Well, from a bean counter's POV, one could develop a statistical correlation between the changes in watering schemes and variations and time lengths of weather patterns. In my situation, this may require a few years of data acquisition since I'm only watering at most five months out of the year.
Here saw my progress over the years based on old and new satellite pictures. IE: I have Terra server pictures which I utilized to see.
Initially here did much infrastructure stuff relating to run off et al and eating top soil stuff. Concurrently also added mechanisms of recording stuff. Primarily it was all 1-Wire stuff.
The software evolved a bit originally running it as a plugin for Homeseer. I had so many connections to the software went to running it independantly from Homeseer. Mostly though with all the doo whats of analog connectivity mixed in with historical values and internet live values the irrigation is based on ET values.
Yea, I'm sort of expecting some wacky numbers etc. Thus, the reason I'm starting with a pilot project of only three zones. As you would say "baby steps". The upside is that there are quite a few soil moisture sensor modules on the market and they're all relatively inexpensive. Maybe, just maybe I might be able to find a very reliable sensor. Every project sounds great in theory but in my experience, actual implementation often provides a lot of unexpected gotcha's.
Really you would have to have hundreds of reliable sensors maybe to come up with some good numbers unless your topology is all the same, top soil is the same, et al.
Have a look:
Chapter 5 - Introduction to crop evapotranspiration (ETc)
Following soil wetting, the vapour transfer rate from the soil is high, especially for crops having incomplete ground cover. The combined surface resistance of the canopy and of the soil determines the (bulk) surface resistance, rs. The surface resistance term in the Penman-Monteith equation represents the resistance to vapour flow from within plant leaves and from beneath the soil surface.
Ideally then if you take your local analog values, mixed historicals, area weather values, UV / solar et al you can guesstimate how much water you need to have a nice lawn.
So far what I am seeing with the internet connected irrigation controllers is mostly the ability to remote control your irrigate with a smart phone which really doesn't automate your irrigation. They haven't figured out the smart pieces of the irrigation and just attract customers with the eye candy.
Old irrigation companies are now offering smart irrigation controllers which sort of work but still depend mostly on external resources which at best will give some very round numbers. Here started by installing a Rainbird system years ago.
I did totally take apart and had a look at the original analog timer. I didn't bother with it and replaced the the solenoid control with a couple of Rain8Nets in the early 2000's. From here went to software serial control of said valves. Basically the more sensors I added and the more historicals and internet data I added the better the irrigation got.
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How does the ESP-SMTe Save Water
The ESP-SMTe integrates technology used by top golf courses for decades and puts it into a user friendly controller.
- On-site rainfall data - The ESP-SMTe collects site rainfall amounts and uses this information to re-calculate run times for each zone.
- Historical weather data – The internal memory of the ESP-SMTe contains over 8 years of historical weather data. This data, along with the onsite rainfall and temperature information is used to adjust the watering schedule on a daily basis.
- Reduced water run-off –The ESP-SMTe Cycle and Soak™ feature allows the controller to adjust zone run times based on soil conditions and slope to reduce/eliminate water run-off.
