Seed moisture content (SMC) is the amount of water in a seed, expressed as the percentage of water contained in the seed relative to the total seed weight. SMC management influences many physiological parameters essential to seed quality and longevity. It can be measured directly through the oven-drying method, described in the International Rules for Seed Testing (ISTA 2005).
To apply this method, you need technical equipment like a precision balance and a mechanical-convection oven. It is time consuming, and most importantly it is a destructive method that uses and kills a significant number of seeds. For this reason we do not recommend using it. Instead, you can rely on the relative humidity measurement as an alternative non-destructive method. However, you can use the method below if you have an abundance of seeds and wish to determine the SMC of your species for research purposes.
These are the simplified steps:
- Take two samples of 0.5–1 g of seeds, or at least 10 seeds, as representative samples of the seed collection (make sure to mix the seeds first and take a random sample).
- If the seeds are large or with thick, impermeable coats, you need to grind them into smaller parts.
- Weigh the seed samples (wet weight) using an analytical balance.
- For oily seeds, place the samples in an oven at 103°C ± 2°C for 17 ± 1 hour, while for non-oily seeds, place them in an oven at 130–133°C for 1 to 4 hours. If unsure, it is recommended to use the low-temperature method.
- After oven-drying, make sure your seed containers are put directly in a desiccator so that the dry seeds do not absorb more moisture.
- Weigh the seed samples again (dry weight).
- Finally, calculate the moisture content as the difference between the weights before and after the oven treatment (which is the water lost in the process) as:
SMC = [(wet weight - dry weight) * 100] / wet weight
For further reading, please consult the Procedures for Handling Seeds in Genebanks (Hanson 1985).