Soil development models as a component of slope models

The interaction of slope profile models with soil profile models is discussed in general terms to show the external constraints on each individual soil profile which set it within its catena context. The soil profile models discussed are primarily chemical, and treat the soil hydrology as externally imposed. Soil inorganic minerals are treated as mixtures of elementary oxides, using modified values for Gibb's free energies which are approximately valid for silicates. Soil organic matter is considered to consist of carbohydrates, amino acids and lignins, in order to simulate soil organic matter distributions with and without vertical mixing. The soil CO 2 distribution is simulated via gaseous diffusion of the CO 2 produced by organic matter decomposition. Soil pH is calculated with reference to the CO 2 distribution, and allows the solubility equations to be solved through the resulting inorganic soil profile. A worked example is given for a soil profile in equilibrium with given external rates of mechanical and chemical denudation.