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Cold weather and late winter storms have kept many farmers out of the field later than usual this spring.

It is hard to start thinking about planting soybeans when the weather hasn’t cooperated.  Corn seed will tolerate colder soil conditions than soybeans, and there is more potential lost yield if corn is planted later than normal than soybeans. So the focus this spring will be to plant corn first and then think about planting soybeans second. However many farmers run several planters today and switch one to soybeans before corn planting is even done.

In Illinois, many acres of full-season soybeans are planted in May, which leaves enough time in the season to maximize yield. Planting in April can work, but it also increases the risk of reduced yields from poorer stands and seedling diseases. Once you get past May 15, yields can go down, but the yield penalty is relatively small.

For soybeans the period from April 20 to May 10 creates the best yield opportunity. According to research conducted by the University of Illinois, soybean yield losses average about 0.3 percent per day when planting is delayed,  from May 1 to May 10; 0.4 percent per day for delays from May 11 to May 20; and 0.5 percent from May 21 to May 31. If you can’t plant until the end of May, the estimated yield loss amounts to about 15%. And in some years that happens with some full season beans and double crop beans being planted at about the same time.

What are the best conditions for planting soybeans based on soil temperature and physical conditions? For a long time farmers followed the old adage that soybeans should be planted when soil temperatures reached 55^o F. That wasn’t too hard to follow since soybeans were planted after corn, using 4 to 8 row planters and by then soil temperatures would be in the mid-50s. Today, however, monitoring soil temperature isn’t as important.

With today’s range of seed treatments as well as a seed’s ability to tolerant cooler soils and still germinate and maintain vigor, seed can seemingly withstand sitting in the soil as much as two weeks before emergence. Of course the one caveat to that is the risk of excess rainfall and saturated soil— particularly a cold rain. Seed cannot withstand more than 3 days sitting in water-saturated soils. Seeds are living entities that need oxygen and respire carbon dioxide. Deprive them of oxygen and they eventually will die. And a cold rain will be even more deadly to a seed since it can disrupt cellular member formation as seeds germinate.

Of course the soil has to be fit for planting. And that means the soil has to crumble apart between your fingers which happened when moisture levels are about 60 to 70 percent of field capacity. The soil will not compact when trafficked and will not smear causing sidewall compaction that could impede root growth. Planting when soil conditions are favorable is important to give the seedling the best chance of emerging properly. 

Today, the best signal to plant soybeans is planting after corn and when soil conditions are favorable. Rushing to plant in cold or wet conditions can lead to problems that reduce yield potential.

When it comes to planting soybeans, what triggers your urge to pull seed in the soil?

Dr. Daniel Davidson, agronomist posts blogs on agronomy related topics. Feel free to contact him at djdavidson@agrwrite.com.com or post a comment on the Illinois Soybean Advisor.