Which of the following measures the ability of soil to hold and exchange cations?

The ability of soil to hold and exchange cations is specifically quantified by the ion exchange capacity (IEC). This property refers to the total capacity of the soil to retain cations, which are positively charged ions such as potassium, calcium, and magnesium. The IEC is crucial for understanding soil fertility, as it affects how well plants can uptake essential nutrients. Soils with a higher ion exchange capacity can hold more cations, making them more fertile and capable of supplying plants with the necessary nutrients for growth.

Other measures mentioned, such as bulk density, soil pH, and nutrient status, play important roles in soil health and productivity, but they do not specifically address cation retention and exchange. Bulk density relates to soil compaction and porosity, while soil pH reflects the acidity or alkalinity of the soil, impacting nutrient availability but not directly measuring ion exchange capacity. Nutrient status indicates the presence and concentration of different nutrients in the soil but does not provide a direct measure of how well the soil can hold and exchange those nutrients. Thus, cations specific to the properties of soil are best represented by ion exchange capacity.