minutes the duration of the second and subsequent cycles are progressively decreased the second cycle may have a duration of 18 minutes the third cycle 16 minutes etc when the valves 14 are divided into two substantially equal sets the percentage cutbacks in water during the stage of the irrigation wherein the valves in the two sets are alternately turned off and on is 50 i e total flow of water per increment of time is 50 of the total flow if all valves were open continuously various other percentages of cutback can be achieved by varying the duration of the on and off portions of each cycle for example if all the valves are operated as one set i e all the valves are simultaneously opened and closed the percentage cutback can be controlled by varying the ratio of duration of the open and closed portions of the operating cycle for a 33 cutback the time duration in which the valves are open is twice the time duration in which the valves are closed to achieve a more uniform draw of irrigation water from the source thereof the valves 14 are divided into sets such as the two equal set arrangement as described hereinbefore for a system utilizing 33 or 66 percent cutback the valves 14 are divided into three sets with substantially equal number of valves in each set for 33 cutback the valves are operated in repeating cycles wherein each cycle comprises three stages in the first stage the first and second sets of valves are open and the third set of valves is closed in the second stage the first and third sets of valves are open and the second set of valves is closed.