It used to be that if Bruce Wessling and his dad Roger finished planting corn in April, they parked their planters until May 1, the date conventional wisdom said to start planting soybeans in west-central Iowa. But about 10 years ago, the Wesslings, Grand Junction, IA, decided to see what happened when they planted beans earlier - around April 25.

What they found were noticeably higher yields. Bruce Wessling recalls that the beans planted in April produced about 10-15% more bushels per acre than beans planted later in the spring. They saw similar results when they experimented with planting dates over the next few years.

“Now it has become a goal to get our beans planted early,” Wessling says. The Wesslings operate several farms in Boone and Greene counties, with a 60-40 split between corn and soybeans.

Soybean grower Jim Legvold, of Vincent, IA, likes to plant his soybeans as soon after the date the federal crop insurance program allows, normally about April 24 in his area in north-central Iowa.

Legvold, who sits on the United Soybean Board, says he believes early planting helps combat drought problems later. “You are going to get the beans into a more mature reproductive state before we get into the usually hot, dry scenario of August,” he says.

Iowa State University's (ISU) Palle Pedersen isn't surprised growers like the Wesslings and Legvold find good results with earlier planting dates.

In the past, ISU recommended growers wait until soil temperatures reached 55-60° F before planting beans. But Pedersen, a soybean Extension agronomist, has conducted extensive research - 32 experiments between 2003 and 2007 - that demonstrated farmers get their highest yields by planting earlier. (Pedersen says trial results in 2008 were not conclusive due to the erratic weather patterns.)

Because of his research, funded by Iowa Soybean Association and Iowa checkoff, Pedersen now advises growers who farm in the southern two-thirds of Iowa to start planting soybeans during the last week of April if seedbed conditions are good. For those who farm in the northern one-third of the state, he recommends planting the first week of May, again if seedbeds are dry and in good shape for planting.

The response from earlier planting dates depends on yield potential, according to Pedersen. “In a high-yielding environment, say 60+ bu./acre, you can lose as much as ½-1 bu. a day by delaying planting,” he says.

West Central Cooperative Agronomist Sheila Hebenstreit estimates approximately 10,000 acres of her clients' soybeans, including the Wesslings, are routinely planted prior to May 1.

“Unscientifically, we noted that our best yields were coming from our earliest-planted beans,” Hebenstreit says of her growers' crops. “I tell them, ‘If you are done with corn and planting conditions are good, go ahead and plant beans,’?” she says.

“If a plant emerges May 1 instead of May 25, that gives you close to a month of extra growing time,” she says. “My presumption is that if you have that much more energy or growth time, you get more nodes.”

Pioneer Hi-Bred Agronomy Sciences has just released a three-year study that supports the call for early planting. The Pioneer study was designed to determine the optimum soybean seeding rates for maximizing profitability at early or normal planting dates, and also to evaluate the use of three different seed treatments.

Nine locations (in Nebraska, Iowa, Illinois, Indiana and Minnesota) were studied, producing 23 site-year results. Conventional tillage and corn-soybean rotations were used. Planting dates for the study varied by geography and year, but generally early planting was considered late April through early May and normal was mid- to late May.

Pioneer Agronomy Research Scientist Jim Trybom says the study showed a trend toward higher yields from earlier planting dates (see top graph).

“Late April and early May plantings are generally what yield higher,” says Trybom. “I think the longer the growing season we get for soybeans, the more potential they have for higher yields.” Complete study results are posted on Pioneer's GrowingPoint Web site.

There are certain management precautions that must be addressed when planting early, say the experts:

  1. DON'T GO TOO FAR. “Probably one of the bigger fears is a real hard killing frost where you'd have to replant,” says Bruce Wessling. “So far, it hasn't ever happened, but it could,” he says, adding that April 20 is the earliest he's attempted to plant beans.

    “If you plant too early, you risk plants emerging a time that has a probability of a late spring frost,” agrees Pedersen.

  2. WATCH SEEDBED CONDITION. “We don't want farmers to go out and mud in their soybeans,” Pedersen says. “Seedbed conditions are critical.”

    The Wesslings, who practice conventional tillage, watch soil conditions closely and make sure they aren't attempting to plant beans in “mushy” conditions in order to avoid soil compaction problems.

    Legvold, who has been 100% no-till for the past four years, says he's also very careful about seedbed condition but has learned to manage wetter soils since going to no-till. “I plant a little shallower to avoid crusting problems,” he says.

  3. MANAGE BEETLES. “Bean leaf beetles can cause problems, but we can manage them very easily with insecticide seed treatments,” says Pedersen.

    Legvold says growers who plant beans early without using insecticide-treated seeds provide a smorgasbord for beetles drawn to the earliest emerged fields.

    “Bean leaf beetles are a big issue if you are planting early - you've either got to be prepared to spray or use a seed treatment that protects against them,” agrees Wessling.

  4. AVOID SUDDEN DEATH syndrome (SDS) and other diseases. “If you are planting early and choose a variety that is susceptible to SDS and also susceptible to cyst nematodes, you'll get hammered in August on SDS,” says Pedersen.

    “SDS symptoms do seem to increase with early planting,” says Wessling. “If we have fields that we know have a history of SDS, we'll hold off and plant those fields last.”

    Hebenstreit says new seed ratings help. “Seed companies are starting to rate their seeds for SDS so we can rate what we can count on,” she says.

NOT EVERYONE CONVINCED

Not everyone is convinced earlier planting dates necessarily improve yield. Dennis Egli, a soybean researcher at the University of Kentucky, examined the data from a large number of experiments in the Midwest, middle South and the deep South. He summarized the yield responses for a paper that is now awaiting publication at the Agronomy Journal.

“In late April and May plantings we couldn't show any advantage for earlier planting, and there are some disadvantages,” Egli says. “If you plant in cool, wet soils, emergence is often reduced,” he says. (He points out his research excluded the very early soybean production system used successfully by growers in the Deep South.)

Egli points out earlier planting dates can be risky with lower seeding rates. “In the past, if you got 50% emergence you were still OK. Now if you cut back (seeding rates) and get 50% emergence, then it's not going to be fine,” Egli says.

University of Illinois Extension Agronomist Emerson Nafziger says he doubts planting dates are a typical limiting factor in soybean yields. “This year we ended up with good yields and almost nobody planted early,” he says. “Our recommendation (to Illinois growers) is that it is best to plant soybeans in the first three weeks of May.”

Seth Naeve, an associate professor and Extension agronomist at the University of Minnesota, maintains planting in late April in Minnesota may produce positive yield results some years, but stand losses other years.

“Early planting can position a producer to have increased yields, but they probably have to have a longer season variety than they normally would plant with good conditions after planting to allow good emergence and early season growth, coupled with good conditions late in the season. If you have all of these conditions, altogether, then you can have a nice benefit from early planting,” he says.

But in other years early planting can spell loss, says Naeve, due to extended periods of very cold and wet conditions after planting that drastically delay emergence.

“When we average yields over a long period of time, we get basically a flat yield response because of this variability early on,” Naeve concludes.

Naeve, Nafziger and Egli all agree there is no reason not to plant if seedbed condition and weather are favorable in late April. “If you get a stand, there is no disadvantage that I know of to early planting,” Egli says.

Pedersen remains confident in his advice that Iowa growers should put soybeans in the ground in late April or early May, as soon as seedbed conditions allow. “If I get all of Iowa's soybeans planted by May 15, I will be very satisfied,” he says.