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A collaborative blog by UC farm advisors and specialists in subtropical horticulture in California.
Bush Poppy
by Verne Arnold
on September 6, 2017 at 8:01 AM
Another opportunity and teaching moment from our very own, Ben Faber.  
My practical take aways: 1). sensors placed at plant root zones effecting water absorption, and, 2). familiarity with soil sub plots; their influence and interaction they exhibit towards species being irrigated.  
Thank you, Ben
Reply by Ben Faber
on September 6, 2017 at 8:26 AM
Thanks Verne  
If I get it right, sensors need to be placed in representative sites - trees that are typical of the area being irrigated - and they need to be placed in the root zone where water is being taken up.  
They need to be near healthy trees that have a healthy root system.  
They need to be in the root zone, not where it's convenient to read. I've seen sensors that are out in the middle of an alley where there are no roots.  
They need to be in the wetted area, not outside of the wetted area.  
And when they are installed, they often destroy the immediate root system, so initial readings are not going to be accurate, because there are not roots there. It takes a while to establish a new balance once the sensor is in place.  
And to the second comment. Sensors are measuring what is at that placement point. Some can read a little further out from that spot, but most are only reading several inches at most the volume of soil around the sensor tip. So if the sensor is in a sandy part of the orchard, it's not going to tell you what's there in a spot that is in a heavier soil part of the orchard. It can reflect the rate of removal by trees of similar dimension since water removal is driven by evapotranspiration. But the sandy soil sensor wont tell you how much water is left in the heavier soil site. It can tell you for that irrigation block when is the best time to irrigate, though, for that whole block.
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