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Research Conducted
The project goal was to compare soil moisture differences based on how long rye remained in a rye/soybean relay. After rye green-up, rye glyphosate termination occurred weekly for 7 weeks (different plots). Soil moisture was recorded in each plot weekly through rye anthesis and every 2 weeks thereafter. Soybeans were planted at rye boot stage. This research was the focus of several workshops in summer 2018 including the Advance Crop Advisor’s Workshop and CREC Fall Row Crop Tour, and data were prepared for the CREC annual report and Wild World of Weeds Workshop.
Why the Research is Important to ND Soybean Farmers
Winter rye is growing in popularity as a cover crop prior to soybeans. However, past research has documented instances of rye growth reducing soybean yields under dry conditions. During wet seasons the soybeans can be planted ‘green’ (but terminated soon after) into the rye with little change in soybean yield. Other years, rye needs to be terminated several weeks prior to soybean planting to prevent soybean yield reduction. This project aims to develop a set of guidelines for rye termination timing so that producers can predict when their soybean crop may be at risk from the rye.

Final Findings of the Research
Water use patterns were fairly consistent with expectations. Peak rye water use occurred around anthesis, while soybean peak water use peaked in mid-August. Rye that was terminated at or before soybean planting had similar soil moisture as soybean-only plots. Rye continued to use water for approximately 7 days after termination. Even though there was a spike in rye water use when terminated 1 week after soybean planting, the soil moisture status improved enough that soybean yield was not affected. Only further delaying termination removed enough water to reduce soybean yields. Terminating rye at anthesis reduced soybean yields by approximately 10 bu/a. In 2018 1.5” water deficit in the top two feet of soil triggered yield reductions in soybeans.

Benefits/Recommendations to North Dakota Soybean Farmers and Industry
We are continuing to evaluate how water deficit will impact soybean yields over multiple years. Based on this and past research, the safest approach is to terminate rye two weeks prior to planting, which is also consistent with insurance guidelines. We are currently working to build a prediction tool that can be used to determine soybean yield risk from rye to assist with termination timing.