Bulk density = Oven dry soil weight / volume of soil solids and pores. Bulk density of mineral soils commonly ranges from 1.1 to 1.5 g/cm3 in surface horizons. It increases with depth and tends to be high in sands and compacted pan horizons, and tends to be low in soils with abundant organic matter.
When soil is compacted, porosity decreases and bulk density increases. Typical increases in bulk density are shown below, with other compacting activities included for comparison. As a result, permeability of air and water in soil decreases, soil water-holding capacity is reduced, and root growth is impeded.