[permaculture] Natural hydroponics, aquatic foodweb & quality food

venaurafarm venaurafarm at bellsouth.net
Sun Apr 7 00:55:51 EDT 2013

On 4/7/2013 12:40 AM, venaurafarm wrote:
> On 4/7/2013 12:25 AM, Steve Hart wrote:
>> On the subject of hydroponics I do recall a recent debate raging about
>> acquaponics which like hydroponics has little to do with

You participated in that discussion.

>   >>> Which the way I understand hydroponics:  There's no soil, no
>   >>> soil-food-web, no soil biology - it's not even agriculture (much less
>   >>> permaculture), which helps explain why I become distempered if I eat
>   >>> even a little (something which I would not knowingly do).
> There is no soil, there is aquaculture foodweb and biology. Read the
> thread on this and pay attention to Toby's input. That will explain all.
> Then Google the subject for more detailed information.

Here you go:

Toby Hemenway toby at patternliteracy.com:

Well-aerated, nutrient-rich water can grow vastly more microbes than any 
soil. I used to run a fermentation lab, so I've done it, easily. This is 
why wetlands are so important--and they work because wetland plants pump 
out oxygen at far higher rates than most terrestrial plants, and 
nutrient diffusion rates in water are far higher than in soil. Plus soil 
is mostly rock or carbon, which displaces bacteria, while water doesn't 
displace them--the sheer density of microbes in water can be far higher. 
The few billion bacteria per gram of healthy soil are a fraction of what 
a healthy wetland or an aquaponics system can achieve.

Like any system, aquaponics is not appropriate for every situation. But 
in places where land is scarce (cities), conditions are unreliable (many 
places), technical resources are more available than soil, and a number 
of other situations, aquaponics can allow food--and dense protein--to be 
grown where it otherwise can't.

You can get rid of fungi and other diseases more easily than in soil 
because you can circulate a treatment through the entire system very 
quickly or even replace the water, unlike soil.

I'm grateful to Kathryn K for staying so level-headed and reasonable in 
the face of some assumptions not well based in fact. I used to have a 
strong prejudice against aquaponics, but it pretty well dissolved after 
I learned more about it. I'm awfully fond of soil-based systems, but 
aquaponics has its advantages in some places. It's a useful tool.


I, like most people, have a strong preference for working in the dirt 
instead of using a bunch of tanks and pipes to grow food, but, then, 
soil ag, too, is pretty mechanized these days.

To sum up: there is nothing special about soil, in one sense: it is a 
medium for the propagation of the microbes that convert manure and other 
non-available nutrients into plant-available nutrients, and it can hold 
water and air.  Same with water. Instead of a rock-based medium to hold 
microbes and nutrients, aquaponics uses water as the medium, which is a 
nice stacking of functions, if you think about it, because soil has to 
be kept wet for microbes and plants to grow, while water doesn't, and 
most of the nutrients that plants use are water soluble, converted into 
that form from insoluble form by microbes. The carbon, the energy source 
for the microbes, is provided by the OM in the fish manure instead of OM 
from insect frass and animal manure.

And aquaponics has a couple of advantages over soil systems, because a 
water medium can transport nutrients to microbes and plants much more 
quickly than soil. In soil, water moves by diffusion, and once the 
water, or the nutrients in it, are used up in one area, the organisms 
must wait for more to diffuse in before they can feed or get moisture, 
and that can take time--and sometimes it doesn't happen, and the plants 
or bugs die. Same with oxygen, which can't travel well in compacted soil.

But in a water medium, nutrients are constantly being circulated to 
where they are needed, as is air. That's one reason that growth rates in 
aquaponics is much faster than in soil.

To make it clear: Aquaponics is not hydroponics plus fish. Hydroponics 
uses water-soluble nutrients from the get-go, with no microbes in the 
mix. Aquaponics, just like soil ag, relies on microbes to convert manure 
into plant-available form. Big difference--the former is chemistry, the 
latter is an ecosystem.


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.


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