Corn crops in the lower Southeast states of Alabama and Georgia looked promising as growers headed into the critical month of June.
“We’ve had some cloudy weather, and that’ll undermine some of our crop, but as I travel around the state, it’s probably the best crop I’ve seen in a long time,” said Dewey Lee, University of Georgia Extension agronomist.
On May 29, Georgia corn producers reported that 27 percent of the crop was fair, 49 percent good, and 20 percent was in excellent condition. In Alabama, 27 percent was fair, 63 percent good, and 8 percent excellent.
Now, it’s up to producers to help finish out the crop, and this is where irrigation strategies become important, says Lee. Of all crops, corn responds best to irrigation, he said during a recent Alabama Cooperative Extension System Corn Management webinar focusing on irrigation.
“Depending on the year, corn is likely to average nine to 10 bushels per inch of irrigation,” he says. “The challenge in watering corn is determining when water has declined sufficiently to impact your yield and applying that water in a timely fashion.”
If water supplies are limited, a pre-planned application can protect your yield, says Lee. “At $6 per bushel, if water costs you $6 per inch, it only takes two bushels to pay for irrigation. If you have water, use it.”
He noted that a south Georgia corn grower made 364 bushels per acre in 2011, “and he did it because he managed the crop all season long, and he managed it through his irrigation system.”
In situations where water is limited, three well-timed applications can protect your yield, he says.
“Target your irrigation at tasseling, pollination and early grain fill. There are 18 to 20 days from tasseling to early blister that are highly critical, and you can make 50 to 60 percent of your total yield during that time if you haven’t had four weeks of vegetative drought.
Keep plant moving
“If you’re going through that type of drought, use one of your irrigations during that time to make sure you keep plant development moving. Water again at tasseling and then at blister and early grain fill.”
Producers need to take a more holistic approach to corn irrigation, says Lee.
“One of the important things is getting water to the crop area and to the crop area only. With today’s technology, we can use end-guns to expand the pivot or area and also to cut it off when we get towards roadways and other areas that don’t need water,” he says.
Lee says it’s troubling to see center pivots in parts of Georgia and Alabama that cover 150 to 200 acres.
“Whenever we have that many towers, it’s important that we don’t put that full pivot strictly over corn. We need other crops under there because the critical water demand period for corn is going to be earlier than that for cotton, peanuts or soybeans. By splitting it, you can apply water on corn early and often and not be limited by your application and application efficiency.”
Growers today have access to shut-off technology for extremely wet areas and they have variable-rate technology, notes Lee. These can be important in minimizing drip and evaporation. Some producers also are using subsurface drip irrigation tape, especially for irregular-shaped fields.
“The question is whether or not subsurface drip is good enough to use in multiple years. We’re exploring that now, and the jury is still out. If you’re a dryland producer, I think we can smooth out some of that variability from year to year with drip tape.”
With subsurface drip irrigation, there are no drip or spray losses, and 100 percent of the water gets into the soil, he says. However, the leaching capacity is greater, and you don’t get a wet surface.
“So you can’t use subsurface drip to get germination, to activate herbicides, or to dissolve fertilizer, and that’s the disadvantage. The advantage is that it’s highly efficient and be used in irregular-shaped fields. But if you place it too deep, you reduce the impact on your water and your yield.”
It’s important, says Lee, that growers get water into the root zone and not behind it. “There are new devices that can help you understand water use in the ground and prevent you from allowing the subsoil moisture to become dry. They maximize irrigation and water use efficiency.
“The prices of some of these tools are declining. They help us just as a tool, and we can use them in different soil types to help us become very efficient in how we water our crop.”
No problem with drop nozzles
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.”