ABSTRACT
The processes by which soil formation, or pedogenesis, occurs, are known collectively as pedogenic processes, of which there are four main groupsadditions, transformations, transfers and losses (Figure 1.2). Additions involve both organic and mineral material, and can occur at the surface or within the soil itself. These materials are then transformed by the processes of organic matter decomposition, mineral weathering and clay mineral formation. Soil components can also undergo transfer from one part of the soil to another by a variety of processes which involve either transport in water or mechanical mixing. Some of the material will be lost from the soil via a number of processes, either as individual components or in combination with others. The pedogenic processes produce soil horizons, which combine to form soil profiles, different horizon combinations giving rise to different soil types. This chapter will first examine each group of pedogenic processes in turn, although it is important to recognise that these processes rarely occur in isolation; soil profiles are products of the combined operation of a number of processes. This will be considered later in the chapter, by examining the formation of soil horizons and a series of pedogenic pathways which produce basic types of soil profile. Finally, the classification of soil profiles will be discussed, looking at different methods of classification and their relative merits.
