Soil genesis and profile differentiation

The formation of a soil from raw parent material or from a pre-existing soil encompasses the concept of soil genesis, or pedogenesis. Soil genesis involves both progressive and regressive processes (Johnson and Watson-Stegner 1987). It includes all processes operative within the soil, whether they act to promote horizonation, preserve it, or even destroy it. And it is the underlying principle behind many soil classification systems which endeavor to group soils of similar genesis, based on observable morphology or chemical properties (Cline and Johnson 1963, Smith 1986). The link between soil genesis and classification, shown in one respect in Fig. 7.6, can also be envisioned as follows: soil-forming factors → soil-forming processes → diagnostic horizons and materials → soil taxonomic system (Bockheim and Gennadiyev 2000).