The concept is that plant growth is often restricted by adverse physical and chemical properties of subsoils yet these limitations are not revealed by testing surface soils and hence their significance in crop management is often overlooked.
The major constraints can be physical or chemical. The physical limitations comprise: poor/nil subsoil structure or dense pans so roots can not penetrate subsoil; very sandy subsoils that do not provide adequate water or very gravelly subsoils and; high water table, etc.
Chemical constraints include acidity/alkalinity, high extractable Al or Mn, low nutrient availability, salts, boron toxicity and pyritic subsoils.
Some of these constraints are inherent properties of the soil profile while others are induced by crop and soil management practices.
For all these constraints the emphasis within chapters is on defining the constraint, and discussing amelioration practices and benefits.