Field capacity is the amount of
soil moisture or
water content held in the
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...
after excess water has drained away and the rate of downward movement has decreased. This usually takes place 2–3 days after rain or irrigation in pervious soils of uniform structure and texture. The physical definition of field capacity (expressed symbolically as θ
fc) is the bulk
water content retained in soil at −33 kPa (or −0.33 bar) of
hydraulic head
Hydraulic head or piezometric head is a specific measurement of liquid pressure above a vertical datum., 410 pages. See pp. 43–44., 650 pages. See p. 22.
It is usually measured as a liquid surface elevation, expressed in units of length, ...
or
suction pressure Suction pressure is also called Diffusion Pressure Deficit. If some solute is dissolved in solvent, its diffusion pressure decreases. The difference between diffusion pressure of pure solvent and solution is called diffusion pressure deficit (DPD). ...
. The term originated from Israelsen and West and Frank Veihmeyer and Arthur Hendrickson.
Veihmeyer and Hendrickson realized the limitation in this measurement and commented that it is ''affected by so many factors that, precisely, it is not a constant'' (for a particular soil), ''yet it does serve as a practical measure of soil water-holding capacity''. Field capacity improves on the concept of
moisture equivalent by
Lyman Briggs. Veihmeyer & Hendrickson proposed this concept as an attempt to improve
water-use efficiency
Water-use efficiency (WUE) refers to the ratio of water used in plant metabolism to water lost by the plant through transpiration. Two types of water-use efficiency are referred to most frequently:
*photosynthetic water-use efficiency (also ...
for farmers in
California
California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...
during 1949.
Field capacity is characterized by measuring
water content after wetting a
soil profile, covering it (to prevent
evaporation) and monitoring the change
soil moisture in the profile.
Water content when the rate of change is relatively small is indicative of when drainage ceases and is called ''Field Capacity'', it is also termed ''drained upper limit'' (DUL).
Lorenzo A. Richards and Weaver
found that water content held by soil at a potential of −33 kPa (or −0.33 bar) correlate closely with field capacity (−10 kPa for sandy soils).
Criticism
{{unreferenced section, date=September 2021
There is also criticism of this concept; field capacity is a static measurement: in a field it depends upon the initial water content and the depth of wetting before the commencement of redistribution and the rate of change in water content over time. These conditions are not unique for a given soil.
See also
*
Available water capacity
*
Integral energy
Integral energy is the amount of energy required to remove water from soil with an initial water content \theta_i to water content of \theta_f (where \theta_i > \theta_f). It is calculated by integrating the water retention curve, soil water pot ...
*
Nonlimiting water range
*
Pedotransfer function
*
Permanent wilting point
*
Water potential
Water potential is the potential energy of water per unit volume relative to pure water in reference conditions. Water potential quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure and ...
*
Water retention curve
References
Soil physics
Hydrology