Rangeland Soil Practice Exam

In soils, cations are positively charged ions that occupy exchange sites on clays and organic matter. Calcium is a common soil cation because it is a major plant-available nutrient present as Ca2+ and acts as a base cation that helps flocculate soil particles, improving structure and porosity. The other substances listed are anions, carrying negative charges: nitrate (NO3−), sulfate (SO4^2−), and chloride (Cl−). They can move in the soil solution but do not occupy the positively charged exchange sites like calcium does. Therefore, calcium is the example of a soil cation among the options.