Sprinkler packages and nozzles must be carefully chosen to keep instantaneous irrigation application rates below average soil intake rate (infiltration rate). The instantaneous rate is not the planned total application (say 1 inch per irrigation). It is the application you would feel if you were standing under the system. That may be one-twentieth of an inch per minute or less. It seems like a mist at first, but you quickly become soaked. So do soils. Intake rate of soil is high if the soil is dry. As the surface wets during irrigation, intake slows dramatically. If the application continues above the slower intake rate runoff results.

Sprinkler systems were originally designed to spread water out large distances to lower the instantaneous application rate. That led to droplets that partially evaporated before the reached the soil, and fine droplets drifted away in a light breeze. Using spray nozzles with larger droplets that don't spread as much reduces the evaporation and drift, especially when they are placed closer to ground. However the smaller pattern means that the instantaneous application rate is increased. Runoff is more likely to occur, especially near the end of center pivots where spray patterns overlap.

Even systems properly designed to distribute water uniformly at rates below the average soil infiltration rate may have runoff problems. Soil and crop or residue cover change throughout the growing season. Bare soils created by clean tillage and planting are particularly vulnerable to soil crusting. A single rain shower, or even an irrigation, may create a crust. With crusts a thin layer of sand and clay forms a tight layer 1/4 to 3/4-inch thick. Infiltration through the crust is less than in other conditions, and the crust may impede emergence of newly germinated plants. During subsequent irrigations, water that doesn't penetrate the crust runs off.

Compaction from wheel traffic is another common cause of runoff. Even one pass will compact as much as a one-foot layer of loose soil into a dense layer that has low infiltration. Subsequent passes make the problem worse widening the original tracks or adding new tracks in other beds. The wheel tracks provide ideal channels for irrigation water to runoff rapidly through or away from the field. Tracks from pivot tower wheels causes a similar problem, although the area affected is less extensive.

Regardless of the cause, less rainfall and/or irrigation will infiltrate, less water will be available to the plants than planned, distribution will not be uniform, and irrigation water will be wasted.