Soil compactness is also called soil hardness or soil solidity or soil penetration resistance. It is generally expressed by the resistance of a metal plunger or probe when it is pressed into the soil (unit: Pa). Soil compactness refers to the ability of soil to resist compaction and fragmentation by external forces and is one aspect of soil properties. In addition, soil physical properties include soil texture, structure, porosity, etc., involving soil solidity, plasticity, permeability, drainage, water storage capacity, and the difficulty of root penetration, etc.