Grass seeds with backlight illumination to enhance the caryopsis inside the seeds
Physical purity testing of seeds
What is physical purity? Physical purity testing quantifies the weight percentages in a seed lot of
- pure seed
- other crop seeds
- weed seeds
- inert matter (other matter than seeds: broken seeds, chaffs, sterile florets, stems, and stones)
All species of seed and all types of inert matter present shall be identified. Physical purity testing is regulated by International Seed Testing Association (ISTA) rules.
Physical purity imaging of seeds
While physical purity imaging is not the same as physical purity testing then it quantifies similar properties of a seed lot in order to:
- work as an aid in ISTA regulated physical purity testing,
- estimate physical purity in unregulated seed analysis,
- optimize seed processing by choosing the right kind of processing equipment, adjust the equipment, and predict the yield of a given seed lot,
- integrate physical purity tests with destructive tests where a fraction of the pure seeds are needed e.g. germination tests, vigor tests, and seed health tests. The sampling of pure seeds may be done by robot picking.
Physical purity imaging can in principle measure samples in a similar way to physical purity testing. From an industry and cost point of view there are, however, important advantages to harvest from this new non-contact sensing technology if we
- measure number percentages instead of weight percentages. Number percentages are already used in other parts of seed testing like germination, vigor, and seed health testing and may make sense for physical purity as well. Optical weight estimates are also possible based on size (area, volume) and a density assumption for each fraction.
- measure on one side of the seed only. This will make the mechanical presentation of seeds much easier, and will allow larger seed samples to be handled more robustly. Larger sample sizes will reduce the sampling variation and balance the loss of information in one-sided analysis.