Organic 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.