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Soil moisture

2007 Schools Wikipedia Selection. Related subjects: Geology and geophysics

   Soil moisture is the amount of water present in the soil.

   Gaps between soil particles are called pore spaces or voids. These
   voids contain various amounts of either water or air. Soil moisture
   content can be expressed in different basis:
     * Gravimetric: the mass of water/mass of solid material
     * Volumetric: the volume of soil/total porosity

   The amount of void space within a soil depends on the distribution of
   particle sizes, and is quantified by soil porosity.

   Soil moisture may be measured in situ with different instrument, such
   as Time Domain Reflectometry (TDR), neutron probe, frequency domain
   sensor, tensiometer, capacitance probe, etc. In the laboratory, it is
   measured gravimetrically; by weighing the moist volume of soil, drying
   it, and then weighing it again. The difference in mass corresponds to
   the mass of water which was in the soil (water is of a known density,
   therefore the volume of water can be determined).

   When the soil gets too dry, plant transpiration drops because the water
   is becoming increasingly bound to the soil particles by suction. Below
   about a certain point, called the wilting point in agricultural
   settings, plants are no longer able to extract water. At this point
   they wilt and cease transpiring altogether. Conditions where soil is
   too dry to maintain reliable plant growth is referred to as
   agricultural drought, and is a particular focus of irrigation
   management. Such conditions are common in arid and semi-arid
   environments.

   Soil moisture is more generally considered within the context of
   hydrology, where it represents the immediate store of infiltrating
   rainfall, before it either evapotranspires or contributes to
   groundwater recharge.

   Retrieved from " http://en.wikipedia.org/wiki/Soil_moisture"
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   with only minor checks and changes (see www.wikipedia.org for details
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