Row spacing, tillage focus of Georgia corn research

Tillage, row spacing and double-cropping are the focus of corn research being conducted by the University of Georgia, said Extension agronomist Dewey Lee at the recent Georgia Corn Short Course, held in Tifton. Southeast Farm Press is a sponsor of the annual meeting.

"We've looked at a high-residue conservation-tillage approach in corn production," says Lee. "We compared three different types of cover — black oats wheat and winter weeds." Black oat, he explains, is a forage-type oat from South America. It's ability to produce cover and forage is about twice that of conventional oat hybrids.

"Wheat is the preferred cover crop only because of the cost of wheat seed. It's less expensive than either oats or rye. The winter weeds consisted of species such as cutleaf, primrose, chickweed and henbit," says Lee.

Two tillage packages were compared, he continues. These included subsoiling in the row, with a ParaPlow or v-ripper, and a straight no-till system. In some cases, researchers superimposed a surface-tillage on these systems.

"We compared all of this to a straight no-till system. This is a system with no in-row disruption whatsoever. We looked at fixed and variable costs, incorporating the planting and production of black oats and wheat. Our yields ranged from 142 bushels up to 176 bushels per acre," says Lee.

Overall, he says, there was a trend towards lower yields where wheat was used as a cover crop. "Compared with no cover or winter weeds and black oats, there was a definite trend towards lower yields when wheat was used. That's a disturbing trend because a majority of our corn cover crops in Georgia are wheat. Looking at the overall effect — statistically — we saw an advantage with black oats or no cover crop when compared to wheat."

There was a strong trend towards higher yields when using black oats as a cover crop for corn, says Lee. Research has shown that the root strength of black oats is superior to that of either wheat or rye, he adds.

"Wheat is a major cover crop for Georgia corn growers, so we might want to consider switching to something like rye or oats to improve the value of our corn crop or to at least get away from this trend towards a yield disadvantage," says Lee.

Surface-tillage, he says, showed a yield response in 2000 probably due to improved water infiltration. Several years of data across all crops shows an advantage in disturbing the hardpan of sandy loam or sandy clay loam soils, says Lee. Three years of corn research show a very large tillage effect in south Georgia soils, he says.

Corn research conducted from 1999 through 2003 shows a strong trend towards improved yields with narrow-row corn, says Lee. "When you go to the Corn Belt, you'll see this data isn't as strong. Going from 30-inch to 20-inch or 30-inch to 15-inch doesn't resonate as well in the Corn Belt as it does in the Northeastern or Southeastern United States. The yield response is significant when we look at the 20-inch versus the 36-inch rows, and there's a statistical difference in 20-inch versus 36-inch rows.

"We looked at the conventional rip-and-bed and the KMC strip-till unit, comparing 36-inch rows, and we saw a slight yield trend towards the strip-till. We also see this trend in peanuts and cotton. If you haven't considered strip-till production or conservation-tillage, you might want to do so. There's a definite benefit to shifting your production in that direction. You might want to keep this in mind if you're changing and upgrading your equipment, and if you're growing corn, peanuts or cotton."

Researchers also are looking at the PATS tillage system, he says. "This is a very heavy ‘industrial strength’ unit, and it's more of a compression unit. When you disturb the seed furrow, this machine compresses it back with pneumatic tires. The problem in our study is that when we compressed the furrow, we pinned our seed and had a poor stand. But that's one study, and we'll continue to work out the problems with this system."

Research conducted in a dryland environment in North Carolina, says Lee, showed a benefit in narrowing corn rows and spreading out the seed population over the rows.

"We got a significant response in Georgia to narrowing our rows when we compared 20-inch corn to 36-inch corn. This also is true for silage. But the big question is, can we afford to do it? Do you have the equipment to harvest narrow-row corn? This may be something to consider for growers in east Georgia, where there are more corn and soybean rotations."

Comparing twin-row corn and 36-inch corn resulted in a "wash," says Lee. "We see a significant yield increase in some years with twin-rows and no increase in other years. That’s important because many peanut growers are using twin-row planting units, and they could utilize that same equipment in producing corn. There’s not a real disadvantage to twin-row corn.

"But you’ll have problems if you try to harvest twin-row corn at the same speed as single rows. It takes time to adjust, as you’re watching those twin-rows and trying to keep those two rows going into the header. "

Turning to double-cropping corn, Lee says the most important question growers must answer is which crop they want to follow with double-cropped corn.

"Some growers might want to follow small grain silage and plant corn about 15 to 30 days later than the normal planting date. Others might want to follow string beans in June, watermelons in July or corn silage in July and August. The crop you’re following will make a big difference in your ability to extract yields from the hybrids available to you."

Growers must consider the cost of their inputs versus what they’ll get out of the crop. "Is the corn being grown for grain, or will you cut it for silage and sell to a dairy. All of these factors will affect the choices you’ll make when you try and select a hybrid that’ll fit into this particular environment."

Researchers from Florida looked at double-cropping corn with both Bt and non-Bt hybrids, says Lee. "With the advent of Bt technology, there was hope that we would see a yield improvement. As we get later into our production season, pressure increases from fall armyworms and corn earworms. The Bt technology also has been placed into tropical corn hybrids."

Data from the Florida study is typical for planting date studies, he says. "As we delay planting from March towards July and August, we see a decline — a severe decline when we get into May and June. Part of that is due to temperature, water and disease pressure."

As the planting date moves into May, the advantage trends toward tropical varieties, says Lee, because they’re suited more for that environment.

"If you’re double-cropping corn, it’s best to first choose a hybrid with good defensive characteristics or disease resistance. Then, you can consider yield and Bt technology. When you’re double-cropping corn and you use Bt technology, you’re limited to 50-percent usage of that Bt trait. It’s more important in double-cropping corn to have good resistance to leaf blight and rust, and a few hybrids are available that’ll give you that opportunity.

"The opportunities for double-cropping corn become highly limited as you get into May and the first part of June. You get down to either the tropical hybrids, or a couple of other hybrids with good disease resistance."

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