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

2009 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
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.


Greenhouse Work

Greenhouse work summarized in last years report was published in 2009 in the Journal for the Science of Food and Agriculture (see JSFA.pdf). The work has also been presented at the 2009 American Society for Horticultural Science annual meeting held in St. Louis. MO (attachment 2). Pamphlets describing the work were presented to approximately 100 growers, agricultural professionals, and members of the public at the 2009 Sustainable Agriculture Field day held at the UH Agricultural Research Station in Waimanalo, O’ahu 9/26/09 (Attachment 3).

Greenhouse work was expanded in 2009 to include multiple soil types representative of Hawaii’s unique agricultural soils as well as soil biological properties. Pak-choi plants were grown in Oxisol (series), Mollisol (series) and peat based media fertilized with commercial green waste thermophilic compost. Vermicompost extracts were prepared with various extraction methods using 1:10 chicken manure based vermicompost to water dilution and applied weekly at the rate of 200 mL per plant for four weeks. Application of vermicompost extract regardless of extraction methods enhanced plant production, total root length, root surface area, mineral nutrient content, total carotenoids and total glucosinolates in plant tissue across the soil type. Vermicompost extract had negative effect on total phenolics compared to that of mineral nutrient solution and control. All vermicompost extracts regardless of extraction methods provided equivalent effect on plant growth and nutrient concentration in peat based media. However, aerated vermicompost extract with microbial enhancer had smaller effect on plant growth and nutrient concentration compared to that of aerated vermicompost extract and non aerated vermicompost extract in both soils. Greater effect of vermicompost extract over mineral nutrient solution suggests contribution of additional factors besides mineral nutrition. Vermicompost extract improved mineral nutrient status and microbial properties of Oxisol, Mollisol and peat based media. Dehydrogenase activity of vermicompost extract treated soil (133 µg TPF g-1 soil) was approximately 45% higher than that of not treated soil (90 µg TPF g-1 soil). Vermicompost extract effect on soil respiration (CO2 Fluxes µmol m-2sec-1) was generally similar to that of dehydrogenase activity. Moreover, the dehydrogenase activity was positively correlated (r = 0.64) with the soil respiration. The findings of this study suggest that vermicompost extract can serve multiple purposes including supplemental source of plant nutrient and enhancing soil biological properties. This work will be presented by graduate student Archana Pant at the 2010 Annual Conference of the American society for Horticultural Science at Desert Springs (Attachment 4).

Also during the reporting period, the effect of compost type on extract (tea) quality and plant growth was evaluated. The objective of this study was to determine chemical and biological properties of compost extracts produced from different types of compost and to examine their effects on plant growth. Five different composts: chicken manure based thermophilic compost (CT); green waste thermophilic compost (GWT); food waste vermicompost (FWV); aged chicken manure based vermicompost (ACV); fresh chicken manure based vermicompost (FCV); and their extracts were evaluated for chemical and biological properties. Aerobic aqueous extract of each compost was applied to pak choi ‘Bonsai’ grown in peat based media. Mineral nutrients, humic acid, and microbial activity present in each compost extract were generally representative of those properties of the respective compost sources. N and K content in all compost extracts were negatively correlated with C:N and C:K ratio of the compost sources. Humic acid among compost extracts ranged 98.6 – 550.5 mg L-1 in the order of GWT > ACV = FCV > FWV > CT while N content ranged 8.71 – 328 mg L-1 in the order of CT > ACV > FWV > FCV > GWT. Active bacteria and active fungi were higher in the vermicompost sources compared to thermophilic compost. Indole-3-Acetic Acid was detected only in vermicompost sources. Except for the extract of GWT, all other compost extracts enhanced plant growth compared to control. However, the extracts of ACV and CT positively influenced plant growth to a greater extent than the other compost extracts. Although N content in CT extract was double that of ACV extract, plant dry weight, root biomass, total root length and root surface area was higher in ACV compared to the CT treatment. This suggests that compost extract effect on plant production is due to the combined contribution of mineral nutrients, organic acid and microbial activity. This work will be presented by PhD student Archana Pant at the 2010 Annual Conference of the American society for Horticultural Science at Desert Springs (Attachment 5).

Field Trials

Waimanalo Experiment Station.
A field trial at Waimanalo Agriculture Research Station was conducted to examine the effects of vermicompost tea on soil biological properties, yield and phyto-nutrients by crop type (red choi and tomato) under chemical and organic source of fertilization. Three fertilizer treatments and three vermicompost tea treatments (5 & 10% vermicompost tea and a water control) were tested. Soil respiration, dehydrogenase activity and NO3 concentration in root zone have been measured periodically during the plant growth. Both 5 and 10% tea equivalently enhanced red choi yield across the fertilizer regimes compared to control. Effect of tea on red choi yield was higher than its effect on tomato yield. Analysis of carotenoids, total phenolics and total glucosinolates has not been completed yet. A second iteration of this trial is underway at Poamoho experiment station. (Figure 1). A separate series of trials have been initiated investigate the impact of non-manure vermicompost tea injected through the drip lines to avoid contact with leaf surfaces (Figure 2).

Adaptations Inc. (Farmer: Tane Datta)
Two varieties of Pak Choi (‘Bonsai’ and ‘Shogun’) have been grown continuously throughout the reporting period by the participating grower in beds receiving tea and in beds from which tea has been excluded. Tea was produced using on farm compost and a commercial brewing system similar to that employed in the greenhouse work described above. Over 100 yield measures have been made and samples have been collected for tissue analysis of phytonutrients. Data Analysis is under way.

Kupa’a Farm (Farmer: Gerry Ross)
Two trials have been completed during the current reporting period by the participating grower. The first trial employed sweet corn as the target crop, and the second was with multiple varieties of potatoes. In both experiments, tea was applied as IS common practice by the grower, or withheld. Tea was produced from compost made on-farm and extracted in a 200 gallon commercial brewing system (Geotea®, Figure 3). Yields, chlorophyll count and soluble sugars (brix) were slightly lower in tea treated corn compared with plots not receiving tea, suggesting that primary metabolism may have been depressed in favor of secondary metabolism. A second trial using purple, red and white varieties of potato was completed to test this hypothesis (Figure 4&5). Tissue samples have been prepared and pytochemical analysis is on-going. Data analysis is pending.

Ho Farms
A pilot on-farm composting project on this 40-acre conventional farm was initiated by Extension Agent Jari Sugano, with the intent to evaluate extracts of the compost (Tea) as an injected amendment in the farm’s fertigation regime. Wood chips were combined with cull vegetables (cucumbers and tomatoes) and passively composted in bins for six months, at which time compost was harvested screened and analyzed (Figure 6). Compost quality was found to be comparable or superior to commercially available thermal composts. Ongoing experiments are evaluating the impact of extracts from this compost as injected through the drip lines of irrigated vegetables at the Waimanalo Experiment Station (Figure 2).

Education/outreach activities and products have been initiated and include:

1) A 25-page color resource manual consolidating information on the making and use of compost tea for tropical Pacific region. The editors of this manual have communicated regularly throughout the reoprting period. Manual content has been outlined and participating growers and industry members confirmed.

2) Research updates have been provided to agents and other agricultural professionals (attachment 6). Extension fact sheets, including economic evaluation of compost teas at the whole-system level are pending.

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