Which statement accurately describes cations in soils?

• A. Cations carry a positive charge
• B. Cations carry a negative charge
• C. Cations are neutral
• D. Cations do not exist in soil solution

Answer: (A)

Cations in soils are positively charged ions that interact with negatively charged soil surfaces. Soil minerals and organic matter carry negative charges, so they attract and hold positively charged ions like calcium, magnesium, potassium, sodium, and ammonium. This is why soils have a cation exchange capacity—the ability to adsorb and exchange these positively charged ions on the surface sites. Because of this positive charge, cations exist both in the soil solution and on exchange sites, ready to be taken up by plant roots or displaced by other cations. The other statements don’t fit because cations are not negatively charged, they are not neutral, and they do exist in soil solution as well as on exchange sites.