Field capacity

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Field capacity is defined as the amount of water 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 term originated from Israelson and West (1922) and Frank Veihmeyer and Arthur Hendrickson (1931).

Veihmeyer and Hendrickson (1949) 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 (1944) found that water content held at potential of -33 J/kg (or 1/3 bar) correlate closely with field capacity. Various potentials was 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.

[edit] See also

• Available water capacity
• Integral energy
• Nonlimiting water range
• Permanent wilting point
• Pedotransfer function

[edit] References

• Israelson O W and West F L 1922 Water holding capacity of irrigated soils. Utah State Agricultural Experiment Station Bull. 183, 1-24.
• Richards L A and Weaver L R 1944 Moisture retention by some irrigated soils as related to soil moisture tension. J. Agr. Res. 69, 215-235.
• Veihmeyer F J and Hendrickson A H 1931 The moisture equivalent as a measure of the field capacity of soils. Soil Sci. 32, 181-193.