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.

Results

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.

This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.