How to use water, an egg, and salt to assess paddy rice seeds

An article by network member Abena Konadu Oppong in EDN 164 shares a low-resources way of assessing the quality of paddy rice (Oryza sativa) seed. See the full article for details and a discussion about the importance of seed quality assessment.

  1. Gather materials: A plastic container, freshwater, salt, a raw egg, and paddy rice seeds. The egg should not be more than three weeks old.

  2. Prepare the container with water: Clean a container or vessel to make sure there are no foreign particles in the container. Fill it with water, taking into consideration the amount of water should be sufficient to cover the paddy rice seeds completely.

  3. Add ingredients: Add an appropriate amount of salt into the water. In the absence of a specific gravity meter, a raw egg can be used to indicate how much salt can be used. Place the egg into the salt solution. Add salt until the egg floats, indicating that the density of the salt solution is high enough for good separation between low- and high-quality seeds. Remove the egg, as it has now served its purpose. Testing at ECHO, with several chicken eggs and a duck egg, showed that a 10% salt solution (equivalent of 2 kg salt per 20 L of water) was the minimum amount required for an egg to float. Kim et al. (2022) suggested a 21% salt solution (4.2 kg salt in 20 L of water), an amount that will cause the egg to float higher in the water (Figure 15). Experiment to determine the minimum amount of salt that causes low-quality/damaged seeds to float while allowing quality seeds to sink.

  4. Put an appropriate amount of paddy rice seeds into the salt solution.

  5. Stir thoroughly making sure that the seeds are completely immersed and coated with the solution.

  6. Wait for about 5 minutes and observe the behavior of the paddy rice seeds. Seeds should not be soaked in the saltwater for a long period of time as prolonged exposure to salt can hinder seed germination.

  7. Remove and discard the floating paddy rice seeds from the water as they are considered low-quality seeds which may likely yield low-quality rice.

  8. Seeds that settle at the bottom of the container are considered high quality. Strain and wash the seeds to remove any remaining salt or other residues.

  9. Seeds may either be planted afterwards or stored for future use. For later usage, dry seeds immediately after conducting the float test and rinsing, before they absorb water (which could result in premature germination). Spread the seeds in a shaded, well-ventilated area to retain their quality. Ensure that they are well dried before storage.

Remaining questions include:

  • How long can seeds selected using this technique be stored before use?
  • How much paddy rice should be placed in the saltwater?

Do you have experience with this technique and would like to share your knowledge? How do you assess the quality of your seeds before planting or storage?