Effects of Organic Matter and Live Plants on Sulfidic Soil pH, Redox and Sulfate Content under Flooded Conditions

In an undisturbed state below the water table, the sulfidic soils are benign, unless exposed due to various natural processes or anthropogenic activities and sulfuric acidity is produce, which has negative impacts on the environment. This paper examines the effects of organic matter, organic matter co-existing with live plants or live plants alone on sulfidic soil pH, redox and sulfate content under flooded conditions. In almost all cases, organic matter without plants induced ameliorative effects on sulfidic soil chemistry. In soils with or without organic matter, presence of plants led to higher Eh values, lower pH and higher sulfate contents. The reduction reactions of the added organic matter and the anoxia created by flooding were ineffective in reducing the amount of oxygen that was pumped into the rhizophore via the arenchymatous tissues in all the soils with plants. Under falling soil moisture regimes, e.g. during a drought event, presence of this type of plant species would aerate the reduced soil conditions. Aeration would then lead to oxidation of sulfides, producing sulfuric acid, which in turn would have negative impacts when released into the environment. One strategic option to reduce the amount of oxygen entering the soil would be to slash the shoots and leave them on the surface to help generate more alkalinity upon decomposition, even if the culm would continue to facilitate oxygen transport.