Cover Crop Cocktails: Evaluating Costs and Benefits of Mixed-Species Plantings

Project Overview

Project Type: Professional + Producer
Funds awarded in 2016: $41,606.00
Projected End Date: 04/15/2019
Grant Recipient: Oahu RC&D
Region: Western
State: Hawaii
Principal Investigator:
Dave Elliott
Oahu RC&D

Annual Reports


Not commodity specific


  • Crop Production: cover crops, intercropping
  • Natural Resources/Environment: biodiversity, soil stabilization
  • Pest Management: mulches - living
  • Production Systems: general crop production
  • Soil Management: green manures, organic matter, soil analysis, soil microbiology, soil quality/health

    Proposal abstract:

    Cover crops are non-cash crop plants that are planted by farmers to cover and improve the soil, suppress weeds, and attract beneficial insects.  Certain cover crops, especially those in the legume family, provide extra nitrogen to the soil that can be taken up by the succeeding crop, in some cases replacing synthetic fertilizers as a nitrogen source.  Other cover crops take up and recycle excess nutrients that the cash crop cannot or does not use, preventing excess nutrients from leaching into soil and surrounding waterways.  Cover crops can also be tilled into the soil and thereby provide additional biomass, or “green manure”, which increases the level of soil organic matter.  Increasing organic matter may increase microbial activity which then helps to make nitrogen more available to cash crops and may also utilize additional carbon.  Recent efforts to promote the use of cover crops have resulted in increased awareness and adoption rates among Hawaii producers.  Real-world experience among project collaborators indicates that the three most commonly used cover crop species are oats (Avena sativa), sunn hemp (Crotolaria juncea) and buckwheat (Fagopyrum esculentum).  Species used to a lesser extent include clovers, cowpea, lablab, and ryegrass.  In nearly all situations on the ground in Hawaii, the recommendation and / or implementation of cover crops reflects use of a single species, and there is limited understanding of which multi- or mixed-species plantings are best suited for Hawaii.  Mixed-species plantings (aka Cover Crop Cocktails) utilize up to six different plant species, combine benefits of individual species and result in increased biomass and nitrogen production, increased habitat for a variety of beneficial insects, improved tolerance of adverse conditions, and may increase the duration of active growing period.  Multiple studies have been conducted on the mainland to evaluate cover crop cocktails and there is growing interest in their use, as well as recognition among farmers and agricultural professionals that they provide increased benefits.   Conversely, mixed-species plantings may result in higher seed costs and more complicated management needs (e.g. best time to kill one crop may not be the best for a different crop in the same mix).  Oahu RC&D staff, project partners and collaborating producers will - evaluate cover crop cocktails to determine direct economic costs; - establish on-farm demonstrations to assess cover crop cocktail benefits to soil health (measuring effects on physical, chemical and biological soil characteristics); - share results with producers and agricultural professionals at two field days, reaching an estimated 60 producers; - present findings at the 2018 Hawaii Agriculture Conference (or similar event), reaching an estimated 100 producers and agricultural professionals; - publish results in an updated edition of Oahu RC&D’s Cover Crop Handbook, which will be distributed to project participants and made available for free download from our website. The utilization and assessment of cover crop cocktails on farms in Hawaii will expand the opportunities for producers and agricultural professionals to evaluate and select the mixed-species planting that best meets producer goals and can be incorporated into existing production systems. 

    Project objectives from proposal:

    Project Objectives

    1. Identify cover crop species currently used and available in Hawaii.
      • 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.
      • Summarize information related to planting rates, costs, days to maturity, etc. / November 2016.
      • Utilize information to determine cover crop cocktail mixes and planting rates / December 2016. 
    1. Evaluate economic costs and soil health benefits of mixed-species cover crop plantings.
      • Summarize economic costs (ie. cost of seed per acre) of cover crop cocktails / January 2017.
      • Establish five demonstration plots in diverse geographic locations on Oahu / January – March 2017.
      • Conduct physical, chemical, biological, and agronomic evaluations at pre-project, mid-project, and post-project intervals / approximate dates: March 2017, March 2018, March 2019:
        • Physical: moisture, temperature, bulk density.
        • Chemical: pH, total nitrogen, total carbon, phosphorus, potassium.
        • Biological: presence of earthworms, soil respiration (Solvita).
        • Agronomic: biomass of cover crop and weeds (used to determine relative weed suppression), percent soil coverage, presence of beneficial insects.
      • Gather anecdotal feedback and observations from host farms / March 2018, March 2019, and throughout project period.

    Notes: Plantings will be repeated at each site as permitted by crop rotation, with the goal of having two years of production observations.  

    1. Share results with producers and other agricultural professionals.
      • Employ surveys to gauge familiarity with common cover crop species / October 2016, July 2018, March 2019.
      • 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.   
      • Incorporate findings into a revised edition of the Cover Crop Handbook produced by Oahu RC&D / March – June 2019.
      • Present findings at the 2018 Hawaii Agriculture Conference (or similar venue) / September 2018.
      • Disseminate resources, results and related information via social media networks and producer-to-producer networks / entire project period.
    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.