What does the term "soil fertility" refer to?

Soil fertility is fundamentally about the suitability of soil to support plant growth, primarily through its nutrient content. This refers to both the types of nutrients available in the soil—such as nitrogen, phosphorus, and potassium—and the amounts of these nutrients that are present. These nutrients are critical for plant development and affect everything from root growth to flowering and fruit production.

The other choices, while important aspects of soil and agriculture, address different attributes. The physical structure of the soil refers to how well the soil can hold and retain various elements, which influences water retention and root penetration but is not a direct measure of fertility. The drainage capacity relates to how easily water can move through the soil, which affects moisture availability but doesn't inherently define fertility. Lastly, the biological activity is crucial for nutrient cycling and overall soil health but does not directly describe the nutrient content itself. Thus, the correct understanding of soil fertility centers on the nutrients available and their availability to plants.