The project has three objectives:
1. Set up an aquaculture and fertigation project to raise tilapia fish for local sale and to use the wastewater from the aquaculture to irrigate and fertilize taro, bananas and watercress
2. Demonstrate that tilapia can be grown economically on the island, and wastewater from the fishponds can replace expensive imported fertilizer
3. Use the project as a demonstration site for other farmers
Agricultural properties on the islands of the Commonwealth of the Northern Marianas are typically small and must be farmed intensively. Input costs for production can be exorbitant owing to high shipping costs and what appear to be monopolies among suppliers.
The intent of this project is to demonstrate intensive multiple use of land in a way that provides inputs for one enterprise from wastes of another. In this case, the water and effluent from the fishponds will be used to irrigate and fertilize crops like bananas, coconuts, taro, turmeric, citrus and betel nut grown near the ponds. Irrigation is done through a modified flooding with discharge water delivered through PVC pipe to certain areas of the plantation as needed, typically on the soil surface above the plants.
Meanwhile, the market for tilapia is being developed. The local Chamorro population has historically eaten marine fish, tending to prefer the red tilapia, while the immigrant Filipino and Bangladeshi population prefer the black tilapia. Both types are being produced.
In addition, a marine shrimp is being considered for sale to the hotel and tourist market. Fish and shrimp fry are available from hatcheries on Rota and Guam.
The farm is located next to a flowing stream, and the three ponds have been constructed to take advantage of the grade. The ponds can be filled independently or in a series, and irrigation water can be taken from any of them. The upper two ponds are lined with concrete, the lower pond is earthen.
The combined capacity of the three ponds is 12,240 cubic feet, or 91,800 gallons. To maintain oxygen levels, the flow rate of water entering the ponds is maintained at about 1 gallon per minute, resulting in more than enough water to irrigate the acre of crops. Initially, too much water was drawn from the stream, reducing water for downstream farmers, but better water control and improved distribution of the overflow has eliminated the problem. Excess water infiltrates the soil behind the berms before returning to the stream.
Currently, overflow from Pond 1 is being used to irrigate the crops. The effluent from Pond 2 is discharged through a series of channels leading to Pond 3. Taro (Colocasia esculenta) and water convolvulus (Ipmoea aguatica) have been planted in the trenches and along the berms of the channels as well as along the shores of the pond. The convolvulus trails into the pond, providing increased algae growth area and fish food. In the channels, the plants absorb nutrients from the discharged water.
The project has been delayed because of typhoon damage to the local hatchery, which meant tilapia fingerlings didn’t become available until March 2002. So far, project coordinator Vince Calvo says he has sold 100 pounds of tilapia at $1.75 a pound. He has also donated about the same amount to local community functions as a family commitment and a means of promoting the fish. His family has eaten another 50 pounds. Meanwhile, about 3,000 fish remained in the ponds as of this report, averaging 4 ounces each, or 750 pounds. Feed costs had totaled $139.50.
Damage from three typhoons prevented sale of any crops from the farm. Still, Calvo’s evaluation and experience suggest that he has plenty of water and fertilizer, although he must take care to prevent any problems from excesses of either. The taro and convolvulus and taro in the water channels are growing well, even with the water flow disruptions from Typhoon Pongsona in December 2002. Watercress production, on the other hand, has failed because of high clay content in the soil. Calvo says he plans to plant the watercress in raised beds with soil amended by organic matter and drip irrigated with water from the ponds.
“The project has benefited my family financially through the sale of fish and by providing food for them and for social commitments,” says Calvo. “There is visual evidence that the irrigation has replaced the use of commercial fertilizer in my crops.”
FARMER ADOPTION AND DIRECT IMPACT
As an outcome from this project, two farmers who visited Calvo’s project have started or are planning their own tilapia farm. Another farmer has begun planning to channel his effluents to fertigate his citrus trees and other crops.
In addition, Northern Marianas College on Rota created an aquaculture position, which will focus on helping farmers produce tilapia, shrimp or other products of aquaculture.
RECOMMENDATIONS OR NEW HYPOTHESES
Calvo said he learned that tadpoles from the cane toads compete with fish for feed, but he has yet to determine how much they eat or how to control them. He says work is needed to find the best method of delivering the nutrient-rich irrigation water from the ponds to the plants. The nutrients encourage rapid algae growth, which clogs the drip openings. In addition, he says that proper analysis must be conducted to ascertain the nutrient value for the plants.
DISSEMINATION OF FINDINGS
More than 50 people have visited the project, including family members, local farmers, staff of the Department of Lands and Natural Resources, NRCS and Simon Ellis, aquaculture technologist from the regional aquaculture center in Pohnpei in the Federated States of Micronesia. A field trip during the Aquaculture Hatchery Management Training workshop, conducted by the Northern Marianas College for Department of Land and Natural Resources staff and farmers on Rota, also visited the site.
The communications specialist from Northern Marianas College has taken film for a 15-minute video. When edited, the video will be aired on the local cable channels on Rota, Saipan and Tinian, and copies will be distributed in schools.