Many farmers throughout Illinois are giving serious consideration to double-crop soybeans after the harvest of their winter wheat this year, reports Bob Frazee, University of Illinois Natural Resources Educator.

Double-crop soybeans are typically planted following the harvest of the winter wheat crop, which usually occurs in late June or early July. According to Frazee, the high market price for soybeans, coupled with excellent soil moisture and a maturing wheat crop offer extra incentives for these Illinois soybean producers to try double-cropping this year.

Historically, the main problem encountered with double-cropping soybeans is when an exceptionally early frost occurs in the fall, before the soybeans have reached maturity.

Research from throughout the Midwest on double-crop suggests that planting with a grain drill is best to obtain the full yield potential of double-cropped soybeans, though 15-inch rows may produce yields almost as high. According to Frazee, double-crop soybeans are usually considerably shorter in height than soybeans planted in a May seeding and thus are more responsive to narrow-row planting.

Also, research has shown that increasing plant densities by 50% to 100% in conjunction with timely spring seeding has shown significant yield increases. Greater numbers of small soybean plants are required to capture sunlight effectively. Because July and August are typically hot with limited rainfall, Frazee emphasizes planting double-cropped soybeans with a no-till drill is also a very practical means of conserving soil moisture.

Double-cropped soybeans typically germinate in a much warmer environment than when planted in May, and thus will result in rapid emergence if soil moisture is available. However, Frazee cautions that higher temperatures, especially at night, will limit vegetative development before flowering beings.

Frazee suggests soybean varieties which are best suited for double-cropping are those that are those high-yielding varieties classified as midseason to full season for the area. Research shows if a variety is early for a location is planted, then the time for vegetative development prior to flowering is extremely limited. Also, those varieties with determinate growth habit should not be planted for double-cropping as this will result in an extremely short plant with low yield.