Maximum Rate of Soil Evaporation

Calculation Models

• Rates of evaporation from the soil are typically calculated using computer models. These mathematical equations can adjust for different inputs, such as hours of sunlight, temperature and amount of moisture received. Using a computer model is the best way to estimate the maximum rate of evaporation from a certain soil. Climate information can be found on the Internet from university and government websites. After you have entered the necessary inputs into the model, it can be run to indicate the maximum rate of evaporation from your soil.

Soil Type

• Soils are classified according to several features. The texture of the soil is one way that its type is defined. Soil texture is the amount of sand, silt and clay that it contains. The finest particles in the soil are clay-sized. The more clay a soil contains, the longer water is held in the ground. A soil with a high clay content has a much lower maximum evaporation rate than a soil with lots of sand. Organic matter is another soil characteristic that defines what type of soil it is. The more organic matter a soil has, the lower its maximum evaporation rate is, because it bonds very strongly to water.

Surface Area

• A smooth surface on a soil reduces its maximum evaporation rate. A rough soil surface has a greater surface area. This allows for increased contact with environmental conditions. Higher wind speeds help to increase a soil evaporation rate. Rough, newly plowed soil evaporates much faster if there is a wind than a smooth soil in the same conditions. To preserve soil water, it is best to keep the soil as flat as possible. On the other hand, if you are trying to dry a soil out, keeping it as rough as possible to increase its surface area is a good idea.

Ground Cover

• Soil with anything growing on it has a lower maximum evaporation rate than a bare soil. The denser the plants, the lower the evaporation rate is. For example, if a soil is covered with dense sod, it is protected from climate conditions that cause an increase in the soil evaporation rate. In the same way, mulch made from bark, gravel, wood chips or grass clippings holds moisture in the soil and lower its evaporation rate by protecting it from sunlight, temperature and wind. A good way to preserve soil moisture is to keep the ground covered. To increase a soil's evaporation rate, make it as bare as possible.