Enhancing Phytonutrient Content, Yield and Quality of Vegetables with Compost Tea in the Tropics

2008 Annual Report for SW07-073

Project Type: Research and Education
Funds awarded in 2007: $162,500.00
Projected End Date: 12/31/2011
Region: Western
State: Hawaii
Principal Investigator:
Dr. Theodore Radovich
University of Hawaii, Manoa

Enhancing Phytonutrient Content, Yield and Quality of Vegetables with Compost Tea in the Tropics


Compost teas (defined here as aerated, aqueous extracts of compost) have been demonstrated to improve crop yield and nutritive quality. The potential benefits of compost tea are substantial and are particularly relevant to agricultural production in tropical island environments through their promotion of reduced reliance on off-island inputs, employing natural biological cycles to mitigate year-round pest pressure, environmentally sound waste management to protect watersheds and reefs, and improved profitability of small and mid-sized farms that predominate large farms in these areas. The goal of this project is to improve our understanding of the interactions between compost quality, crop physiology and environmental factors as they relate to plant yield and phyto-nutrient content, particularly under tropical conditions.

Objectives/Performance Targets

1) Quantify the independent and interactive effects of compost quality and vegetable type under synthetic and organic fertilization on yield and phyto-nutrient content of model root, fruit, and leaf vegetables.
2) Determine, at the whole-farm level, the effect of compost tea applications on yield, phyto-nutrient content, and profitability with commercial vegetable operations on three islands in Hawai’i.
3) Build and enhance the capacity of at least 300 growers to effectively employ compost tea to increase vegetable yield and phyto-nutrient content on their farms.


Composts have been evaluated to identify those with the greatest potential to produce quality compost tea. Dozens of samples of thermal and worm-produced compost have been analyzed for chemical composition, including total nitrogen and carbon, and mineral nitrogen concentration. Worm-produced compost has been identified as ideal for compost tea production because of its finer texture, relatively high total N content (2-3%), low C:N ratio (<15:1) and high levels (1,500-2,500 ppm) of plant available nitrogen. Quantification of total fungal and bacteria populations in the compost is pending.

Greenhouse work has been completed to determine the effect on plant growth and phyto-nutrient content of pak choi (Brassica rapa) of aerated or passive brewing. Also tested was the influence of including additives to enhance microbial populations on the compost tea effect. All compost teas improved plant growth, and there was no significant difference among compost tea brewing methods or additives in their affect on plant growth (Figure 1). This suggests that costs may be reduced through the use of passive brewing if longer brew times are acceptable (8 days vs. 12-20 hours). Overall, compost tea applications increased total phenolic and carotenoid concentrations in pak choi by ~15% over a tap water control (Table 1). However, there was no clear relationship between compost tea type and total anti-oxidant activity in the plant tissue (Table 2). This work will be repeated under field conditions. The response of fruit and root vegetables to compost tea will also be evaluated.

On-farm cooperators have initiated trials to investigate the effect of compost tea on vegetables under certified organic conditions. Work on a cooperating conventional farm will begin next year. On-farm work will include the development of case studies documenting the variation in production, application and value of compost tea among different farming systems.

Education/outreach activities and products that will be developed during the remainder of the project period include:
1) A 25-page color resource manual consolidating information on the making and use of compost tea for tropical Pacific region
2) Extension fact sheets, including economic evaluation of compost teas at the whole-system level
3) Online database on compost tea hosted at www.ctahr.hawaii.edu/organic
4) Three on-farm workshops
5) Refereed journal articles

Impacts and Contributions/Outcomes

Expect impacts and outcomes include:

1) Reduced reliance on off-island inputs
2) Employment of natural biological cycles to mitigate year-round pest pressure
3) Sound waste management that protects watersheds and reefs
4) Improved profits for small and mid-size farms


Kelly Lange

Hawai'i Organic Farmers Association
PO Box 6863
Hilo, HI 96720
Michael Alms

[email protected]
Growing Solutions
1939 West Second Avenue, Suite B5
Eugene, OR 97402
Office Phone: 8087750616
Tane Datta

[email protected]
Adaptations, Inc.
7 Telephone Exchange Rd
Honaunau, HI 96704
Office Phone: 8083289044
Gerry Ross

[email protected]
Kupa'a Farm
Na’alae Road
Kula, HI
Office Phone: 8088760678
Wei Chong Ho

Ho Farm
PO Box 569
Kahuku, HI 96731
Stephen Talcott

[email protected]
Texas A&M University
Department of Nutrition and Food Science
Centeq Center Room 220F
College Station, TX 77843
Office Phone: 9798624056