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

2009 Annual Report for EW08-013

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

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


A field day was held at the
Date: September 25, 2009:
Time: 1:00pm-4:00pm
Location: Waimanalo Experiment Station on Oahu

Over 20 stakeholders were able to attend our first field day to gain new insight to the performance of a sunn hemp grown during the summer season on the windward side of Oahu. On June 26, 2009, a prepared 0.25 acre site was broadcast seeded at 60 lbs/acre and disked in. Drip irrigation was overlaid at 0.5 m spacings and used to water daily to maintain soil field capacity. Uniform germination was observed in the first week with a uniform stand 20-30 cm tall. In the first samplings, the average stand density was 150 seedlings/m2, which was a rate of approximately 100% germination. Final densities at 6 weeks after seeding were reduced to 100 plants/m2. At 8 weeks, the final stand height was well over 2 m tall with a total biomass was approaching 12 Mt/ha in full sun and adequate soil moisture (fig. 1). This may be the peak performance for sunnhemp in Hawaii due to the short day length and moderate heat index experienced within these isolated tropical islands. Weed populations were very low throughout this study.

Figure 1. Mean (+/- SD, n=3) dry wt. production of sunnhemp in Mt/ha seeded at 60 lbs/A from June 26- Aug 21

A field day was held at our cooperator’s farm on Molokai:

Our last field day was held at Rick Tamanaha’s Organic Papaya Farm in Hoolehua Molokai on January 14, 2010. For this demonstration, we established sunn hemp as an intercropped groundcover in between mature papaya rows. Sunn hemp was seeded on October 14, 2009 at 60 lbs/acre in 4 ft swaths between the papaya crop rows with a direct seeder followed by a chain rake for a light soil cover. Sub-samples within random 1×1 m plots were harvested on December 29, 2010 (11 weeks after seeding).The final stand height was 1.5 m and was only able to produce 2.9 Mt/ha, substantially lower than what was produced in the first seeding trial. This was probably due to the lower temperatures due to the fall season, but also more likely from the significant light interception created by the papaya canopy. Regardless, even with the reduced biomass production, there was still a significant reduction in broadleaf weeds and overall close to a 2-fold reduction in total weed biomass. The sunnhemp intercrop was mowed in the first week of January 2010 and within two weeks almost the entire foliar fraction was completely decomposed with only the stem fraction remaining. Incidentally, the nutritional fractions of sunnhemp leaves and stems were dramatically different with many of the important macro and micro nutrients residing at higher levels within the leaf fraction (Table 1).

Figure 2. Mean (+/- SD) dry wt. of broadleaf and grass weeds within the sunnhemp seeded at 60 lbs/A and a bareground check reported in kg/ha 11 weeks after seeding

Table 1. Percent nutritional content of sunnhemp collected 11 weeks after seeding. * indicates a significant difference at P< 0.05
C N P K Ca Mg
Leaves 43.8 5.3* 0.4* 1.6 2.1* 0.7*
Stems 45.4 1.1 0.1 1.7 0.3 0.2

Field day announcement:
The benefits and challenges of a Sunn Hemp (Crotolaria juncea) groundcover intercropped with organic Papaya
Date: Thursday January 14, 2010
Time: 1:00pm-4:00pm
Location: Rick Tamanaha’s papaya farm, 131 Moomomi Ave., Hoolehua, Molokai
Attire: The demonstration is in the field. Dress in field attire including closed toed footwear for your safety.

Groundcovers utilized in an orchard production system provide alternatives to a monoculture system with many attributes associated with biodiversity, weed suppression, erosion control and overall improved soil health & water conservation.
Please attend and view a 1-acre demonstration of sunn hemp planted as a groundcover in an organic papaya orchard. Along with sunn hemp we also have plantings of buckwheat (Fagopyrum esculentum) and oats (Avena sativa). The groundcovers were seeded in October, 2009 and have successfully established. We will learn about the attributes of a groundcover in soil fertility and pest management. In organic systems, where resources are limited, farmer adoption of a groundcover management system could vitally stabilize harvestable production by maintaining soil health and fertility as well as mitigating pest infestation.

Refreshments will be provided

To RSVP or if you have any questions, contact Lisa Schofield, 808-483-8600 ext 119 (Oahu)
James Leary, CTAHR Extension Specialist, 808-352-8774
Alton Arakaki, CTAHR Extension Agent, 808-567-6934 (Molokai)

Field Day presented by: University of Hawaii, College of Tropical Agriculture and Human Resources and Cooperative Extension Service, Oahu Resource Conservation and Development Council, Crop Care Hawai`i, LLC. Special Mahalo to Rick Tamanaha for his cooperative effort to make this successful.

This Project is supported by the United States Department of Agriculture Natural Resources Conservation Service under the Conservation Innovation Grant Program and the Western Sustainable Agriculture Research and Education Professional Development Program EW08-13.

A news article was published in the local news paper:

Field Trip | The Molokai Dispatch
Rick Tamanaha admits he didn’t know anything about growing organic papayas when he started his farm three years ago. He began with federal loans and a lot of help from Molokai farmers. He was also advised by Alton Arakaki, the Molokai agent from the College of Tropical Agriculture and Human Resources at the University of Hawai’i at Manoa. Arakaki and his colleague, James Leary, have now turned Tamanaha’s Kaleikoa Farm into a classroom for sustainable farming.

Last Thursday, Arakaki, Leary and Lynne Constantinides of Care Crop Hawaii presented a Sustainable Farming Practice Field Day for practitioners and gardeners on Molokai. Tamanaha’s farm served as an example of the importance of groundcover crops, and Conrad “Zuzu” Aquino’s farm showed how livestock can be used to clear fields.

Rick Tamanaha and his daughter, Taylor, are both working the papaya farm: Taylor is studying the effects of sunn hemp, micro sprinklers and lime on organic papaya for her eighth grade science project.Leary explained how groundcover can prevent soil erosion and add organic matter to crops, which means buying less fertilizer for the farmers,. He used sunn hemp as an example, planted between rows of tall papaya trees on Tamanaha’s farm.

“Sunn hemp behaves in a way that provides benefits to the system as a whole,” Leary told the crowd of around twenty.

Joe Campbell, owner of Molokai Island Farms is an organic farm that has been using groundcover to help his crops. Campbell said he has been using groundcover on his crops for years, because that’s what it takes.

“To do this [ground cover] successfully, you have to do it for 10-15 years,” he said. “The more people learn about ground crops, the better health will happen on this island.”

The field trip continued to Aquino’s farm, where he was using his goats to clear land that would be used to plant crops in the future – saving money on equipment and gas, and feed for his goats.

“The sustainable idea is that [Aquino] is trying to maximize his farm’s resources,” Arakaki said.
For the demonstration, Aquino’s 12 goats cleared roughly two of his 30 acres in about a month’s time. Now ready to start planting on those two acres, he will keep shifting the goats to different parts of his farm, clearing the whole places.
He then uses portable electric fences, run on solar power, to keep the goats away from his various vegetable crops.

Aquino and Tamanaha now have new sustainable tools to more effectively and economically keep their farms running.
Tamanaha said he realizes the potential for his farm and wants to extend his 15 acres to the full 35 on his lot in Ho`olehua, providing more jobs to Molokai and stimulating growth. “This can save this island,” he said. “We haven’t even scratched the surface of the industry.”

molkai virtual field day


Dr. Koon-Hui Wang

Assistant Professor
University of Hawaii
3090 Maile Way
Honolulu, HI 96822
Dr. Theodore Radovich

Assistant Professor
University of Hawaii
3190 Maile Way
Honolulu, HI 96822
Jari Sugano

Extension Agent
University of Hawaii
3090 Maile Way
Honolulu, HI 96822