Hydric soils are created by oxidation-reduction (redox) chemical reactions that occur when a soil is anaerobic and chemically reduced. The redox reactions produce signs in the soil that they have occurred, and these signs are described in this chapter as

morphological features of reduction


hydric soil field indicators

(Hurt et al. 1998). A “reduced” soil is one in which redox reactions have caused reduced forms of O, N, Mn, Fe, or S to be present in the soil solution. “Reduced” is a general term that implies that some elements in addition to O

are present in their reduced form. Common reduced forms of elements or compounds that are found in hydric soils include: H

O, N

, Mn

, Fe

, and H

S, while their oxidized counterparts are O

, NO

, MnO

, FeOOH, and SO

, respectively. This chapter will focus on morphological features that form in soils that have been reduced periodically or seasonally. Hydric soil field indicators are the subject of Chapter 8.