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Corn+Soybean Digest

How To Hit 100-Bu. Beans

You'd almost have to call Palle Pedersen a soybean production evangelist. In the past year he's crisscrossed the U.S. preaching the 100-bu. yield story from the soybean production pulpit.

Fact is, after you've sat through one of his sermons you'll likely become a believer that bumping bean yields to 100 bu./acre is entirely possible.

“You need to understand the interactions among weeds, insects and pathogens,” explains Pedersen, Extension soybean specialist at Iowa State University. For the record, he says one of the first documented 100-bu. yields occurred in Japan in September 1954.

Over the past 10 years — on average — national soybean yields have been stuck at around 40 bu./acre. That's about a 0.4 bu./acre/year average increase vs. a 1.5 bu./acre/year for corn, according to Jeff Volence, Purdue agronomist.

For more information on tracking soybean genetic progress see “Bean Genetics Gain Ground,” pages 34-35, 38 in the Dec. 2004 issue.

Pedersen claims major roadblocks growers face today for attaining higher yields are implementing solid production practices in an era of mounting soilborne pathogens. “Raising beans is getting more complicated because of our short rotations,” he says.

Still, he's convinced you can grow 100-bu. soybeans. To do that, he outlines seven key production areas that need to be addressed:

  1. Cultivar selection

    “It's the the most important factor in achieving higher yields,” Pedersen says. “Farmers rarely spend enough time selecting soybean seed.”

    He suggests recording a history of what you've planted and monitoring fields to see if there are any patterns.

    “It's all about managing diseases,” says Pedersen, who urges growers to pay attention to soil pH because of soybean cyst nematode (SCN) when selecting varieties. “Unlike a few years ago, for example, there's no longer a yield lag with SCN resistant varieties. Still, they need to be improved.”

    He says to be sure to check state-replicated university variety trials at multiple locations as well as seed company research reports. In selected copies of this issue, you can also find independent on-farm soybean yield trials in the Soybean F.I.R.S.T. Special Report or visit our Web site

  2. Early planting

    Getting seed in the ground early, but not too early, can bump yields dramatically, Pedersen says.

    Iowa studies in 2003 show that for every day after early May farmers lose 0.26 bu./acre yield.

    “Last year, in high-yielding areas of Iowa, we lost 0.9 bu./acre/day for delaying planting from the optimum window (last week of April and first week of May in Iowa),” says Pedersen. “All it takes is making one or two mistakes and you could end up with 35 bu./acre yields.”

    Also be careful not to plant so early you could still get hit by a late frost. And if you plant too early and it's too cold, soilborne pathogens will take over and kill the plants, he says.

    See “Effect of Planting Date on Soybean Yield (Southern Wisconsin)” below left.

  3. Narrow row spacing

    “If you're in a high-yielding environment, narrow rows always yield more than 30-in. rows,” Pedersen says. “Usually you'll increase yields by 5-8%. The largest increases are usually found in the northern Corn Belt.”

    In low-yielding areas, he says you won't see benefits to rows narrower than 30 in., especially if you already have pathogens or diseases that put stress on the plant. Sixty percent of soybeans in Iowa are currently planted in 30-in. rows, so he says there's still a lot of improvement to be made.

  4. Crop rotation

    Bar none, the most profitable crop program remains the corn-soybean rotation, Pedersen says. The only way to change that would be to add a third crop into the rotation, like wheat, but it's not going to be profitable enough for the Corn Belt.

  5. Soil fertility

    Be sure plants have good nodulation. Pedersen says if they don't, or are grown on sandy soils or the field hasn't been planted into soybeans in the last 3-5 years, use inoculum.

    “The only things we really need to fertilize for are potassium and phosphorus,” he says. “In Iowa, that's generally not an issue because we have so many nutrients from livestock. Be sure to soil test every year.”

  6. Plant populations

    Pedersen is studying ways to optimize plant population rates and avoid overseeding. His conclusions so far: “At 30-in. rows, many farmers are planting too high at about 140,000 seeds/acre. Planting 125,000 is enough. Seeding rates of 125,000 should yield 110,000 plants,” he says. (See chart above.)

  7. Tillage

    In most cases soybeans don't respond well to tillage, based on many long-term studies in Wisconsin and Iowa, Pedersen reports. “You can do just as well with no-till as with tillage,” he says. “To get no-till to work it's critical not to plant too deep. Plant a maximum of 1½ in. deep and use good pressure on the closing wheels so the rows are closed.

“If the soil is wet and you have a history of soilborne pathogens, use a fungicide seed treatment when planting early,” he says.

So can you hit that 100-bu. target? It depends on your ability to harness all the management skills necessary.

“Most varieties have genetic yield potential above 100 bu., but it depends on Mother Nature and soil variability,” Pedersen says. “We need to be much better managers if we want to get higher yields.”

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