Uniformity of spray also is extremely important, he says. Nozzles on drops can be dragged through mature corn with few problems.

“But even before corn grows tall enough, the uniformity of a package sometimes is reduced. It’s good to see some of these older pivots change from the impact to the drop nozzles because you’re reducing the amount of evaporation, and even though uniformity of spray may not be quite the same, we need to be getting it into the soil.”

Some growers prefer to apply fungicides, insecticides or fertilizers through their systems, says Lee, but it depends on how old your system is as to how effective you might be with fertigation or chemigation.

“The impact sprayers tend to have an advantage in that area, but we also lose a little water simply because of evaporation. If you’re trying to put down 8/10 inch of water, you have to consider the evaporation plus the evapotranspiration that’s occurring in the plant.

“Sometimes, a grower will mistakingly think he’s put out 8/10 of an inch just because that’s how much he has on the ground.”

Getting water to penetrate deep enough into the root zone without leaching out is a very important consideration, says Lee. Knowing water-holding capacity and current water content takes time to learn, and you have to match the soil with your irrigation capabilities.”

“It’s harder to move water into and through a dry soil than a moist soil. Some growers think that if they let the crop dry for awhile, the roots will go down into the soil and seek moisture. That’s not true with corn.

“If the subsoil ever begins to dry out, it’ll be extremely hard to catch up. It’ll confuse the corn crop. For intake efficiency, it’s very important to monitor that top 4 to 6 inches, 6 to 12 inches, 12 to 18 inches, and 18 to 24 inches.

“Corn growers can make irrigation more efficient by using soil sensor technology or a checkbook method,” says Lee. Programs are available such as IrrigatorPro and the simple growth-stage Extension model, he says.

“These programs help you to know what your crop is using on a daily basis and to know the rainfall you’re receiving. If you do a really good job of keeping up with it, you can nearly match what a sensor does. There’s not a lot of yield penalty in checkbook versus soil sensor technology.”

In the first week, says Lee, the estimated water use of corn is 2/10 inch. As those leaves are expanding, the amount of water use is expanding.

“We lose yield whenever we lose dry matter — we’re not growing as big of a plant. There’s a big relationship between corn plant size and grain yield. Don’t be afraid to water early and often.

“By the time you get to the V7 stage, the tassel is developing, you’ve used up at least 5 inches of water, and you’re beginning to see a rapid change in how water use is taking place. If you’ve got a moisture-holding capacity of 1 inch, you’ve got less than five days’ supply of water, at 2/10 inch per day, so you need to stay on schedule.

“Once roots get down into 12 to 16 inches of soil, it’s easy to exhaust that supply. As you get into expanding those, it’s harder to catch up.

“At V16, where you’re getting closer to 3/10 inch of water per day, the crop will pull water at least 18 inches deep. At that point, you can never catch up if you get behind.”

“If you have limited water supplies, such as a cable tow or hard hose, then you need to be irrigating corn during the plant’s most critical phases, says Lee.

“Corn irrigators vary their use between none maybe up to 30 times a year, depending on the rainfall during the season.

“Sometimes, we’re creatures of habit. Using sensor technology or a checkbook is as important in a wet year as in a dry year. At black layer, the crop is still pulling out about 2/10 of water per day.

“You want to maintain a good water supply. When the stalk is slightly green, it harvests so much better than when it’s completely dry, and there aren’t nearly as much harvest loss.”

phollis@farmpress.com