Measuring water in seeds
Measuring the amount of water in seeds is helpful at various stages of a seed’s development. In the field, it is important to measure the moisture content when assessing how close seeds are to harvest and dispersal. For seeds that have already spent time in storage, measurement can yield useful information about whether the seeds are alive and how close they are to germination.
The traditional approach, commonly used in the seed trade, is to find out the moisture content using the gravimetric (oven) method. The idea is to dry out seeds completely, then measure the change in weight, which is assumed to be water that has evaporated away. This drying is done in an oven, either at a temperature of 103°C or 130°C. It is a destructive process, requiring large samples of seeds, and may be regarded as rather wasteful, given the effort and resources genebanks devote to seed conservation.
Activity 1
Allow 5 minutes for this activity
This activity walks you through how to calculate moisture content of seeds using the gravimetric method.
A scientist places a sample of fresh seeds into a dry crucible and weighs them.
- Weight of crucible: 50g
- Weight of crucible plus seeds: 55g
What is the fresh weight of the seeds? Use the text box below to write your answer, before pressing ‘reveal’ to check you got it right.
When you are ready, press 'reveal' to see our comments.
Discussion
Fresh weight = 5g
The scientist places the seeds in the oven at 103°C for 17 hours. Next, the scientist cools the sample for one hour, and weights it again.
- Weight of crucible plus seeds after drying in oven: 54.4g
Assuming the weight difference is entirely due to water evaporation, what is the dry weight of the seeds? Use the text box below to do your own calculation before checking the answer.
When you are ready, press 'reveal' to see our comments.
Discussion
dry weight = 4.4g
The moisture content can be expressed as a percentage of fresh weight:
What is the moisture content of this sample? Write your answer in the text box below before checking.
When you are ready, press 'reveal' to see our comments.
Discussion
Moisture content = 12 % f. wt.
Pause for reflection
Can you think of any reason why these calculations of dry weight, moisture content and water content, based on the gravimetric method, may not be accurate? Use the text box to write your thoughts.
When you are ready, press 'reveal' to see our comments.
Discussion
The gravimetric method is based on an assumption that all the weight loss is due to evaporation of water. However, this may not be the case: some of the weight loss could be due to loss of volatile components of the seeds.
Some definitions