There's a gallons per plant per day formula that delights college mathematics majors, challenges determined agricultural specialists and terrorizes those of us that squeaked through high school algebra. However, this formula can be brought to its knees with a few simple tables and a pocket calculator.
The formula looks like this:
Gallons Per Plant = .623 x plant area x plant factor x P.E.T.
Per Day The decimal equivalent of drip irrigation efficiency for the given climate type.
But I Prefer:
If you have all your field data concerning the job site, the following pieces to this puzzle fall together easily.
The constant of .623 is a conversion factor that reconciles the plant area which is in square feet, the P.E.T. which is in inches per day, with gallons of water which is part of the answer we are after. If you are really interested, here's how that number came up.
One cubic foot of water equals 7.48 gallons (someone measured it). If you take a one inch deep slice off this cube you have one square foot of area and one inch of water depth and. .623 gallons of water.
For the climate variable in the formula, if you don't have the precise P.E.T. rate for your area, table "A" below has the information necessary to help you select a ballpark figure.
P.E.T. stands for potential evapotranspiration. Evapotranspiration is defined as the loss of water from the soil both by evaporation and by transpiration from the plants growing thereon. Table "A" shows this potential range in inches per day for various climate types.
*"Cool" equals under 700 F as an average mid-summer high.
"'Warm"' equals between 70 degree and 90 degree F as mid-summer highs.
"Hot" equals over 90 degree F. "Humid" equals over 50% as average mid-summer relative humidity (dry=under 50%).