Formation of Vertisols

Abstract

Soils dominated by smectitic clay minerals that are found in a strongly seasonal climate, usually exhibit ‘vertic properties’. These are a combination of 1) deep cracks when dry (Fig. 10.1), 2) intersecting slickensides in the subsoil (polished and grooved shiny surfaces, produced by one mass of soil sliding past another) 3) wedge-shaped structural aggregates in the subsurface soil (25 to 100 cm deep), and 4) a strong, nutty structure at the soil surface. Often, these soils show a so-called gilgai microrelief: rounded mounds and depressions or series of ridges and inter-ridge depressions, with distances between highs and lows of 2 to 8 m and vertical differences of 15 to 50 cm. The combination of these properties characterizes vertisols. Two sets of processes related to the genesis of vertisols will be discussed: the formation of smectitic clays, and the development of the typical physical characteristics.