Key points

• Acidity should be addressed early and managed with regular applications of lime.
• Subsurface soil acidity and stratification are emerging as serious constraints to crop production.
• Traditional soil sampling of the 0-10cm layer can lead to misdiagnosis of acidity issues.
• Ideally, growers should test soil in 5cm layers. Testing to a minimum depth of 20cm is recommended.
• Lime can take many years to move through the soil profile without incorporation or physical mixing of the soil.
• In no-till systems, growers may need to consider strategic tillage to increase lime effectiveness.

Subsurface acidity refers to a soil pH (measured in calcium chloride) of 5.0 or less, occurring at depths below 10cm from the soil surface. Acid soil stratification can occur anywhere in the soil profile, from as little as 2cm below the surface. Under no-till systems lime applied to the soil surface may move very slowly into soil. Traditional soil testing of the 0-10cm layer is often ineffective in detecting low pH in stratified soils. New techniques for testing at depth must be applied to ensure the best management practices can be implemented.