Final answer:
Humus has higher cation exchange capacity than montmorillonite due to its organic composition and structure. Humus contains functional groups that attract and hold cations in the soil solution. Montmorillonite, being an inorganic clay mineral, has a lower cation exchange capacity.
Step-by-step explanation:
Humus has a higher cation exchange capacity than montmorillonite due to its organic composition and structure. Humus is made up of microorganisms, dead animals and plants that are in various stages of decay. This organic material contains functional groups such as carboxyl and phenol groups which have a negative charge. These negatively charged groups attract and hold positively charged ions, or cations, in the soil solution.
On the other hand, montmorillonite is a type of clay mineral that has a lower cation exchange capacity because it primarily consists of inorganic mineral particles, such as aluminum and silica, which do not possess high cation exchange capacity.