Increasing Varietal Suitability and Availability of Cowpea and Forage Radish Cover Crop Seed for Northern Climates

Cowpeas:

Before SARE funding expanded our project, NPSAS, NDSU, and NRCS performed a screen of 10 accessions of cowpeas (provided by the USDA National Plant Germplasm System) near Belfield, ND in 2011 and over 90 accessions of cowpeas (provided by the USDA National Plant Germplasm System) at Bismarck and Carrington, ND in 2012. Seed from the three accessions that matured seeds in 2011 and from the eighteen accessions that matured some seeds in 2012 were sent to the University of Puerto Rico for increase over the winter of 2012-2013. Seeds of five more varieties available commercially or via Seed Savers Exchange were also sent along to provide additional insights into early cowpeas. A total of 25 varieties were sent for increase and seeds of 23 of the varieties came back in spring of 2013, with one variety increased up to 17 pounds from 100 feet of row. There were enough seeds from 21 of the varieties to use in replicated trials that summer at Dickinson, ND, Carrington, ND, Beresford, SD, and Madison, WI. An early cowpea variety flowering in Minnesota. Seed was germination tested and seed counts were determined before shipping seeds and OMRI approved inoculant (Guard-N) to each university collaborator in 2013. Three replicates for seed production were planted in early June with a goal density of four plants per foot. A similar set of replicates was planted after local small grain harvest at each location. Plots at most locations were two rows, twenty-five feet in length, while plots in Wisconsin were three rows, eight feet in length. Row widths were 2.5 feet. Plots were on organically managed ground at each location, and we controlled weeds with mechanical cultivation. Emergence was determined as days from planting to 50% emergence. Seedling vigor was rated on a 1-5 scale two weeks after first emergence. Plant form was rated as erect vs spreading and vining vs determinate. Canopy closure within rows was rated on a 1-5 scale five weeks after emergence. Days to flowering was determined as days from planting to 50% flowering, and days to physiological maturity was determined as days from planting to 80% tan pod color (R9). Yield of seed was calculated as pounds per acre, and seeds were counted and weighed to determine 1000 seed weight in grams. The cover crop trial was evaluated in a similar manner, although dry biomass was calculated as pounds per acre from a sample of at least six feet of row. At Wisconsin 3-5 plants of each variety were also dug and the number of root nodules counted. Cover crop trials did not establish in North Dakota, but were successful in South Dakota and Wisconsin. Seed was harvested at all locations. Data were summarized across the locations and discussed among FBC members and participating scientists to choose those to move forward. We then sent seeds of twelve varieties (ten USDA NPGS accessions and two commercially available varieties) to Puerto Rico for further increase. This increase was very successful, with up to 60 pounds returned for several of the varieties. Seed was germination tested and seed counts were determined before shipping seeds and OMRI approved inoculant to each location for continued trials.

Seed evaluation plots were again planted late due to the extended rain and cold in the spring of 2014. Rain prevented weed control at the South Dakota site and those plots were terminated. Cold continued throughout the summer and only one variety matured seeds in Dickinson, ND. Plants were stressed at the Carrington, ND and Arlington, WI sites but full maturity was achieved at these locations. Late planted cowpeas for the cover crop trial failed in North Dakota and were not attempted in South Dakota, so only Wisconsin was able to get cover crop data for this planting period in 2014. Late planted cowpeas grew well enough to provide cover crop and forage opportunities in southern Wisconsin.

Storage of the seeds, however, hit a big difficulty by mid summer of 2014 as hundreds of cowpea weevils (Callosobruchus maculatus) began emerging and overrunning our storage space. Seed was bagged in an extra garbage bag and frozen for a week in order to kill these pests. That and freezing over the winter seems to have ended the infestation in the extra seeds that remained in storage. We made sure to freeze all future seed going into storage for several weeks to control this pest. Cowpea weevils were a problem in seed coming back from Puerto Rico. Freezing the seed eliminated this problem in storage.

We summarized the results from 2014 and again sent it out to scientists and FBC members to help choose the varieties we wanted to move forward for the last year of work. We sent six accessions identified from our results in 2014 as being especially promising (PI 293499, PI 293525, PI 293570, PI 352903, PI 493446, and PI 493468) and two commercial controls (Iron and Clay, Red Ripper) to Bryan Brunner at the University of Puerto Rico research station in Lajas for increase in January, 2015. The growing season in the winter of 2014-2015 was very wet and the seed was planted late. It was also later to mature and to receive back in North Dakota, so seed was shipped to collaborators in North Dakota (Pat Carr, Steve Zwinger, Hans Kandel), South Dakota (Peter Sexton), Minnesota (Tom Michaels), and Wisconsin (Erin Silva) in late May. Remaining seed was frozen for several months and trials conducted as before. Since late planted cowpeas had failed for two years, the North Dakota sites planted their cover/forage crop trial in early July, the time when many ranchers there are planting cover/forage crop mixes. The organic winter nursery in Puerto Rico was essential for moving our evaluations forward.

We applied for and were awarded an extension to finish out the project in 2016. University collaborators at Carrington, ND, St. Paul, MN, and Arlington, WI planted cowpea seed production plots as they did in previous years. Hail destroyed the plots in North Dakota, but yield data and other information was collected at the other two sites. FBC members used a summary of the data to identify varieties they felt were most likely useful for their farms. Remnant seed was provided to PulseUSA for increase and commercialization. They planted out seed increase fields in the Dakotas in 2016 with the goal of some sales perhaps as early as 2018. One accession failed at increase, so the backup seed of that accession (PI 293570) was sent back to Puerto Rico in December, 2016 for increase and later commercialization.

Radish:

FBC member Emily Stiegelmeier conducted a screen of fifty-four accessions of big rooted radishes from the USDA National Plant Germplasm System on her South Dakota farm in 2011. A group of FBC members helped to dig and evaluate roots in October of that year and posted a video about the process. Storage of these selected, but not fully matured, roots in a refrigerator proved difficult and failed. Emily replanted remnant seeds of the very best accessions in 2012, saving seeds from the plants that made seeds by late August from a May planting and also making additional root selections from a late planting of these exceptional varieties. However, as in 2011, she was unable to keep the small roots of the late-planted accessions through the winter for replanting in the spring, and seed production via this seed-to-root-to-seed method did not materialize as we had intended. FBC members did discuss the progress and challenges of our work with radishes during the member update workshop at the NPSAS Winter Conference in Aberdeen, SD in January, 2013. Our SARE project work with radish was to build on Emily’s on-farm selections, but with no roots and very little seed we were greatly hampered in that objective and had to start over.

FBC choose eight of the top performers from Emily’s 2011 evaluation (Table 1) and Kat Becker planted them on her farm in Wisconsin as early as she could, given the wet and cold spring they were having in 2013. Kat harvested seed from this mixed planting later in the summer.

Table 1. Radish accessions selected from 2011 screen in South Dakota.

Kat Becker grew out a large seed increase plot of radish in 2014 from the seeds of these accessions that were intermated in 2013. This summer was similarly cold and damp, which resulted in very low increase of seed, with only two pounds of clean seed for planting in 2015. However, this additional generation should have resulted in further genetic recombination and a new composite population was born.

Although our supply of radish seeds was not very large after the wet year in 2014, Owen Trangsrud planted most of the two pounds of seed on his farm near Enderlin, ND as early as he could in spring of 2015. This worked to vernalize and promote flowering in radish in all of our experimental plantings in North Dakota and Wisconsin, and it was again successful. Just over ten pounds of organically grown radish seed resulted. With the very late fall in 2015, we were unexpectedly able to continue our radish work in November. There were a large number of volunteer radish roots that established after Owen’s seed harvest in August. As these started growing at about the time most late cover crops are planted, we were able to dig and inspect the roots and evaluate the diversity of the new population and its ability to grow big roots quickly while not bolting too early. Harvested radish roots for seed production (stecklings) were first trimmed of all of their leaves. They were then immediately sent to Hugh Dufner’s potato storage facility in Minnesota to see if we could successfully store these somewhat immature roots long enough to plant them out for intermating and seed increase in the spring of 2016. Successful storage would show that the seed to root to seed approach could work even in North Dakota when careful storage with high humidity is provided. Owen also mulched some of the remaining volunteer plants to see if that would be enough to safely overwinter the roots in place. Additional selection with the same population was conducted in South Dakota in 2016. A strip of about one acre was planted with the FBC experimental plot drill at Emily Stiegelmeier’s organic farm near Selby, SD in August. In early November roots were again dug, selected, trimmed, and stored in Minnesota for ongoing selection work. In 2015 radish variety demonstrations were also planted at Carrington, ND and Arlington, WI with FBC seeds and seed of other radish varieties donated by Gabe Brown (Bismarck, ND) and La Crosse Seed. These were standard small plots and were featured during station field events to highlight our project and radish as a cover crop.

In 2016 radish variety trials with the same varieties were planted at three locations (Carrington, ND, St. Paul, MN, and Arlington, WI) in August. Plots were five x twenty feet in size and seed was planted at 10 lbs/A in North Dakota and Wisconsin. The plots were of similar size in Minnesota but the seed was broadcast at a rate of about 15 lbs/A. Vigor was rated on a 1-5 scale two weeks after emergence and ground cover visually estimated later in October. Plants were counted in three 0.1 m2 subplots and averaged. At the Carrington site, plants and roots in these subplots were also harvested and dried to estimate biomass on a per acre basis. Data analysis for the cowpea work is ongoing, and we have a goal of a research publication to describe the work. Our simple Randomized Complete Block design for the radish variety trial was analyzed for each location using ANOVA and Least Significant Difference tests. Results for the initial radish variety trial and our first successful selections with radish will be shared with farmers via NPSAS outreach channels.