With crop planted, corn growers turn attention to potential yield

With the corn crop in the ground and, hopefully, growing, it's time now for growers to turn their attention to those practices that'll produce the highest yields possible, says Dewey Lee, University of Georgia Extension small grains specialist.

One place to start is with fertilizer efficiency and maintaining the pH for corn production in the 6 to 6.5-range, says Lee. “You maximize the amount of phosphorus and potash that'll be taken up if you have a pH close to 6 to 6.5. If you get down to 5.6 or 5.7, your fertilizer efficiency will drop to 70 percent and you'll lose money and yield,” he says.

With the basic phosphorus, potash, magnesium and zinc applied according to soil test recommendations, nitrogen should be applied according to yield goals or field capability, says Lee. “If your field is capable of 200 bushels per acre, then use a minimum of 240 pounds of nitrogen. If you're a dryland producer, and you're looking at about 100 bushels, then you'll put out 120 pounds — maybe 130 pounds on deep, sandy soil or 110 pounds on a heavier-textured soil,” he says.

If growers have the time and equipment, Lee recommends they put out 35 to 40 percent of their nitrogen at the V5 stage and 40 to 45 percent at the V7 to V8 stages, assuming that about 20 percent of the nitrogen needs were applied at planting.

“This needs to go by the row in a liquid form, but it may not be possible depending on the management capabilities of those farmers with limited labor. You may have to apply your nitrogen in a layby broadcast over the top. That's efficient, but less efficient in sandier soils than applying down by the row,” he says.

There was a time, says Lee, when fungicides were not discussed in corn production. But that has changed.

“Today, we have fast-growing, susceptible hybrids. Data in Georgia demonstrates that susceptible hybrids will respond to a strobilurin application at the tassel stages. We need yield this year, and companies are touting the yield enhancement properties of some of these products where there is no disease pressure. It's not very well understood. Data suggests that some of these strobilurin chemistries applied at a very specific time result in some yield enhancement.

“But they're sold as a fungicide, and they should be applied as a fungicide. Until this is better understood, I would look at controlling diseases on highly susceptible hybrids so we can get the most yields from it. We protect yield by protecting the stalk so it doesn't lodge as badly. If we get Southern leaf blight on a susceptible hybrid at about tassel stage, it will respond to a fungicide treatment,” he says.

Available products include Quadris, Headline, Stratego, Quilt and Tilt, he says. “I'd suggest that if you have a lot of pressure from Southern leaf blight or even rust, you might use Quilt and Stratego followed 14 days later by two applications of Headline or Quadris under severe disease pressure. Sometimes, one application will be sufficient,” says Lee.

Growers who can irrigate their corn crops this year should do so wisely, he says. “The price of that water could run from $7 to $15 depending on fuel costs. But let your crop stress — you must be aware of the water needs of the corn crop. The water curve for corn is a nice bell-shaped curve. When the crop reaches that pollination phase, it's using about one third-inch of water per day. In our soils, we have a 1 to 1.2-inch water-holding capacity. That means that in those really hot days, you've got about three or four days of water-holding capacity before you need to irrigate again. You need to stay in front of the curve.”

There are irrigation scheduling techniques available for growers, says Lee, including IrrigatorPro for corn from the National Peanut Research Laboratory in Dawson, Ga. Every inch of water that is applied to corn when needed is of significant benefit to the crop, he says.

“Don't miss the first irrigation of the season. When the crop is in the V7 stage, know what's going on. The reproductive stage has begun, and corn stresses during that period of time if it's too dry. Dryness can actually have an impact on yield at that early stage. So being aware of the growth and water needs is the first thing you need to know.”

If your subsoil dries out, you'll never be able to catch up and make a good corn crop, says Lee. “Too much of a root system in dry soil means you'll never benefit fully from the water you're putting on the crop, so you need to monitor and stay in front of the growth curve. You need to anticipate the time to apply water to the field. Sometimes, two or three-day delays are normal. But in irrigating corn, it can be somewhat costly.”

Research conducted in Georgia has shown the negative effects of delaying irrigation on corn, he says. With a one-day delay, yields are at about 98 percent of the fully irrigated site. There was a loss of about 10 percent after two days and a 20-percent yield loss after three days.

Studies also have shown that irrigation will pay for itself on corn, says Lee. With the price of corn at $3.50 and the cost of irrigation at about $9, it takes about 2.6 bushels to pay for 1 inch, he says.

“Could you have captured 2 to 3 three bushels of yield from that irrigation? Absolutely. If there's any crop we grow in Georgia where irrigation pays for itself, or that responds to water, it's corn. On average, Georgia farmers are applying between 10 to 12 inches of water each year.”

In comparing the checkbook method of irrigation scheduling versus using sensors, Lee says growers can do well with the checkbook method if they follow the growth of the crop and keep up with water requirements.

“When you look at the checkbook method versus a soil-moisture trigger, if you follow your growth curve and keep account of the water, you can come close to matching a sensor.”

Growers who have a limited amount of water should carefully consider when they apply irrigation, says Lee. “If you have enough water on your farm to make three or four applications in a tough year, how do you maximize it? If water is limited or if your labor to set up irrigation is limited, pre-planned irrigation may protect most of your yield. When we fix our schedule, we can more closely approximate the total needs of the crop and stay within 75 to 80 percent of the fully irrigated top yields.”

If a grower is limited to three irrigation applications, Lee recommends they be made at the tasseling, pollination and early grain stages, about 1.5 inches, seven to 10 days apart. If possible, a fourth irrigation could be made at the V7 stage, he says.

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