SOM and pH

I am a little confused about how soil organic material related to PH. What I am thinking is that the decomposition of SOM will release CO2 which combines with H2O, so carbonic acid forms. Therefore pH decreases. Am I right?

Could you tell me more about the relations between CEC ,SOM and pH? Rex

Rex, you are correct that decomposition of SOM leads to the formation of carbonic acid, and characteristically lower pH. But also consider the impact of functional groups e.g. R-COOH and buffering capacity.

CEC is linked to pH in soils with significant SOM; consider pH dependent charge.