You are right that I did not express that well, because as said it is true only in natural places, not in artificial cultures.
For modern cultivated lands potassium must be indeed used as a fertilizer, because much of what exists in the soil is removed by remaining in the plant parts that are harvested then transported elsewhere. Another part of the potassium may be washed away by intensive irrigation.
So the potassium that is taken away depending on the cultivation methods that are used must be replenished. However its abundance is such that this will never be a problem.
