The term boomback doesn’t seem like it would be related to center pivot irrigation. But boomback products have been used on center pivot and linear move equipment for more than 30 years. Their function is to reduce the sprinkler package Instantaneous Application Rate (IAR) on the soil. This will eliminate or reduce water runoff, increasing the application efficiency of the equipment.
The IAR, typically measured in inches/hour, of a center pivot gradually increases from a very low value near the center point to a high value at the end of the machine. Another way to describe IAR in terms of rainfall is the area near the center point is a light drizzle and the area at the end of the machine is a heavy rainfall. If the IAR exceeds the soil infiltration rate, runoff will occur.
Studies done by research facilities show that using Boombacks can reduce runoff. The recent study “Efficacy of Boom Systems in Controlling Runoff under Center Pivots and Linear Move Irrigation Systems” published in Applied Engineering in Agriculture by Troy Peters, an extension irrigation specialist at Washington State University, found that boombacks can reduce runoff by 24 percent. (Find the full study here.)
Field conditions with heavy soils and/or slopes are examples where boombacks are frequently used. A typical installation will have boombacks fitted on the last 25 to 33 percent of the center pivot length.
A boomback is designed to place a low pressure sprinkler 12 to 15 feet (length depends on the manufacturer) away from and perpendicular to the span pipeline. This effectively increases the footprint of the sprinkler package water pattern 24 to 30 feet, decreasing the IAR. Boombacks can be installed using one per sprinkler position, alternating them on each side of the span pipeline in successive sprinkler positions, or two boombacks per sprinkler position, one on each side of the span pipeline at each sprinkler position.
Another function of boombacks is to use them with part circle sprinklers near a drive unit. In this application, the boombacks are all placed on the same side of the span pipeline opposite the direction of travel.
For part circle center pivots and linear machines, double boombacks are available with specialized control hardware to turn on the correct sprinklers based on the direction of travel.
Keeping water away from the wheel track area as the machine moves through the field, will reduce rutting and the possibility of drive wheels getting stuck.