Classes and subclasses may be combined as desired. Model-based curves that relate gravimetric water content and suction are available for many soils (Baumer, 1986). These curves may be used to determine upper water retention and the midpoint water retention, and to place the soil material in a water state class based on gravimetric water contents. The walls of road cuts in thick loess stand nearly vertical for years.
Vegetation Correlations between vegetation and soils are made for three main purposes: (1) understanding soil genesis, (2) recognizing soil boundaries, and (3) making predictions from soil maps about the kind and amount of vegetation produced. Information about the time since the mass movement took place may be very useful. Observations of the growth of native vegetation and cultivated crops aid in recognizing soil boundaries and provide direct information about the behavior of specific plants on different kinds of soil. Overland flow gradient is the slope of the soil surface in the direction of flow of surface water if it were present. Wetness markedly restricts the growth of mesophytic crops, unless artificial drainage is provided.
The soil material is smeared out between thumb and first finger to form a flattened body about 2 mm of thickness. Four kinds of accelerated water erosion are commonly recognized: sheet, rill, gully, and tunnel (piping). Sheet erosion is the more or less uniform removal of soil from an area without the development of conspicuous water channels. For further help about how to use formatting on pages, see Help:Wiki markup. Lacustrine deposits.—These deposits consist of material that has settled out of bodies of still water.