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Corn+Soybean Digest

How To Chop Yield Drop

With corn acreage almost sure to increase in 2007, Extension specialists from across the Midwest have been cautioning farmers to expect about a 10% average yield penalty when growing corn after corn compared to growing corn after soybeans.

Farmers often dispute whether yield penalties are associated with raising corn in consecutive years, but land-grant university research consistently shows a significant yield penalty from doing so, says Jim Gerwing, South Dakota State University Extension soils specialist.

“Most research shows you'll have about a 10-12 bu. yield reduction from growing corn after corn, compared to corn after beans, with potentially higher yield penalties in reduced or no-till systems,” says Gerwing. “The big reduction comes after the first year you grow corn after corn and then it levels off. Yields don't come back up until the land returns to a corn-soybean rotation.”

No magic bullet exists to eliminate the yield reduction that occurs when switching away from a corn-soybean rotation to corn following corn, says Gerwing. “You cannot recover this yield loss simply by putting on more fertilizer,” he emphasizes. “Something else is going on that we don't understand yet.”

The decision to grow corn following corn is a complex one, requiring a fair amount of advanced planning, says Clarke McGrath, an Iowa State University (ISU) agronomist with the Corn and Soybean Initiative. However, several key management decisions can make the difference between experiencing either a small or a large yield reduction when growing corn after corn, he adds.

Gerwing, McGrath and several others provide the following five tips to help farmers minimize any yield reductions that would otherwise occur when choosing to grow corn following corn. Their advice is to:

  1. Select the right genetics. Planting corn after corn can create a challenging growing environment early in the season, says McGrath. “You'll want to plant a high-yielding hybrid with exceptional emergence and seedling health — something that is able to handle a lot of disease pressure.”

    Early vigor is essential to hybrid selection for corn following corn, agrees Roger Elmore, ISU Extension corn specialist. “It's important to select a hybrid with a nice package of disease tolerance, root health and stress tolerance in corn following corn,” he says. “Also, make sure to switch hybrids annually. Don't grow the same hybrid in the same field two years in a row. In Iowa, gray leaf spot and northern leaf blight are the two major diseases that might occur with more frequency in corn planted into corn.”

    Anthracnose and diplodia ear rot are two more common diseases to watch in Indiana and Ohio, says Bob Nielsen, Purdue University Extension agronomist. Both Nielsen and Elmore stress the importance of considering hybrid performance across multiple sites as the best means to predict the future performance of a hybrid on any given farm.

    On-farm test plots can also help to identify hybrids that yield better when planted into corn following corn than other hybrids, says Trav Bratland, a corn grower from Willow Lake, SD. “We've had corn-on-corn test plots for three years, and there are definitely certain varieties that do much better than others.”

  2. Consider a Bt corn rootworm hybrid. Planting transgenic hybrids with built-in corn rootworm protection may also help farmers reduce their yield penalty from growing corn following corn compared to corn following soybeans, says Elmore. He cites research from the University of Illinois during 2005 and 2006 that shows Bt corn rootworm hybrids often yielded better than non-Bt rootworm hybrids in fields planted to corn after corn.

    While almost all corn planted after corn will be at risk to rootworm injury, farmers aren't locked into just using Bt corn hybrids, points out Nielsen. “Granular soil insecticides also give good control for corn rootworms,” he says.

  3. Clear away crop residue. Too much residue from corn after corn can cause planter problems, particularly with no-till. “If the planter is challenged, it will take a toll on plant population, uniform stand establishment and grain yield,” cautions Nielsen. “For no-till, row cleaners, seed firmers or customized furrow closers can help to improve planter performance in a high-residue environment. Another alternative would be to consider strip-tillage practices that result in a residue-free planting zone.”

    Residue managers are essential to creating a highly productive seedbed when following corn with corn, agrees McGrath. “You'll need the right attachments to move away the crop residue and to plant at a consistent and even depth,” he says. “We have farmers in Iowa who can run planters through high-residue corn on corn, even with a no-till system, but they have to have the right row cleaner and seed firmer attachments to do it.”

  4. Pick productive fields. Drainage can play an important role in determining whether high-residue, corn-on-corn fields will be a detriment to planting and stand establishment, notes Nielsen. “In the Eastern Corn Belt, putting your continuous corn acres on the lighter, better-drained soils would be preferable to the heavier, poorly-drained soils,” he says.

    However, in South Dakota, “corn on corn won't work well on our sandier, lighter soils,” says Bratland. “For '07, we've moved all our corn-on-corn acres to our heaviest soils.”

    Compacted fields are also worth avoiding when planting corn after corn, he adds. “We take compaction probes into our fields to see where compaction problems are,” says Bratland. “Then we run a ripper on affected fields to eliminate it.”

    Fertility and compaction management are essential to grow corn following corn, agrees McGrath. “Pick fields with optimum fertility,” he advises, “and don't leave nitrogen (N) on top of the fields — either inject or incorporate N fertilizer.”

    In the Western Corn Belt, pre-season soil nitrate tests help to determine how much fertilizer to apply, says Gerwing. “On average, we'll recommend about 15 lbs. less N following corn after corn this year than corn following soybeans,” he says. “It's a function of corn not getting as high a yield as expected due to the dry weather or by having put on more N than was needed in the first place. There is typically a lot of nitrate carried over after corn in South Dakota, compared to corn after soybeans, especially after a dry year like 2006.”

    However, in the Eastern Corn Belt, where moisture is more plentiful and pre-season soil nitrate tests aren't typically reliable, more N will likely be needed. “You'll need 30-50 lbs./acre more N here in Indiana on corn on corn compared to corn after soybeans,” says Nielsen. “A wet winter or a wet early spring could cause a lot of N loss.”

    In Iowa, Elmore recommends “about 60 lbs. more N on corn following corn than corn following soybeans.”

  5. Expect more weed problems. “A high-residue, high-moisture cool environment from corn after corn favors different weeds than what occurs in corn after soybeans,” says Nielsen. “That might catch some growers off guard.”

Both Nielsen and Elmore recommend using different modes of action and a pre-emergent herbicide in addition to a postemergent herbicide for optimal, early weed control.

Greater efficiency from spraying operations will be needed as well. “With more corn acres planted, you'll have a fairly small window to spray everything at the optimal time, especially if the weather is unfavorable,” says McGrath. “Growing more corn acres will present a lot of challenges in a lot of areas, but the successful growers will find ways to deal with those challenges before they affect their bottom line.”

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