Cover Crop Cocktails: Evaluating Costs and Benefits of Mixed-Species Plantings
Mixed-species cover crop plantings (aka Cover Crop Cocktails) offer multiple benefits to producers. Through a collaboration with five Oahu-based producers, this project aims to identify viable cover crop cocktails for producers in Hawaii. Research and field demonstrations will be used to evaluate economic costs, and to measure effects of cover crop plantings on soil health. Information will be shared with producers through on-farm field days, presentation at the Hawaii Ag Conference, and through Oahu RC&D’s Cover Crop Handbook.
Project Objectives and Target Dates as identified in our proposal:
- Identify cover crop species currently used and available in Hawaii.
a. Conduct a survey of cover crop users, seed sales locations, and agricultural professionals to identify which cover crop species are currently in use / October 2016.
b. Summarize information related to planting rates, costs, days to maturity, etc. / November 2016.
c. Utilize information to determine cover crop cocktail mixes and planting rates / December 2016.
- Evaluate economic costs and soil health benefits of mixed-species cover crop plantings.
a. Summarize economic costs (ie. cost of seed per acre) of cover crop cocktails / January 2017.
b. Establish five demonstration plots in diverse geographic locations on Oahu / January – March 2017.
c. Conduct physical, chemical, biological, and agronomic evaluations at pre-project, mid-project, and post-project intervals / approximate dates: March 2017, March 2018, March 2019:
i. Physical: moisture, temperature, bulk density.
ii. Chemical: pH, total nitrogen, total carbon, phosphorus, potassium.
iii. Biological: presence of earthworms, soil respiration (Solvita).
iv. Agronomic: biomass of cover crop and weeds (used to determine relative weed suppression), percent soil coverage, presence of beneficial insects.
d. Gather anecdotal feedback and observations from host farms / March 2018, March 2019, and throughout project period.
- Share results with producers and other agricultural professionals.
a. Employ surveys to gauge familiarity with common cover crop species / October 2016, July 2018, March 2019.
b. Hold two field days to demonstrate cover crop cocktails. Field days will be held at host sites, and will include presentations from the host farmer(s), 2-4 agricultural professionals on featured topic(s), and a tour or hands-on activity / September 2017, September 2018.
c. Incorporate findings into a revised edition of the Cover Crop Handbook produced by Oahu RC&D / March – June 2019.
d. Present findings at the 2018 Hawaii Agriculture Conference (or similar venue) / September 2018.
e. Disseminate resources, results and related information via social media networks and producer-to-producer networks / entire project period.
Two student interns spent the summer conducting research and identified a suite of species commonly used for cover crops, and then interviewed producers and agricultural professionals to narrow our focus to species common and readily available in Hawaii. This effort resulted in a spreadsheet and a working list of 11 species. Cover Crop Inventory_11.29.16
For the majority of the 11 species we were able to identify planting rates, growth habits, and seed cost. And for about one-third of these species we found published seeding rates when used in a mixed planting. This information was used to identify four potential “recipes” for cover crop cocktails and to estimate relative costs.
In December 2016, preliminary field trials were established at DuPont Pioneer’s research farm in Waialua. Observations from these early plantings will be used to tweak cocktail recipes for use on participating farms.
We will conduct initial soil tests and begin establishing demonstration plots on participating farms in February 2017.
Additionally, we developed and distributed a cover crop survey. Forty-six people responded, but we have not yet analyzed or summarized the results.
Impacts and Contributions/Outcomes
Thus far, the greatest outcome has been an increased understanding of the various cover crop species available in Hawaii. We’ve spent a lot of time musing about recipes, and feel like there is not a lot of published data that offers definitive seeding rates for mixed cover crop plantings.
To avoid the potential for an infinite and unmanageable number of recipes, we decided to focus our efforts on four mixes. This approach aligns with input from producers who need practical and economically viable options.