Practical - Measuring seed moisture status

Improving the identification, handling
and storage of ‘difficult’ seeds
Seed Air Moisture Relations Practical Exercise:
Measuring Seed Moisture Status
Introduction
This practical compares destructive and non-destructive methods for determining seed
moisture status. The data obtained will enable the construction of isotherms for two
species: one oily and one non-oily.
Objectives
• Determine seed moisture status using a) the oven method and b) a digital
humidity sensor
• Plot the relationship between seed moisture content and equilibrium relative
humidity.
Materials
• Samples of oily (e.g. sesame, groundnut, sunflower) and non-oily (e.g. sorghum or
other cereals) seeds, pre-equilibrated 1 to different moisture levels. The greater the
number of moisture levels used, the more accurate the isotherm will be.
• Rotronic AWVC-DIO or similar digital humidity sensor.
• Plastic sample dish
• Ventilated fan-assisted oven
• Desiccator
• Metal crucible
• Curved forceps
• Spatula
• 5 place balance
Method
Determine seed moisture content using the oven-drying method:
• Weigh an empty container (Dish Weight) and clearly label with sample
number
• Add seed to the container and reweigh (Fresh Weight). Use less than 0.3g
seed per cm² of dish area. For example, for a 1cm diameter crucible, allow
approximately 1g seed.
• Place container, with lid removed, in a ventilated fan assisted oven for 17
hours at 103°C (oily seeds) or 1 - 4 hours at 130°C (non-oily seeds).
• Cool samples in a desiccator, over silica gel for 1 hour.
1 Methods for equilibrating seed samples to specific moisture levels are available here:
http://www.kew.org/msbp/scitech/publications/09-Seed-air%20moisture%20relations.pdf
If Lithium chloride is not available, equilibrate seeds in environments of different moisture level, such
as in a dry room or over silica gel in a sealed box, under ambient conditions in a lab, in a cold room,
and over water in a sealed box.
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Improving the identification, handling
and storage of ‘difficult’ seeds
• Weigh container with seed (Dry Weight).
• Calculate moisture loss and express as % (fresh weight basis):
Moisture content (% fresh weight) = fresh weight – dry weight x 100
fresh weight – dish weight
Determine seed eRH using Rotronic AWVC-DIO.
• Remove the lid from a plastic sample dish containing seeds and place this in
the chamber. The seeds should take up a minimum of 20% of the chamber in
order to dominate the system within the chamber.
• Clamp the Rotronic probe to the chamber and leave the lid, clearly labelled,
next to the instrument.
• Once the sample has equilibrated (approximately 15-20 min) return to take a
reading of eRH.
Results
Species Sample Rep Dish
Weight
Oily: 1 I
II
2 I
II
3 I
II
4 I
II
Nonoily:
1 I
II
2 I
II
3 I
II
4 I
II
Fresh
Weight
Dry
Weight
Moisture
Content
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Improving the identification, handling
and storage of ‘difficult’ seeds
Species
Oily:
Non-oily:
eRH reading
Sample
eRH Temp ºC
1 %
2 %
3 %
4 %
1 %
2 %
3 %
4 %
Moisture Content
Plot mc against eRH
25
20
MC%
15
10
5
0
0 10 20 30 40 50 60 70 80 90 100
eRH%
Questions
• What was the temperature at which you recorded eRH?
• If the eRH measurements had been taken at a higher temperature, what effect
would this have had on the isotherm?
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