The soil bulk density (BD), also known as dry bulk density, is the weight of dry soil divided by the total soil volume. The total soil volume is the combined volume of solids and pores which may contain air or water, or both. The average values of air, water and solid in soil are easily measured and are a useful indication of a soils physical condition. Bulk density is commonly used as a measure of soil compaction, but is also necessary in calculating soil properties per unit area. This influences seasonal fertiliser requirements.