ABSTRACT
Thanks to the studies of M. Bornand, and by underscoring the evolution of the coarse fractions, the Luvisols Rhodic of the Rhône valley have enabled us to develop our concepts of pedogenesis still better. In these soils, in the B horizons, the carbonates dissolve in place. Igneous rocks are weathered in situ to form clays that rubefy. Siliceous fragments resist weathering. On the surface of the soil, more precisely in the A and E horizons, degradation is manifested at the same time by acidification, disappearance of red colour, transformation of smectite to kaolinite (desilication) and finally by loss of iron accompanied by partial solubilization of the clay minerals. This results in a high contrast between A and B. Besides the evolution of iron, there is thus a great similarity to what happens in Luvisols and Planosols discussed earlier. The Mediterranean red soils have permitted the Roman civilization to develop around the Mare nostrum, this with relative food security. But poor land management has led to disappearance of the forests and planing down of the soils. Of course, soil productivity is not the first worry of developed civilizations in our times. But up to what level of world population?
