Cover Crops for Major Cropping Systems


Cover crops are crops that are grown to provide soil coverage during seasons when a crop is not actively growing.  Cover crops are useful management tools for enhancing the sustainablity of agroecosystems and reducing negative environmental impacts in the corn and soybean system.  Cover crops have potential to decrease soil erosion, provide green manure for incorporation and to produce bioenergy, forage or grain for harvest.  Cover crops also improve agroecosystem functioning by recycling nutrients, improving soil structure, increasing soil organic matter, suppressing weeds, and disrupting pest and disease cycles.   Cover crops play a unique role in remediation of excess soil nitrogen that can damage water quality by taking up water and nitrates from the soil in the late fall and in early spring when substantial amounts of nitrogen leach through the soil.  We will present both annual and perennial crover crops solutions.  Winter annual cover crops lengthen the “green phase” of a corn-soybean croppping system by growing in the months between harvesting  and planting.  We have ongoing programs on five annual cover crops: winter barley, winter peas, hairy vetch, winter rye, and brassicas, and one perennial cover crop:  Kura clover.


Winter Peas - A High Value Winter Cover Crop

Austrian winter pea

Austrian winter pea

Winter pea has potential for dual use as a winter cover crop and as a high value food crop.  Current cultivars lack sufficient winter hardiness to consistently survive as a winter annual in the Midwest.  A Minnesota cropping system use scenario would consist of peas being planted during September and harvested for grain the following June.  Following pea harvest, corn would be planted.   Austrian winter peas, often referred to as ‘black peas’, have been produced in the Pacific Northwest as a green manure and for mature dry seed production since the 1930s. The USDA-ARS Grain Legume Genetics and Physiology Research Unit at Pullman has been developing improved breeding lines with greater winter hardiness for their climate and higher food quality.

The University of Minnesota has established collaborative relationships with pea breeders from the USDA-ARS and North Dakota State University to evaluate plants for testing in Minnesota.  However, our ongoing experiments have shown that plant materials developed by these programs have only a moderate level of winter hardiness and inconsistent winter survival.  Minnesota farmers would benefit from the establishment of a dedicated winter pea breeding program, which could provide lines adapted to the state’s unique conditions including winter temperatures, snowfall, spring freeze and thaw cycles, and soil moisture patterns. Specific plant breeding objectives for a winter pea breeding program involve identifying winter pea germplasm that: 1) has sufficient winter hardiness to consistently survive winter conditions, 2) has increased biomass production, 3) nodulates and has a high potential to fix atmospheric nitrogen in the fall and/or early spring, and 4) has early maturity to allow double cropping of corn or soybean after pea seed harvest. In addition, agronomic research is also needed to reduce the risk of planting winter peas for growers.

Our research has shown that winter hardiness in pea is highly sensitive to time of seeding. Survival also depends greatly on snow cover, which is increased by the presence of stubble or other plant material that can hold snow in place over the course of the winter. Agronomic research objectives include 1) determining which areas of Minnesota are most suitable for winter pea production, 2) establishing recommendations on timing and methods of planting, and 3) determining suitable methods of providing cover to catch snow, including no-till planting into stubble and intercropping with other fall-planted cover crops.


Hairy Vetch - A Traditional Legume Cover Crop to Improve Modern Crop Rotations

hairy vetch

Hairy vetch

Hairy vetch is an annual legume that has been used as a winter annual cover crop.  It is unique in that it is the only legume that can be fall seeded and reliably overwinter in Minnesota.  In addition to providing winter cover and reducing soil erosion potential, hairy vetch can capture and fix nitrogen for subsequent crops through biological nitrogen fixation.  A use scenario for hairy vetch consists of planting it late in the summer in standing crops or late in the fall following corn and soybean harvest, killing regrowth in the spring, and planting a grain crop in the spring that requires high nitrogen fertility.  In our ongoing research, we have selected Minnesota ecotypes for increased winter hardiness.  However, there is a need to enhance this initiative and develop a breeding program with the objectives being 1) to select for additional reliable winter hardiness to allow for later planting dates in October and November after soybean and corn harvest and 2) to select for earlier maturity in the spring.


Winter Rye - Using a Traditional Small Grain Cover Crop to Improve Modern Crop Rotations.

winter rye

Winter Rye

Winter rye grain is an excellent winter cover crop especially in the upper Midwest because of its winter hardiness, ability to scavenge nitrogen and sequester carbon, and ability provide effective ground cover in the fall, winter and early spring.  It is the only small grain with sufficient winter hardiness to reliably overwinter in Minnesota.  In addition rye herbage contains chemicals that upon decomposition suppress the growth of weeds.  A use scenario for winter rye consists of planting it in a standing crop in late summer or late in the fall following corn harvest, then killing the regrowth in the spring, and planting a crop with low nitrogen requirements like soybean in the residue. Unfortunately, there has been no recent variety development of winter rye varieties and all commercial varieties mature in late June nearly a month later than the recommended soybean planting dates.  The objectives of the winter rye cover crop breeding program are to develop varieties that: 1) flower earlier in the spring to allow earlier seeding of the subsequent crop, and 2) have increased early season biomass (by May 15) compared to existing varieties.


Brassicas - A Traditional Non-legume Cover Crop to Improve Modern Crop Rotations

brassica cover crops

Brassica cover crops include radish, turnip, mustards, and winter rape or canola.  They are fast-growing, deep-rooted, and excellent nitrogen scavengers.  Their rapid growth and high protein content means they have great potential for use as an emergency forage.  Spring canola is also grown as an oilseed crop.  The University of Minnesota has tested brassica cover crops over the past two years in partnership with Michigan State University.  Radish and mustards winterkill in our climate, which makes them well-suited for situations in which an overwintering cover crop is not desired.  Winter rape and turnip showed some ability to overwinter in variety trials conducted in St. Paul over the past two winters, but do not overwinter reliably.  A use scenario for brassicas consists of planting them in late summer following a processing vegetable or small grain crop or into a standing grain crop, grazing them in late fall, allowing them to winterkill or killing the regrowth in spring, and planting corn and soybean.  There is a need to develop a breeding program to select for improved forage quality and increased winter hardiness.


Kura Clover - Living Mulch for Corn and Livestock Production System

Corn in Kura CloverKura clover

Left: Corn planted into kura clover. Right: Kura clover in bloom.

Kura clover is a rhizomatous, perennial clover that has shown considerable promise in the north central United States as a long-term alternative to other short-lived legumes.  Kura clover is remarkably persistent and can withstand extreme environmental conditions including drought, water logging, and cold. It can also tolerate a wide variety of defoliation intensities. First introduced to the United States in 1911 from the Caucasus region of Europe/Asia for use as a honey crop, Kura clover has shown superior yield, persistence, and forage quality under a diversity of grazing systems and livestock.  Kura clover also has unique applications in soil conservation and as a living mulch crop.  We propose to promote use of Kura clover as a living but suppressed perennial sod into which corn or other grain crops is planted into strips killed with an herbicide.  When the crop is harvested, Kura clover, which has spreading underground rhizomes, can regrow into the space where the corn was grown.  The Kura clover can then be grazed in the late fall and following year.  

The Minnesota Kura clover breeding program has selected germplasm for a diversity of traits related to forage and cover crop utilization.  These include seedling vigor, early flowering, forage yield, plant architecture, and spreading ability.

However, inadequate seed supplies remain a significant limitation to widespread use of Kura clover.  We propose to expand our plant breeding program using our improved populations with the objectives being to 1) improve seed yield and 2) to increase the harvest ability of the seed with improved ease of threshing. 


Deborah Allan, Professor Emerita, Department of Soil, Water and Climate

John Baker, USDA-ARS, St. Paul

Nancy Ehlke, Professor, Department of Agronomy and Plant Genetics

Axel Garcia y Garcia, Assistant Professor, Department of Agronomy and Plant Genetics

Julie Grossman, Assistant Professor, Department of Horticultural Science

Paul Porter, Professor, Department of Agronomy and Plant Genetics

Craig SheafferProfessor, Department of Agronomy and Plant Genetics

M. Scott Wells, Assistant Professor, Department of Agronomy and Plant Genetics

Don WyseProfessor, Department of Agronomy and Plant Genetics

Cover Crops for Major Cropping Systems: Topics

covercrops 2-pager front page image

winter/summer pea 2-pager front page image

Cover Crops for Minnesota's Farms

UMN ForeverGreen--Cover crops for Minnesota's farms