Measuring seed moisture
Accurate measurement of seed moisture status is essential to successful
seed handling and processing. Seed collectors in the field need to
know the moisture level of freshly collected seeds in order to handle
collections properly; seed bank staff need to know that seeds are
dry enough to store, and scientists addressing seed longevity need
to know exactly how much water seeds contain.
Digital humidity sensor used to measure seed moisture status.
The most common method of measuring moisture status is by oven drying a sample of seeds at 103°C for 17 hours. Seed moisture is then expressed as percentage moisture content. The major disadvantage of this method, particularly when dealing with collections of rare and threatened species containing limited numbers of seeds, is that seeds are killed at such temperatures. It is also time consuming. To get around these problems the MSB uses a rapid, non-destructive method based on humidity sensors.
This method relies on the fact that seeds rapidly gain or lose moisture depending on their surroundings. Moist seeds in dry air lose moisture; dry seeds in moist air gain moisture. After about 30 minutes there is no further movement of moisture between seeds and air, and seeds are said to be at equilibrium.
Digital humidity sensors measure the amount of water vapour in the air at equilibrium with a sample of seeds enclosed in a sealed chamber. The reading is generally expressed as equilibrium Relative Humidity, or eRH, and may be related to conventional percentage moisture content.
Key findings:
- The speed and simplicity of this method encourages users to monitor seed moisture status.
- Portable hygrometers, used with care, can greatly assist post-harvest handling decisions in the field as well as in the seed bank.
- The temperature of the seed sample must be equilibrated to the sample chamber temperature.
Further information:
Technical information sheet: Measuring seed moisture status using a hygrometer
Probert, RJ, Manger, KR and Adams, J. (2003.) Non-destructive measurement of seed moisture, pp.367-387. In: RD Smith, JD Dickie. SH. Linington, HW Pritchard &. R.J Probert (eds) Seed conservation: turning science into practice. Royal Botanic Gardens, Kew, UK.