The agriculture authority in my area is Texas A&M Agrilife Extension. When calculating water requirements, in addition to factoring in Potential Evapotranspiration (ETo) and Crop Coefficient (or rather what they call Turf Coefficient in the case of grass or Tc), they use a Quality factor. Their reasoning is that the standard formula for water requirements (ETo x Tc) maximizes growth or in their words “maximizes grass clippings” and what you really want is a healthy green lawn using as little water as possible.
They therefore use a Quality factor (Qf) and define water requirements as ETo x Tc x Qf. They specify the following table of values for Qf, depending on the quality of turf you are willing to live with:
Quality Factor (Qf)
|Very High Stress||0.4|
This is likely one reason the watering times I receive from their WaterMyYard app are consistently about 1/2 what the Rachio 3 is scheduling. I assume they are probably using a Quality factor of 0.6. Their app also utilizes local weather parameters to calculate irrigation requirements and reports it to me weekly. I used it for a number of years prior to buying the Rachio 3 with pretty good results. (Just hated having to manually adjust the run times each week.)
I am considering multiplying my Crop Coefficient in the Rachio 3 using the above chart and see where it gets me. Thoughts? Experiences?
Thanks in advance all.
For those interested, see TexasET Network (tamu.edu) and select “ET and Weather Data–>Turf Coefficients” from the drop down menu.