What does cation exchange capacity (CEC) measure in soil?

Cation exchange capacity (CEC) is a critical concept in soil science that specifically assesses the soil's ability to hold and exchange positively charged ions, or cations, such as calcium, magnesium, potassium, and sodium. This property is crucial because cations are essential nutrients for plant growth. A higher CEC indicates a greater capacity for the soil to store, hold, and supply these nutrients to plants, which is fundamental for healthy plant development and productivity.

In contrast, soil moisture retention, temperature variation, and soil color and texture do not directly relate to the soil's nutrient storage capacity. While moisture retention affects how well plants can access water, it does not involve the binding of nutrients, which CEC specifically measures. Similarly, soil temperature variation and the physical characteristics of soil such as color and texture are important for understanding overall soil health, but they do not pertain to the ability of the soil to exchange and retain nutrients. Thus, the correct answer highlights the fundamental relationship between cation exchange capacity and nutrient availability in soil.