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Corn+Soybean Digest

Chasing High Yields

With last year's bin-busting record corn and soybean harvest, you might think it's a bit premature to think about management strategies that will help boost yields.

But like a roll of the dice, reaching higher yield goals for corn and soybeans can often be elusive at best. Weather always remains the unknown factor that can alter even the best of plans and quickly change one's fortune.

As in any business, good management practices are important in reducing risk and reaching your goals. This is especially true in hitting your yield targets.

Aside from the disease and insect problems, those management practices may include five factors: variety selection, row spacing, seeding rates, planting dates and crop rotations.

  • Variety Selection

    “I can't emphasize enough the importance of doing your homework in selecting good varieties that meet your management strategies,” says Emerson Nafziger, University of Illinois crop production specialist. “Obviously, weather will always be a big factor. However, we still need to choose varieties carefully because no matter what happens in the field, variety choices usually set yield potential.”

    Nafziger recommends examining those varieties that have been the most widely tested over a wide range of growing conditions and performed consistently well since they exhibit the best stability.

    “Closely examining results on a regular basis from university trials, as well as those from seed companies, will offer producers a good idea of which varieties may fit in well with their management plans,” he says.

    The University of Illinois conducts variety trials on corn and soybeans, as well as other crops, in about a dozen locations across the state, according to Nafziger.

    Because weather is so unpredictable, you can't always assume that a local trial will consistently predict performance of varieties on your farm.

    “That's why we average the results over various areas in the state,” says Nafziger. “You can't really go wrong if you average data across similar locations and then choose from among the better performing varieties.”

    Also, research has shown that the highest yielding variety from a single location will always yield less at that same location the following year, according to Virginia Tech. In some cases, the highest yielding variety could even yield less than average. On the other hand, the highest yielding variety from multiple-location averages will usually result in high yields at any location the following year.

    Virginia Tech advises to look at average yields across locations in addition to selecting varieties based on local yield data. Multi-year averages give greater confidence to variety performance.

    To maximize soybean yield, David Wright, coordinator of the Plant Health Initiative, suggests working closely with your seed supplier to ensure you're getting the highest yielding variety with the agronomics you need. He also recommends being field specific in variety selection.

    Testing fields for the presence of the soybean cyst nematode and selecting varieties with the highest level of resistance, including the Rps1-k gene for Phytophthora resistance will also help reach yield goals. These two pathogens consistently rob the most yield, he says.

  • Row Spacing

    Although row spacing narrower than 30 in. tends to produce higher soybean yields, according to Nafziger, once you get below 20 in. or so — at least under Illinois conditions — narrowing the rows further will have a minor effect.

    Also, the combination of placing soybean seed with a “row unit” or “splitter unit” has shown positive results. “However, in field trials we normally don't see much of a yield difference between 15-in. and drilled rows,” says Nafziger.

    In 2003, Nafziger says row spacing effects were reported by producers in some areas to be unusual — 30-in. rows seemed to yield more than narrower rows. While that may have been true in some cases, data from two northern Illinois locations did not show this, he says.

    For corn, Iowa State University (ISU) examined the yield effect of 15-, 30- and 38-in. row spacings. That research conducted several years ago showed that narrowing rows to less than 30-in. showed small and inconsistent results in terms of yield differences. Overall, the research concludes that there isn't much yield benefit in using row spacings less than 30-in.

    Past research comparing 30- and 38-in. row spacings indicated a 4-6% yield advantage for 30-in. rows. However, additional trials at ISU now suggest that the yield benefit will vary from year to year and the overall effect has decreased to only a 3% advantage for 30-in. rows.

  • Seeding Rates

    “With seed prices edging higher, I think anyone seeding more than 200,000 seeds per acre might consider the costs in using a slightly lower rate,” says Nafziger. “Our best information suggests that a seeding rate somewhere in the 150,000 range is adequate — regardless of row spacing, as long as you have an expectation of a reasonable emergence percentage.

    “Most of our data suggests that if you have 100,000 plants, you're probably going to maximize yield in most cases,” he says. “However, if planting has to be done later for some reason, you might want to make an exception by edging up the rate to compensate for the likelihood of smaller plants.”

    It's also possible to apply economics to find optimum soybean seeding rates, according to Nafziger. For example, several years ago he conducted research at several locations in Illinois that examined seeding rates and yields. In one example, he found with soybean seed priced at $22.50 per 50-lb. bag (150,000 seeds at 3,000 seeds/pound), the optimum planting rate calculated to be about 131,000 viable seeds/acre — or about 145,000 seeds/acre at 90% germination.

    Nafziger also cautions against trying to finesse canopy management for diseases like white mold with lower seeding rates.

    “White mold appeared in some fields this year, no matter what row spacing or plant population was used,” he says. “In the long run, trying to create a more open canopy with lower seeding rates to help curb white mold probably isn't a sound strategy, especially if it costs yield under normal conditions.”

    For corn, Nafziger says trying to hit high yield conditions usually requires relatively high plant populations.

    “In highly productive soils, most producers seem to be aiming in the 30,000 plant population range at harvest,” he says. “And some farmers may finesse that up or down by several thousand. In fact, some have gone up to 33,000, 34,000 or 35,000, and that still worked well.”

    Modern hybrids don't falter much, even when reaching populations higher than the optimum under various growing conditions, Nafziger says.

  • Planting Dates

    For soybeans, Nafziger's research at Urbana concludes that it's more detrimental to yield to plant before mid-April than it is to plant in late May, and the response to seeding rate doesn't change a great deal as planting dates change.

    Seed treatments produced almost no response in this study, Nafziger reports. It didn't affect stand in most cases, regardless of planting date. And when averaged across planting dates, it had no effect on yield, he says.

    While this isn't evidence that a seed treatment is never needed, Nafziger says it clearly shows that sometimes there will be no response to a seed treatment even when planting early.

    “Our results also show that using a later-maturing variety might be a useful strategy if planting very early,” says Nafziger. “The late variety also produced the most stable yield across planting dates, but the mid-season variety produced the highest yield averaged across planting dates.”

    Nafziger doesn't see a reason to change from mid-season varieties when planting is delayed. However, he says the results suggest that simply choosing a high-yielding variety may be more important than its maturity.

  • Crop Rotations

    According to the Plant Health Initiative, researchers in several states have used long-term crop rotation studies to determine the yield of corn (C) and soybeans (S) when grown in continuous corn, C-C-S and C-S rotations.

    Those studies suggest that on average, second-year corn yield will be suppressed about 10% or more. This is supported by earlier research that reported a 15% yield decline when corn was planted where corn was grown the previous year.

    Research conducted at the University of Wisconsin concludes that second-year corn yielded no differently than continuous corn.

    Corn grown in monocultures for two or more years is susceptible to increased levels of soilborne pathogens and root-damaging insects, according to the Plant Health Initiative.

    It's believed that these pathogens reduce root vigor, and water and nutrient uptake. However, not all researchers agree. Some have reported that neither foliar nor soilborne pathogens were involved in the monoculture yield decline.

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