Last questions!!

Soil Organic Matter (SOM), pH and CEC:

SOM has an important influence on CEC and pH as SOM contains a large number of functional groups (e.g. R-COOH, R-OH etc.) and deprotonation of these functional groups will 1) increase the net negative charge of the soil colloids (e.g. R-COO^-), and 2) increase H in the soil solution (buffer capacity).

Additionally, decomposition of SOM by soil organisms releases CO₂, which combines with water to form carbonic acid (lowering soil pH)