Organic decomposition

Lecture notes on SOM mentions various factors influencing decomposition time, including pH and water content. How does pH affect SOM decomposition, is it slower in acidic conditions? And does increased water content (when well drained and unsaturated) increase decomposition?

Acidic soil inhibits microbial activity, and hence slows down organic matter decomposition. Increasing water content reduces decomposition as there will be less oxygen available for the aerobic microbes. Most of the microbes that decompose organic matter are aerobic; and anaerobic decomposition is much slower than aerobic one. Having said that, aerobic microbial decomposition requires some moisture: the ideal soil water contents for the decomposition is around the soil's field capacity.