What is the definition of bulk density in soil?

Bulk density in soil refers to the weight of the soil per unit volume, which encompasses both the solid particles and the pore spaces containing air and water. This measurement is important in understanding soil structure, porosity, and the capacity of the soil to support plant life, as it directly impacts root growth and water retention.

When considering the characteristics of soil, bulk density serves as an indicator of compaction and can influence physical properties like drainage and aeration. It is calculated by dividing the mass of soil (usually measured after drying) by its volume. This measurement is crucial for determining the volume of soil needed for various agricultural and engineering applications and assessing the soil's ability to hold moisture and nutrients.

The other options provided do not accurately capture the essence of bulk density. While one might consider concepts like compaction levels or water content as related to soil properties, they do not define what bulk density specifically measures. Therefore, identifying bulk density as the weight per volume of soil is the most accurate choice.