[Effects of Water Management Coupled with Sulfur on the Reduction of Soil Cadmium and Arsenic Activities].

In order to study the synergistic effect of water management combined with sulfur application on the reduction of soil cadmium （Cd） and arsenic （As） activities， a total of 30 treatments were set up under three water conditions，namely， flooding （F）， alternate flooding and moist （FM）， and moist （M）， with five concentration gradients of sulfate （SO₄^2-） and elemental sulfur （S⁰）. The results showed that compared with that under the non-sulfur treatment （CK）， the application of sulfur under the F treatment significantly reduced the content of soil Cd extracted by 25.59%-35.56%. The increase of moisture promoted the conversion of exchangeable Cd to reducible Cd and oxidizable Cd. Under the three water conditions and S⁰，the As content of soil was reduced by 24.43%，19.65%，and 25.69%，respectively，and the As content of the soil extracted state was reduced by 13.22% under the condition of SO₄^2- and M. Moreover， the content of obligate adsorbed arsenic decreased with the decrease of soil moisture content， and the content of amorphous iron-manganese oxide-bound arsenic and crystalline iron-manganese oxide-bound arsenic increased with the decrease of soil moisture content. In this experiment， the content of Cd in the extracted state of soil was the lowest when F was combined with S⁰. The As content of soil extraction was relatively low when two kinds of sulfur were applied together. FM coupled with two kinds of sulfur fertilizer reduced the extractable cadmium and arsenic content in soil and remained at a relatively low level. Additionally， the effect of supplying S⁰ on the reduction of soil extractable Cd and As content was stronger than that of supplying SO₄^2-. According to the correlation analysis， soil available Cd and As were significantly correlated with soil pH， complex iron oxide （Fe-p）， and free iron oxide （Fe-d）， which suggested that the coupling of sulfur in water management could reduce soil Cd and As activities via changing the soil pH and the transformation of iron morphological induced by the soil redox state. In summary， appropriate water management （alternating flooding and wetting） combined with exogenous elemental sulfur application can be adopted to reduce the availability of Cd and As in soil by regulating soil redox potential （Eh）， pH， and soil iron occurrence morphology for Cd and As-contaminated soils.