wireless soil moisture sensor?

Has anyone seen a wireless soil moisture sensor for use with sprinkler system?
I have a rain sensor that defeats the timer if rain is falling, and I've seen a one like it that also has a wind sensor. I'm looking for something similar that senses soil moisture.
Ideally (yeah, yeah, I know), I could set the system to water every day, then let the sensor override every day until the ground gets dry enough to need water. I've found lots of commercial products, but I'd like to avoid either trenching 150' or running a wire under 50' of concrete.
I'll keep my fingers crossed that someone has seen something that I missed, but I won't hold my breath.
Thanks,
--
Steve B.
New Life Home Improvement
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