Water Cycling

Water Management-Water Cycling

	As part of a SARE-funded project at the University of Arizona, grower Craig Collins raised olive trees irrigated from his shrimp pond. Photo by Kevin Fitzsimmons

Some farmers and ranchers seeking to maximize every drop of precipitation are creating systems that double the benefits of a water source by applying it to two enterprises. Many of them pair crops with aquaculture, which not only recycles water but also provides nutrients from fish waste. Worldwide, aquaculture is expected to grow at about 7.3 percent annually, from $66 billion in 2003 to more than $93 billion in 2008 in response to market demand.

University of Arizona researchers funded by SARE integrated shrimp ponds with olive trees on a Gila Bend, Ariz., farm to test the benefits of running irrigation water through two systems. Researchers designed a plot of 120 trees, irrigated them from the shrimp pond, and compared canopy height and trunk circumference to a set of trees watered from a well. Watering trees from the shrimp ponds also supplied saplings with 1.6 to 5.6 kilograms of nitrogen per row from the shrimp waste. In the second year, they met the full nitrogen recommendation for olive trees.

“We wanted to show how to pair crops with aquaculture, running water through fish or shrimp first, then putting it on their crops,” said project leader Kevin Fitzsimmons, a soil, water and environmental researcher. “The trees grew significantly better with the effluent than the trees that were on well water.”

Fitzsimmons also tested shrimp pond sludge – shrimp waste that settles to the bottom – on tomato plots at the university’s Environmental Research Lab. The tomatoes amended with sludge in Fitzsimmons’ project produced significantly more fruit than the tomatoes in the control plot with unamended soil: 141 grams of fruit per plant compared to 39 grams in the control plants. “A major point is that we’re using the N and P in the waste from the shrimp to replace the N and P fertilizers that farmers would otherwise have to buy,” Fitzsimmons said.

Through field days, Fitzsimmons’ team publicized their results and, since then, close to a dozen Arizona crop farmers are trying to integrate fish and shrimp farming into their systems.

The climate on the U.S. Virgin Islands is also semi-arid, and Islanders view water as a valuable resource. To help the small, high-value market crop farmers on
St. John, researchers at the University of the Virgin Islands explored ways to use tank-grown tilapia to add fertility and recycle water.

Project leader Don Bailey hopes to raise the standard of living by introducing a marketable new product in a territory that imports more than 80 percent of its seafood and 90 percent of its fruit and vegetables.

“Fish is an alternative crop for farmers to diversify their income beyond field crops,” said Bailey, who tested tank-raised fish on a St. John farm growing organic greens, using dried fish sludge as a soil amendment. Tilapia can bring up to $3 a pound and costs just $1.25 a pound to produce.

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