Evapotranspiration

Evapotranspiration referred in meteorology, the sum of transpiration and evaporation, so the evaporation of water from animal and plant life, as well as from soil and water surfaces. The Evapotranspirationswert plays an important role in hydrology and agriculture and horticulture.

Depending on factors

  • Water content of the soil
  • Intensity ( biomass production) and species composition ( some plants evaporate more than others) the vegetation
  • Covering of soil and sunlight
  • Humidity
  • Temperature of the ground or water surface
  • Temperature of the boundary layer air
  • Wind speed at the surface

Possibilities of instrumental measurement

Evaporimeter

Evaporation measurements are carried out with Atmometern. One way of evaporation measurement is class- A pan ( Evaporimeter or evaporation boiler), a circular water-filled measuring boiler to measure the potential evaporation from land surfaces ( land evaporation boiler).

This was introduced by the Americans evaporation measurement method consists of a flat, mounted on a wooden lattice frame, water-filled cylindrical shape. The water level is 35 cm above the soil surface. The Evaporimeter has an area of 1.17 m². The water is exposed to the open atmosphere of the evaporation, the water loss is in 24- hour clock eg measured by pressure sensors.

With this measuring method, the so-called potential evapotranspiration ( ET p ) can be measured. It indicates how much water would evaporate in circumstances when there is enough water. However, this measurement method is not very suitable for a statement of the actual evaporation. The water surface is a kind of "island" in the country through the constantly newly brought up, unsaturated air, and a greater willingness of the water in the basin to evaporate (compared to ground water), can not be traced back to the real evaporation (ETR ) taken out of the ground be. The water surface is not representative enough for the country to evaporation. The class -A pan is used, however, by the standardized size of various well for a comparison of the ETP areas. In parallel, the precipitate can be measured in order to register the entered into the tub amount of water for evaporation measurement with the class A- pan needs.

For evaporation measurements that take into account wind effect, use Piche atmometer or Czeratzki - atmometer.

Lysimeters

Further can be used to measure a lysimeters.

FAO -56

A widely used method for the measurement of evapotranspiration, the calculation of the above mentioned climatic factors for a recommended by the FAO method that ( "modified Penman - Monteith " formula, FAO -56). Here are the necessary parameters - air temperature and relative humidity, wind speed and solar radiation - recorded by a weather station and processed in a computer model. This so-called reference evaporation ( ETo ) corresponds to the evaporation, as it would appear on a flat, uniformly grassy area. Since this value for the crop has little meaning, culture-specific correction values ​​are used. With their help you get to the crop-specific evapotranspiration ( ETc ), which supplies taking into account the phenological stage of the plant already a fairly reliable value. Of practical importance is the calculation of evaporation, especially for the adequate control of irrigation systems, which is aimed at carry out the proper amount of water to the soil and the plant as a function of evaporation and growth requirements.

Film

Particularly complex, but something more specific, it completely seal a plant or a location with a film. The evaporating water into the foil is collected and measured. It should be noted here is that the film, of course, is a significant factor.

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