If you've been following the soil moisture stuff I've been playing with you will have seen me referencing many others' work, both hobbyists and pros. This isn't new stuff, though it's poorly documented on the 'net and hard to find.
It turns out there's a mailing list dedicated to the topic - but you'd be really, really lucky to find it. Check the archives out here, they're seriously informative:
The group moved from its old hosting to Google Groups a while ago, but the best stuff is in the old archive on sowacs.com. It's a bit patchy, frustratingly, and there don't seem to be mbox files of the archives to download, but it's still very informative.