Interactions of calcium sulfite with soils and plants

CaSO₃ is a by-product formed by several of the processes used for scrubbing SO₂ from flue gas produced by coal-burning power generators. Using CaSO₃ to improve the calcium status of acid soils would be a beneficial alternative to disposal in landfills. CaSO₃ has biocidal properties and is used as a disinfectant and food and drink preservative. It is important to evaluate under what conditions application to soils would not harm plant growth. Laboratory experiments confirmed that two transformations of CaSO₃ occurred in soil systems: (1) decomposition to produce SO₂ gas, and (2) oxidation to calcium sulfate. Conversion to SO₂ occurred in solution and soil at low pH, and acid soils treated with CaSO₃ were initially toxic to seedling root growth. The degree of toxicity was time-dependent, with reduction in toxicity occurring as CaSO₃ oxidized to calcium sulfate. Soil reaction also influenced toxicity, and at soil pH levels above 6, little seedling toxicity was evident.