Comparing effects of ammonium and nitrate nitrogen on arsenic accumulation in brown rice and its dynamics in soil-plant system

Purpose Nitrogen is widely used in agricultural production, including in arsenic-contaminated soil. However, there is a lack of systematic studies on the arsenic (As) dynamics in soil porewater-root surface-rice system after applying different nitrogen fertilizers to As-contaminated soil. Materials and methods Three treatments (CK, Nitrate-N, and Ammonium-N) were applied before rice planting to investigate the effect of nitrogen forms on arsenic accumulation in brown rice and its dynamics in soil-plant system. Results and discussion Compared to Nitrate-N and CK treatments, Ammonium-N treatment increased rice biomass and yield. Compared with CK treatment (0.12 and 4.48 mg/kg), Ammonium-N treatment (0.08 and 2.71 mg/kg) reduced the As concentrations and Nitrate-N treatment (0.18 and 6.20 mg/kg) increased the As concentrations in brown rice and shoots. Nitrogen application reduced Fe plaques concentration on roots, but Ammonium-N treatment increased the total As accumulation in Fe plaques. In soil porewater, Nitrate-N treatment reduced the concentration of As (III) in the first month (5.2-47.0 mu g/L) but increased its concentration in the last month (137.6-183.1 mu g/L). However, the concentration of As (III) in Ammonium-N treatment (58.5-168.6 mu g/L) was similar to that in CK treatment (72.8-138.8 mu g/L) in porewater. Conclusions The application of Nitrate-N caused the decrease of As in porewater during the seedling stage; however, the As concentration in rice grains was increased due to the increase of As (III) in porewater during the ripening stage. The application of Ammonium-N reduced the As concentration in rice tissues by increasing biomass and accumulating more As in Fe plaques.

Automated summary

This study investigated the effects of different nitrogen fertilizer treatments on arsenic accumulation in brown rice and its dynamics in the soil-plant system. The results showed that Ammonium-N treatment increased rice biomass and yield, reduced arsenic concentrations in rice grains, but increased total arsenic accumulation in Fe plaques. Nitrate-N treatment decreased arsenic in porewater during the seedling stage but increased arsenic concentration in rice grains during the ripening stage.