On May 12, the ISRC held its first ever research project webinar on the recently concluded multi-year study on Optimizing Continuous Soybean Production, which was selected for ISRC funding in the fall of 2022. The webinar was held exclusively for the center’s Industry Advisory Council to provide findings and answer questions about the project. ISRC Co-director Mark Licht served as the webinar host with the project’s lead researchers Sotirios Archontoulis, agronomy, and PhD student Carolina Freitas providing an overview. Collaborator, Greg Tylka, plant pathology, entomology and microbiology, joined the group for a question answer session to provide insight on soybean cyst nematode (SCN) counts.
Currently, the study (specific to Iowa) seems to be disproving the long-held theory that soybean should be rotated with corn to avoid yield penalties, especially from increased disease pressure, particularly from SCN, as well as potential nutrient and water loss in the soil. Since continuous soybean is a lower cost system, in tough economic times, when nitrogen and other crop production inputs are high, growing soybean a second or third year in a row may be more cost-effective.
Archontoulis says Iowa soils seem good for supporting a continuous soybean system and that improvements in plant traits and crop management have likely helped to reduce the yield penalties researchers thought they would see. However, he urges caution in growing soybean exclusively year after year due to concerns with soil composition and weed management associated with herbicide resistance.
The project evaluated environmental impacts such as soil moisture, nitrogen losses and SCN pressure. While researchers found similar seasonal water use between continuous soybean and corn-inclusive rotations, nitrogen loss was significantly lower in the continuous soybean system. And, when cereal rye cover crops were added, nitrogen losses were reduced even further.
Tylka provided information on SCN counts, which were expected to be one of the major causes for yield penalty; however, over the years of the study big increases in SCN populations have not been seen.
While more time is needed to see how long continuous soybean can be grown without eventually seeing major yield penalties, initial results are positive. This project is continuing with funding from the Iowa Soybean Association. More information on this project can be found in the ISRC’s April newsletter and in this article by the Iowa Soybean Association.
