Soil E is also largely a function of hydrological conditions. In the event of a flood, saturated soils can shift from oxic to anoxic, creating a reducing environment as anaerobic microbial processes dominate. Moreover, small anoxic hotspots may develop within soil pore spaces, creating reducing conditions. With time, the starting E of a soil can be restored as water drains and the soil dries out. Soils with redox gradients formed by ascending groundwater are classified as gleysols, while soils with gradients formed by stagnant water are classified as stagnosols and planosols.
Soil E generally ranges from −300 to +900 mV. The table below summarizes typical E values for various soil conditions:
Generally accepted E limits that are tolerable by plants are +300 mV  ) is also closely tied to pH, and both have significant influence on the function of soil-plant-microorganism systems. The main source of electrons in soil is organic matter. Organic matter consumes oxygen as it decomposes, resulting in reducing soil conditions and lower E.