Evapotranspiration Rate (ET) is a good method to plan for future irrigations, evaluate past irrigations, and to gauge irrigations in progress to make sure they make sense.

ET rates are calculated using several weather values and gives an indication of how quickly water is leaving the soil-plant system. These values are adjusted to reflect specific crops by applying a crop coefficient (Kc).

While we give apply the regional Kc model for your crop and area, you may have a better model, or you may wish to adjust the ET rate to account for irrigation efficiency losses, cover crops, late-season croppings, or low water use in immature permanent crops.

The steps below show you how these adjustments can be made.

How to change Kc Model

5. On the next page you can select from Kc models that are already in the system.

6. Or you can use the slider to the right to increase or decrease the selected ET value by the percentage you choose.

For example, if you wanted to account for irrigation efficiency losses, you may want to increase your ET measurement by 10%, thus you would slide the selector to 110%. Or, if you had 3rd leaf pistachios, you may want to only account for 30% of ET, thus you would slide the selector to 30%.

7. After you have made the changes you wish to make, select “Save Changes” at the bottom right of the screen.

Creating a Custom Kc Model

2. Select "Evapotranspiration" from underneath "Water Management".

3. Select "New Kc Model"

4. In the next window, name the new model,

5. Select the Organization and crop it will apply to.

6. Create your custom model by adding new data points for each time period and the appropriate Kc value.

7. When finished, save the model by selecting, "Create Kc Model".

You have created the new model. This new model can now be selected from the list of models available on that property. (See above for steps to follow.)