In late April, there is often a lot of interest in getting soybeans planted in the region. But, how early is “to early” without taking on a lot of risk? Though we are now at a time when soybean planting is going fast and furious as weather allows, there are still some interesting items to review when making soybean planting decisions.

One of the biggest advantages of early planting is that it provides a longer planting window for attaining maximum yields. University agronomists in other states have reported that the newer soybean varieties are more tolerant of adverse, early-season conditions than older varieties. In Northern Minnesota, generally soybeans planted from May 1 to May 15 in most years will have comparable yield if the maturity rating is the same.

Our planting date trial in 2006 had an optimum planting date of May 16.  Our first planting date on April 25, yielded 7 bushels less and planting on May 1 yield 4 bushels less than planning on May 16.  Soybean planted in late May and early June usually have lower yield potential than soybean planted in early May.  From the 2006 trials yields continued to decrease after May 16 with the last planting date on June 15 yielding 20 bushels less.

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 is also 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°F for damage to occur if soybeans are just emerging at the cracking stage, or cotyledon stage, and can with-stand some frost. At the unifoliate and 1st trifoliolate leaves, soybeans are very vulnerable to killing frosts at or below 32 F. There is also risk that soil-borne diseases may damage soybean seed planted into cool soils.

When deciding soybean planting decisions, you should consider the following recommendations: