Phosphates are a chemical, easy to add if needed - for a price. Many soils have far more than needed, so the farmer won't add more. 30 years ago farmers never measured sulfur content of their soils - acid rain replenished it - now the coal has cleaned up their emissions farmers buy sulfur. Farming is still a learning game. When John Deere bought a tractor company they wrote a letter (in 1918) to their dealers stating more or less that tractors are an interesting fad, but the company is well aware that the horse drawn plow will forever be the backbone of the American farm.

Note that I said for a price. Farmers who buy that stuff and let it run off lose money in the long run and go bankrupt.