Which of the following is NOT a requirement for the formation of redox features?

The formation of redox features in soil is closely associated with the presence of certain conditions and elements that facilitate anaerobic processes. The correct answer points to the role of organic matter in the soil. A low amount of organic matter can limit the availability of microbial food sources, which are critical for sustaining anaerobic microbial activity that leads to redox reactions.

In the presence of adequate organic matter, microbes flourish, especially under saturated conditions where oxygen is limited. These microbes decompose organic materials, engaging in redox processes that result in the reduction of iron and manganese, contributing to the development of redoximorphic features, such as mottling or color changes in the soil profile.

Conversely, a situation with low organic matter would not support the necessary microbial populations needed for redox reactions to occur effectively. Thus, the absence of sufficient organic matter is indeed a limiting factor for the formation of redox features, making it the correct choice for this question.