Bulk Density – Measurement
- Bulk density is the weight of soil in a given volume.
- Soils with a bulk density higher than 1.6 g/cm3 tend to restrict root growth.
- Bulk density increases with compaction and tends to increase with depth.
- Sandy soils are more prone to high bulk density.
- Bulk density can be used to calculate soil properties per unit area (e.g. kg/ha).
Background The soil bulk density (BD), also known as dry bulk density, is the weight of dry soil (Msolids) divided by the total soil volume (Vsoil). The total soil volume is the combined volume of solids and pores which may contain air (Vair) or water (Vwater), or both (figure 1). The average values of air, water and solid in soil are easily measured and are a useful indication of a soils physical condition. Soil BD and porosity (the number of pore spaces) reflects the size, shape and arrangement of particles and voids (soil structure). Both BD and porosity (Vpores) give a good indication of the suitability for root growth and soil permeability and are vitally important for the soil-plant-atmosphere system (Cresswell and Hamilton, 2002; McKenzie et al., 2004). It is generally desirable to have soil with a low BD (<1.5 g/cm3) (Hunt and Gilkes, 1992) for optimum movement of air and water through the soil.