Sieving soils

Principle: soil samples are typically sieved to remove pebbles and rocks, and to break up large soil aggregates. Usually sieving is easiest for air-dried soils.

Materials needed

  • Air-dried soil samples
  • One or two round sieves with 2 mm mesh, clean and dry
  • The trays designed to fit on the sieves
  • A tared aluminum weighing boat for each sample, if the samples contain rocks or indurated nodules
  • A mortar and pestle, clean and dry, or improvised system with tray and brass cylinder (Fig. 1)

Procedure

  1. Fit the sieve into the sample tray.
  2. Pass the sample through the 2 mm sieve into the tray without strong pressure, using your thumb or the back of a spoon. Don't push too hard; the sample should mostly pass through easily.
  3. Remove the rocks and rock-like nodules remaining on the sieve to the weighing boat to record their mass later.
  4. Remove the soil aggregates and other material remaining on the sieve and grind in the mortar and pestle under light pressure: the goal is to break up aggregates but not to grind grains of sand or micas into smaller particles. Return the ground material to the sieve and pass it through.
  5. Carefully collect the sample from the sieve tray.
  6. If you are processing multiple samples, the sieves, trays, and mortar and pestle should be clean and dry between each use. You can rinse a sieve and put it into a 105-degree oven to dry while you work on the next sample.
Figure 1: Breaking aggregates using light pressure from a brass ring on a sample tray
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