You won't find this piece of anecdotal advice in any textbooks we're aware of. And we're not aware of scientific studies proving that soybeans yield better following several years of corn compared to corn/soybean every-other-year rotation fields. But anecdotal evidence over a number of years suggests that soybeans yield 5 to 10% more on fields following where corn has been raised several years in a row.
That theory may soon be tested again if farmers follow through with coffee-shop talk and switch heavily toward corn next year. Most of those extra acres they put into corn would normally have been soybeans in a corn/soybeans rotation. If that happens, then in 2 or more years there should be considerable acreage where soybeans have not been grown for several years.
Some folks believe in this concept so strongly that they say it's even worth paying a little more cash rent to get land that has been in corn several years, then growing soybeans.
Why could such a phenomenon possible be true? Agronomists suggest checking the disease angle. "Phytophthora root rot was once at the top of the most troublesome pests for soybeans lists here," says Brian McBlain, Stewart Seeds. Phythphora is a fungus.
Today sudden death syndrome, also caused by a fungus, and soybean cyst nematode, vie for the dubious honor of top spot as soybean pests in Indiana. SDS and cyst nematode are not believed to be tied directly together, although they often show up in the same field. Having cyst nematodes in the field can set up plants to be more easily infected by SDS, agronomists say.
Bot SDS and SCN can build up in the soil over time, McBlain says. And both can be causing enough root damage to limit yields, even though there are no visible symptoms aboveground that might lead you to expect there is a problem belowground so intense that it could affect yields.
When fields aren't in soybeans for a while, it stops promoting buildup of the pathogens. However, a lot still must be learned about this phenomenon. How long will SDS remain viable in the soil? What about cyst nematodes?
No one is saying to switch to continuous corn just so that you might se a yield kick on soybeans in the not-so-distant future. But it is a factor worth understanding should you be headed toward more corn anyway, experts say.