Planting Green in the Frozen North

Objectives & Approach

This project will address multiple agronomic impacts of planting green (i.e., planting soybeans into a living rye cover crop). This project will meet this goal by achieving the following objectives:

1. Determine optimal combinations of seeding rate and termination timing for planting green in a wheat-soybean, corn silage-soybean, or corn grain-soybean rotation.

   Cereal rye is a hardy, overwintering cover crop capable of surviving the harsh winters of the Northern Great Plains. The tradeoff for its winter-survivability is that it requires additional attention in the spring to avoid interference with the subsequent cash crop. Because we will be planting green, we cannot use tillage to terminate the rye cover. Instead, we will rely on glyphosate for rye termination. Finding both the optimal seeding rate and the optimal termination timing will be critical to control the rye cover and avoid associated soybean establishment issues in the spring.

2. Quantify the effect of cereal rye on agronomic production impacts such as: a) soybean nutrition, b) soil microbial activity, and c) incidence of soybean disease and weed pressure.

   Cereal rye is often promoted for its ability to scavenge nutrients from the prior year’s cash crop. Just prior to cover crop termination, we will sample above-ground cereal rye biomass to assess nutrient content. To determine the timing of nutrient release by the rye cover crop, we will collect soil samples from the top 8 inches of each plot twice during the growing season (4 weeks and 12 weeks following cover crop termination). Target nutrients that we will monitor will include nitrogen, phosphorus, potassium, sulfur, and chloride.

   Soil microbial activity is a key factor in residue decomposition, nitrogen availability, and carbon sequestration potential. These effects will be monitored by measuring potentially mineralizable carbon (as described in Franzluebers et al. 2000) and organic nitrogen pools (as described in Hurisso et al. 2018) in soil samples taken from each plot at 4- and 12-weeks following cover crop termination. Soil moisture and temperature in each plot will be monitored on a weekly basis. Soil aggregation, a common soil health metric, will be monitored in each plot at the beginning and end of the experiment.

   Each year, an estimated 1.48 acres in western Minnesota are at risk of producing soybeans that suffer from iron deficiency chlorosis (Hansen et al. 2004), a disease common to NW and WC MN that can reduce yield by more than 32%.  Excess nitrates in the soil profile can worsen IDC symptom severity (Wiersma, 2010). We will monitor incidence and severity of IDC in the different plots, to cross reference with plant-available nitrogen measurements. The effects of cover crop treatment on weed species composition and biomass will also be assessed. Specifically, weed species composition, percent control and total above-ground weed biomass from three areas of each plot will be determined 28 days after cover crop termination (Yenish et al. 1996).

3. Develop educational and outreach material on the nutrient scavenging potential of cereal rye in Minnesota

   This work will provide valuable insight into what agronomic impacts farmers can expect to see when integrating cover crops into their rotations. Our project team and our farmer collaborators will work together to share the benefits and challenges of cold-climate cover cropping through on-farm field days. These on-farm meetings will highlight our farmer-collaborators and will serve as kick-off points for the initiation of peer-to-peer support networks with the aim of increasing cover crop acres. Findings will also be shared with 5000+ people through UMN Extension’s platforms (e.g., websites, social media, newsletters, radio interviews, press releases, a fact sheet and podcast), and through all team members’ (including our farmer-collaborators’) broad social networks.

Experimental Design

In Summer 2021, we established a large-scale, coordinated experiment across seven on-farm research sites and two Research & Outreach Centers to design viable continuous-living-cover systems for the North Central region. Funding for the first year of this project has been provided by MN Soybean Research & Promotion Council. NCR SARE funding allows us to continue this experiment for three more years for a combined total of four soybean cropping years planted green (Figure 1).

Figure1_v1

This project will use a two-pronged approach to evaluate both practice efficiency and practicality. Plot-scale research will allow us to determine the most effective approaches. On-farm research will test the viability and practicality of these options. Post-cover crop yield and nutrient use efficiency of these systems will be quantified and demonstrate the benefits and challenges of introducing cover crops into the cold-climate cropping systems of the North Central region.

On-Farm Locations

We have established strip plots at seven on-farm locations for the 2022 growing season. If successful, we will continue this project with our farmer collaborators for three additional growing seasons (2023-2025). This will allow us to evaluate planting green over two complete cycles of a wheat-soybean, corn silage-soybean or corn grain-soybean rotation. Special considerations for field management will include fall tillage and herbicide options. We will evaluate the following four treatments at on-farm sites:

1. No cover crop control
2. Rye terminated 7-14 days prior to planting
3. Rye terminated within 24 hours of planting
4. Rye terminated 7-14 days after planting

Each treatment will be replicated three times, for a total of twelve harvested strips. Strips will vary, but be wide enough to allow for one combine pass in soybeans that excludes sprayer track damage.

Research & Outreach Center Locations (Crookston and Morris)

We have also established plots for the 2022 growing season at the Northwest Research & Outreach Center in Crookston, MN and the West Central Research & Outreach Center in Morris, MN. The two Research & Outreach Center sites will focus on optimizing management of cereal rye. These plot-scale experiments will assess two seeding rates of cereal rye, two tillage systems, and three termination timings with four replicates:

Tillage treatments:

1. Fall chisel plow and field cultivation
2. No-till

Cover crop seeding rate treatments:

1. No cover crop
2. 20 lb/A Cereal Rye
3. 40 lb/A Cereal Rye

Cover crop termination timings:

1. 1-2 weeks before planting
2. At planting
3. 1-2 weeks after planting

All Sites

Both spring rye survival and soybean establishment following rye termination will be evaluated. We will monitor soil fertility and chemical properties including soil macronutrients, organic matter, pH, and electrical conductivity. Soil health tests will assess biologically relevant nutrient pools such as potentially mineralizable carbon, water-extractable carbon and nitrogen and aggregate stability. Soil moisture levels will be monitored throughout the year to evaluate moisture uptake by the growing cover crop and/or water retention by crop residue.

Soybean disease, pest pressure, and weed management will also be evaluated. Symptoms of iron deficiency chlorosis will be visually assessed from three areas of each plot using a visual rating scale. Walking a transect through each plot, plants will be visually inspected for disease incidence and severity and insect injury in the lower, middle and upper canopy. The effects of cover crop treatment on weed species composition and biomass will also be assessed. Specifically, weed species and total above-ground weed biomass from three areas of each plot will be determined 28 days after cover crop termination.

This project has a high potential for impact. All team members are committed to engaging with farmers on how best to achieve continuous living cover cropping systems. Project findings will be shared with farmers at winter extension meetings, at summer field days, and through fact sheets, news articles, social media, and radio, and with the scientific community through society meetings and peer-reviewed publications.

References

Franzluebbers, A.J., R.L. Haney, C.W. Honeycutt, H.H. Schomberg, and F.M. Hons. 2000. Flush of Carbon Dioxide Following Rewetting of Dried Soil Relates to Active Organic Pools. Soil Science Society of America J. 64: 613-623.

Hansen, N.C., V.D Jolley, S.L. Naeve, and R.J. Goos. 2004. Iron Deficiency of Soybean in the North Central US and Associated Soil Properties. Soil Sci. Plant Nutr. 50(7): 983-987.

Hurisso, T.T., D.J. Moebius-Clune, S.W. Culman, B.N. Moebius-Clune, J.E. Thies and H.M. van Es. 2018. Soil Protein as a Rapid Soil Health Indicator of Potentially Available Organic Nitrogen. Agric. & Environ. Letters, 3: 180006.

Wiersma, J.V. 2010. Nitrate-induced iron deficiency in soybean varieties with varying iron-stress responses. Agronomy J. 102(6): 1738-1744.

Yenish, J.P., A.D. Worsham, and A.C. York. 1996. Cover crops for herbicide replacement in no-tillage corn (Zea mays). Weed Technol. 10: 815-821.