The severe drought plaguing Nebraska the last 14 months may have some agricultural growers looking at the possibility of fall irrigation to refill or partially refill the soil profile.
However, two University of Nebraska irrigation experts recommend not irrigating this fall, despite dry fields. The NU Institute of Agriculture and Natural Resources experts say to wait and see what the off-season precipitation will be this fall and winter and assess the need for irrigation next spring.
Irrigation specialists Bill Kranz of Norfolk and Dean Yonts of Scottsbluff agree the potential for off-season precipitation looks good. If the state receives average precipitation this fall and winter, additional water from fall irrigation could result in deep percolation of water and push nutrients below the root zone.
And if the off-season moisture doesn't come, Kranz said, usually there will be enough time to refill the profile close to capacity next spring using center pivot irrigation.
Al Dutcher, NU state climatologist, said predictions show from now through spring, there are equal chances of receiving above normal, normal or below normal precipitation and temperatures.
"We may be going more toward a normal pattern," he said.
However, "based on the current weather patterns, we (could) see a winter of extraordinary extremes and tremendous swings in temperatures," Dutcher said.
Yonts said average annual precipitation varies significantly in Nebraska, ranging from less than 15 inches in the west to more than 35 inches in the southeast. Most irrigated fields have an estimated 3- to 4-inch depletion of the soil profile. Refilling that profile should be possible next spring.
"We probably have drawn quite a bit of the moisture out of the soil, but (not irrigating this fall) is recommended and with the forecast it's best to wait," Yonts said. However, irrigation certainly would be needed for those trying to establish a fall cover crop, Yonts said.
If fall irrigation is used, the only real advantage is the insurance of a fall soil profile. The disadvantage is the risk of over applying water.
Soil type also plays a role, Yonts said. Heavy soil, such as loam soils, can store an inch or more of water in a foot of soil that is available for the plant to use without stress. Coarse or light-textured soils may hold only a half-inch of water in a foot of soil that the plant can easily use.
In addition to soil type, the irrigation system also plays a role. If using furrow irrigation, although not recommended this fall, a late fall irrigation would require less labor if the pipe is still in place and ready to use, compared to next spring before, or soon after, the crop is up, Yonts said. However, furrow irrigation tends to refill the soil profile and leaves little room for additional water without the threat of deep percolation.
With center pivot or sprinkler irrigation, only a portion of the soil profile may be filled, leaving room for later precipitation. Irrigating in the spring when the amount of water needed is known will be more cost effective, Yonts said.