Field capacity is the amount of soil moisture or

water content Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, crops, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as ...

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 te ...

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

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. 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 Moisture equivalent is proposed by Lyman Briggs and McLane (1910) as a measure of field capacity for fine-textured soil materials. Moisture equivalent is defined as ''the percentage of water which a soil can retain in opposition to a centrifugal f ...

Lyman Briggs Lyman James Briggs (May 7, 1874 – March 25, 1963) was an American engineer, physicist and administrator. He was a director of the National Bureau of Standards during the Great Depression and chairman of the Uranium Committee before America e ...

. 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 cal ...

for farmers in

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

during 1949. Field capacity is characterized by measuring

after wetting a

soil profile A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. ...

, covering it (to prevent

evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...

) and monitoring the change soil moisture in the profile.

Water content Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, crops, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as ...

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 Lorenzo Adolph Richards (April 24, 1904 – March 12, 1993) or known as ''Ren'' was one of the 20th century's most influential minds in the field of soil physics. Biography Early life Lorenzo A. Richards was born on April 24, 1904, in the town of ...

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.

References

Soil physics Hydrology

Criticism

See also

References