Ian McCann, Irrigation & Water Management Specialist; mccann@udel.edu
The UD irrigation program in Georgetown, with cooperation and support from NRCS, has evaluated the performance of over 170 center pivot irrigation systems on Delmarva. There are some problems we have observed that growers can easily correct. As we enter a new growing season, here are some suggestions:
1. Check the pressure gauge and replace if broken or missing. This is simple and cheap, but improper pressure can significantly alter the performance, particularly on systems that do not use pressure regulators.
2. Take time to ride or walk the length of the system while it is operating and replace any missing sprinklers, spray plates, plugs etc. and unplug any plugged tips. Sprinkler flow rate increases down the length of the system, and so each sprinkler is sized according to the distance from the pivot. A single plugged tip at 700 ft that causes reduced or no irrigation over a 10 ft section affects an area of 1 acre over a complete circle. The same situation at 1100 ft affects almost 1.6 acres. If replacing a sprinkler or tip, be sure to use the correct size, as we have observed that incorrectly sized sprinklers are a common source of unwanted variability.
3. It is difficult to accurately determine how uniformly a pivot system is applying water, or how much it is applying at any given timer setting. The best test involves setting out cans or rain gauges every few feet along the length of the system, as we do in the evaluation program. This gives a very accurate average and also catches any points with too little or too much water. This is not feasible for most growers, but perhaps checking the volume of water in 5-10 cans or gauges spaced along the system would identify major problems and give an indication of the average irrigation amount at the particular timer setting. Manufacturers provide a chart that shows the irrigation amount at various timer settings. We have observed that charts are generally quite accurate on new and unaltered systems, and are built in on systems with programmable electronic panels. However, on older systems, especially if you have replaced some components or are running at different pressures, taking the time to find out if the system is putting out what you think it is can be a valuable exercise, particularly considering the rising cost of pumping water.