[permaculture] Aquaponics productivity, energy use, "sustainability" etc...
les at mulder.com.au
Tue May 3 21:11:39 EDT 2011
I've been running aquaponics for some years now and have made a number of observations in comparison to soil based systems and extensive aquaculture (all of which I'm playing with in my small suburban back yard).
Handily, Frank Gapinski came here a week ago with Geoff Lawton to film for their upcoming Urban Pc DVD and Frank has put up a couple of blog entries with graphics, so you can see my setup exactly.
The "traditional" aquaponics system is chronicled here:
And the extensive system here:
I agree that aquaponics can be incredibly productive, as ours was in its first year. But there are many downsides that are not discussed much.
Our growbeds use perlite as the grow media, which I got cheap as a result of a screw-up at a local manufacturer's. Downside is it floats, so makes flood and drain harder to set up. Upside is it retains moisture, so extended pump failure does not lead to pump failure.
The gardens on the other hand, are no-dig raised beds, using Toby Hemenway's recipe for sheet mulch from Gaia's Garden.
Like all aquaponics setups, we have more fish than will survive if they are left to fend for themselves. Therefore, we need to feed the fish. The pellets contain commercial fishing by-catch as well as chicken guts sourced from industrial chicken farms, neither of which could be described in any way as sustainable. I've heard of some pellets recently that are made from rape (canola), but am sure this comes from industrial canola farming, so ditto. I haven't managed to source any of this yet, so don't know if they're any good. And I don't have enough land to grow food for them here...
I have enough surface area to ensure the pond gets enough oxygen that the fish don't die if the pump fails, but it's pretty marginal in summer, when the water holds less oxygen. Every backyard aqaponicer I know has had at least one episode of pump failure and mass fish death.
With only a few exceptions, the taste and quality of food grown in soil is superior to that in the aquaponic system. The exceptions are Tuscan kale, which takes on a lovely subtle flavour compared to the stronger tasting soil borne variety and silverbeet (chard), ditto. Most everything else has a more intense flavour out of the garden, and for us, this is desirable for most things we grow.
We've found that aquaponically grown plants get big very quickly and seem to have weaker structures as a result. They are then far more susceptible to attack by chewing and sucking insects than the plants grown in soil.
We also have a bacterial wilt that got into the system two years ago that wiped out all the solanaceae. This year we've been able to use actively aerated compost tea to outcompete the wilt, but the plants in the growbeds get the wilt harder and faster than those in the garden.
The extensive system:
The pool setup in the link above is fundamentally self-managing. I have a small pump to stop the water at the bottom of the deep end of the pool going anaerobic, as happens in some pool conversions. I only do this because we still swim in the pool and don't want to stir up smelly muck while doing so. Otherwise, pump failure has zero impact on this system. I added the gravel filter beds just as an extra to help get the water balanced and clean faster. The floating garden beds would be sufficient for this, had I not done the filters. Adding biofilters as in the aquaponics system would get it going properly even faster.
The fish (100 Silver Perch or Barcoo Grunter) are an Australian native and omnivorous. They eat the algae that grows in the pool and any insect attracted to the water. We no longer have any mosquitos in the house through the summer. They were introduced to the pool in October or November last year and were mostly 10mm long. Without any food added (other than bits of bread when we want to show off), the largest are now around 25cm and the smallest are at least 10cm. There is clearly no shortage of food for them.
At this point, we're only growing aquatic plants with this bunch of fish. The aim was to introduce more veggies as per an aquaponics setup, but this will have to wait for another time, as we're putting the house on the market so we can attack all these concepts in a more serious manner outside the city.
So, what do I think of aquaponics? In a small space with lots of energy, you can produce a lot of food. Handy if you live in a city. Is it sustainable? About as sustainable as the city in which it is placed - i.e. not at all sustainable. I also have animal cruelty concerns about small tank systems with high stocking rates, as are commonly advocated by tank manufacturers.
Will I use aquaponics when I move to the country? Only as described in the pool to pond article above, with a few veggie beds attached.
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