New cover cropping opportunities in Minnesota
Cover cropping practices have been gaining popularity and interest across the agricultural landscape as systems evolve to optimize land and resource management for greater economic and environmental sustainability.
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 25 kg ha-1 (22 lbs/ac) of nitrate-nitrogen is lost through subsurface tile drainage between mid-September and May every year.
Minnesota cover crop research
The primary challenge facing successful cover cropping in Minnesota is the short growing season. There is rarely ample time and favorable field conditions to plant and establish a cover crop after the grain harvest and before winter sets in. Current research at the University of Minnesota is working to identify and develop viable options for interseeding cover crops into standing corn. Field sites are at the University of Minnesota Southern (Waseca) and Southwestern (Lamberton) Research and Outreach Centers, and trials have been conducted for the past two years (2014 and 2015).
The study is looking at 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).
Figure 1. High clearance drill (InterSeeder™) planting cover crops into standing corn at Lamberton, MN (June 26, 2015)
The three cover crop planting methods are as follows:
- 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
Cover crop biomass and soil NO3-N levels were assessed following corn harvest (late September) and again in the spring (mid-April) prior to termination. The covers were sprayed out with glyphosate and soybeans were no-till planted into the residues, as well as check plots with no cover crops.
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 + incorporation planting method resulted in competitive stands especially in the small seeded species such as red clover (Figure 2) and pennycress.
Figure 3. Cover crop spring biomass by species and planting method prior to termination and soybean planting in Waseca, MN, 2015.
Following the 2014 planting at Waseca, all species (except for NitroMax CC1) overwintered and produced significant biomass in the spring (Figure 3). At 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 4). Soybeans no-tilled into the residues (with no fertilization) all yielded competitively, as well (Figure 5).
Figures 4 and 5. Corn (left) and soybean (right) yields measured from different interseeded cover crop treatments in Waseca and Lamberton, MN, 2015. Cover crops planted into V7 corn and soybeans were no-till planted into the cover crop residue.
HV=Hairy vetch; N-Max=NitroMax mix (pea, oat, tillage radish); PC=Pennycress; RC=Medium red clover; WR=Winter rye; CHK=Check (no cover crop).
Other cover crop uses
In addition to ecological benefits, cover crops are being developed and utilized 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. This time can be utilized as a greater window for establishment of a supplemental winter annual forage crop.
The fall of 2015 was a prime opportunity for such cover cropping. Figures 6 and 7 illustrate the establishment of a rye cover crop no-till planted into corn stubble following a silage harvest near Canby, Minnesota. This stand will likely provide spring forage for approximately 2 months of grazing before it is terminated and planted with short season soybeans in the spring of 2016.