SUBSOIL CONSTRAINTS WORKSHOP

SPRING RIDGE

3rd August 2004

What are subsoil constraints?

• A subsoil constraint is any chemical or physical feature that restricts root extension into the subsoil layer.
• This limits water and nutrients available to the plant.

Examples of Constraints.

• Salinity, alkalinity, sodicity, toxic nutrients, compaction, rock etc.

Testing for Subsoil Constraints.

• A series of in field tests are available for carrying out to establish if subsoil constraints exist.
• Tests include:
• pH Testing (using garden pH test kit)
• EC1:5 Testing (using an EC1:5 meter)
• An Aggregate Stability in Water Test ‘ASWAT’ (using distilled water with a jar lid or petrie dish)
• Field Texture to determine ECe

Indicators of Subsoil Constraint.

• pH: when pH exceeds the boundaries of pH<5 or pH>9 then this will have adverse effects on plant growth.
• EC1:5 : is the test to determine electrical conductivity. (i.e. generally the amount of salt in the soil.)
• ECe: is the conversion of a soil texture factor to determine actual
• Salt effects on plants.
• ASWAT: is used to determine how compactive the soils are. If soils disperse in water then they will be more susceptible to compaction.

Management of Subsoil Constraints.

• Adopt controlled traffic techniques to reduce compaction.
• Increase soil organic matter.
• Keep soil profile dry by response cropping.
• Increase barley and cotton plantings as they are more tolerant.
• Manage inputs according to the amount of plant available water (PAWC).
• Consider planting pastures in severe cases.