Particle density of soils refers to the density of the solid particles collectively. It is expressed as the ratio of the total mass of the solid particles to their total volume, excluding pore spaces between particles. Convenient unit for particle density are megagrams per cubic meter (Mg/m3), or the numerically equal grams per cubic centimeter (g/cm3).

Particle density of a soil sample is calculated from two measures quantities, namely, the mass and volume of the sample. The mass is determined by weighing; the volume, by calculation from the mass and density of water (or other fluid) displaced by the sample.

Soil bulk density is the ratio of the mass of dry solids to the bulk volume of the soil. The bulk volume includes the volume of the solids and the pore space. The mass is determined after drying to constant weight at 105°C, and the volume is that of the sample as taken in the field.

The method in our laboratory is using core method.

An aggregate is a group of primary particles that cohere to each other more strongly than to other surrounding soil particles. Stability of aggregates is a function of whether the cohesive forces between particles withstand the applied disruptive force.

The retention between the soil water content and the soil water suction is a fundamental part of the characterization of the hydraulic properties of a soil. The relationship is identified in the literature by various names, including water retention function, moisture characteristic, and the capillary pressure-saturation curve.

Soil is mainly composed of minerals and organic matter, like decaying plants and animals, as well as living organisms. The organic matter in soil derives from plants and animals. When it decays to the point it is no longer recognizable it is called soil organic matter.

The hydraulic conductivity is a measure of a soil's ability to transmit water. Water movement, whether under saturated or unsaturated conditions, is highly dependent on the hydraulic conductivity.