Physical Soil Constraints fact sheet

The villains of hard subsurface layers in sandy soils.

Key points

• Sandy soils commonly have physical constraints that reduce crop root growth and exploration and water use efficiency, which ultimately reduces yield.
• Hardened subsoil layers within sandy soils vary in nature and distribution through the soil profile. They are typically categorised
  into two forms:
  • Traffic-induced compaction (cultivation pan) – soil particles bind together tightly due to the application of external forces, such as the weight of machinery, mainly when the soil is wet.
  • Natural subsurface hardening
    • Hardsetting – a reversible chemical process in which a hard layer forms as the soils dries out, restricting root growth, but softens on wetting
    • Cementation – an irreversible chemical process in which salts precipitate (solidify) and cause cementing, even when wet.
• Understanding the differences between soil-hardening processes can assist with amelioration strategies and future planning.