Bringing the Benefits of Legume Cover Crops to Northern Midwest Climates

Bringing the Benefits of Legume Cover Crops to Northern Midwest Climates

Summary

See Accomplishments/Milestones

Objectives/Performance Targets

Learning outcome 1: Growers will learn if application of nitrogen fixing rhizobia inoculant is necessary with selected cover crop ecotypes. We will characterize nodule occupants among the cover crop varieties in Y1. Mature plants will then be evaluated for nodulation, total biomass N, nitrogen fixed, and rhizobia occupancy.

Learning outcome 2:  Growers will learn basic soil ecological principles to help them manage legume cover crops for optimal function and performance. Blending farmer needs with available data on cover crop biology and soil science, we will develop two hands-on workshops including evidence-based responses to grower knowledge needs. Workshops will be taught as part of grower conferences in the region (i.e. MOSES, Sustainable Farming Association of Minnesota Annual Conference) in the final year of the project.

Action outcome 1:  At least 25 farmers will plan to use a legume cover crop in their farming operation in the three years following project termination. To conduct the formative evaluation, surveys will be provided to workshop attendees and undergraduate course attendees that ask about the degree to which these offerings were useful, met their needs, and what additional questions they still have. Additionally, in the months following the workshops, attendees will again be surveyed and asked to rate their knowledge about utilizing cover crops and the degree to which they are utilizing (farmers) or recommending (those who work with farmers) such practices. Those farmers who identify having most successfully implemented these approaches will be interviewed by phone to understand how and why they were able to engage in these practices. (i.e., what were drivers of their success).

Action outcome 2: At least 60 students will be exposed to examples of legume cover crop use. To meet this action outcome we will develop 4-8 media-rich online case studies showcasing exemplary growers who use cover crops in the North Central SARE region, and highlighting both their successes and challenges in using cover crops. Dr. Grossman will be leading a course in biological principles for use in organic farm management as part of the University of Minnesota’s recently developed Food Systems major, and the development of the case studies dovetails beautifully with this new and innovative program. The case studies will be developed as a course assignment for Dr. Grossman’s class in Y1 and Y2 of the grant, with students conducting all interviews, taking video footage, editing, and developing study questions to be part of the case-study package.

Accomplishments/Milestones

• Planted field experiments at two research station locations. Data on rhizobia and nitrogen fixation was collected in spring of 2016.
• Planted a second year of field experiments in Fall 2015, including two on-farm locations for workshops and outreach.
• Presented to Southern Sustainable Agriculture Working Group (over 200 farmers reached and 150 surveyed) on January 29 and 30th, 2016
• Presented to Midwest Organic and Sustainable Education Service (MOSES) organic farming conference February 26, 2016 (over 150 farmers reached)
• 55 undergraduate students at the University of Minnesota, many who are at the early-learning stages about organic agriculture, communicated with organic farmers about cover crop use and are developing video case studies on the farms.

Impacts and Contributions/Outcomes

Year 1 (2014-2015): Cover crops species, including a rye non-legume control (RYE), rye/field pea (PEA), red clover (CLO), hairy vetch ecotype 1 (V1), hairy vetch ecotype 2 (V2), hairy vetch ecotype 3 (V3), with and without inoculant (WIN or NIN), were planted at the SWROC and NCROC research stations in Lamberton and Grand Rapids, respectively, in September 2014. The natural abundance method, based on isotopic fractionation, was used to determine biological nitrogen fixation (BNF) prior to cover crop termination.  Biomass was sampled on June 9, 2015 and June 11, 2015 at Lamberton and Grand Rapids, respectively, and terminated on June 11, 2015 and June 12, 2015 to obtain accurate N readings at termination.  Samples were taken using 4 ½ m2 quadrats/treatment cutting the stalks to ground level.  Samples were dried at 65ºC and ground at 2mm for analysis.  Samples were then packaged in aluminum for analysis using an Elementar™ vario PYRO cube to obtain total C/N and isotopic ratios.  Preliminary data of V1, V2, CLO, and rye suggest that the two vetch varieties introduced the most cover crop N into the system, ranging between 8-34 Kg N ha-1.  These numbers are lower than expected, attributed to late planting and severe winter kill.  CLO plots in particular experienced significant weed competition.  Preliminary data from our vetch varieties at the Lamberton field site indicates that approximately 40-50% of the aboveground plant tissue nitrogen is nitrogen derived from the atmosphere.

Nodulation efficiency was evaluated in all legumes. Three mature cover crop root systems were carefully harvested from each treatment on June 9, 2015 and June 11, 2015 at Lamberton and Grand Rapids, respectively, prior to cover crop termination. Nodule number per plant was recorded followed by rhizobia isolation. Three nodules from each plant were surface sterilized then crushed and streaked on YMA media plates supplemented with congo red for rhizobia selection and isolation.  Single isolated strains were then subjected to 16S rRNA gene sequencing. While nodule mass was planned to be collected nodules, most of the nodules decomposed during rhizobia isolation and only the root dry weight per plant was recorded. In Lamberton, clover had the highest nodule numbers (ranging between 102-178 nodule per plant) while the three vetch varieties had less nodules. Inoculation did not have effect on nodule numbers at either location.

DNA sequences were obtained for the small subunit ribosomal RNA (16S rRNA) gene of 73 rhizobial strains isolated from four legume hosts (V1, V2, V3 and Clo) in Lamberton. The 16S rRNA phylogeny from partial DNA sequences illustrated the close relationship between isolated Rhizobium strains with Rhizobium leguminosarum species found at the Lamberton site, regardless to the legume host species or inoculant application. Future work may include symbiotic region (nodulation genes) in isolated rhizobia strains as compared to rhizobia strains from inoculants to characterize nodule occupancy between inoculated and non-inoculated treatments.

SARE-Report_Figures-and-captions

Year 2 (2015- March 2016):

Experiment station studies

The cover crop study was modified in Year 2 to account for observable differences in survival and crop success.  Treatments in 2016 are: Vetch 1 (Albert Lea Seed variety, MN 2014 #23), Vetch 2 (Buckwheat Growers variety, MN 2014 #25), Red clover (Albert Lea 2014), Vetch 2 + rye, Rye, and bare ground control. Poorly performing vetch variety #3 (Welter Seed) was eliminated due to poor biomass production.  Similarly, Austrian winter pea was eliminated as it performed poorly in Y1. We also included a rye/vetch mix (rye and vetch variety 2) to account for commonly used integration of legume cover crops.  A large swath of farmers employ grass/legume mixtures and we wanted the experiment to reflect this choice.  In addition, legume performance may be improved in mixtures as grasses often take up available nitrogen, increasing fixation rates. Lastly, we have become increasingly interested in the potential contributions of legume cover cropping systems to increase soil organic matter (SOM) in agricultural soils of the upper Midwest.  Emerging understandings of SOM development pay particular attention to the role of low molecular weight inputs and microbial activity as a potential driver of SOM stabilization.  This is also a component that greatly expands our understanding of cover crop role in nitrogen transformations.  Therefore we included a bare ground plot that will serve as a control for SOM studies.  This was not necessary in the first iteration of the experiment, as a non-leguminous rye plot could be used to control for nitrogen fixation contributions from legume treatments.

On-farm demonstrations

Demonstrations were planted in fall 2015 at Phil Batalden’s 350-acre organic grain farm in Lamberton, MN and Rodrigo Cala’s 40-acre organic vegetable farm in Turtle Lake, WI.  We consulted with both farms regarding species mixes and specific cover cropping challenges in their operations.

Cover crop video case study development

In Year 1, students in Spring 2015 Student Organic Farm: Planning, Growing and Marketing (HORT 3131) were matched with six enthusiastic organic growers who have been moderately successful in using cover crop legumes in the upper midwest. Students established relationships with the growers via email, Google Hangout, and phone, and developed farmer profile fact sheets describing the farming operations and how cover crops were used. In Spring 2016 (Year 2), a new class of students was paired with the same growers, and is using the farmer profiles to learn about the farm. Students are receiving training on design and creation of 3 minute movies highlighting cover crop use on each farm, and have plans to visit the farms in April, 2016 to take video footage and develop their farmer profile videos.

Outreach and workshops

Jule Grossman conducted a workshop on cover crop legumes to over 200 farmers at Southern SAWG in January, 2016 and collected data (still being analyzed) via surveys about knowledge increase resulting from the workshop. A subset of growers offering their contact information will be contacted in early fall to determine if they are using the information learned during the workshop. Grossman also presented to another 150 growers at MOSES in February, 2016. A field day has been scheduled for spring 2016 at Phil Batalden’s farm.  Rodrigo Cala is a farm trainer with the Minnesota Food Association and Latino Economic Development Center’s immigrant farm training programs and cover crop demonstrations will be integrated into these organization’s trainings.

Collaborators: