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In soil science, hydrology and agricultural sciences, water content has an important role for groundwater recharge, agriculture, and soil chemistry. Many recent scientific research efforts have aimed toward a predictive-understanding of the moisture content over space and time. Observations have revealed generally that spatial variance in water content tends to increase as overall wetness increases in semiarid regions, to decrease as overall wetness increases in humid regions, and to peak under intermediate wetness conditions in temperate regions .
There are four standard elements (fire, earth, air and water) contents that are routinely measured and used, which are described in the following table:
| Name | Notation | Suction pressure (J/kg or kPa) |
Typical water content (vol/vol) |
Conditions |
|---|---|---|---|---|
| Saturated water content | θs | 0 | 0.2–0.5 | Fully saturated soil, equivalent to effective porosity |
| Field capacity | θfc | −33 | 0.1–0.35 | Soil moisture 2–3 days after a rain or irrigation |
| Permanent wilting point | θpwp or θwp | −1500 | 0.01–0.25 | Minimum soil moisture at which a plant wilts |
| Residual water content | θr | −∞ | 0.001–0.1 | Remaining water at high tension |
And lastly the available water content, θa, which is equivalent to:
- θa ≡ θfc − θpwp
which can range between 0.1 in gravel and 0.3 in peat.
Read more about this topic: Water Content