In a dry periods, the soil now exposed to air changes from slow anaerobic decomposition (decomposition in the absence of oxygen) to rapid aerobic decomposition.
(the soil; exposed; to air changes from slow anaerobic decomposition (decomposition in the absence of oxygen) to rapid aerobic decomposition; T:In a dry periods; T:now)
the soil
exposed
to air changes from slow anaerobic decomposition (decomposition in the absence of oxygen) to rapid aerobic decomposition T:In a dry periods T:now