I think your hypothesis needs to be more refined, you'll need a large sample, and you'll want to do some other additional research first.
It's not that you will never have a broody quail, it's that they usually don't. And that is usually how it is described, not with the "never ever broody" statement.
So you'll have to refine your statement...eg "I will show that coturnix quail can go broody with the Johnson grass in various environments that are listed: a, b, c, d, etc". But keep in mind, one way to fully prove that would be, you have to have a bird that is usually not broody, and add Johnson grass, and verify that she is now broody. Your sample size will need to show that the same bird in all these nesting conditions, was not broody, but once you introduce the right conditions, such as the grass, she was broody.
Otherwise, you may have a fallacy because you already had a broody bird even without the grass, or that the environment was already condusive to going broody for that bird.
These are just some ideas off the top of my head and that's why I think your hypothesis will need a bit more research and refinement.