Promoting Adaptive Management With 'Tropic Sun' sunn hemp (Crotolaria juncea) in Hawaii for Ecological Strategies in Weed Control, Nematode Suppression and Nutrient Management

Project Overview

Project Type: Professional Development Program
Funds awarded in 2008: $53,768.00
Projected End Date: 12/31/2011
Region: Western
State: Hawaii
Principal Investigator:
Dr. james leary
University of Hawaii at Manoa
Dr. Brent Sipes
University of Hawaii

Annual Reports

Information Products

Sunn Hemp postcard (Fact Sheet)


  • Fruits: general tree fruits


  • Crop Production: conservation tillage
  • Education and Training: extension, on-farm/ranch research
  • Pest Management: biological control, mulches - living, mulching - vegetative, weed ecology
  • Production Systems: transitioning to organic
  • Soil Management: green manures, organic matter, soil analysis

    Proposal abstract:

    The scientific information regarding the beneficial attributes of ‘Tropic Sun’ sunn hemp (Crotolaria juncea) as a cover crop is abundant. The major bottleneck to adopting sunn hemp cover crop systems in the Pacific has been the lack of sufficient commercial seed sources. Recently, infrastructure has been put into place for commercial-scale seed production of Tropic Sun. In the first year, Crotolaria Seed LLC was able to produce 12,000 lbs, with goals to increase production to over 200,000 lbs in the next 4-5 years. With available seed sources, it is timely to reintroduce the utilities of sunn hemp as cover crops in ecologically-based strategies in weed control, nematode suppression and nutrient management. Sunn hemp has been most commonly utilized as a green manure crop for N input and nematode suppression, which requires intensive tillage practices for residue incorporation into the soil. All of Hawaii’s agricultural lands are within designated coastal zones and are highly prone to soil erosion. Based on its growth habit and productivity, sunn hemp can provide excellent soil cover and weed suppression in a no-tillage or conservation tillage system. We will demonstrate an ecologically-based weed management strategy using sunn hemp in a reduced tillage system while still being able to provide some of the benefits of N inputs and nematode suppression. This project will provide outreach to University of Hawaii-CES and USDA-NRCS personnel with three on-farm demonstrations established on the islands of Oahu, Maui and Molokai in organic and transition production systems demonstrating alternative uses of this important cover crop species. In this project we will be able to create a web of new partnerships with participation from at least four different local farmers, up to ten different NRCS personnel and eight CES and college personnel. The goal is to generate an outcome of expanded utility and increased implementation of sunn hemp cover crops in Hawaii’s diversified agriculture leading to better mitigation of soil erosion and an overall reduction in our dependence on synthetic herbicides and fertilizers.

    Project objectives from proposal:

    • Farmer participants seed materials: 50 kg of Tropic Sun seed will be distributed to each of the three producer participants following the completion of the demonstrations. We will request each of the participants to use this seed within the next year at their discretion. We will monitor their experiences as a follow-up case study. NRCS Technical Note: The information generated from field demonstrations will be compiled for publication as a NRCS technical note and will go through the formal federal review process under the guidance of the plant materials specialist on Molokai (Bob Joy, MS). Standard information for a NRCS technical note includes growth rates, dry matter yield and N content of Sunn Hemp from these three separate locations. We will also be able to report on organic management techniques, weed suppression and nematode suppression. CD of PowerPoint voice presentations: All CTAHR participants will produce narrated presentations that will be made available to all CES and NRCS staff and accompanied with downloadable segments on the CTAHR Sustainable Agriculture web site: New partnerships will be developed between the seed producer, growers and personnel for developing a consistent market for this important cover crop species in Hawaii.
    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.