Director of Research, Iowa Soybean Association

Soybean production practices in the United States have changed tremendously in the last 20 years often responding to advances in technology and equipment design and availability.  As farmers strive to find new information and new technology to improve soybean yield they may try any number of seed or soil inoculants that are currently marketed. However, the odds of getting a yield increase from inoculants may not be good.

A 2007 survey of farmers by crop specialists at land grant universities found that 18 percent of farmers in Indiana used an inoculant while a separate survey in 2008 found 85 percent of farmers in Wisconsin used one. Inoculating soybeans with products containing the bacterium Bradyrhizobium japonicum is considered an inexpensive management tactic to increase yield. The bacterium forms a symbiotic or beneficial relationship with soybean roots allowing for nitrogen fixation to occur.

Current recommendations for the use of inoculants in the Midwest suggest they should be used if soybeans have not been grown in a field in the last 5 years or if a field has been flooded for more than seven days.

Purdue University researchers concluded in 2005 that “Inoculant use [in a soybean/corn rotation] may be a viable method of increasing soybean yield.” In contrast, researchers from the University of Nebraska-Lincoln recently published that the use of inoculants in a field that had been planted to soybeans in the recent past was unnecessary.

University soybean specialists from several Midwest states recently took a big-picture look at the data from several research trials investigating the performance of inoculants for soybeans.  They found that 51 inoculant products had been evaluated in 73 experiments conducted between 2000 and 2008 in Indiana, Iowa, Minnesota, Nebraska, and Wisconsin.

The result?

The research team reported that sixty-three of the 73 environments (environment = year x location) showed no significant yield response to an inoculant. Four of the environments showed a negative response from the inoculants between the range of five and seven percent. And only six of the environments showed a positive response between five and twenty-three percent greater than the control.

Rising input costs, escalating land prices, and volatile commodity prices are all driving the need for soybean producers to improve profitability. However, the use of inoculants to increase yield may not be the solution farmers are looking for, especially if soybeans have been grown in the recent past.  In fact, the prophylactic use of inoculants without an active on-farm testing program could be costing you money. However, if a field has not produced soybeans in the past four or five years or has never produced soybeans, an inoculant is needed for nitrogen fixation to occur.

Higher soybean yields can be achieved with greater levels of management and the adoption of current, science-based best management practices. Many of these recommendations can be found at www.planthealth.info, the North Central Soybean Research Program’s website for information on soybean production. That’s your soybean checkoff. Delivering Results.