Summer Cover Crop System Management: New options for Upper Midwest vegetable producers

View the project final report

Commodities

• Vegetables: broccoli, greens (leafy), greens (lettuces)

Practices

• Crop Production: catch crops, cover crops, nutrient cycling
• Education and Training: demonstration, workshop
• Natural Resources/Environment: habitat enhancement
• Production Systems: organic agriculture
• Soil Management: green manures, soil microbiology

This project, Summer Cover Crop System Management: New options for upper Midwest vegetable systems, worked to improve grower knowledge of summer cover crop use, including species selection, growth period timing, and management. Growers are increasingly interested in adding cover crops to rotations to improve soil health, break disease cycles, and provide ecosystem services, particularly biological nitrogen (N) fixation. Summer cover crops are an often overlooked and minimally researched option for growers in the Upper Midwest, but present a promising opportunity for fitting cover cropping into diversified vegetable rotations, which include multiple potential fallow periods due to the varying growth periods of vegetable crops.

UMN researchers worked with collaborators serving indigenous, immigrant, and underserved farmers to conduct field trials and farmer education with the goal of expanding cover crop options available to diversified vegetable growers. We conducted a three-year field experiment investigating the effects of six summer cover crop options, including legumes, legume-grass mixes, and non-legume broadleafs, on ecosystem services including nitrogen provision and retention, attraction of beneficial insects, and vegetable crop productivity. The arrival of a graduate Fulbright fellowship student allowed us to broaden the ecosystem services studied by collecting additional data on microbially mediated nutrient cycling in our treatments. We also worked with collaborating farmers to conduct demonstration plantings of summer cover crop species on their farms, and collected qualitative feedback on ease of management and effectiveness of cover cropping practices, which complemented our research findings in developing presentations aimed at enabling farmers to more profitably and confidently include cover crops in seasonal rotations, improving nitrogen management for cash crops following summer cover crops, and reducing nitrogen losses that can lead to environmental degradation.

All the cover crop species used in this trial proved to be potentially viable options for both early spring and midsummer planting at southern MN sites. However, performance was inconsistent, likely due largely to stresses during establishment. Measurements of soil N pools following cover crops suggested that, while the contribution of biologically fixed N from legumes is a valuable service, non-legume biomass (even from weeds) can also make important contributions to building long-term nutrient reserves and biologically active soils. Phacelia proved to be an appealing new broadleaf cover crop option, providing thick, weed-excluding and abundantly flowering stands highly attractive to native pollinators when establishment was successful. However, summer cover cropping did not provide an immediate yield boost to vegetable production, and in some cases resulted in yield reductions compared to a bare fallow. This indicates a need to emphasize in our outreach to farmers the role of cover crops as a long-term fertility management strategy rather than a quick fertilizer source.

Both our replicated trial results and the feedback we received from farmers who planted demonstration plots of summer cover crops reinforced the importance of trialing and teaching scale-appropriate practices for stand establishment. Small-scale and emerging farmers may be working with limited equipment, often on shared or rented land where weedy ground cover may be well established. Therefore, we should emphasize the need for favorable establishment conditions, including preparation of a weed-free seedbed, seed placement for good soil-seed contact, and adequate moisture.

We shared the results of this research through print fact sheets, web resources, and videos; and at grower meetings and on-farm field days. Educational activities focused on cover crop species and timing options for vegetable systems, cover crop establishment and termination methods for small farms, nitrogen availability from cover crop biomass, and identification of key beneficial insect families. Collaboration on this deepened the partnership between the Grossman Lab and Big River Farms, resulting in a successful joint proposal to explore farmer and educator knowledge and support needs in the emerging farm community, and develop tools for soil health planning and train-the-trainer curriculum on cover cropping and other soil health practices for educators and mentors working with emerging farmers. The activities of that project have extended the project team's ties throughout the network of organizations supporting emerging farmers, and we are actively engaged in ongoing consulting and teaching in this community.

Objective 1: Identify summer cover crop management best suited for north central vegetable growers. 

Objective 2: Determine the effects of legume and non-legume summer cover crop options on nitrogen fertility and ecosystem services in organic vegetable systems 

Objective 3: Develop resources on cover cropping and legume-based fertility for immigrant and minority farmers.