Irrigation Water Budgeting Parameters – Evapotranspiration, part 2

Evapotranspiration (ET) is the combined processes of evaporation and transpiration which occur simultaneously.  In this segment, we are going to focus on transpiration (you can learn about evaporation by clicking here).

When the liquid water contained in plant tissues is vaporized and then removed into the atmosphere, it is called transpiration.  The vaporization occurs within the leaf of the plant.  Nearly all water taken up through the roots of the plant is lost by transpiration – only a small fraction is used within the plant.

There are many factors that affect the rate of transpiration.  These include climate factors such as amount of sun, air temperature, air humidity and wind.  The water content in the soil and the ability of the soil to deliver water to the roots also determines the transpiration rate.  Additional soil characteristics like waterlogging and salinity also affect transpiration.  Finally, the transpiration rate is influenced by plant characteristics and environmental aspects.

As you can see, there are many variables to calculating a plant’s water requirements.  That is why landscape water budgeting involves complex mathematical equations – much more than just programming 5-minute intervals, two or three times a week, into your irrigation controller.

Read more in our Science & Technology section to learn more about parameters of landscape water budgeting.

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