The influences of soil sulfate content on the transformations of nitrate and sulfate during the reductive soil disinfestation (RSD) process

Abstract

The transformations and products of sulfate (SO42−) and nitrate (NO3−), especially the influences of SO42− content on the transformations during RSD process, are unclear. In this study, a series of soil SO42− contents (from 333 to 3000 mg S kg−1) were prepared before RSD treatment. The results indicated that nearly all the cumulative NO3− (>98.6%) was removed and not affected by the soil SO42− content. The 15N recovery results showed that 0.57–1.24% and 2.94–4.59% of NO3− translated into ammonium (NH4+) and organic N, respectively, and high SO42− contents stimulated the processes of NO3− dissimilatory reduction and NO3− immobilization. The soluble SO42− contents decreased by 397–922 mg S kg−1, but the contents of total sulfur, sulfide, and sulfate precipitation varied slightly after RSD, indicating that the decreased SO42− was mainly immobilized into organic sulfur in all soils. In addition, a fraction of decreased SO42− was adsorbed to the soil with a relatively high SO42− content. The leaching of SO42− was high (42.9–602 mg S kg−1) during the RSD process, and the leaching amounts increased with increasing soil SO42− content. In terms of the gases emitted from the transformations of NO3− and SO42−, the cumulative emissions of nitrous oxide (N2O) and six sulfurous gases (hydrogen sulfide, carbonyl sulfide, carbon disulfide, methyl mercaptan, dimethyl sulfide, and dimethyl disulfide) were in the ranges of 17.1–21.2 mg N kg−1 and 7.78–23.5 μg S kg−1, respectively, during the whole RSD process. The emissions of sulfurous gases were inhibited by high soil SO42− content, but the N2O emissions were unaffected. In conclusion, the soil SO42− content influenced the transformations of NO3− and SO42− during RSD process, and the SO42− leaching and N2O emissions might threaten the environment which should be concerned.