Seed Vigour: What a Seed Still Delivers Under Poor Conditions
Two lots both give 95 % germination in the laboratory. In cold, wet spring soil one comes up cleanly and the other patchily. That difference is seed vigour: how the seed performs when conditions fall short of ideal. A germination test does not measure it, because the test creates precisely the good conditions under which both lots look equally sound.
Why hemp has a gap here
The rulebooks of the two major testing bodies contained a standard germination test for hemp in 2019 and no procedure for its vigour. Both rulebooks are reissued yearly; whether one has since been added has not been checked here.
That leaves this species without the very figure that matters most in field production. Anyone who knows only the germination capacity knows the ceiling of what a lot can do, not how it behaves when things go wrong.
The accelerated ageing test
One proposed method ages the seed artificially. It sits for forty-eight hours at 43 Β°C and near-total humidity, far warmer and damper than any store, and is then germinated under the usual conditions of 20 Β°C to 30 Β°C over seven days. Whatever survives that stress counts as vigorous.
The figures drop sharply. For one of the varieties tested they stood at 64 % from the upper and 70 % from the lower part of the plant after ageing, while a staining test had shown 97 % to 98 % living seeds in the same lots beforehand. Among the seeds that failed to germinate after ageing, 19 % to 25 % were still alive; the authors consider a secondary dormancy triggered by the treatment possible and have not tested it.
The second route: measuring speed
Alongside the stress test sits a figure for speed, the speed of germination index. Counting runs daily from day two to day seven, with a seedling counting only once root and shoot are sound and the shoot measures at least 5 mm, roughly the length of one seed. A higher value means faster germination. The calculation itself refers back to an older paper and was not retrievable in the full text read here.
The two routes measure different things. One asks what survives a load, the other how briskly an unstressed lot gets going. A lot can do well on the first and poorly on the second.