Olive Irrigation Formula for drip lines

Okay, here's what I'm doing.  The state of California has weather stations which calculate the daily evapotranspiration (ET) of a known water intensive crop, in the case of our local station in Diamond Springs, a cover of grass is monitored (ETo).  Each day a number for ETo is given which represents the water losses for that grass.  Yesterdays was .31 inch.  That is the amount of water required by that  crop for the conditions present such as temperature, wind, cloud cover, etc, which need to be replaced.  To convert the number to the amount an olive tree uses I need a conversion factor.  This is published and remains constant during certain yearly growth stages.  The number is .75 and is represented by (Kc).  Meaning an olive tree requires 75% of the water that the grass (ETo) does.  This new number is the ETc for olives.

I also need to take into account the size of the tree.  Basically I find the diameter of the tree canopy, square it and multiply it by conversion factor of .7854 to get the area (A).  For example our trees are averaging about a 4' diameter, so 4(4).7854 = 12.6 sq. feet

Also since the formula I use needs to reconcile the Area and ETc  (ETc = ETo X Kc) which is given in inches to gallons, I use a conversion factor of .623

The formula is as follows:

Gallons/tree/day =  ETo(Kc)A(.623) / .9

The .9 is the efficiency of the water delivered via drip lines.  It is the most efficient value for any water delivery system.

So to water I do the following: 

                                       .31(.75)12.6(.623) / .9  =  2gallons/tree/day

 So every tree, were it fully grown at this size, requires 2 gallons.  Since these trees are still small they will require ~30% more water to make up for loss of shade and wind protection afforded by larger trees, and to make up for my poor weed control.  That bumps me up to around 3 gallons a day.  

I water every other day in the Summer which comes out to around 6 gallons.  Since I have two 1 gallon/hr emitters a tree, I simply divide the total gallons needed by 2 to get my run times required to keep healthy growing trees.  

We'll talk about a controlled defict for for fine olive oil production later.  Right now these trees are new and I want them growing.

Keep in mind this is a basic formula and their are many other ways to take into account a plethora of variables to further fine tune your irrigation needs.

Resources

Californis Irrigation Management Information System (CIMIS)

Mike Terrell, WSU, Master Gardeners

Drip Irrigation Formula

Olive Irrigation and problems