Is a variable citrus crop coefficient (Kc) possible?


I’m a new Rachio 3 user, and am currently familiarizing myself with setting up zones with a view to using Flex Daily schedules in the near future. I live in Tucson, AZ where the soil is sandy/rocky/caliche and mid-desert conditions prevail (20’s to 100’s). In this environment, we are mostly growing xeriscape trees and shrubs, also palms, but also some citrus trees (which do quite well here given enough water).

My question is about the latter. I will need to use the advanced zone settings for at least some of my zones, and see that there is only one setting for crop coefficient (Kc) for a given zone. Per the University of Arizona Cooperative Extension, the Kc for citrus here varies by month, from 0.5 (Nov-Feb) to 1.0 (Jul-Sep). Note that this assumes E (class A pan evaporation) = ETo x Kc. So the UofA Extension’s recommendation cannot be met by merely having the Rachio 3 look up the daily predicted ETo and multiplying by a single Kc value. The doubling of the crop coefficient from winter to summer (because of our wide temp range) does not lend itself to picking a single average value and using that all year around.

So my question is whether there is a way to set up a Flex Daily schedule for my citrus trees that can handle a variable Kc, or whether I will need to tweak the crop coefficient 5 times per year?


There is no way that I know of to automate changes to the Kc. I don’t think setting Kc is exposed in the webhooks API. I use reminders or calendar events to remind me to change my Kc on a monthly or seasonal basis (if necessary) for my citrus and stone fruits. In California, the stone fruits really benefit from monthly adjustments (large seasonal swings too) while the citrus only require minor adjustments usually ±10% around 75%.

Thanks @Kubisuro. That’s what I was suspecting.

It would be a nice enhancement at some point to allow multiple monthly coefficients for those crops that have a widely-ranging seasonal Kc.

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