Crop rotations in Manitoba have shifted significantly in the past 10 years with the rapid expansion in soybean acres. This raises important questions about the opportunities and implications on how to optimize soybean in rotation with other crops, such as canola, wheat, and corn. This 4 year rotation study evaluates the impact of the frequency of soybeans in rotation on soybean production, economic return, and soil health in central Manitoba. As the funding for this project covered the first three of four years, this final report is reporting on an on-going project. Project funding for the final year of the project has been awarded.

Soybean Production:  The four year rotation cycle continues into 2021 with the soybean test crop year. Significant project activity will be occurring in 2021 to quantify rotation impacts on soybean performance and assess soil health over the four years.

Soil Health: Within the three years of current project funding, this project has monitored rotational crop yields, annual spring soil fertility, and carbon inputs for each rotation treatment. New methods to evaluate soil health, including active soil carbon and three soil enzymes (?-glucosidase, ?-glucosaminidase, and acid phosphatase), were used to compare the soil health impacts of rotation treatments. Active carbon was highest in the rotations that included contain corn and soybean and surprisingly in the rotation with canola and soybean at both study sites. Soil enzyme analysis did not identify differences at any of the sampling timings during the growing season. Soil enzyme activity was highest in the spring and fall, and lowest in the middle of the growing season.

Flooding: The flooding study conducted using soil from the crop rotation study found that Bradyrhizobium japonicum populations in the soil were not reduced following flooding when compared to a control treatment. This was regardless of the duration of flooding (1, 3, 6 weeks) or temperature (5, 25^oC). This observation was also confirmed when we inoculated soybean seedlings with rhizobium from the flooded and control soils and measured nodule numbers on roots after 5 weeks. These results indicate that recent soil flooding may not be an important criteria when deciding to inoculate a soybean crop in fields with soybean history as soil populations can tolerate flooding.

This study continues to serve as a platform for multidisciplinary collaborations including plant pathology for soybean root and foliar diseases and for soil microbial community analysis including soil populations of Bradyrhizobium japonicum.