How To Use Evapotranspiration (ET)

How To Use Evapotranspiration (ET)

Evapotranspiration (ET) is not a new concept in modern agriculture; it was developed a long time ago.  In the last few decades, however, its use has increased to improve the efficiency of irrigation management by many growers.  Before talking about how to use the ET, growers first need to understand what ET is.  ET relates to the loss of water from the soil in two different ways . . . evaporation from the surface of the soil, and the process of transpiration from plant leaves (a mechanism whereby plants give off moisture to cool themselves, similar to sweating).  Factors that affect the rate of evapotranspiration include the amount of solar radiation, temperature, relative humidity, wind speed, and other factors. 

There are many methods for measuring ET; the most common equation for ET was developed by Penman-Monteith and was adopted by the Food and Agriculture Organization (FAO) of the United Nations in 1990.  This methodology uses temperature, solar radiation, wind speed, and relative humidity data from weather stations to calculate the ET.  Most modern weather stations have incorporated this formula into their software.

The importance of knowing the value of ET helps define the quantity of water that the soil and crop are losing to help avoid water stress.  Rainfall or irrigation that replenishes moisture in the soil is only one side of the equation.  Measuring the amount lost to the atmosphere helps provide a more complete picture.  ET readings can either be in inches or millimeters; one inch of ET means that growers would need to irrigate 27,154 gallons of water per acre to replace the amount lost to the atmosphere, and 1 mm of ET equates to 10 cubic meters per hectare.  By knowing how much water is lost, growers have a better understanding of how water is being used and how to better manage this important resource.

All the best,

Related Links:
WatchDog 2900ET Weather Station
ET Gauge
 

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