When you consider corn yield potential, it’s at its highest when it’s coming out of the bag and going into the ground, says Erick Larson, Mississippi State University Extension small grains agronomist.

“The difference between corn and other crops is that corn has much less compensation ability than some of the other row crops,” said Larson at the recent Alabama Corn/Wheat Short Course in Shorter. “Corn is a crop where you put a seed in the ground and get one plant that produces one stalk, and one piece of fruit on that plant and one ear generally. It does have the physiological ability to put out more than that, but you’re never going to be in a situation where you’re optimizing yield relying solely on the plant.”

That makes it all the more important to get a good stand, he says.

“There are some management strategies you can perform during the season – certainly irrigation is becoming more important, even in dryland areas – but we need to start out with as much yield potential as we possibly can,” says Larson.

The ideal situation is for all plants to come up at the same time and be spaced as evenly as possible, he says.

“One of the things we’ve looked at over the last several years in our research is methods to improve planter performance. We’ve looked at planter ground speed and the effect that may have on uniformity, along with the seed metering system.”

Larson has tested a standard John Deere planter with a 30-seed cell metering system as well as the same planter outfitted with an eSet-type metering system for precision planting. “We measured the plant spacing variability between all plants in the treatment and came up with a representation of how uniform it is.

“Increasing planter speed from 3 to 4 to 5 to 6 miles per hour, the amount of variability in planting increased with each increase in miles-per-hour. Stands are definitely more uniform at the lower speeds, but the eSet overall produced more uniform plant spacing than the standard John Deere unit.”

The yield results were inverse from the plant-spacing results, he says. The yields for the standard John Deere system fell off slightly more than with the after-market metering system, and the average yields for the after-market metering system were at a higher level than the standard metering system.

“This is something very easy can be done to achieve higher yields. With the John Deere system, you’re losing about 4 ½ bushels per acre, and with eSet, you’re losing about 3 1/3 bushels. So you’re losing somewhere between 3 and 4 ½ bushels per acre for each mile-per-hour increase in speed, and that becomes even more of an issue considering how cropping systems in the MidSouth have changed,” he says.

 In Mississippi, farmers are planting three times as much corn compared to the mid-1990s, says Larson. “We’re trying to cover a lot more acres, especially in years like last year when we didn’t have a lot of time to get into the field. We’re trying to cover a lot of acres in a short amount of time.”

If growers want to optimize yield potential, they obviously need to slow down, says Larson, but they may want to increase their equipment capabilities in order to plant more while achieving optimal yields.

Research looks at narrow rows

Larson and other researchers have also looked at narrow –row systems, and the interest in those has increased along with corn and soybean acreage in the MidSouth. “As you transition into a soybean/corn production system, there’s a whole lot more potential there for you to realize benefits from narrow-row systems.”

In addition to narrow rows, researchers also looked at twin rows, says Larson. “We wanted to look at the yield capability of corn in 30-inch rows versus the wider 38 to 40-inch rows. We also looked at that same 38 to 40-inch row in twin rows, to evaluate the pluses and minuses and put some MidSouth numbers to them.”

The trials involved different hybrids and various plant populations, he adds.

“We also looked at this in an irrigated culture. Nearly 50 percent of our corn in Mississippi is grown under irrigation, and we wanted to optimize the yield potential to see how corn might perform in the narrow-row systems versus the wide traditional systems.”

Light interception was an important consideration, says Larson. “It’s important because that’s the goal of the plant’s vegetation – to intercept as much light as possible. You want to be intercepting from 90 to 95 percent of the available light during the day when the sun is overhead to optimize yield potential. If you narrow those rows, you obviously have more potential to do that because you don’t have more light getting down into the middle of the rows, and the light is spread out over the leaves of those plants where it’ll be used more efficiently.”

Research results were pretty much as expected, he says. “The wide single rows had the lowest amount of light interception, the twin rows increased it a little, and the narrow rows increased it even further.”

However, he adds, light interception did not necessarily translate into higher yields for the twin-row systems. “It doesn’t mean the potential isn’t there. For one reason or another, we just weren’t realizing our potential for the yields in twin rows.”

The bottom line, says Larson, is that of those three systems, there was a significant advantage for the narrow rows, with yields 8 to 9 percent higher in the 30-inch rows than in either of the wide-row systems.

This is consistent with similar research from the Corn Belt, he says.

“Twin rows did not improve yield, though they did improve light interception. I think the reason that twin rows didn’t work quite as well in terms of yield were issues associated with raised-bed systems. I don’t think you would have seen some of the same stand issues with flat-planted corn.”

Corn has a determinate growth habit, and that’s important in terms of its inability to compensate whenever there are issues early in the season, says Larson.

Simulating late emergence

Researchers also simulated late emergence in planting corn, says Larson. “Then we harvested the treatment plants individually to see what kind of differences we saw. We had four intervals where we simulated late emergence. Each of those intervals produced about a half-leaf difference compared to the uniform stand. We’re losing a huge amount of yield, 20 to 25 bushels per acre, in the late-planted corn.”

Three different treatments ranged from 7 percent of the plants being late to up to 20 percent being late, he says. In some farmer’s fields last year, 30 to 40 percent of the plants were coming up late, says Larson, so yield differences can be even more substantial than in the research plots.

“What can we do better to get an improved stand? A lot of people think about calendar date, and it obviously can have an impact, but it’s not something that I’d want to hang my hat on. Last year we had extremely cold conditions throughout March, and we had a lot of corn that was planted and sat out in the field for three and a half weeks or more before it came up.

“The calendar date can provide some general guidelines, but we need to be looking more at our environment, how warm and how moist the soil is, looking at real variables that have an impact on seed germination. Keep in mind that soil temperature is the No. 1 factor affecting germination rate and how fast that plant emerges and gets out of the ground.”

The minimum temperature for corn germination is 50 degrees F, says Larson. “We’d prefer to have it up to 55 degrees. As the soil temperature increases, the rate of germination increases exponentially. If the soil temperature is 50 to 55 degrees, it’ll probably take a minimum of three weeks for that corn seed to come up.”

The key, he says, is to go out first thing in the morning and stick a soil thermometer in the soil to see what you’re working with.

“If you have a soil temperature of more than 55 degrees first thing in the morning, you can almost guarantee yourself that plant will be up within a two-week period, and your likelihood of having uniform emergence is much, much greater than if the soil temperature is below 50 degrees.”

Another general guideline is to check nighttime low temperatures, he says. The soil temperature generally will be close to the nighttime lows.

“The corn seed has to be in the ground 24 hours per day, so if it gets down to 40 degrees at night, it may have sufficient temperature for emergence only six to eight hours each day. It’ll be dormant the rest of the day, and a lot could go wrong.

“Normally in the South, soil moisture is our biggest limitation during planting season. You may have dry-enough soil moisture in part of the field, but where the soil is heavier, it might be too wet for optimal planting when the planter goes through the field.