Chances are that you have seen an advertisement or read a book or article that is really intended as an advertisement with a statement like this:
"It only takes 10 years of intensive agriculture to completely deplete the soil of all its minerals. "
Statements like this beg a question. If there aren't any minerals in the soil, how do crops grow to be harvested? After all, plants need minerals, too.
It's a myth that humans suffer mineral malnutrition because soils are depleted. Every plant on the face of the earth is not destined for human consumption, and every soil isn't suitable for human agriculture. Some soils support plants that feed other animals and that just grow for their own sake.
The idea that depleted soils cause mineral malnutrition originated in the 1930's, but it was promulgated by in a bestselling book about 20 years ago. The authors of the book had tested tomatoes grown in New England and tomatoes grown in Florida. They found vastly different amounts of key minerals in the different samples, and their publisher concluded that this could only be because the Florida soils had been depleted. The publisher did not know that bacteria are needed to bring minerals to plants, and that summer heat in Florida kills microbes in the top layers of soil.
In any case, no one ever actually tested the soil to see whether it was deficient in minerals or not. The publisher concluded that "Southern farmers are not as smart as Yankee farmers" and blamed farmers for not maintaining soil. Various commentators have spun this misinformation into condemning "strip farming," which is actually a practice of minimal cultivation, planting crops in strips surrounded by natural vegetation, which conserves the minerals in the soil and makes them more available to both crops and wild plants.
As a result, millions of people started taking mineral supplements (not that mineral supplements are always bad, as will be discussed in just a moment) when what they really needed was locally grown produce picked that the right time of year when microbes were active in the soil and plants received optimal amounts of minerals for humans. From the plant's perspective, of course, minerals are always sufficient or the plant doesn't grow and isn't ever harvested! And if the soil is relatively deficient, the microbes that help the plant are simply more active. You eat plants, not dirt.