Double-cropped soybeans, planted after winter wheat harvest in mid- to late June or early July, can often be successfully grown in southern Illinois and occasionally in central Illinois. However, the likelihood of achieving good yields decreases as one moves north of Interstate 70. Double-cropping tends to be more successful in southern Illinois due to earlier wheat harvests and planting times, along with warmer fall weather and later frost dates, which provide better conditions for crop maturation.

In recent years, interest in double-crop soybeans has increased, driven by higher wheat and soybean prices. This interest has extended into central Illinois, where wheat acreage has been limited in recent decades. The yield potential for double-cropped soybeans typically ranges from 40% to 60% of that achieved with full-season soybeans planted in early May, but yields can fluctuate significantly year to year. As previously mentioned, soybean growth and development can be affected by late planting, dry conditions after emergence, and high nighttime temperatures. These challenges are often compounded when soybeans are planted into dry soil, requiring rain for germination. Additionally, ripening wheat depletes water from the upper soil layers, often leaving the soil dry by the time soybeans are planted. While early fall frosts can damage the crop, the risk has diminished somewhat due to warmer temperatures in recent years.

Table 1 presents data from an on-farm crop rotation trial in Piatt County, Illinois, conducted between 2016 and 2023. The trial involved three fields, each following a different phase of a corn-soybean-winter wheat/double-crop soybean rotation. Wheat was planted in 15-inch rows using the same planter as for soybeans. The trial showed strong yields, with full-season soybeans averaging 83 bushels per acre, compared to 41 bushels per acre for double-crop soybeans. These results are reasonable expectations for productive soils in central Illinois, though double-crop yields can vary year to year.

Getting double-cropping done

The success of doublecropped soybeans in Illinois has increased in recent years, due to genetic improvements, better planting equipment, and rotary combine technology that has enables wheat harvest at high moisture. Breeding for somewhat earlier-maturing wheat varieties, including at the University of Illinois, has helped as well. These all take on added importance as doublecropping is moved northward into central Illinois. Following is a summary of practices that can help increase chances of success when doublecropping soybeans:

Harvest wheat as early as practicable: Early harvest at wheat grain moistures up to or slightly above 20% moisture does two things: it lowers chances of repeated cycles of wetting and drying in the field that diminish grain quality; and it moves doublecrop planting earlier. The development of rotary combines largely solved the problem of physical damage to (soft) grain at high moisture. Wheat reaches physiological maturity (maximum dry weight) at moistures above 30%, so there’s no danger of losing yield when harvesting wheat at 20% moisture. Very early-maturing varieties may reach 20% moisture a few days earlier than most varieties used in Illinois, but these tend to break dormancy earlier in the spring, which can increase chances of freeze injury, and they may not yield quite as well as medium-early varieties.
Dry high-moisture wheat quickly: Because it’s usually warm when wheat is harvested, drying wheat from around 20% down to 13 % moisture can often be done with unheated air, as long as air can be moved through wheat grain fast enough to prevent spoilage. That usually means using high-capacity fans and limiting the depth of the grain layer in the bin so that air can get through more easily. Flow-through dryers may work well, and heating the air will lower the relative humidity and speed the drying process.
Handle straw to prevent planting difficulties: If there is no plan to harvest the straw, cutting a foot or more above the ground will lessen the amount of straw moving through the combine and make planting soybeans easier. Straw can be dropped behind the combine and baled off if there is a market for it, but this adds a soil-compacting and time-consuming operation. If the straw is not harvested, it should be chopped and spread uniformly across the entire combine pass width.
Make sound variety and seed treatment choices: Soybeans planted in late June or early July will experience nights long enough to cause plants to flower as soon as they reach stage V3, regardless of whether they’re in maturity group 3 or 4 in central Illinois. Later-maturing varieties might set pods for a few days longer than early-maturing ones, but whether or not that helps yields depends on how well seeds fill and when the first frost arrives. Some seed treatment might be helpful, although soybeans planted into warm soils usually emerge and grow quickly. Treated soybean seed generally cannot be carried over, so treated seed that was returned to the dealer may be available for a lower price, and might be a choice worth considering.
Plant without delay: Most double-crop soybeans are planted without tillage, usually in 15-inch rows. When soils are dry, the perennial question is whether to wait until it rains to plant or to plant then hopes it rains. If rain is in the forecast, it makes sense to plant, keeping planting depth shallow (an inch or so) for quick emergence. If it’s dry with no rain is in the forecast, it might make sense not to plant at all, especially if it’s already after July 1.
Keep costs low: The decision whether or not to plant wheat is more important than decisions regarding double-cropping soybeans after wheat harvest. Once wheat harvest approaches and double-cropping soybeans looks favorable, it still pays to minimize costs, given the variability in DC soybean yields. Getting lower-cost seed (with good germination) can help. Waiting to apply herbicides until the crop has been established can also help. If, at any point during the season, it appears that the DC soybean crop won’t return enough to pay the additional expenses, it can be treated as a cover crop in preparation for the next year.

Giovani Preza Fontes, Extension Agronomist

Reviewed in 2024