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Irrigating during a drought

10/01/2012 @ 1:14pm

Does it do any good to operate a center pivot during extreme weather conditions such as high winds, high temperatures, and low relative humidity?

That depends, says Bill Kranz, a University of Nebraska irrigation specialist. It depends on your irrigation system's capacity and type of sprinkler package used on the pivot.

“If your system has a limited capacity, it is likely better to continue to apply water even though you may have 15% evaporation and drift from high-pressure impact sprinklers,” Kranz explains.

High wind and watering

Regarding the effects of sprinkler types, Kranz says if your pivot uses coarse- or medium-groove deflection pads, your evaporative loss will be minimal since most droplets are large enough that little evaporation occurs even in very windy conditions.

“The small droplets you get on your windshield driving downwind of a pivot don't amount to much of the total application occurring in the field,” he says. “However, windy conditions do impact water-application patterns. I often suggest that producers limit the amount of time the system operates in windy conditions.”

Another way to limit the impact of wind speed is to stagger the start times so water is applied to a specific area of the field at different times of the day.

One aspect of pivot design that can result in nonuniform water application is sprinklers that are too widely spaced. Spacing issues can be exacerbated by positioning sprinklers to operate within the crop canopy.

Unfortunately, this problem often is not obvious and may only become apparent during extremely dry weather, when continued nonuniform water application results in dry areas between sprinklers.

Nebraska irrigation specialists determined this from aerial photographs of pivots that showed well-watered and underwatered rings when sprinklers were placed in the canopy.

Overhead nozzle effects

When sprinklers are operated above the canopy, the overlap between patterns is usually adequate, but it may become limited once corn grows above the sprinkler height.

Research indicates that if sprinklers are located too far apart (generally greater than 7½ feet apart), you may have dry rings around the field, and their impact may not always be visible. This phenomenon will increase as the pivot makes more and more circles. The wet areas will have normal growth, while the dryer areas will be shorter in stature, and yield may be affected. A University of Nebraska study found yields in the dry areas were 20 to 40 bushels less than in the well-watered rings. Early-season precipitation will mask this effect during vegetative growth. But later in the season, it may affect yield.

“Unless you go out and look, your yield monitor will not pick up the difference in yield as it takes in both the well-watered and underwatered rows together,” Kranz explains. “After an application, go into the field and use a soil probe to check several consecutive rows that are perpendicular to the length of the pivot. If one row is extremely wet and the next is almost dry, you have application issues.”

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