Quantitative models for pedogenesis — A review

Pedogenesis models should give us answers to: how does soil form, how does it evolve, where does it come from and how long does it take to reach this state? This paper reviews quantitative models that describe pedogenesis ab initio and the processes that directly lead to development or evolution of soil. We review factorial, energy, and mass-balance models. An early conceptual model comes from James Hutton. The factorial model of Jenny provides the first definition of soil system and quantitative approach in pedology. Much works in pedology were devoted to proposing variations of the factorial model in a qualitative way, such as the pathways, and energy models. The energy model of Volubuyev attempts to calculate the energy of soil formation at a macro-scale and the entropy of soil at the profile scale. The energy model is used mainly as description of the state of a soil. From conceptual, empirical models, a move towards mechanistic models of soil formation followed at a slower pace. The landscape model from geomorphology has made lots of progress in quantifying and modelling soil weathering and distribution in the landscape. These models usually consider physical weathering and treat the soil as a single layer of regolith. Meanwhile mechanistic pedology models consider weathering in a profile scale at a nearly level landscape. Approach to combine these two approaches has recently been proposed. We demonstrate that a rudimentary mass-balance model can simulate soil thickness and organic carbon content variation in the landscape. A soil profile can be created by applying fundamental physical and chemical processes. The mass-balance model provides a valuable platform to model soil and link pedology to other modern earth science disciplines. We discuss some criteria for pedogenesis models and possible integration of the factorial, energy, and mass-balance models.