Irrigation Calibration Update- for Animal Waste Operators

Eve H. Honeycutt, Extension Livestock Agent, Lenoir and Greene Counties

Recently, NCSU Specialists in the Department of Biological and Agricultural Engineering announced that using rain gauges to perform an irrigation calibration is no longer necessary for swine farms in NC.

Calibration of the irrigation system is still a requirement under the State general permit, and it must be performed every other year. Previously, NCSU and NC Soil and Water guidelines stated that using the rain gauges to test for uniformity was recommended every 3 years. New guidelines have been established that recommend rain gauges no longer be considered an acceptable method of calibration.

Acceptable methods of irrigation calibration include using a flow meter, and performing a field calibration. Using the flow meter is easy and only requires that the flow meter be properly connected, then the user reads the flow rate that shows up on the meter. Proper documentation must be kept as a record of the flow meter use. There is a flow meter for rent in the Greene County Extension office for $25. Anyone can rent the meter by calling 252-747-5831.

Performing a field calibration is also easy and does not require any specialized equipment. Three measurements need to be recorded- the wetted diameter, the nozzle/ring size, and the pressure at the gun. To measure wetted diameter, turn the system on and measure the diameter of the spray area. For ring/nozzle size, you may find the size stamped on the end of the nozzle. If you can't find it, you should measure it accurately with a pair of calipers. Finally, make sure you have a working pressure gauge at the gun and record the pressure with the system in operation. Once you have these three measurements, you should look at the manufacturer's performance chart for your equipment. It can be found online, or with the help of your Extension agent. The chart, along with your measurements, will help you determine the flow rate for your equipment. All of this data should also be documented for your records.

Having your irrigation system calibrated ensures that you are applying your nutrients at the proper rate. It is also a requirement of your permit, so don't forget this important procedure as you prepare for the fall season.