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.”