Effect of Temperature and Organic Carbon on the Development of Reducing Conditions in Soils.

The onset of reducing conditions in soils is driven by microbial activity, which can be affected both by soil temperature and by the level of soil organic carbon (OC). Therefore, the purpose of this study was to evaluate the impact of temperature and soil OC content on the development of reducing conditions. A mesocosm design was utilized with 6 different soils ranging in OC from 5.6 to 68 g/kg. Saturated mesocosms were maintained at temperatures of 2, 5, 8, 11, 14 and 17 degrees C, and reducing conditions were evaluated using three approaches: 1) Eh was measured using 5 replicate Pt electrodes; 2) the presence of Fe²⁺ was documented in the soil pore water by testing with alpha-alpha-dipyridyl; 3) the removal of Fe oxides from IRIS tubes was quantified. Conditions in the mesocosms were monitored over a period of four to eight weeks. The development of reducing conditions in all soils was strongly related to temperature. The impact of soil OC on the development of reducing conditions was less straightforward.