Densitometers are instruments used in soil science and agriculture to measure soil bulk density. They work by determining the mass of soil per unit volume. This is typically done by measuring the weight of a small volume of soil in a container of known volume. Densitometers are important tools for assessing soil health and fertility, as bulk density can affect water and nutrient availability in soil. They are also commonly used in the construction industry to test the compaction of soil for building foundations and roadways.