Sampling for moisture determination

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Sampling for moisture determination
Dr. Leena Pietilä ISTA Bulking and Sampling
Committee
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ISTA Rules and sampling for moisture determination

• The sub-sample for moisture determination must
  be done in such a way that changes in moisture
  content are minimal (2.5.1.5)
• Submitted samples must be dispatched to the seed
  laboratory without delay (2.5.1.6)

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The Rules and sampling for moisture determination

• The seed may not be exposed to the air during
  sample reduction for more than 30 seconds
  (2.5.2.2 9.1.5.2)
• Take first the sub-sample for moisture
  determination from the composite sample
• Mixing by stirring the sample with a spoon
• OR Pour the sample back and forth between two
  containers (9.1.5.2). The openings of the
  containers need to be of similar size.

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Taking a sub-sample for moisture determination

• Take at minimum three spoonfuls (2.5.2.2
  9.1.5.2)
• As much air as possible must be excluded from the
  container (2.5.1.6 9.1.5.1), e.g. the
  container must be filled to the brim

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Examples of containers that are used for samples
for moisture determination

• Re-sealable plastic bags
• Foil or polythene bags that can be heat-sealed
• Glass or polythene bottles with an airtight top
• It may be worth of testing whether the container
  is moisture proof

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Sample reduction

• The ISTA Rules describe eight different sample
  reduction methods
• The ISTA methods must be followed, if the aim is
  to issue an ISTA certificate

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Sample reduction

• If the composite sample is too big, it must be
  reduced to a size prescribed in the Rules
• Before reduction, the composite sample need to be
  mixed
• Chaffy species three times, non-chaffy species
  two times

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Sample reduction

• No mixing before reduction is needed, if rotary
  divider or variable sample divider are used
• All the composite sample must be reduced

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Instruments for sample reduction

• sample dividers
• by hand

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Working quality of sample dividers

• Working quality of sample dividers must be
  checked regularly
• ISTA Handbook on Seed Sampling (Chapter 6.6)
  gives guidance
• Also other methods are used e.g. comparison of
  the halved samples with ISTA tolerance tables
  (Tables 3.3, 4.1, 5.2)

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Checking working quality of dividers (ISTA
Handbook on Seed Sampling)

• Prepare a standard sample by mixing two kind of
  seeds
• E.g. 20 of small seeded species, 80
  large-seeded species
• Reduce the sample to 1/8
• Take one of the 1/8, separate the different seeds
  by a sieve and weigh the fraction
• Re-combine the fractions
• Repeat 9 times

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Soil divider

• Results shows that reduction made by different
  persons may give different results
• It may be useful that working quality of the
• soil divider and persons doing the reduction are
  checked regularly

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Hand halving method

• Strictly restricted to the genera that are listed
  in the Rules (2.5.2.2.4)
• Trees and shrubs Acer, Aesculus, Ailanthus,
  Castanea, Cedrela, Corylus, Fraxinus, Juglans,
  Liriodendron, Platanus, Populus, Quercus, Salix,
  Tectona, Ulmus
• For all other species it can be used only to
  obtain a working sample for health tests

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Spoon method

• Recommended method sample reduction for seed
  health testing
• Can be used for all the seeds smaller than wheat
• Seed is taken at least from five random places

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Thank you for your attention!