In your spirit, dear Hugo, I’ll have to challenge you on that assumption. If what you mean is that farmers could only speak to their immediate neighbors. It might just be, that the development has been the other way.
Archeological evidence show that farmer (and gardener and forager-gardener) cultures exchanged techniques on impressively continental scales as far back as prehistory. The tendency until very recently has actually been the opposite of what I think you imply: As populations have gotten larger, our social worlds have gotten smaller, more differentiated and provincial, more limited by loyalties towards culture, class and language. This process is what anthropologists sometimes calls “schismogenesis” - societies explicitly defining themselves against each other (“those people always till the soil before planting potato, but we never till the soil” etc). Go back thousands of years and you find that places like Poverty Point in Mississippi seems to have exchanged knowledges with people as far away as Mexico, Peru and the Great Lakes to the north. Similar huge distances can be found in other places.
Perhaps a bit tangential, this point I’m making. But I think it is important to remember that people have been very capable of “globalizing” their knowledge before and that - even with the amazing capabilities of the internet - there are still today (perhaps more so) other factors at play that limit the diffusion of ideas for good or worse.
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