First of all, the time in history which you seem to be referencing was
much later than the Middle Ages, as you suggested. (by at
least 400 years)
I'll assume you are talking about the Irish Potato Famine, since it is a famous historical event.
From what I remember, it wasn't that the Irish refused new methods of agriculture, but they couldn't afford to practice them. Everyone was starving or dying of the potato disease.
The Blight (as it was called) must have been a huge factor in disregarding new methods, since it would have caused the workforce to become very poor and degraded.
I'm sure the geographic isolation also played a factor into the ignorance of new agricultural methods.
Concerning the French Revolution, it had more to do with the political and financial mess that Louis XV had put the country in. Starvation and disease was also a factor in the upset, but the true beginning of the Revolution was a political act, beginning with the storming of the Bastille among other political upsets.
Poor agriculture was surely a factor in the Lower Class upset, this is well known, but again it would seem more likely that they could simply not
afford any new techniques, instead of outright opposition towards them.
I'm no expert, and surely probably made a few oversights here, but for the most part I recall my History lessons.