Oganic Hydroponics

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When the manure shells are placed in the hydroponic troughs, and sunk down a few inches into the aggregate, with only the upper portions remaining exposed, they slowly release their nutrient contents into the growing medium. These then become available to the plant's roots as food. Covers should be placed over the vessels, and from time to time they may be refilled with nutrient sludge or topped up. Every three months the beds should be flushed through with plain water to cleanse them . . . .

Another experiment with an organic nutrient solution is briefly described on page 135 of the Portola Institute's Energy Primer ($5.50 from your local bookstore or MOTHER'S Bookshelf, P.O. Box 70, Hendersonville, N.C. 28739). Here, the water from aquaculture tanks is used as a, growth medium:

Finally, associated with each main [fish tank is a hydroponic growing compartment where the culture water from the main tanks (a "soup " of excellent fertilizer) is flushed through gravel beds planted with vegetable crops.

My initial feeling when I read this was that the fish tank effluent probably would not supply an adequate variety of nutrients for the plants' optimum growth. Consequently, to test this assumption I started growing some pinto beans hydroponically, using only the water from my own aquaculture tank as a culture medium.

At first, the bean plants put on amazing growth, rising several inches above some "control" seedlings (which were growing in a commercial nutrient solution). After a couple of weeks, though, the "commercial" beans began to catch up with those receiving only fish tank water . . . and by the end of the month, the fish tank beans which had become pale and sickly in appearance?had all but stopped growing, while the other beans were normal in all respects.

These results seem to parallel those obtained by workers at the U.S. Fish & Wildlife Service's fish farming experiment station in Stuttgart, Arkansas. In the May?June 1975 issue of Aquaculture and the Fish Farmer, investigators Sneed, Allen, and Ellis report on an experiment in which the effluent from a raceway complex containing 10,000 pounds of channel catfish was flushed into hydroponic troughs containing 17 varieties of vegetables. Their results?like mine?were disappointing:

The yield of edible tissue varied widely among different vegetable varieties. Although [all] varieties produced some edible tissue, eleven were of very poor quality and quantity. Three varieties produced average yields and three produced yields considered to be above average for home gardens. The best yields were produced by green peas and cucumbers.

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