I would say Middle Earth just lacks fertilizer. That fertilizer would be needed to free a lot of people from menial field work and allow them and their childre

I would say Middle Earth just lacks fertilizer. That fertilizer would be needed to free a lot of people from menial field work and allow them and their children to dig for coal or toil in factories. Imho coal is not all that necessary for an industrial revolution. To run factories, one could use water power for the textile industry for example. And i would recommend to make charcoal out of Lóriens forests for the smelteries (which actually would be quite good due to the low sulfur content of charcoal).