Mitigation of Arsenic Accumulation in Rice through Organic Amendments and Water Regime Management

Abstract

A field experiment was carried out with paddy rice (Oryza Sativa L.) for two consecutive seasons, namely 2017 Boro season and 2018 Boro season to observe the effects of two organic amendments (cow dung at 5 and 10 t/ha and poultry manure at 5 and 10 t/ha) and three water regimes (No SW, 3-cm SW, and 5-cm SW) on the accumulation of arsenic in different parts of BRRI dhan 28. The main objective was to see the possibility of mitigating arsenic uptake by water management and the application of organic amendments. The growth parameters such as plant height, fresh weight, dry weight, and yield were recorded. The effects of organic amendments and water regimes were also studied for phosphorus and iron concentrations in plants. The water regime was found to have no significant effects on plant height, fresh and dry weight of biomass, and the yield (p>0.05). However, organic amendments were found to have significant effects on the studied growth parameters (p<0.05). For both seasons, poultry manure at 10 t/ha was found to be the best treatment in terms of plant height, fresh weight, dry weight, and grain weight. In both seasons, water regime was found to affect the arsenic accumulation in rice root, straw, and husk (p<0.05). However, the grain arsenic concentration did not differ significantly among the water regimes (p>0.05). No SW regime, i.e. the absence of standing water, was found to be the best treatment in terms of reduced arsenic accumulation. On the other hand, the highest accumulation of arsenic was observed under 5-cm SW regime. Cow dung at 10 t/ha application was found to promote the uptake of arsenic in root, straw, husk, and grain of rice. On the other hand, the lowest uptake of arsenic was observed when plants were dosed with poultry manure at 5 t/ha. Arsenic concentration was significantly different in root from that of straw, husk, and grain (p<0.05) and the transfer factor (TF) followed the order: root > straw > husk > grain. The highest root P concentration was observed under 3-cm SW regime (both 2017 and 2018 seasons). For husk and grain P concentrations, the effects of water regime were not consistent. Among the organic amendment treatments, poultry manure at 10 t/ha was found to be the best for root P and straw P concentrations. No significant differences were observed among the organic amendment treatments for grain P concentrations (p>0.05). Rice root and straw iron concentrations did not differ significantly among the water regimes (both 2017 and 2018 seasons). In 2017 and 2018 seasons, the highest grain Fe concentrations were obtained under 3-cm SW regime, which is significantly different from the rest of the treatments. The study demonstrated that No SW water regime along with poultry manure at 5 t/ha was the optimum treatment combination for mitigating arsenic uptake in rice grains. Other water regimes and a higher dose of poultry manure might promote the uptake of arsenic despite having some positive effects in terms of growth parameters.