Particle Density:

• Particle density is the mass per unit volume of soil particles.
• Particle density is a relatively constant parameter and is sometimes assumed to be 2.65 g/cm3.
• e. Particle density = Weight of dry soil (g)/ Volume of water displaced (cm³).

Factors affecting particle density of soil:

• Factors affecting Dp affect Db but all factors affecting Db may not affect particle density.
• Size of particles of a given mineral & arrangement of soil solids & pore spaces have nothing to do with Dp.
• Dp depends on chemical composition & crystal structure of mineral particles.

1. Soil minerals:

• Soils having higher content of mineral particles are high in Dp.
• Dp varies depending on the nature of mineral particles.
• Most of the arable (cultivated) soil has Dp 2.4 to 2.7 gm/cm3 because they contain quartz, feldspar, mica & colloidal silicates, which have smaller Dp.
• If soil is rich in heavy minerals like magnetite, hornblende, epidote, tourmaline, the Dp will be higher (>2.75 gm/cm3).

2. Organic matter:

• The greater the OM in a soil, the lesser the particle density.
• OM weighs much less than an equal volume of mineral solids having a Dp of 1.1 to 1.4 gm/cm3.