Field capacity
Encyclopedia
Field capacity is the amount of soil moisture or water content
held in soil
after excess water has drained away and the rate of downward movement has materially decreased, which usually takes place within 2–3 days after a rain or irrigation in pervious soils of uniform structure and texture. The physical definition of field capacity (expressed symbolically as θfc) is the bulk water content
retained in soil at −33 J/kg (or −0.33 bar) of hydraulic head
or suction pressure. The term originated from Israelson and West and Frank Veihmeyer and Arthur Hendrickson.
Veihmeyer and Hendrickson realised 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 earlier concept of moisture equivalent
by Lyman Briggs.
Veihmeyer & Hendrickson proposed this concept as an attempt to improve water use efficiency for farmers in California during that time.
Field capacity is characterised by measuring water content
after wetting a soil profile, covering it (to prevent evaporation
) and monitoring the change in 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 at potential of −33 J/kg (or −0.33 bar) correlate closely with field capacity. Various potentials were also suggested from −1 J/kg for organic soils, −5 J/kg for soils in the UK, −10 J/kg for loamy soils, and −100 J/kg for heavy clay soils.
There are also critiques 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.
Water content
Water content or moisture content is the quantity of water contained in a material, such as soil , rock, ceramics, fruit, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 to the value of the materials' porosity at...
held in soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
after excess water has drained away and the rate of downward movement has materially decreased, which usually takes place within 2–3 days after a rain or irrigation in pervious soils of uniform structure and texture. The physical definition of field capacity (expressed symbolically as θfc) is the bulk water content
Water content
Water content or moisture content is the quantity of water contained in a material, such as soil , rock, ceramics, fruit, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 to the value of the materials' porosity at...
retained in soil at −33 J/kg (or −0.33 bar) of hydraulic head
Hydraulic head
Hydraulic head or piezometric head is a specific measurement of water pressure above a geodetic datum. It is usually measured as a water surface elevation, expressed in units of length, at the entrance of a piezometer...
or suction pressure. The term originated from Israelson and West and Frank Veihmeyer and Arthur Hendrickson.
Veihmeyer and Hendrickson realised 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 earlier concept of moisture equivalent
Moisture equivalent
Moisture equivalent is proposed by Lyman Briggs and McLane 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 force 1000 times that of gravity...
by Lyman Briggs.
Veihmeyer & Hendrickson proposed this concept as an attempt to improve water use efficiency for farmers in California during that time.
Field capacity is characterised by measuring water content
Water content
Water content or moisture content is the quantity of water contained in a material, such as soil , rock, ceramics, fruit, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 to the value of the materials' porosity at...
after wetting a soil profile, covering it (to prevent evaporation
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
) and monitoring the change in soil moisture in the profile. Water content
Water content
Water content or moisture content is the quantity of water contained in a material, such as soil , rock, ceramics, fruit, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 to the value of the materials' porosity at...
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 A. Richards
Lorenzo Adolph Richards or known as Ren was one of the 20th century’s most influential minds in the field of soil physics. Richards was born on April 24, 1904, in the town of Fielding, Utah, and received a B.S. and M.A. degree in Physics from Utah State University...
and Weaver found that water content held at potential of −33 J/kg (or −0.33 bar) correlate closely with field capacity. Various potentials were also suggested from −1 J/kg for organic soils, −5 J/kg for soils in the UK, −10 J/kg for loamy soils, and −100 J/kg for heavy clay soils.
There are also critiques 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 capacityAvailable water capacityAvailable water capacity or available water content is the range of available water that can be stored in soil and be available for growing crops....
- Integral energyIntegral energyIntegral energy is the amount of energy required to remove water from an initial water content \theta_i to water content of \theta_f...
- Nonlimiting water rangeNonlimiting water rangeThe Non-limiting water range represents the range of water content in the soil where limitations to plant growth are minimal...
- Permanent wilting pointPermanent wilting pointPermanent wilting point or wilting point is defined as the minimal point of soil moisture the plant requires not to wilt. If moisture decreases to this or any lower point a plant wilts and can no longer recover its turgidity when placed in a saturated atmosphere for 12 hours...
- Pedotransfer functionPedotransfer functionPedotransfer function is a term used in soil science literature, which can be defined as predictive functions of certain soil properties from other more available, easily, routinely, or cheaply measured properties...