I also looked just on google and found a few papers, both on seeds and oil. It does seem to be a thing!Thanks for providing the terminology. I used the terms antimicrobial plants to find an informative paper. The author is speaking of ingestion, not gardening, and of humans, not chickens, but it's a start.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC88925/
I haven't yet turned to the databases. Or Google Scholar.
Mark said crops like corn and suflowers and hay suck nutrients from the soil in a way that would be beneficial to future chickens on that soil. Something like that. He always packs so much detailed information into our very short conversations, I rarely take it all in. He assumes people can keep up with him, and I can't, which gives me an important lesson to hold on to wrt conversations with inexperienced thinkers in my own field.
Before talking to him, my own thinking was that well-established turf would provide a barrier between chickens and bacteria, but if chickens live on it all day long, it won't be long before there's none left.
About the soil and the bacteria : two days ago I had a talk with the man who owns the house above us, he's some kind of manager for the gardeners in the town of Nice. I was telling him how much trouble we had in our greenhouse this year with the drought, we take off the plastic in winter so the soil can breathe, be fed and get watered, but last winter there was almost no rain or snow. He said water was absolutely necessary to allow the bacterias in the soil to live, and that if the soil had been dry in depth for too long, the bacterias wouldn't be able to survive and grow back, even when we started using the drip irrigation system. This isn't scientific information, but I think if you have a dry climate covering the soil with a black sheet for a few months would also probably work. But you would have a dead soil- killing everything even the good stuff.