[permaculture] pc aquaponics
dhondt at eircom.net
Tue Oct 9 17:19:23 EDT 2012
I was obviously too fast again when I called a water environment basically
anaerobic. That would only be the case in a static situation. Moving water
can have enough oxigen to enable salmon to perform very powerful leaps.
However, if you had numbers of micro-organisms in water as high as in good
soil your water would be anaerobic and it would look rather unclear and
Those huge numbers in soil are important because in a good ecosystem like
good soil, bacteria and fungi have very much closer relations with plants
than just turning amonia into nitrate. It is known that micro organisms
exchange complex molecules like amino acids and vitamins (B12 has been known
for this for decades) with plants for plant made sugar. In some places like
India people used sugar as sole fertilizer and saw no lack of nitrogen. I
can well believe that for I used Sitka spruce saw dust (with virtually no
nitrogen) on top of rock and could not find nitrogen being a limiting
factor. Of course we seldom have a problem with too little rain here in
Ireland and that helps.
Fungi/mycorrhizae live partly inside plant roots, exchange molecules and
information and are known to protect plants from environmental stresses like
acid rain and diseases caused by other fungi and bacteria.
I love my soil ecosystems for they enabled me to get rid of potato blight
and crucifer clubroot without any chemical intervention and even without
rotating crops much for 20 years. What do you do when your aquaponic system
develops a disease problem? You probably have a better chance in Tassie or
the US but here in Ireland blight and other fungal spores are everywhere.
Still, how would you solve disease if it occured?
G'day John & others,
If I read John's reply correctly, he seems to imply that aquaponics systems
are anearobic. Not so. The bacteria that convert the ammonia to nitrites,
and other species that convert the nitrites to nitrates, all require oxygen
to thrive. Hence the use of air bubblers in most succesful system to get the
dissolved oxygen (DO) levels to the maximum. And to prevent the fish from
going belly up, of course. DO is VITAL to the operation of aquaponics. This
is further mitigated by system design, e.g. the commonly used flood and
drain system gradually floods the growing media with poop water, then the
water flushes away quickly which effectively "sucks in" O2 from the air
above the growing bed. Then the bacteria go to work to do the conversions so
that the plants can thrive. Without O2 (by definition, anearobic
conditions), the bacteria die -> poop remains poop -> fish die of ammonia
poisoning. BIG PONG.
Areas that get clogged up in the grow beds, e.g. tomatoes have vigorous root
systems that sometimes lead to "dead" spots in the beds, get anaerobic. When
you stick your hands in there, it pongs. As you would expect. These dead
areas mean that the overall conversion efficiency of the grow bed (i.e.
natural filter) becomes less efficient. A regular testing regime (e.g.
weekly) for ammonia and nitrates will show you how efficiently the
conversion is happening, and will point out when there are problems in the
system. That is one reason for instance why sand is a Really Bad Growing
Medium in aquaponics, because it simply clogs up with poop and plant roots
Earth worms are often put into the growing beds, where they work further on
the sludge and enable the most to be made of the nutrients contained
Lastly, there are very few places on this planet where the perfect combo of
soils & climate occur. (I happen to be in one such place, being NW
Tasmania.) So even in organic soil-based ag, one would have to import
micronutrients in the form of rock dusts, kelp meal etc. to get the soil in
balance. This can also be done in an aquaponics system. Most systems are run
in the pH range of 6.0-6.2, which means that rock dust amendments will get
dissolved by the slightly acidic water, thereby making the nutrients
avaliable to the entire system (plants & fish). Quite commonly, sea weed
extracts are also added for the same purpose.
>From: John D'hondt <dhondt at eircom.net>
>To: permaculture <permaculture at lists.ibiblio.org>
>Sent: Tuesday, 9 October 2012 8:22 AM
>Subject: Re: [permaculture] pc aquaponics
>My problem with aquaphonics is not just disolved chemicals aka nutrients.
>Soil is an ecosystem consisting for at least ten % out of microorganisms
>often a lot more. To a large extend these soil organisms are aerobic. It is
>as good as impossible to maintain a large aerobic community in water.
>> On 10/7/2012 9:52 PM, Scott Pittman wrote:
>>> I too have serious misgivings about aquaponics. It is always presented
>>> some kind of perpetual motion machine that provides for all its needs
>>> the system, which I doubt. I also do not believe that it could possible
>>> have the nutrients necessary for providing wholesome and nutritious
>>> foodstuff. We are talking about the primary nutrient source being fish
>>> in this closed system, where does the selenium, calcium and phosphorous
>>> from? The co-evolution of plants with soil organisms and minerals has
>>> created the human nutrition story and without soil I think the actual
>>> nutrient content will be woefully inadequate.
>> I would never try to grow food for myself in an aquaponics system unless
>> its nutrients came from extracts of soil-based systems (don't quite know
>> how that would work given the anaerobic aspects of aquaponics systems. I
>> did find through a Google search a site with pictures of a soil-based
>> aquaponics system but they were growing ornamental aquatic plants in
>> submerged perforated barrels with a soil mix in them. The root crowns of
>> the plants were slightly above water level.
>>> I would love to see some data on nutrient content of hydroponic vs soil
>>> based vegetables.
>> There is probably no comparison with the nutrient dense food crops grown
>> in enriched soil with balanced nutrients and minerals.
>>> I would also point out that both the rice paddy system and chinampa
>>> are soil based systems with a lot of water to maintain growth they are
>>> by any means hydroponic or aquaponic. You might also throw in the fast
>>> disappearing mangroves as an example of aquaponics but again you would
>> In Eritrea they are developing an array of sustainable farming systems
>> that use sea water, They impound water in lagoons and grow shrimp in
>> them. That nutrient-rich water is released down stream to fertilize and
>> irrigate salt-tolerant land based crops. These crops are used to human
>> as well as livestock feed and to make rope or cloth. They are also
>> propagating, planting and harvesting mangroves for firewood, livestock
>> feed and construction wood. They are not reducing the populations of
>> mangroves along the coastline where their project is located. There is a
>> PBS documentary about this well worth watching, maybe viewable online or
>> for $$$ for the dvd.
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