Effects of Using a Native Legume as a Cover Crop in Small Scale Vegetable Production

View the project final report

Commodities

• Agronomic: peas (field, cowpeas)

Practices

• Crop Production: cover crops

Cover crops also known as green manuring is one of the lynchpins of an ecologically based farming system. Some of the benefits of cover cropping include:

• Increasing earthworms and beneficial microorganisms
• Increase plant available Nitrogen
• Increase organic matter content
• Preventing erosion
• Mining of minerals
• Providing habitat for beneficial insects and organisms
• Improving soil structure
• Increased water holding capacity
• Reduced weed populations
• Reduced pest populations

Using native cover crops has the potential to increase the number and diversity of beneficial insect thus increase the overall number of species present on a site (Tallemy, 2018). Native cover crops are easier to establish than there non-native counter parts and promote the presence of less pests and diseases and compete less  with the main crop for soil resources like moisture (Danne, Thomson, Sharley, Penfold, and Hoffmann, 2010). This project will also demonstrate how low income, socially disadvantaged farmers can successful harvest wild plants and use them as cover crops thus eliminating or greatly reducing the cost of the cover crop. Growing native plants as cover crops have the following potential benefits:

• Reduced establishment costs;
• Reduced loss of topsoil;
• Nutrient mining;
• Attracting beneficial organisms;
• Reduced soil erosion;
• Feeding microorganisms;
• And, Adding soil biomass (Koperek, 2018)

This project will be carried out in two phases. Phases I involves observation of wild Chamaecrista fasciculata (partridge pea) and an initial determination of seeding rates for coastal plain soils. The principle investigator for this project is a permaculturist. Permaculture design is based on the careful observation of patterns found in nature. It is the goal of this first phase of research to characterize and document the wild growth habits of Partridge pea. In phase I we will use the visual reconnaissance method to identify wild patches of partridge pea growing at the Airport Food Forest Farm. By carefully documenting the life cycle and seasonal growth patterns of wild partridge pea we will create a blueprint for those wishing to use a wild plant or plants as a cover crop.

The sampling procedure will be as follows:

The site will be divided into three plots of the following sizes 50’ x 100’; 50’ x 180’; and 50’ x 180’.

A hand drawn map will be made of each plot. We will use a compass to draw a line along the long axis of the map. A line will also be drawn along the short axis of the map roughly perpendicular to the long axis. We walk along these lines to visually identify populations of partridge pea. Each wild plot of partridge pea will be flagged. We will note the following items: Size of stand, members of plant community, stage of plant development, soil moisture level, soil ph., light conditions (estimate); beneficial insect and animals, growth habits (date of first emergence, date of first flowering, date of pod formation, plants physical characteristics).  A summary of the collected date will be submitted in the final report.

The second part of year one is an initial varietal trail to determine the proper seed rate. For our experiment we will use seeding rates of 10, 15, 20, 25, 30 lbs/ac for each available commercial variety. The varietal trial will be held at Dayspring Farm (DSF). The plot size will be at least 1/10 or 4000 ft2.  Each variety of partridge pea will be planted at 5 different seeding rates with no control. A total of 20 plot will be used averaging 200 ft.2.  

Assessment

An initial assessment of partridge pea varieties will be conducted in the spring of 2021 to help determine spacing for maximum potential of the cover crop. Varieties used for test plots will depend on the availability of seeds. Potential varieties for trails are Comanche (cultivar); Shelly (cultivar); Lark Selection or Non-specific variety (NSV).  Half of the seeds at each site will be inoculated with cowpea inoculant to determine if this makes a difference in nitrogen fixation rates.  We will use seeding rates of 10, 15, 20, 25, 30 lbs/ac for each available commercial variety Plots will be assessed monthly for ground cover, height and biomass. A 15in x 15in section of each plot will be randomly selected. Measurements will be taken weekly after the first month of growth from the randomly selected site. Coverage is measured by assigning a visual score from 1-10 (1 least covered to 10 most covered). Height is measured and recorded. The same sample will be cut to 1 inch, the sample bagged, the bagged material dried, and weighed to determine above ground biomass in tons per acre. When testing for nitrogen we propose to use the following procedures: We will be drying cover crop samples to estimate biomass. We will send the dried samples to a lab get N per acre. b to determine total N analysis. We will multiply the biomass per acre by the %/N/100 to get lb N per acre.

Phase II

In phase I we endeavored to learn the natural growth habits of partridge pea and the best potential variety and seeding rate to use in a commercial vegetable farming cover crop rotation. After learning the best performing variety, we will compare the top performing variety to the native variety found at the Airport Food Forest Urban Farm (AFF). If enough seed is not collected from the AFF or if special procedures such as scarification is needed for germination of the native seed collected at the AFF, then both sites  AFF and DSF will only use the top performing varity of partridge pea for the phase II experiment. We will compare the perform of partridge pea at both sites to a commonly use cover crop plant, “Iron and Clay” southern peas (Vigna unguiculata). This cover crop exhibit some of the characteristics of partridge peas. Site 1 is AFF. Site 2 is Dayspring Farm (DSF). In Phase II we will use two economic factors, seed cost and differential impacts on production of the brassica crop to determine the economic viability of partridge verses a tradition covercrop--iron and clay cowpeas.  AFF will plant native variety and or top performing variety in a 400 ft2 plot.  DSF will plant the naitve variety and top perform variety from the field trial in a 400 ft2 plot. Both site will plant iron and clay cowpea at the equalivency rate in a 400 ft2 plot. We will again measure cover crops biomass, height, and ground cover for the partridge peas and the iron and clay cowpea. Pre and post soil tests will be taken from both sites at planting and 7 days after termination of crop and incorporation of biomass. The same varieties brassicas will be planted at both sites after termination. Weeding and water schedule will be the same (unless variation is justified). Performance of each cover crop will be based on crop yield performance of the brassicas.

Summery of Experiment

• We are looking at beginning the partridge pea variety trail in May of 2022.
• For the phase II study we are proposing to compare all the following at both sites:
• Best variety #1 at best seeding rate (based on Phase I variety trial at Dayspring Farm).
• Best variety #2 at best seeding rate.
• Native partridge pea from AFF at comparable seeding rate.
• Southern pea at 50 (drilled) or 80 (broadcast and raked) lbs./ac
• We test for nitrogen by multiplying the biomass per acre by the %/N/100 to get lb N per acre.
• We will follow all cover crop with the same varitey of brassicas and compare each performance in terms of yield (weight per plot).
• Economic comparison points: Cost of seeds and yield of brassica crop.