Soybeans have become an integral part of the cropping mix on Manitoba farms; however, little research information is available about longer-term effects of including soybean in rotation. A better understanding of the effects of rotation on agronomic and economic performance may help growers identify those rotations that will be profitable and sustainable in the longer-term.

In 2014, a randomized, replicated study with five rotations of soybean(S), canola(C) and wheat (W) as follows – SC, SW, SWC, SCW, SSW – was established near Brandon, MB to determine the effect of rotation length and crop sequence on soybean root rot, yield and quality, nutrient cycling, and economics for individual crops and the entire rotation over time.  The current project covered the period 2016-2021, during which 2-year rotations completed three full rotation cycles, and 3-year rotations completed two full rotation cycl

Growing season conditions varied considerably over the period 2016 to 2021, which affected crop growth, yield potential, and in turn nutrient removal in harvested grain to varying degrees.  Soybean root rot severity increased in all treatments over the period 2014-2018 before declining significantly in 2019, possibly due to dry early-season conditions, before gradually increasing again in the last two years of the study.  Effects of rotation on root rot severity also changed over the course of the study.  Based on analysis conducted to date, rotation had no effect on wheat yield, influenced canola yield in 1 of 6 years, and influenced soybean yield in 4 of 6 years although no clear and consistent trends were evident across all years.  Rotation generally had limited effects on test weight and seed size, with more frequent effects evident on % protein and % oil in seed. Preliminary economic analyses based on 2022 input and output costs aggregated over eight years of the study (2014-2021) demonstrated a higher net return in SC, SCW and SWC compared to SSW and SW, with the main driver of this difference in net return being the inclusion of canola in rotation given its high value.  This rotation study will be continued for an additional 5 growing seasons (2022-26) to better understand the longer-term effects of rotation, with further analysis of the current data also planned going forward.