Farmers who have struggled to justify the expense of planting cereal rye can now give it a virtual shot, thanks to a tool that simulates a field’s past and future growing seasons with the cover crop.

In the first of many versions, this cover crop decision support tool gives farmers projections for managing cereal rye termination and calculating how much nitrogen the crop keeps from leaching into waterways.

Related: 5 tips for cutting weed pressure with cover crops

The Farmdoc project at the University of Illinois plans to release updates to this cover crop analyzer in the future. The web tool relies on field boundaries from the Farm Service Agency, along with data from cover crop trials, the Illinois State Water Survey and USDA’s SSURGO (Soil Survey Geographic Database) soil survey, says Jonathan Coppess, U of I ag policy specialist.

“A farmer can open the tool and select their field,” he explains. “After running the simulation, you can take the results to your landlord and say, ‘This is what adding cover crops in this specific field would do, or what we would expect will happen.’”

Farmers can even apply the tool to their field in a previous year, thanks to archived weather data, and see exactly how the cover crop would have worked for them. If they select a future year instead, they can choose an average for temperature and precipitation for the field over the past 10 years. They can also choose to simulate cover crop growth during extremes over the past 10 years, like the drought year of 2012 or wet seasons like 2019.

At this point, the cover crop analyzer only works for cereal rye, but Coppess says his team is working on including more species. Cereal rye was the easiest to model due to its similarities with wheat, which is one of the 42 crops scientists have already developed growth simulations for. For hairy vetch and other crops, they must start from square one.

Biomass, C-N ratio

To make it easier to use, the tool generates defaults for a given field based on available USDA data. This includes crop history, average seed population and the average nitrogen application in the field’s region. But farmers can change those figures to be more specific.

“If you apply more than 180 pounds of N per acre, for example, you can change the default through the ‘My Farm’ tab,” Coppess says.

Two key numbers the simulation puts out involve the biomass and carbon-to-nitrogen ratio of cereal rye. From there, it calculates nitrogen uptake and how much nitrogen loss the crop could prevent. Farmers can look at how these numbers vary by running the simulation multiple times with adjusted inputs, such as less applied nitrogen.

Understanding biomass growth also helps farmers plan for terminating the cover crop before it gets so large that it’s harder to manage or plant into.

“Biomass will change based on weather, based on the day you choose to terminate. But having that number simulated before you even plant is important to understand the timeline you’re working in,” Coppess says.

While an abundance of residue is a common reason farmers cite for not adopting cover crops, after years of using them in a given field, microbe populations are built up to where they decompose corn and soybean residue faster. This helps cover crop farmers plant earlier, but it takes three years for the effect to show up. The next iteration of the cover crop analyzer tool will include simulated decomposition of cereal rye.

The Walton Family Foundation is funding future developments in the cover crop analyzer, which will be implemented by U of I’s National Center for Supercomputing Applications.