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Adjust corn management for top yield

Aiming for corn yields averaging 200 bushels or more per acre in the Mid-South is realistic, but hitting these top yields may require a slight shift in production management, according to Extension specialist Erick Larson.

Speaking at the Delta Ag Expo in Cleveland, Miss., Larson said Mississippi's corn yields are increasing at a faster rate than cotton, rice or soybeans. In fact, the state corn average in 1990 was 100 bushels per acre, and by 2001 that number had increased to 125 bushels per acre.

“In the Delta, a goal of 175 to 200 bushels of corn per acre is attainable, but to get to those levels you'll need to manage your crop for yield, and increase some inputs,” says Larson, Extension agronomist with Mississippi State University.

The abbreviated recipe to top yields includes the four key ingredients of increased nutrient levels, uniform plant growth, increased plant population, and intensive scouting.

Obtaining high corn yields first requires feeding the plants the increased nutrients needed to produce bumper yields — soil testing, bumping up potassium and phosphorus levels, splitting nitrogen applications several times during the season, insuring that nitrogen is getting to the plant, and using starter fertilizer.

Starter fertilizer, Larson says, results in earlier maturity, lower moisture levels at harvest, and a potential 5 percent or more yield advantage. “This supplement to your overall fertility program is most beneficial in reduced tillage programs,” he says.

Nutrient requirements often differ depending on planting history. Rotating other crops with corn can increase your yields by 10 to 15 percent, interrupt pest cycles and improve soil condition. However, it can also result in fertility problems when rotating back to corn.

“High levels of both potassium and phosphorus are required for a high-yielding corn crop. Corn generally needs twice the amount of phosphorus that cotton or soybeans need, and potassium deficiencies are likely in corn following high-yielding soybeans, particularly in no-till fields,” Larson says.

Research suggests that for every bushel of soybeans removed, or harvested, from a field, approximately 1.4 pounds of potassium are also removed. Any resulting deficiency is likely to show up as yellow streaking in the corn crop, especially in fields where a tillage instrument has not redistributed the soybean residue.

Larson recommends counteracting any potential nutrient problems with soil testing, followed by a maintenance fertilizer application. “Keep in mind that the base nutrient recommendations for corn is the highest of all Delta crops.”

In those cases where corn is planted following rice, a severe phosphorus deficiency may occur. After a flood is removed, phosphorus converts from soluble ferrous-P to ferric-P, which is a form of phosphorus the corn plant cannot use.

Your options, Larson says, are either to apply substantial amounts of phosphate fertilizer to your corn, or not grow corn in that field.

How you put your corn crop in the ground can also affect yield potential. Larson suggests planting slowly at 2 to 4 miles per hour, with a uniform seeding depth of 1.5 to 2 inches and row spacing not any closer than 6 inches between plants.

“Improved genetics over the past few years have resulted in higher yield potentials. We're also planting earlier and earlier with the newer, 113- to 119-day maturity hybrids, and improving our yield potentials because of that,” Larson says.

“Increasing our plant population above 28,000 plants per acre allows us to make the most of these newer hybrids. You may be able to increase your yield with higher population numbers, but you will quickly trade off stalk quality for that increase.”

Another factor that can make or break yield is insect pressure, and bin-buster yields require intensive scouting.

“We estimate Southwestern corn borer harvest loss at more than 1 bushel of yield for every stalk borers put on the ground over about 100 feet of row,” Larson says. “Physiological, or hidden, yield loss resulting from vascular damage due to tunneling activity in the stalk results in either fewer kernels per ear, or less weight in the kernels.”

As a rule, growers should calculate an 8 percent reduction in yield loss per tunnel per plant. What's more, the loss caused by Southwestern corn borers is cumulative, according to Larson.

“In Mississippi, we experienced substantial yield losses in 2002 due to the damage caused by corn borers. In many cases, growers saw a 20-plus bushel per acre yield decrease from this one insect. I believe corn borers are stealing a lot of yield potential from us,” he says.

Fall tillage can aid in limiting corn borer populations, as can altering planting dates. Larson suggests planting early and harvesting conventional hybrids before Aug. 20. “Late-season corn borers are attracted to the greenest, youngest corn plants, and will favor the later-planted corn because the earlier-planted crop is beginning to dry down, making it a less attractive host for corn borers,” he says. “By the time we hit the third generation corn borers, population levels are very high in the Delta.”

Planting a Bt hybrid also offers protection from Southwestern and European corn borers, as well as corn earworm suppression. However, Bt hybrids will not protect you from other early-season pests that attack corn as it emerges.

Because it is difficult to predict in-season corn borer populations based on over-wintering populations, Larson says growers should use their field history as a guide.


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