How is bulk density calculated in soil science?

Bulk density in soil science is calculated by taking the dry weight of the soil and dividing it by its volume. This measurement provides insight into the soil's compaction and porosity, which are critical factors in understanding soil health, root growth, and water movement.

When soil is dried and weighed, the resulting mass reflects only the mineral and organic components, excluding any water that may have been present. By measuring the volume that this dry soil occupies, one can determine bulk density, expressing it in units like grams per cubic centimeter (g/cm³).

In contrast, the other options do not accurately describe how bulk density is calculated. For example, relating volume to organic matter content misrepresents the relationship, and using water content or organic matter divided by total weight does not pertain to the definition of bulk density, which strictly focuses on dry weight relative to volume. Understanding bulk density is crucial in fields such as agronomy, environmental science, and land management, as it affects soil fertility, drainage, and the habitat for soil organisms.