Wisconsin farmers reported irrigating about 497,000 acres of land on 2400 farms for a variety of crops with vegetables, potatoes, sweet corn and grain/seed corn being the largest segment covering 87% of the irrigated acres. Sprinkler type irrigation accounted for 97% of the irrigation systems used, of which center pivot systems make up 86% of the sprinkler systems. Irrigators reported that 31% of the systems were operated at high pressures, 54% were medium pressure systems and 15% were low pressure systems as reports in acres irrigated. Irrigation pumps were powered by electric motors on 73% of the pumps, diesels engines on 24%, Gasoline engines on 2.6% and less than 1% were powered by LP or natural gas engines. Reducing center pivot system pressure from high pressure (greater than 60 psi) to medium (50-60 psi) or to low pressure (about 30 psi) can save approximately 15 to 20% and 30% respectively. With new sprinkler technology, most of the high pressure systems can be changed to medium pressure systems and a few to low pressure systems.

Testing of irrigation systems should be done every 2 to 5 years to ensure proper operation. Uniformity testing measures how evenly the water is spread on the field and helps identify worn nozzles, improperly installed sprinkler packages or leaks. Pump/well testing will check that the pump is operating properly, providing the expected pressure and water flow and can uncover issues such as an engine that needs maintenance or if the water level in the well has dropped causing the pump to cavitate. A pump / well test is good insurance that the pump will work when needed during the irrigation season.

Irrigation scheduling is another management tool to aid in identifying when irrigation is needed. Irrigation scheduling can usually reduce irrigation by one or two events per season, saving water and energy. In some cases, growers may not be starting irrigation soon enough or not applying enough water, irrigation scheduling can help identify when that is happening. For more information on irrigation, go to the UW-Extension Crop Irrigation web page.

Irrigation Testing

Uniformity Testing

Uniformity testing is a troubleshooting procedure to check that the water distributed by the irrigation system is being applied uniformly to the field within practical limitations. The test procedure only measures the amount of water applied to the soil surface and is not intended to indicate the amount of water that infiltrated the soil into the root zone. Evaporation, runoff and leaching could all affect the amount of water available to plants in the root zone. A low coefficient of uniformity could lead to plant stress and disease issues because of a water deficit or too much water in different sections of the field despite the average application rate being acceptable. The goal for the coefficient of uniformity is greater than 90%. A higher coefficient results in higher utilization of water per unit of yield.

For more information on testing procedures and kits go to the Crop Irrigation web page.

Pump/Well Testing

Pump testing is another important testing procedure. It is typically done in an open discharge method were the pump is disconnected from the irrigation system and a flow meter, pressure indicator and valve is installed on the pump output. The pump is started and the valve closed partially until the design system pressure is reached. The system is allowed to run for a period of time, generally 15 minutes, and then the valve is opened and closed to obtain enough points to draw a pressure / flow curve. The static water level should be recorded as well as the water level at each flow point. The net positive suction pressure of the pump should be determined to ensure that the pump is deep enough in the well to prevent cavitation from a lack of water. Irrigation contactors or well drillers generally provide this type of testing service at a cost of usually less than $500 per test. It is recommended that pumps and wells be tested every 2 years.

For more information on pump / well testing go to the Crop Irrigation web page.

The University of Wisconsin Extension’s Crop Irrigation website has many resources that can help with understanding the basics of irrigation scheduling, types of irrigation systems, sources for equipment and tips on operation and maintenance for peak performance.

If you have questions about the information on this site, please contact
Scott Sanford, Distinguished Outreach Specialist, University of Wisconsin, sasanford@wisc.edu.