Claire LaCanne, University of Minnesota Extension educator-crops, Jeff Vetsch, Researcher, Southern Research and Outreach Center, Axel Garcia y Garcia, Sustainable cropping systems specialist, Southwest Research and Outreach Center, and Liz Stahl, Extension educator-crops
Cover crops are grown when there would otherwise be no crop on the ground, typically seeded in the fall and killed before spring planting. Cover crops have the potential to improve water management, protect soil, and scavenge nutrients, but similar to a cash crop, cover crops need attention and intentional management to ensure success. On the February 18 Strategic Farming: Let’s Talk Crops program, Jeff Vetsch, UMN Researcher, Axel Garcia y Garcia, UMN Sustainable Cropping Systems Specialist, along with moderator Liz Stahl, UMN Extension educator in crops, discussed cover crops and how we can manage them for optimal results. They also discussed the level of establishment and growth we might realistically expect in Minnesota.
Previous studies investigated whether incorporating winter cereal rye or a mix of annual cover crops into a corn-soybean rotation can serve to scavenge nitrogen and reduce nitrate loss in a tile drainage system. Cover crops were broadcast seeded into a standing crop in September. In late fall, the plots were strip-tilled. Biomass was measured in the fall and spring, and the cover crop was then terminated in the spring. Water samples were collected throughout the year to measure nitrates in the drainage water. This past study essentially found that sufficient biomass production is imperative in order to impact nitrate losses, and getting decent biomass was difficult in most years in a typical corn-soybean rotation with full-season hybrids.
To investigate a system where cover crops fit and can grow a little easier, a different ongoing study is attempting to assess the nitrate in drainage water from continuous corn systems compared to rotations that include silage corn followed by either a winter cereal rye cover crop that was terminated with herbicide in the spring or mix of annual cover crops (oats, forage pea, and radish) which terminated in the late fall from cold temperatures. A silage corn system is of interest in this study because silage corn allows for a longer period of establishing and growing a cover crop.
In this study, silage corn is harvested in early September and then cover crops are seeded soon after with a no-till drill, with cover crops growing within 6 weeks of planting. Plots are then strip-tilled in early November because they are on poorly drained, heavier clay loam soils. Also in early November, phosphorus, potassium, and sulfur fertilizers are also applied, but no nitrogen. By late November, the annual cover crop mix is dead and much of the residue blows away, leaving minimal cover in the winter and spring. On the other hand, winter cereal rye overwinters and provides cover in the fall, winter, and grows even more in the spring. Winter cereal rye was terminated with herbicide in the middle or end of April in response to weather conditions, but always 7-10 days before planting with a goal of planting by May 10.
Total growth and biomass of cover crops were impacted by weather and moisture, with some years having pretty good cover crop growth but other years having minimal growth. Overly dry conditions caused poor cover crop germination and growth. Though there were nuances, in most years (2022 - 2025), the silage corn with no cover crop had the largest concentrations of nitrates in tile drainage water. This was not the case in the year that had particularly low cover crop growth, making no real differences in the silage corn treatments with or without cover crops. This makes sense because if there isn’t good growth, a cover crop won’t mitigate nitrate losses because the cover crop won’t take up excess nitrogen.
Additionally, the winter cereal rye cover crop reduced nitrate concentrations in three of the four years, and the mix of annual cover crops that grew only in the fall reduced nitrates just one of the four years. This indicates that fall terminated cover crops are probably not going to do much for water quality as they are only out there for four to six weeks, maybe two months at the most. There is potential for winter cereal rye to do even more for reducing nitrate losses, but in this study, strip-tillage was used, which did reduce the stands of winter cereal rye.
Interestingly, the continuous corn system that was harvested for grain had lower nitrate losses in three of the four years compared to the silage corn, with or without cover crops. This finding likely indicates that less nitrogen is needed in a corn silage system, but rates were kept consistent in the continuous corn and corn silage systems for this study.
Overall, these studies collectively demonstrate that if a cover crop can successfully establish and grow - and grow long enough - it can reduce nitrate loss in tile drainage water. However, the findings also highlight the challenges of establishing and growing a cover crop in a typical corn-soybean rotation in Minnesota.
However, it is possible to work cover crops into a typical corn-soybean rotation as well. It will require some changes to management practices to help ensure success.
One of the major keys to cover crop success in Minnesota is selecting the cover crop species. We can have a single cover crop species or a mix of species that fits what we are trying to accomplish, be it reducing erosion, reducing nitrate losses, building soil organic matter or some other goal. We also have to use what will work in terms of planting, growth, and termination. Currently the cover crop that we find consistently works well in a Minnesota corn-soybean rotation is winter cereal rye. It’s a tough crop that overwinters well and grows well in the spring after it’s planted. It is a cool season annual cereal grain and can germinate in soil temperatures as low as 34°F, and can survive air temperatures as low as -30°F. It is winter-hardy and grows faster than wheat as well.
Axel Garcia y Garcia highlighted a study that examines how different seeding rates and termination dates impact the performance of a winter cereal rye cover crop and the following cash crop, soybean. The factors measured are biomass, the presence of green cover, water use, and following cash crop yield.
The trials take place at three Minnesota locations: Lamberton, Waseca, and Grand Rapids. The six different seeding rates included 0, 30, 50, 75, 100, and 135 lbs/acre. The cereal rye was terminated 10 days before planting soybean, at planting, or 10 days after planting soybean (planting green: soybeans planted into a green stand of winter cereal rye).
The trials reveal, perhaps unsurprisingly, that the amount of biomass produced is significantly influenced by the timing of termination; later termination results in higher biomass production because the cover crop has more time to grow.
There are some interesting results so far. Biomass has not been significantly different regardless of seeding rate, at any of the termination dates. This was consistent at all three locations. This is important because if there is no difference in biomass regardless of whether a seeding rate of 30 lbs/ac or 135 lbs/ac was used, then there is potential for reducing the cost of our cover crop seed.
Also of note is the fact that soybean yields were similar overall, regardless of seeding rate or when the cover crop was terminated. In Lamberton and Waseca, there were no significant yield differences due to termination timing or seeding rate, and in Grand Rapids, a combination of the heaviest seeding rate and termination 10 days after planting (planting green) resulted in lower yield than the other treatments. This means that even the higher cover crop seeding rates didn’t affect soybean yield at most locations, and planting green didn’t impact yield either.
Cover crops have the most benefit when they can establish and grow well, and it appears that seeding rate does not have much influence, while allowing the cover crop more time to grow has a significant impact on producing more biomass. It’s also encouraging to see that this can be done in a way that does not have significant impacts on soybean yield.
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| Cereal rye cover crop residue in soybean. Photo: Liz Stahl |
Cover crops as a means to reduce nitrate loss
Jeff Vetsch shared results from previous studies and an ongoing study at the University of Minnesota’s Southern Research and Outreach Center in Waseca which examined planting cover crops as a strategy to reduce nitrate loss in agricultural tile drainage systems.Previous studies investigated whether incorporating winter cereal rye or a mix of annual cover crops into a corn-soybean rotation can serve to scavenge nitrogen and reduce nitrate loss in a tile drainage system. Cover crops were broadcast seeded into a standing crop in September. In late fall, the plots were strip-tilled. Biomass was measured in the fall and spring, and the cover crop was then terminated in the spring. Water samples were collected throughout the year to measure nitrates in the drainage water. This past study essentially found that sufficient biomass production is imperative in order to impact nitrate losses, and getting decent biomass was difficult in most years in a typical corn-soybean rotation with full-season hybrids.
To investigate a system where cover crops fit and can grow a little easier, a different ongoing study is attempting to assess the nitrate in drainage water from continuous corn systems compared to rotations that include silage corn followed by either a winter cereal rye cover crop that was terminated with herbicide in the spring or mix of annual cover crops (oats, forage pea, and radish) which terminated in the late fall from cold temperatures. A silage corn system is of interest in this study because silage corn allows for a longer period of establishing and growing a cover crop.
In this study, silage corn is harvested in early September and then cover crops are seeded soon after with a no-till drill, with cover crops growing within 6 weeks of planting. Plots are then strip-tilled in early November because they are on poorly drained, heavier clay loam soils. Also in early November, phosphorus, potassium, and sulfur fertilizers are also applied, but no nitrogen. By late November, the annual cover crop mix is dead and much of the residue blows away, leaving minimal cover in the winter and spring. On the other hand, winter cereal rye overwinters and provides cover in the fall, winter, and grows even more in the spring. Winter cereal rye was terminated with herbicide in the middle or end of April in response to weather conditions, but always 7-10 days before planting with a goal of planting by May 10.
Total growth and biomass of cover crops were impacted by weather and moisture, with some years having pretty good cover crop growth but other years having minimal growth. Overly dry conditions caused poor cover crop germination and growth. Though there were nuances, in most years (2022 - 2025), the silage corn with no cover crop had the largest concentrations of nitrates in tile drainage water. This was not the case in the year that had particularly low cover crop growth, making no real differences in the silage corn treatments with or without cover crops. This makes sense because if there isn’t good growth, a cover crop won’t mitigate nitrate losses because the cover crop won’t take up excess nitrogen.
Additionally, the winter cereal rye cover crop reduced nitrate concentrations in three of the four years, and the mix of annual cover crops that grew only in the fall reduced nitrates just one of the four years. This indicates that fall terminated cover crops are probably not going to do much for water quality as they are only out there for four to six weeks, maybe two months at the most. There is potential for winter cereal rye to do even more for reducing nitrate losses, but in this study, strip-tillage was used, which did reduce the stands of winter cereal rye.
Interestingly, the continuous corn system that was harvested for grain had lower nitrate losses in three of the four years compared to the silage corn, with or without cover crops. This finding likely indicates that less nitrogen is needed in a corn silage system, but rates were kept consistent in the continuous corn and corn silage systems for this study.
Overall, these studies collectively demonstrate that if a cover crop can successfully establish and grow - and grow long enough - it can reduce nitrate loss in tile drainage water. However, the findings also highlight the challenges of establishing and growing a cover crop in a typical corn-soybean rotation in Minnesota.
Growing cover crops in Minnesota
There is no guarantee of getting a good establishment or growth of a cover crop. With that in mind, we need to be mindful of the management of cover crops and perhaps prioritize placing them in production systems where they are likely to thrive and not only improve water quality or reduce nitrate concentrations in tile drainage water, but also have benefits for soil health and other goals. Short-season crops like peas, sweet corn, small grains, and corn silage are systems where cover crops may fit particularly well because those systems provide a larger window for cover crop establishment and growth.However, it is possible to work cover crops into a typical corn-soybean rotation as well. It will require some changes to management practices to help ensure success.
One of the major keys to cover crop success in Minnesota is selecting the cover crop species. We can have a single cover crop species or a mix of species that fits what we are trying to accomplish, be it reducing erosion, reducing nitrate losses, building soil organic matter or some other goal. We also have to use what will work in terms of planting, growth, and termination. Currently the cover crop that we find consistently works well in a Minnesota corn-soybean rotation is winter cereal rye. It’s a tough crop that overwinters well and grows well in the spring after it’s planted. It is a cool season annual cereal grain and can germinate in soil temperatures as low as 34°F, and can survive air temperatures as low as -30°F. It is winter-hardy and grows faster than wheat as well.
Axel Garcia y Garcia highlighted a study that examines how different seeding rates and termination dates impact the performance of a winter cereal rye cover crop and the following cash crop, soybean. The factors measured are biomass, the presence of green cover, water use, and following cash crop yield.
The trials take place at three Minnesota locations: Lamberton, Waseca, and Grand Rapids. The six different seeding rates included 0, 30, 50, 75, 100, and 135 lbs/acre. The cereal rye was terminated 10 days before planting soybean, at planting, or 10 days after planting soybean (planting green: soybeans planted into a green stand of winter cereal rye).
The trials reveal, perhaps unsurprisingly, that the amount of biomass produced is significantly influenced by the timing of termination; later termination results in higher biomass production because the cover crop has more time to grow.
There are some interesting results so far. Biomass has not been significantly different regardless of seeding rate, at any of the termination dates. This was consistent at all three locations. This is important because if there is no difference in biomass regardless of whether a seeding rate of 30 lbs/ac or 135 lbs/ac was used, then there is potential for reducing the cost of our cover crop seed.
Also of note is the fact that soybean yields were similar overall, regardless of seeding rate or when the cover crop was terminated. In Lamberton and Waseca, there were no significant yield differences due to termination timing or seeding rate, and in Grand Rapids, a combination of the heaviest seeding rate and termination 10 days after planting (planting green) resulted in lower yield than the other treatments. This means that even the higher cover crop seeding rates didn’t affect soybean yield at most locations, and planting green didn’t impact yield either.
Cover crops have the most benefit when they can establish and grow well, and it appears that seeding rate does not have much influence, while allowing the cover crop more time to grow has a significant impact on producing more biomass. It’s also encouraging to see that this can be done in a way that does not have significant impacts on soybean yield.
Cover Crop Academy registration is open!
Learn more about the management of cover crops by participating in University of Minnesota Extension’s Cover Crop Academy! If you are a crop advisor, crop consultant, Extension educator, or an ag advisor in a Soil and Water Conservation District or the Natural Resources Conservation Service, the Minnesota Cover Crop Academy is for you. The Cover Crop Academy is a year-long, hybrid (online and in-person) course to give you the tools to work with farmers who want to incorporate cover crops into their crop production systems. We’ll explore how to utilize soil health practices that are agronomically and economically successful, how to work with Minnesota's short growing season, and how to help address crop production challenges with cover crops. For more information, visit the Cover Crop Academy webpage.
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