Cover cropping practices have been gaining popularity and interest as agricultural systems evolve to optimize land and resource management for greater economic and environmental sustainability.
Benefits of cover crops
In other agricultural regions, cover crops are used as an effective tool to sequester nutrients, contribute organic matter and protect soils from erosion during otherwise fallow periods. The high-intensity corn-soybean systems of Minnesota could gain similar benefits from cover cropping, particularly in the spring when soil and nutrients are most vulnerable to offsite movement.
In the upper Midwest, these losses occur through leaching and tile drain discharge, as well as surface runoff. Research conducted in southwestern Minnesota estimates an average of 25 kilograms per hectare (22 pounds per acre) of nitrate-nitrogen is lost through subsurface tile drainage between mid-September and May every year.
Minnesota cover crop research
The primary challenge that successful cover cropping faces in Minnesota is the short growing season. There’s rarely ample time and favorable field conditions to plant and establish a cover crop after the grain harvest and before winter sets in.
University of Minnesota researchers are working to identify and develop viable options for interseeding cover crops into standing corn. They conducted trials at field sites at University of Minnesota Research and Outreach Centers (ROCs) in Waseca (Southern ROC) and Lamberton (Southwestern ROC) in 2014 and 2015.
The study examined five different cover crops and three different planting methods around corn growth stage V7. Species include winter rye, red clover, pennycress, hairy vetch and an Albert Lea cover crop mixture called NitroMax CC1 (oats, peas and tillage radish).
Researchers studied three cover crop planting methods:
Drilled with a 3-in-1 InterSeeder high-clearance drill (Figure 1).
Directed broadcast (interrow) with light incorporation (dragging a rake and chain).
Directed broadcast with no incorporation.
Researchers assessed cover crop biomass and soil NO3-N levels following corn harvest (late September) and again in the spring (mid-April) prior to termination. The covers were sprayed out with glyphosate before planting. Then, soybeans were no-till planted into both plots with cover crop residue and check plots with no cover crop residue.
All cover crop species germinated, although establishment and persistence varied across species and planting methods, depending on climatic conditions.
Rye (Figure 2), red clover and hairy vetch (planted with the InterSeeder) had the most successful stands across locations after the corn harvest. However, the directed-broadcast-plus-incorporation planting method resulted in competitive stands, especially in the small-seeded species such as red clover (Figure 3) and pennycress.
Following the 2014 planting in Waseca, all species except NitroMax CC1 overwintered and produced significant biomass in the spring (Figure 4). In Lamberton, only the rye and pennycress successfully overwintered and put on significant spring growth.
Lack of snow cover in Lamberton during the winter of 2014-2015 likely resulted in winterkill of the legume cover crops. Cover crops did not affect corn yield at either location in 2014 or 2015 (Figure 5). Soybeans no-tilled into the residues (with no fertilization) all yielded competitively as well (Figure 6).
Other cover crop uses
In addition to ecological benefits, cover crops are being developed and used as added-value crops or cash cover crops that can be grazed or harvested in the spring prior to (or in relay with) the following warm-season crop rotation.
One example is seeding a winter annual forage crop following a corn silage harvest. Taking a silage crop removes more organic matter and leaves soils exposed for an even longer period of vulnerability than grain corn and soybean. You can use this time to give a supplemental winter annual forage crop more time to establish.
Due to the late frost and warm conditions, the fall of 2015 was a prime opportunity for such cover cropping. Figures 7 and 8 illustrate the establishment of a rye cover crop that was no-till planted into corn stubble following a silage harvest near Canby. Under optimum conditions, a stand like this would likely provide spring forage grazing for a couple of months before it’s terminated and planted with short-season soybeans the following spring.
Reviewed in 2018