arsenic (As) in rice grains produced in anaerobic soils, compared to those produced in aerobic soils. However, there is a lack of information about the association between water stress imposed at distinct phenological phases of rice and the accumulation of chemical elements in grains. The aim of the present work was to determine the levels of As, Cd, Co, Cu, Fe, Mg, Mn, Ni, Pb, Se and Zn in husked grains of three rice varieties cultivated under different soil water tensions, imposed at distinct phases of the development. The study was conducted during 3 years with 3 rice varieties. The higher soil water tension in vegetative phase influenced Cd accumulation, Mn, Cu and Co. The reproductive phase 1 (panicle initiation - anthesis) is the main phase regarding uptake of chemical elements, when the highest soil water tension implied the lowest As accumulation in grains concomitantly with increase of toxic elements Cd and Pb, although keeping them below the threshold levels determined by FAO/WHO, and essential elements as Mn, Zn, Se, Cu, Co and Ni. The increased soil water tension in reproductive phase 2 (anthesis - ripening) decreased the levels of Pb in BRS Pampa. There is association among the contents of chemical elements (especially Cd, As and Pb) in grains, rice variety, grain yield and irrigation scheduling, especially for As.