The information below came for the Internet site directly below.  It is reprinted here because sites sometimes disappear or are moved.  It is obviously Toro information, and it came from www.geoflow.com. Geoflow Inc. is a company that specializes in subsurface drip irrigation.   

http://www.geoflow.com/landscape%20%28inclu%20golf%29/toro/irrigation.html#Irrigation scheduling

Irrigation scheduling with subsurface drip uses the same methods of calculation as above-ground irrigation. The subsurface grid system is designed to wet the irrigated area completely by methods similar to those used in above-ground irrigation, supplying water in inches per hour. For efficient water application, it is necessary to apply water rates equal to or less than the rate at which the plants use water (evapotranspiration rate; ET). The ET rate is expressed in inches per unit of time, thus our application rates are expressed in inches per hour. (For regional ET data, refer to the Toro Rainfall and Evapotranspiration Data Book, Form No. 490-1358.)

The following formula is used to determine application rates for subsurface drip irrigation.

Application rate (inches per hour) = 231.1 x Emitter flow (GPH)
Dripper spacing x Dripline spacing (in inches)

For example: Dripline row spacing = 12"
                     DL2000 emitter spacing = 12"
                     Emitter flow rate = .53 GPH

       231.1 x .53 GPH =    0.85 inches per hour
12 (inches) x 12 (inches)

Or, use the Water Application Rate Table below to determine application rates.

Click here for Table 3.1

Zone Run Time Scheduling Worksheet

To determine zone run times, obtain the following information:

n monthly evapotranspiration value for the location

n irrigation application rate
(For regional ET data, refer to the Toro Rainfall and Evapotranspiration
Data Book, Form No. 490-1358.)

The following formulae can be used to determine run times.
Run time per week = Weekly evapotranspiration rate
                                  Application rate

 
Run time per day = Run time per week
                               Days per week

 

* The number of zones may vary depending on the specific needs of each installation.