On the positive side, lowering the operating pressure of a sprinkler system can reduce pumping costs. On the negative side, lower operating pressure reduces the sprinkler-wetted diameter. Wetted diameter is defined as the distance across a water application pattern from dry soil in front of the system to dry soil behind the system. The wetted diameter defines a circular area that is wetted by a single sprinkler device and by a series of overlapping sprinkler devices. In addition to the sprinkler device selected, operating pressure of the irrigation system and height of operation are factors in determining wetted diameter.
Wetted diameter decreases most significantly with lower operating pressure.
As a result, the rate at which water is applied to the soil increases. This increase in water application rate can in turn cause runoff due to the soil's inability to take in the water fast enough. When sprinkler devices are placed much below the truss rods, and corn is being grown, in-canopy sprinkler operation results. A sprinkler device operated within the crop canopy further reduces wetted diameter as a result of crop leaves interfering with the trajectory of water droplets. Our intuition would tell us that dropping the sprinkler device into the crop canopy will simultaneously reduce evaporation.