Shawn Conley is a soybean specialist for the Wisconsin Extension Service, and he formerly worked here in Indiana. Recently, he shared his opinion about the effect that the drought of 2012 had on rhizobia, the bacteria that live in the soil and work symbiotically with the soybean plant.
Soybeans and rhizobia share a mutually beneficial relationship. The soybeans provide a protected growing environment and nutrients for the bacteria. In turn, the rhizobia “fix” nitrogen from the air in the soil, creating ammonia, which is used by the soybean plant. Nitrogen fixation works best when there is a high number of rhizobia bacteria in the soil at the start of the season.
Conley points out there is there is little research on the subject, but the research that is available does suggest that growers might expect lower populations of rhizobia bacteria in the soil in 2013 because of the 2012 drought. He stops short, however, at suggesting that every soybean acre automatically receive an inoculant treatment at planting time.
Conley also warned of another potential problem. Most soybean acres in 2013 will be planted into corn ground that was subjected to severe drought stress. Since much of that corn crop was stressed, there may be excess nitrogen present for the 2013 soybean crop.
When extra nitrogen is available in the soil, the soybean will generally use that nitrogen prior to initiating maximum nitrogen fixation. This may lead to lush early season growth, which in fields with a history of white mold, may cause problems if weather conditions are favorable. High soil nitrogen reserves may also lead to increased lodging.
In either case, Conley suggests managing your soybean crop to minimize risk of white mold or lodging. This can be accomplished through variety selection (e.g., white mold tolerance, short-statured soybean cultivars or good lodging tolerance), decreasing seeding rates and proper scouting to time fungicide applications if needed.
Jeff Burbrink is an Extension educator in agriculture and natural resources. Write to him at 17746 E. C.R. 34, Goshen, IN 46528; call 533-0554; or fax 533-0254.