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Describing super soybean yields: It's complicated

Fungicides? How about seed treatment? Or foliar nutrients. Inoculants, anyone?

While you might think those are the ingredients for higher-yielding soybeans, you'd only be partly correct. Growers need to first focus on the old-fashioned stuff: good variety selection, early planting, stress management, and good soil fertility. Then they may judiciously use the new stuff.

That's the advice from Shawn Conley, a soybean specialist at the University of Wisconsin-Madison. He knows that super yields are possible.

“We get 90 bushels per acre at some of our locations every year,” says Conley. That's about double the Wisconsin state average and the national average (41.5 bushels per acre in 2011).

Following are three common questions he gets at farmer meetings and his answers to those inquiries.

Q:I'm probably not going to get a 90-bushel-per-acre average, but I would like to boost average per-bushel yields from 45 to 55. How do I do it?

A: Start by identifying your soybean diseases, says Conley. Look for things like soybean cyst nematode, sudden death syndrome (SDS), white mold, and brown stem rot. You can find varieties that resist them or possess some level of tolerance to the common diseases in your fields. Find them and plant them.

“Really study the genetics when you make those selections,” he says. “With corn, some farmers will have 10 to 12 hybrids they choose from, but they only look at two or three soybean varieties. Sometimes, they just go with what their dealer has left over.”

Separate genetics from traits, he says. Genetics is where you actually get yield potential; traits just help protect that yield. Don't just select varieties that yield well in your local area and plot. Broaden your search to a variety of environmental conditions. You'll increase your chance for success, Conley says.

Don't ignore soil tests, either. Farmers fertilize for corn but not for soybeans. The fact is, high-yield soybeans use a large amount of potassium (K). Beans remove about 1.4 pounds for every bushel of grain produced. Plants deficient in K are more susceptible to some diseases and can be predisposed to increased aphid counts – all yield-robbers.

Low sulfur content may also limit soybean yields, particularly in a crop rotation including alfalfa. “Alfalfa is a big user of sulfur,” he says.

Q:When should I plant soybeans, and what maturities?

A: This can be the most important and least expensive cultural consideration that impacts soybean yield, says Conley.

“At our Arlington Research Station, we've seen an average yield loss of 0.4 bushels per acre per day when planting is delayed past the first week of May,” he says. This is because of decreased pod numbers, although soybeans will partially compensate through increased seed size.

Early planting increases risk for some seedling diseases, as well as brown stem rot and SDS. If you plant early, couple it with good disease-resistance management, including seed treatments.

Along with earlier planting, you can also plant later maturity soybean varieties, which give longer pod filling time and increase yields. Of course, you have to balance that with frost considerations.

Q:What about some of the advanced techniques like foliar fungicides and nutrients, seed treatments, and tissue tests that are being promoted?

A: There's plenty to choose from here, says Conley. One ongoing set of studies he and his fellow researchers are conducting is called the kitchen-sink experiment. They're throwing everything possible at soybean fields, including full fertilizer applications, seed inoculants, seed treatment (primarily fungicides), in-season fungicide applications, multiple seed traits, irrigation, and more. Conley expects to find interactions among these inputs and soybean varieties, although those answers will not be known in the near future.

One example of this is the yield interaction that soybeans have had with the Roundup Ready trait. There was a definite yield drag when the first generation of Roundup Ready came along. But that doesn't appear to be the case with the Roundup Ready 2 Yield trait that's hit the market in the past several years.

At issue on the kitchen-sink practices is the cost.

In one comparison from four years ago, Conley totaled the cost of about 15 advanced input practices: They tallied an additional $370 an acre. That was compared to just planting low-end seed at $35 and no other inputs. Conley says those costs are certainly higher today, but so is the selling price of soybeans. It costs about $13 per acre for a soybean fungicide/insecticide seed treatment. The probability of a return on investment is greater than 80%, he says.

At this point in the kitchen-sink soybean research, all the added inputs are producing about an extra 5 bushels per acre. Even at today's prices, that's hardly worth $370, Conley says.

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3 Ways to Boost Soybean Yields

1. Select varieties carefully. Varieties differ in yield potential and interaction to inputs. Remember that while traits are important, they don't make yield; they protect yield. “You don't spray herbicides to get yield; you do it to kill weeds,” says Shawn Conley, University of Wisconsin-Madison. “The yield is in the genetics.”

2. Reduce stressors that you can control. Stressors like weeds tend to reduce pod counts, and pods make yield.

“A good example of this is weed control,” says Conley. “Reliance on total postemergence weed control has made growers a little lazy on this. You wait to control weeds, so you have lots of early weeds. You may kill those weeds later and have what looks like a clean field of soybeans.

“What you don't see is that you lost yield potential early, while the plants were competing with weeds,” he adds. “Use a weed-control program that goes after weeds early.”

Poor soil drainage also stresses plants. “There's a lot of talk about developing soybean plants that have drought tolerance, but just as important is wet tolerance,” he says.

3. Protect early seedlings with a seed treatment. Compared to just 8% of soybean seed in 1996, 50% of soybean seed now gets a seed treatment of some kind.

“Our research shows a lot of variability on the value of this,” says Conley. “We usually get some response, and at worse, it's about a breakeven. We're putting soybean seed out in a field 10 to 20 days earlier than we used to. Not only that, but it's into no-till fields in cold, wet soils. It's no wonder we're looking at things we can do to help that seed get started.

“When we test seed treatments, we often see an interaction by variety of soybean seed,” says Conley. “And that makes sense if we think about it. The good varieties of soybeans tend to last about three years, then there is something new to replace them. So by the time we know that a variety of seed responds well to a seed treatment, it's gone.”

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