I think you are dramatically underestimating the knowledge of modern farmers. Here are some areas that have changed: irrigation has changed radically in the last 40 years, fertilizers, companion planting, industrialized processes, storage and safer practices. Most farmers would make more difference than an engineer would make because in the past the majority of people were farmers. Don't forget that the main reason for migration to cities has been changes in agriculture (less labour needed, lower costs, globalisation).