There is a lot of interest in planting soybeans early, but how early and not take on a lot of risk is the big question.

"One of the biggest advantages of early planting is that it provides a longer planting window for attaining maximum yields," says Duane Berglund, North Dakota State University Extension Service agronomist. "University agronomists in other states have reported that the newer soybean varieties are more tolerant of adverse, early-season conditions than older varieties. In North Dakota, soybeans planted from May 1 to May 15, in most years, will yield somewhat similarly if the maturity rating is the same. The later half of May and early June planted soybeans usually have lower yield potential than early-planted May soybeans."

The primary risk of early planting is that the beans will be damaged by freezing temperatures. This risk is mitigated to some degree by the fact that germination is delayed under cooler soil temperatures. Soybean tissue also is more resistant to freezing temperatures than corn tissue. However, the corn growing point remains below ground for several weeks or more while the terminal bud, or growing point, of the soybean is exposed early upon emergence.

"Typically, temperatures must reach 28 degrees for damage to occur if soybeans are just emerging," Berglund says. "At the cracking or cotyledon stage, soybeans can stand some frost. Once there are unifoliate and first trifoliolate leaves, then soybeans are very vulnerable to killing frosts at or below 32 degrees. There also is a risk that soil-borne diseases may damage soybean seed planted into cool soils."

If you decide to plant soybeans in the first week of May, consider the following recommendations suggested by Berglund:

• Don't plant unless the soil is dry enough to support equipment. Shallow soil compaction will haunt producers the remainder of the growing season.
• Seedbed soil temperatures should be at 46 to 48 degrees or warmer, if at all possible. A chilling injury can occur to germinating soybean seed if soil temperatures are below 44 degrees, which can cause poor seedling vigor and reduced plant populations.
• Plant soybean seeds that have been treated with a fungicide if planting into cool soils and if no-till seeding.
• Plant high-quality seed that was grown in 2005. Don't use old seed.
• Till the field or clear the residue away from the row to allow the soil to warm faster and reduce the likelihood of frost damage.
• Don't plant if the soil is on the wet side. Soybeans mudded in early fail to establish good plant stands.