ABSTRACT
Presented below are several methods for estimating the duration of pedogenesis.
Weathering balance (Lucas 1989) ƒ Let us assume the following data are available: • Average contents (t m-3) of silicon Sir and aluminium Alr of the
parent material of the profile, • Average Sis and Als of the soil profile (t m
–3), • Bulk density of the soil and of the parent material to convert
the analytical data from gravimetric percentage to volumetric percentage values,
• Composition of the water that passes through the profile (lysimetric water) or composition of the drainage water (drawn from the groundwater) and also the quantity that percolates annually in mm y-1; put simply, this is the difference between the annual rainfall and the annual potential evapotranspiration (PET); from these data concerning the water are deduced the quantities exported Ale and Sie per unit area (say m
2) per year. The reasoning used is what had earlier been developed by Isaac Barshad, then clarified and completed by Lucas. Let F be the annual descent (in m) of the weathering front and T the corresponding thickness of the soil formed, also in m (Fig. 5.6).
