Come end of June, Minnesota grower Norm Giese will be planting soybeans again, just like he has done for the last 13 years, successfully. The Appleton, MN, farmer and his son and son-in-law grow 5,000 acres of corn, soybeans and dry edible beans. They also grow 350 acres of fresh peas for a local processor.

After the peas come off in late June, Giese plants a second crop of seed soybeans for Pioneer. Despite the brief growing season here – the farm is at the 45th parallel – Giese has successfully double-cropped peas and soybeans since 1998.

Late planting does reduce yield potential. Yet most years, Giese’s irrigated double-crop yields aren’t much behind his full-season beans, he says. And the combined value of the pea and bean crops makes those fields among his most profitable, he says.

But it takes careful management to squeeze out a second crop in the 80 days or so left after pea harvest. His strategies include:

“It’s not an easy thing to pull off,” says Steve Redepenning, a Pioneer agronomist who works with the Gieses. “Your window for getting the peas off, the soil worked, and the crop planted and watered is very limited.” Late planting also intensifies other crop risks, adds University of Minnesota Extension Crops Specialist Lisa Behnken, including soybean cyst nematode, glyphosate resistant weeds and early frost.

Minnesota is “on the northern fringe of where double cropping is possible,” says Seth Naeve, University of Minnesota Extension soybean agronomist. “Anecdotally, we’ve learned a tremendous amount about planting dates and variety selection from the ‘pea-bean’ guys.” Without much formal research to guide them, these northern double-croppers “have optimized their systems by practicing,” Naeve says. They demonstrate that “farmers can plant soybeans quite late and still have a return.”

In 2011,the Giese family finished harvesting 350 acres of peas on June 25. To prepare the rutted soil for a second crop, they chisel-plowed the pea fields, followed by a pass with a Summers Supercoulter vertical-tillage tool equipped with a harrow. The Gieses’ full-season soybeans are all no-till. But when you’re planting this late, Giese says, “a well-prepared seedbed is extremely important” to ensure rapid emergence.

On June 28,as temperatures pushed into the 80s, the family began drilling soybeans, finishing up July 1. Over the last 14 seasons, the earliest they’ve finished planting their second crop of soybeans was June 18; the latest, July 7. Soybeans planted around July 5 will reach about 50% of their yield potential, Naeve says, due to fewer hours of sunlight during the shorter growing season. “Light is directly related to yield potential.”

For example, University of Nebraska research showed that for each day that soybean planting is delayed after May 1, the yield penalty is ¼-5/8 bu./acre/day. Likewise, research from the University of Wisconsin showed an average yield loss of 0.4 bu./acre/day when soybean planting is delayed past the first week of May. Yield losses accelerate in late June. In University of Minnesota trials from 2007 to 2010, average yields on short-season soybeans dropped 6-8 bu./acre for each week that planting was delayed beyond June 25.

Giese plants double-crop beans in 7.5-in. rows and boosts his normal seeding rate by 50,000 seeds/acre, aiming for a harvest stand of 200,000-210,000 plants. Higher seeding rates tend to increase plant height and nodes per acre, resulting in more pods, he says. “This late in the season we see an excellent yield response to higher population. That part of management is very different from full-season soybean management.”

Giese limits pea-bean production to fields with center-pivot irrigation, so he can count on adequate moisture. Plants emerge in four or five days. “We’ve planted on Friday and ‘rowed’ them on Monday.”

Giese applies enough potash and phosphorus for both peas and beans along with a preplant herbicide before peas. Weed pressure on the second crop is generally light, he says. However, late-planted soybeans “are very susceptible to aphids, so we have to manage that carefully.” CruiserMaxx seed treatment helps, but Giese keeps a close eye on aphid counts and has to spray at least once.

Key to double-crop success

The most important factorin successful double cropping is matching maturity to planting date, Naeve says. The trick is to find the latest maturing variety that will ripen before the first killing frost.

Faster-maturing varieties have lower yield potential: In Wisconsin trials, the yield penalty for planting a short-season bean vs. a full-season bean, ranged from 1% to 9% when seeding took place June 20 or July 1.

Giese takes a conservative approach to soybean-maturity selection, convinced that he gives up little yield in exchange for lower frost risk. That’s especially important because, in his region, double-crop soybeans can’t be insured. “We’ve discovered, over the years, that attempts to gain yield by adding maturity don’t work.”

His full-season beans range from 0.8 to 1.4 RM. On his double-cropped fields, he plants a Group 00 soybean, Pioneer 90M01, rated for North Dakota and northern Minnesota. It’s unusually tall and has a strong set of agronomic traits, including a high iron-chlorosis score. “These extremely early beans come with tremendous defensive traits because they are going into such hostile environments.”

In 2011, an early frost hit Sept. 15, before the beans were mature. Giese watered the plants heavily before the freeze. The top third of most plants died, but the bottom pods continued to fill over the next couple of weeks. The seeds were smaller than normal, yet “very marketable,” Giese says. Last season’s average yield on 350 acres of irrigated double-crop soybeans was 39 bu./acre.

Giese’s 14-year average on double-crop soybeans is around 38 bu./acre, he says. That’s excellent for late-planted soybeans, Naeve says. In four years of trials in southern Minnesota, yields of short-season soybeans planted June 25 averaged 34.3 bu./acre.

In 2010, Giese averaged 45.3 bu./acre on 00 maturity group beans, seeded beginning on June 20. “We had areas of those fields that produced 55-58 bu./acre. This tells me that you don’t have to have a late-season variety to get good yields.”

Nor is it necessary to plant full-season soybeans at the very earliest opportunity, he believes. “We wait until the soil temperature is 55° or 58° F at 10 a.m., and 60° is better.” On non-irrigated fields, “Our most successful full-season no-till beans are the ones that we seed in the last half of the planting schedule.”