Weeds in the Walkways

May 24, 2019

By Sharon Perrone

Mai Moua is no stranger to cover crops; but neither is she a follower. She’s an innovator. Moua is a farmer member of the Hmong American Farmers Association (HAFA), a land cooperative food hub in Vermillion Township, MN, meaning that HAFA growers rent parcels of land owned by the organization and share tools, processing facilities, and contracts. Moua grows a variety of vegetables and flowers for local farmers markets, food co-ops and the HAFA Flower CSA, and her practices helped inspire a collaborative research project between HAFA and Dr. Julie Grossman’s lab at the University of Minnesota’s Department of Horticultural Science.

Cover crops are plants grown in either temporally or spatially distinct spaces from cash crops, primarily in order to improve soil health. By keeping portions of the soil covered that would otherwise remain bare, cover crops can prevent soil erosion, feed soil microbes through root exudates, reduce soil compaction, and maintain soil temperature and moisture. Growers choose a variety of cover crops to meet different goals, constraints, and intended outcomes.  As for Moua, she has been growing weeds in the walkways as a “living mulch” between her dahlias in order to improve trafficability of the field after a rainfall (i.e., avoid muddy soil compaction) and to reduce soil splash, which can spread disease.

HAFA executive director, Pakou Hang, approached Grossman in 2017 with the hopes of developing a project that would compare practices used by growers at HAFA farm to legume cover crops that have shown to be successful in our region. Legumes are a specific type of cover crop that partners with soil bacteria to fix atmospheric nitrogen into a biological form, essentially bringing ‘free’ nitrogen to the soil system to feed plants ecologically. “Chosen carefully, legumes may provide the same benefits as Moua’s living mulch with the additional nitrogen fertility,” explained Ph.D. student Sharon Perrone, the graduate student project lead.

The project was funded in 2018 by the University of Minnesota’s Health Food, Healthy Lives Institute as part of their Community-University Partnership grant program, with the primary goal of improving Hmong farmers’ capacity and self-efficacy to tackle soil fertility issues.  Because Hmong farmers have traditionally faced barriers to land tenure, soil health – which may take years to improve – has been difficult for farmers to invest in or observe. During the annual spring orientation meeting, Perrone and growers worked together to address growers concerns such as crop bed width and walkways. In the end, Perrone and growers decided to use white Dutch clover as the cover crop species due to its short stature and non-spreading growth habit.

“We are thrilled to see farmers learning about legume cover crops through this research project. On-farm research such as this allows farmers to evaluate their options and then choose the system that is right for them,” said Grossman.

And the results?  “We see little difference in terms of soil health parameters between the Hmong living mulch system and the white Dutch clover,” said Perrone.  “That’s not discouraging – it appears that in year one, farmers have the option of which system they prefer.  For example, white Dutch clover required frequent mowing early in the summer to outcompete weeds and establish fully, but weedy living mulches require more frequent mowing towards the end of the summer to prevent heading and spread of weedy species.  A grower can think in advance about points in the season when labor is in lower need and choose a method accordingly.”

Perrone also noted that white Dutch clover is a biennial species, meaning that it puts on its best growth in year two, and that changes in soil health are more likely to be observed when the cover crop is tilled into the soil and decomposed at the end of a season or life cycle.  Although funding for the project has ended, some of the growers have left the clover to overwinter and are looking forward to seeing how it performs after the first year and observing how it impacts their soils after termination.

Ka Yang, HAFA’s research associate, says the iterative process of design and implementation between farmers and researchers was critical to the success of the project.  “Because we can work so closely with farmers onsite, we are able to have a more realistic approach to tackling soil fertility.  It's one thing to conceptualize better soil fertility, but growers are the ones facing this issue directly.  Having this immediate feedback on what is or isn’t both impacting soil health helps farmers build confidence in self-efficacy and decision-making while improving our practices and refining our research methods.”