The famous 12-year Schuphan study tested the nutritional superiority of organically grown foods. Among other things, Schuphan found:
Organic foods have fare higher mineral and trace mineral contents, with the exception of sodium. Organic produce contains far more iron, potassium, magnesium and calcium than conventional crops. (Most studies of this type demonstrate that organic foods have 2 to 10 times the mineral content of conventional foods – you really do get more value for the money).
Organic spinach contained 64-78% more vitamin C.
Organic Savoy cabbage contained 76-91% more vitamin C.
Organic crops had a dry weight (after dehydration) of 69-96% more than conventional crops, demonstrating a higher food-value content.