Soil Water

The soil water content varies seasonally within soils, whereas the soil is influenced by precipitation, streams and / or groundwater (e.g. waterlogging). The soil present in a landscape determines the processes of evaporation, transpiration, infiltration, percolation, interflow and surface runoff, whereas the soil itself is influenced by these hydrologic processes. Slow upward movement of water occurs in response to evaporation from the soil surface. Vegetation offers a much larger surface for the transpiration of water. Soil water is sucked from the soil into the roots and through the plant, to be lost by transpiration from the leaves, which results in an increase in soil water potential. Infiltration is the movement of water into the soil from above, percolation is the throughflow of infiltrated water to the groundwater, interflow is subsurface lateral flow and occurs through soils on slopes, or when vertical flow through subsoil is impeded. The difference between the precipitation amount that reaches the soil surface (net precipitation) and the infiltrated water is the surface runoff.

Soil water, i.e. the soil solution, contains dissolved organic and inorganic solutes and it is an important agent responsible for translocation (e.g. leaching of small soil particles or iron oxides) and transformation of material. (e.g. soil water supports weathering of rocks).

Soil water facilitate growth of plants and other organisms that contribute organic matter. Freeze-thaw and wet-dry cycles are important in producing pedogenic phenomena. The soil pore space is partly (i.e. unsaturated conditions) or totally occupied by soil water (i.e. saturated conditions). Typically, at a variable depth below the surface, depending on the regional hydrology and the soil's permeability, the pore space is permanently saturated with water, which is called groundwater. The upper surface of the groundwater, which may fluctuate with the season of the year, is called the watertable.

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