Soil moisture
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, 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.
*
Water resources*
Water content
