Volumetric Water Content vs Available Water

According to my Web Soil Survey, my soil is a loam with 0.15 in/in available water.

My Rachio 3 says all my zones are at zero percent, but it just rained for 4 days here (SW Montana) so the ground is definitely saturated.

I have a soil moisture meter that reports Volumetric Water Content (VWC) as a %.

I’ve read on a few University Agricultural Extension sites that vwc can be calculated as 75% vwc = 0.75cubic inches of water/cubic inch of soil. That would be way more than the available water though.

How would I take my VWC reading and relate it back to available water? I am trying determine if I should hit “Fill” so my Rachio will adjust watering.

Is this a new controller? They start off only measuring what they applied from the day installed. So it will fill the system. In the advanced settings for each zone you can increase the available water up to an inch for new installed.

No. It’s been in a year, but I did an update on my WiFi so I did a full reset on the controller.

I found out I live 2 blocks from a USDA office and went in to ask this same question, and so I’ve got it about figured out.

For anyone reading…

The “inches water/inch soil” reported is the amount of water from feild capacity to permanent wilting point; aka, soil is wt but the grass cannot access it.

Long story short, imagine a lot of soil. Water it untill it’s soaked and dripping. That’s saturation, aka 100% VWC. When it’s done dripping, you’re at feild capacity, usually 50%-ish. Now there is a range where the plants can access that water, this is the “inches/inch” you’re loading into the app.

So, to answer my own question, I need to dig up some soil, dry it out in an oven, weigh it. Add water until at saturation. Let it get to Fc, measure it with my probe. That’s 100% for my Rachio in my zones. From there, I can relate it back to the WSS inches per inch.