TEST METHOD: Turbidity test for sodicity

Revised: 10 June 2002, links to CRC method updated 10 July 2012

OVERVIEW

Sodicity is an important factor limiting plant growth.

TASK SAFETY REQUIREMENTS

Safety boots are mandatory

SPECIFIC JOB STEPS HAZARDS WITHIN THIS STEP HAZARD CONTROL
Weigh 100 g of air dry soil into a 600 mL screwtop glass jar. Add 500 mL of deionised water, by pouring gently down the side of the jar. Sodic soils take a long time to settle if disturbed. Avoid disturbing the soil too much. The method uses the minimum replicable disturbance to allow for the shortest settling time.
Invert the jar once, and return to original position. Let stand for 4 hours.   Avoid extra shaking or bumping.
A white plastic spoon or spatula is placed into the suspension. If it is:
  • Clearly visible - not sodic (cloudiness = 1)
  • Partly visible - medium sodicity (cloudiness = 2)
  • Not visible - high sodicity (cloudiness = 3)
Defining visibility can be tricky

Use photographs such as those provided by the CRC for Soil and Land Management (there is a printed copy in Delta's library, or Part 1 and Part 2 are available online), OR use a marked plastic sodicity dipstick from the same source.

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