Stem Water Potential calculator app

This free app is designed to help almond and walnut growers determine when to irrigate their trees. The app calculates the ideal stem water potential of a fully-watered crop of trees based on weather inputs, and compares these ideal values with those measured by the grower on their own property. It then advises when irrigation is required.



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Who this tool is for

Almond and walnut growers with access to an Apple mobile device. The tool was created for US growers, but it is equally applicable to Australian and other international growers. 

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Questions this tool answers

  • How water-stressed are my trees?
  • When should I irrigate my trees?
  • How much water do my trees need?

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What this tool does

When a plant is water-stressed, it is experiencing a deficit of water; this deficit is known as the water potential of the plant. 

A stem water potential (SWP) reading tells you the water deficit across an entire root zone, incorporating both soil and environmental factors, to give you an accurate picture of a tree’s level of water stress and irrigation requirements. 

Understanding a plant’s SWP can help you refine your water-management system and irrigation and can supplement soil- or evapotranspiration-based irrigation scheduling.

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  • Select the type of tree you have (i.e. almond or walnut).
  • Enter values of temperature and relative humidity – these can be taken from the nearest weather station or can be pulled in through the app.  
  • Enter the SWP of your trees, which you can measure with a plant pressure chamber.

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Based on the values you enter, the app estimates the ideal SWP reading of a well-watered crop of trees in your region, then offers advice for your next scheduled irrigation (whether you need to irrigate and, if so, how much). The app also gives you weather forecasts for the next seven days.

Results are displayed in the app, and it allows you to email a PDF report of your results to yourself.

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The app was developed by Ignacio Porris Gomez from the University of California’s Lampinen Lab.

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Support available

For further information, contact the app developer, Ignacio Porris Gomez, by email at

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Where to get it

The app is only compatible with iPhones, iPads and iPod touch devices (i.e. it is not currently available on Android platforms).  

It can be downloaded for free from the iTunes App Store.

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            [topic] => When to irrigate almond and walnut trees
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            [summary_region] => Murray River corridor
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JRegistry Object ( [data:protected] => stdClass Object ( [pathwaypage] => 0 [pathwaytype] => 1 [scale] => [topic] => When to irrigate almond and walnut trees [member] => [cost] => Free [summary_commodity] => Almonds and Walnuts [summary_region] => Murray River corridor [tabledisplayscale] => 0 [tabledisplaycost] => 0 [tabledisplaytopic] => 0 [tabledisplaymember] => 0 [tablesubpagetitle] => Page ) )

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