However, we as human beings can utterly prevent the soil’s receiving from the world-circumference, and raying outward in the proper way, what the plants need in this respect. If we continue manuring at random from year to year, we can gradually prevent the Earth from drawing into itself what it needs by way of silicic acid, lead and mercury, which are at work in the finest homoeopathic doses, if I may put it so — coming inward from the world circumference. These influences need to be absorbed into the growth of the plant, if it is really to receive all that it needs from the Earth. For which the help of all that comes from the world-circumference in this fine and delicate condition, the plant builds up its body in the configuration of carbon. (Steiner 2007:44)
STEINER, Rudolf. 2007. The Agriculture Course. (Trans.: George Adams) Shrewsbury: Wilding & Son Ltd.