Farmers Collaborate to Test Nutrients in Cover Crops

Local study finds nitrogen-rich cereal rye could help reduce fertilizer needs

This spring, farmers from Rice and Steele counties joined forces to better understand the nutrient value of cover crops—specifically cereal rye—on their fields. With support from the Minnesota Department of Agriculture and the University of Minnesota Extension, the Soil and Water Conservation Districts in Rice and Steele counties collected biomass samples from ten fields to assess the levels of nitrogen (N), phosphorus (P), and potassium (K) contained in the growing plants.

The lab results revealed that cereal rye biomass held an average of 24 pounds of nitrogen per acre—a nutrient essential for healthy crop production. This data highlights the potential for cover crops to not only protect soil but also contribute to a farm’s nutrient management plan and groundwater protection.

Cover crop height is measured in a Rice County farm field. The measurements were used to determine the amount of nitrogen present in the biomass.

How Cover Crops Work

Cover crops like cereal rye, winter wheat, field peas, and radishes are planted in rotation with or between cash crops like corn and soybeans. Winter annuals, such as cereal rye and winter wheat, germinate in the fall, lie dormant over winter, and resume growth in spring. This seasonal growth cycle allows them to cover the soil during vulnerable times, reducing erosion and improving soil health.

One key benefit of cereal rye is its ability to “scavenge” leftover nitrogen from the soil after harvest, helping to prevent it from leaching into tile drainage systems, groundwater, and waterways. According to a study in Iowa, approximately 60% of the nitrogen stored in above-ground cereal rye biomass becomes available to the following crop within about three months after the cover crop is terminated. This can reduce the need for synthetic fertilizers, especially for corn, which are environmentally and economically costly.

Field Results Vary by Cover Crop Growth Stage

The amount of biomass produced varied widely across the ten fields, ranging from 250 pounds to 4,770 pounds of dry matter per acre. Fields terminated earlier in the spring had significantly less biomass. For instance, a field where rye was only 5 inches tall at termination had the lowest biomass levels, while the highest came from a field where rye reached 33 inches before being harvested as forage for dairy cattle. That same field was later planted with soybeans. In general, the more biomass there is, the more nitrogen the cereal rye is able to scavenge and recycle to the next crop.

Feeding Local Knowledge into Regional Innovation

This local initiative contributes to a broader effort across Southeast Minnesota, where 25 farmers from seven counties submitted a total of 102 cover crop samples. The data is being compiled to support the development of a mobile application that will allow farmers to estimate biomass, nutrient content, and environmental performance in real time by simply using height measurements and the camera on their smartphone.

Once released, the app will help farmers make more informed decisions about nutrient needs, potentially saving money on fertilizer and supporting conservation goals at the same time.

Learn More

If you’re a farmer or own land being farmed and you’re interested to learn about managing cover crops, contact your local Soil and Water Conservation Office. In Rice or Steele Counties, you can call Alan Kraus at 715-897-1646. Funding assistance for cover crops is available. Act soon to learn about program details.

Alan Kraus is a Soil Health Specialist with the Rice and Steele SWCDs. He works with producers and landowners in both counties to implement soil health conservation practices. In Rice County, he also promotes the Soil Health Incentives Program and Custom Interseeding Program.