When I was young I was fortunate in growing up on a nursery, nowadays it would be called "organic" - no artificial chemicals were used at all, relying instead on horse muck, and nicotine shreds as an insecticide. We also had what I suppose you'd call a kitchen garden, kept chicken free-range, and probably did quite well in comparison to other people at the time (rationing was still very much in operation) - I still awake with a shudder at the memory of "Cod-liver oil and malt" and "National Health Orange Juice", which were dished out to the public in attempt to bolster what could be a pretty frugal diet (I was rather partial to "Delrosa" Rose-hip syrup though, which contains loads of vitamin C). In those days there was a load of "bottling" of fruit for winter use, along with jam-making - winter veg were things like spuds, cabbage, kale, sprouts, swede, turnips
The fact remains that the tomatoes my Dad grew contained far more nutrients that the modern bags of chemicalised water - the problem as you say in the 50's was getting them to people in sufficient quantities, ..... they were generally much slower growing, lower yielding than modern varieties, and were grown on soil that still had "crop rotation" practiced so that minerals were not depleted in the way that they are now.
There have been several studies and newspaper articles here in the UK about the lower nutrient levels in modern food in recent years, I thought it was "common knowledge". Another interesting thing is that chicken used to be known as a really healthy meat - it was lean, and had very little fat - as several recent TV programmes have shown all too graphically, modern broiler chicken are "fat bombs", being full of unhealthy fats due to the way they have been bred and reared........
