Research Highlights

Research Highlights
Evaluation of a novel drought-tolerant N-fixing inoculant on soybean yield in the Mid-South

Photo: United Soybean Board

By Julie Meyer

It’s well established that the nitrogen (N) fixing microorganism Bradyrhizobium japonicum has a beneficial impact on soybean growth and yield. Bradyrhizobium japonicum occurs naturally in soils and is also available as commercial inoculant.

In the mid-South region of the United States, which includes Arkansas, Louisiana, Missouri, Tennessee and Texas, N-fixing microorganisms have to tolerate hot, dry conditions in order to establish successful nodulation on soybean plant roots. However, there is very little information on the heat tolerance of N-fixing inoculants under these extreme environmental conditions. 

Woo-Suk Chang, biology professor at the University of Texas–Arlington, isolated a native drought-tolerant strain of Bradyrhizobium japonicum two years ago that showed outstanding performance under hot, dry conditions in nodulation, N fixation, and ability to enhance plant growth and yield by 20-30 percent.

A team of researchers, led by Chang, conducted field trials in five locations across the mid-South to further evaluate the effects of the drought-tolerant inoculant, called TXVA strain, on soybean yield at drought-prone sites. This project received checkoff support from the Arkansas Soybean Promotion Board, Louisiana Soybean and Grain Promotion Board, Mississippi Soybean Promotion Board and the University of Texas–Arlington.


Under non-irrigated conditions in Texas, Tennessee, Louisiana and Arkansas, preliminary results showed a clear trend of higher yield in soybean inoculated with the TXVA strain compared with non-inoculated plants or plants inoculated with the commercial Cell-Tech strain.

Under irrigated conditions, the team did not observe significant effects of inoculants on soybean growth or yield at any location. Similarly, in the clay-rich soils of the Mississippi delta region, there was no difference in soybean yield among the three treatments regardless of irrigation.  

Benefits of biological N-fixation

“Farmers can get two big benefits from nitrogen fixation,” Chang said. “First, they can reduce the amount of N applied to the field, and secondly, there is no negative impact of biological N fixation on the ecosystem.”

Chang also sees benefits for mid-South soybean producers through improved performance of Bradyrhizobium strains, which provide more N to the crop, thereby improving crop performance and reducing the financial cost of N fertilizers.  The team will continue to evaluate and improve the inoculants’ performance and optimize the benefits of biological N fixation under drought conditions in the mid-South.

To find research related to this Research Highlight, please visit the National Soybean Checkoff Research Database.