ABSTRACT
In the sea, where there is no question of plants being nourished by humus, there is a continual turnover of nutritive substances. As for land plants, since they are dependent on two environments and since only the reserves of the atmosphere are unlimited, it is necessary to introduce into the soil certain substances absorbed by plants and thus exported. The basis of agricultural principles is the re-establishment of a state of equilibrium. In particular, phosphates, found in the soil in very low doses, are necessary to plants and must be carefully taken into account, as there is no magic seed. Crop rotation can be used to manage soil reserves to meet plant needs for a certain time. However, eventually it is necessary to use fertilizer to renew the minerals removed by harvesting.
