permaculture

[Toby Hemenway <toby@patternliteracy.com>]

One thing to keep in mind about aquaponics is that bacteria and other 
microbes are as critical a part of the system as in soil. The fish manure is 
not some liquid fertilizer that goes straight to the plants. It contains N 
primarily in the form of ammonia, and the usual bacteria are present in the 
gravel beds (which are best made with lava rock or some other high-edge 
substance) to convert it to nitrite and nitrate. Many of the 
nutrient-releasing processes are the same as in soil. As long as your fish 
food comes from a balanced source, a good nutrient balance will go to the 
plants. (I agree that you probably don't want to make aquaponics your 
exclusive vegetable source.)

People also complain about the embedded energy in these systems, which, 
indeed is higher than the energy footprint of a soil bed. But since most 
farming is done with tractors and other equipment, and chickens live in coops 
made with manufactured materials that have a high energy footprint, and we 
drive to the store to buy our food, etc, etc, I think that argument goes away.

Toby
http://patternliteracy.com