Strategic Farming: Let's talk crops session talks modeling soybean success after a winter rye cover crop

By Angie Peltier, UMN Extension crops educator, Garcia y Garcia, UMN Extension sustainable cropping systems specialist and Seth Naeve, UMN Extension soybean agronomist

On February 19, 2025, Axel Garcia y Garcia, UMN Extension sustainable cropping systems specialist joined UMN Extension crops educator Liz Stahl for a discussion about how he is using crop modeling to help soybean and corn producers gain important insights into how to successfully incorporate a rye cover crop into their cropping system before their soybean crop. This was the seventh weekly episode of the 2025 Strategic Farming: Let’s talk crops! webinars. The series runs through March.
To watch this and other episodes: http://z.umn.edu/StrategicFarmingRecordings

A 12-state effort to assist farmers

Garcia y Garcia and Seth Naeve, UMN Extension soybean agronomist, are the Minnesota representatives of a much larger team of university-based agronomists and cover crops experts working together to gather data and develop tools to eventually assist farmers in successfully incorporating a winter rye cover crop into their soybean rotation with the goal of reducing barriers to and increasing cover crop adoption in the US. The impetus for this project was the observation that despite the known benefits of cover crops, adoption of this practice is very low in agronomic cropping systems. This project is funded by the United Soybean Board and managed by Iowa Soybean.

 
The team modeled cover crop and soybean growth and development across states which include Minnesota, Wisconsin, Iowa, Illinois, Nebraska, Michigan, Indiana, Ohio, Pennsylvania, North Carolina, Louisiana, and Kentucky. They are using statistical procedures to determine relationships among soil and weather variables affecting soybean following a winter rye cover crop, with the overall goal of maximizing the cover crop biomass and determining soybean yield penalty associated with cover crop adoption.

 
Using soil, and daily weather data for a period of 34 years (1990-2023) at each location, the team is modeling cover crop biomass and soybean yield. Model outputs can also be used to assess environmental impacts, economics and resource use (ex. water use) associated with cover crop and soybean production. Simulations are now being compared to real-world data obtained from 48 location-years of on-farm trials. This on-farm data will be used to calibrate and validate the model outputs with the end goal of being able to provide better information about how to achieve benefits and reduce risks from cover cropping.

 
In each participating state, two on-farm experiments in both 2024 and 2025 will be used to calibrate and validate simulated results; Lamberton and Le Sueur are the two Minnesota locations. The soybean varieties used for these trials differ by state to accommodate locally adapted soybean maturity groups.  Four rye seeding dates and four termination dates per seeding date (a total of 16 treatments) also differed by location. At all locations in each participating state, the same rye variety was planted at the same seeding rate, mimicking a drill seeding and termination using herbicides. The other factors that may have varied among states were row spacings and irrigation in Nebraska.

What Modeling Can Tell Us About Planting Date

The models suggest that the best planting date to maximize biomass of the rye cover crop is mid- to late-September in most of the participating states (September 19 in Minnesota), with Kentucky, Illinois and Louisiana as exceptions. In Minnesota, there is a slight yield penalty that could be alleviated if one delays planting by 5 days after termination and a slight yield gain if planting is delayed 10 days after termination. Garcia y Garcia was pleased at how closely the simulations mirrored his decade-long experience experimenting with cover crops in southern Minnesota because his research shows that cereal rye performs well when planted between mid-September and September 20. In Minnesota, the models (and past agronomic experience) tell us that the best rye termination timing typically coincides with the best soybean planting date.

Thanks to the Minnesota Soybean Research & Promotion Council and the Minnesota Corn Research & Promotion Council for their generous support of this program!