Backyard Aquaponics
A place to discuss aquaponics

hypothesis: AP is mainly good because it provides reliable water to growing plants - plants in the soil perform as well as those in AP given the reliable water (especially when considered as EROEI).

A plant will always be limited by some factor, standard soil based cultivation is limited by water availability. (AP nutrients are in essence taken from elsewhere - other plants, other fish or directly from energy; soils can store more nutrients per sq mtr than AP and are the initial source of all nutrients)

Implication: soil based crops (which are far less energy intensive) will outperform AP at systematic level given an effective way to irrigate on demand without loss.

njh- do we really know if soil based crops are less energy intensive.
I suggest not! I say this because if you look at embeded water of crops you will see the huge amount of water consumed to produce those crops.
The extra surface area and the loss thru gravity as well as the other living organisms consuming vast amounts of water, don't forget you have to get the water too them, that has a cost. Further because of the scale of economies it is necessary to grow in large plots some of the costs are invisible. Beyond this, we don't know what harm is being done at a micro level. If you look at where croping has been done for years it is necessary to rotate crops because of mineral loss due to take up from plants. What cost is involved in having a paddock in fallow for example?
Where do the new minerals etc come from and at what cost?
If your looking at the cost to run your system, you are probably seeing the true cost! IMHO
C1

That's what I'm asking If we could reduce the water use to that of the demand of the crop we would match the performance of AP. With the additional benefit that we don't need tanks and pumps and gravel and fish.

People grew (and are still growing) crops indefinitely with good practices. The modern trend to high inheritance based farming (fertilizer, herbicide, insecticide, high energy machinery) is a very short and probably irrelevant blip on the history of farming.

My question is simple: Is the purported advantage of AP due to the high availability of water, or does it provide something else?



Those other organisms may do something in return. That lost water may be stockpiled for a drought year. I assume that natural systems use the available energy and water at their theoretical limit for sustainable growth (assuming that GA are good at finding reasonable global maxima - something that's been claimed for a long time, though probably unprovable).

If this is true, then covering the entire surface with plant may be suboptimal (exercise: why?).



This suggests poor management of resources rather than a fundamental problem with soil based cropping - The chinese used the same land for their crops for thousands of years by ensuring that all the extracted mineral wealth was recycled.

The mexicans (aztecs) developed a sustainable system in mexico city based (interestingly!) on aquaponics + soil based cropping. Their system relied on 100% recycling of the non-volatile minerals.



The cost to the farmer or the cost to the land? I thought both were fairly clear cut?



Well that's what I'm trying to work out Crops are clearly net producers of wealth (converting sunlight to food energy), the question I've been trying to answer for the last 10 years is exactly how much wealth they produce compared to how much inheritance (fossil food) they use up. Hydroponics (and hence AP) is interesting because it allows much tighter accounting on the demands of plants (just like how we worked out which minerals were essential to human health - we simply made exclusion diets, noting which things caused problems). One problem with this approach is that it detects acute deficiencies quickly, but chronic deficiencies (especially non-terminal ones) are almost impossible to detect.

We can remove omega-3s completely from a person's diet and they will live to a ripe old age. But they will never perform as well as those with it. How can we detect this?

Why hydroponics doesn't do is provide a bound for the performance of soil based cropping (something that people keep forgetting). So proving that AP is better than HP is like proving that priuses are better than camrys - interesting, but I'm asking about bikes and public transport. (We could take this analogy further, loosely: this post is about whether electric bikes are better than plain bikes)

Lots of good questions, thanks creative!

I'm wondering if it has more to do with accessibility of air and nutrients. As I understand it, much of the benefit in AP comes from the bacterial culture. And it seems that most of the beneficial bacteria are aerobic. In soil, there will be zones that are anaerobic -- those zones (I'm guessing) would be non- or possibly counter-productive to plant life.

I know from my experience growing bedding plants that a balance has to be struck between water retention and aeration. Our growing media was mostly sphagnum peat -- very similar in many ways to hydroponics -- often we had to water 4 times per day because to get enough air to the roots, the soil didn't retain much water.

I'm not sure how you could remove omega-3's completely from a person's diet.

This would suggest that continuously flooded should perform worse than flood and drain?

It's certainly a tempting theory - I grow my cuttings on open benches in small pots with open media (and hence lots of air). On the other hand, our garden soil is silty loam, and plants seem to do really well in that too.

Lawns are always improved by aeration machines. Don Burke uses crushed sandstone for soil.

I did an experiment several years ago comparing uniform soil particles to 'fractal' particles (i.e. all different sizes) and found that fractal did better than uniform. Uniform should have larger air gaps.



I read a paper on it some time back when O3 were the bee's knees. Perhaps they just removed the majority. The result was poorer mental agility (which is why I need to get my perch up to size faster .

From stuff I've read/heard minerals come naturally, ultimately from rocks. If a system is exporting product (ie a farm, apline zone) then it will become less fertile over time unless it is given a period to recharge (lie fallow), rocks in soil break down slowly releasing nutrients or alternatively minerals are returned to the system in some manner.



Good agricultural soil is not anaerobic which is one of the reasons its "good". Soils tend to be anaerobic when they are water logged, heavily compacted or for some reason are prevented from exchanging gases with the atmosphere (eg dirt under greenhouse floors covered in plastic).

Interesting, and probably right. That irrigation thing is really tricky, though. It may be that we do so much better with AP because it is easier to balance that optimal irrigation. I'm reminded of my father's and my eggplant experiments. We had three plots growing eggplants to see what made a difference. The plot that we actually got eggplants from (in quantities to overfeed 3 families from a 4 foot by 8 foot plot) was the one on an irrigation system. Now I have 2 eggplants in the AP system to see how they do there.

If there are no stagnant spots, CF should perform just as well or better -- according to my theory. My theory is that all nutrients (including oxygen and water) are available all the time to all the roots in AP. I'm postulating that diffusion works much more quickly in water than in a soil-based media.


I was talking about anaerobic zones -- I'm thinking anaerobic areas the size of a golfball around plant roots could hinder growth. A compost pile is aerobic too -- but even the best pile needs to be turned to expose the anaerobic microzones to the air. I don't know if it is related, but I have read about aerated septic tanks -- supposedly running an aerator for 10 minutes every 2 hours or so will decompose 98% of the solids in a septic tank -- basically turning an anaerobic system into an aqueous compost pile. ( the only reason I haven't shoved an air line down one of my cleanouts is that I'm worried that the agitation might stir up enough solids to circumnavigate the baffle in my tank and plug my drainfield)

I'll just expand on my theory a bit more.

In an AP system, whenever a plant pulls a nutrient out of the water -- there will be a lesser concentration of that nutrient right by that roothair. Diffusion will tend to equalize distribution of all nutrients so within minutes or seconds, that nutrient should be replaced. In a soil-based system, water will not be contiguous so it could take hours or days for the nutrients to be replennished at a particularly "hungry" root hair.

Now that I've typed that, I just thought of something else. Perhaps the advantage of AP is the fairly stable temperature for bacteria. I've seen some amazing growth on compost piles -- but it often does not last. Sometimes the compost pile gets too warm and "cooks" the roots. But if we could get aerobic decomposition with a lot of water -- we could have the same bloom of bacteria (with the attendant cocktail of nutrients in various organic bonds) with a stable temperature.

In good soils that tends not to happen right the way through the soil colum As in no anaerobic areas from top to bottom. Oxygen defuses quite easily into soil that has a void. Thats why a significant feature of good soils is that they drain well and are not compacted. Any soil when it becomes waterlogged will become anaerobic relatively quickly. Also an environment that has a very high level of biological activity may also become anaerobic but this is due to oxygen being used up faster than it can be replaced. Plants don't tend to do that where as the bacteria and other beasties you find in compost heaps and septic tanks will.

On our farm you can't see much of difference in growth by soil type at the moment because everything is pretty much bone dry. The growth on the red soil will soon exceed the clay soil production because the roots of the plants on the gray soil are limited to the top few cms of the soil column because thats only how far oxygen can penetrate into the soil because of water logging.

This further slows growth in water logged soils because the plants are so shallow rooted that they can't get very many nutrients because of their shallow root systems that are in constant competition with their neighbours. Plants on the red well drained soil go as deep as they like (2m anyway if they want/can) allowing them to have bigger root systems with less competition to get the nutrients they require.

This second point in combination with Ems point on nutrient availability/diffusion is one of the reasons it was explained to me that AP does so much better. Since plants have all their nutrient requirements laid on. First they have everything they need and second they got it with out having to out lay a significant amount of energy in growing the root system to extract nutrients from a more dispersed source, ie soil.

Bounce! bounce! This is exciting stuff guys!

What experiments could we devise that would find exactly what is causing the difference. If it is air availability, perhaps a continuously flooded system where the water is injected at the base lifting to the surface and an overflow, and the water is drawn from the base of the tank will give poor results (because we avoid oxygenating the water.)

Perhaps someone with a) time and b) existing equipment could run a side by side experiment to see whether flooding from the base is worse than flooding from the top.

If it is the nutrient argument rather than the oxygen argument, then both should do the same.

I believe that in soils water moves very quickly along the surface of the media, and will correct local difficiencies (rather, locally less concentrated) by ion transport.

It is tempting to think that the large volumes moved in AP will increase this transport speed. But as always, the boundary layer will be the main limiting factor. So I'm not convinced about that. Nutrients are also are much higher concentrations in soil than in AP.

Is the energy saved by the plant not growing roots offset by the increased pumping cost?

If the advantage of AP is the nutrients and bacteria, why doesn't hydroponics do as well? If the bacteria are living on oxidation of N we should be able to get the same results doing hydroponics with NH3, urea or nitrite feedstock.

Now that's a very interesting point...... or AP water?

I think an inherent problem with the hypothetical comparison is that we just don't know enough about the nutrient environment to produce optimal results. Both in terms of plant growth and in terms of eating benefit.

Also, I think AP's primary advantage over soil cultivation is its applicability in an urban environment where traditional farming doesn't work all that well.

I've been wondering if it is the bacteria that actually accellerate the process. Some hydro systems use sterilizers -- so they must think certain microbes are harmful. I wonder if we could count the microbes or somehow measure the biological activity in AP water vs soil. From what I've been taught, the top 2 or 3 inches of soil has the most microbial activity. Perhaps with AP we're actually increasing the depth of that "active layer" so we can get more growth per square foot. Tom Speraneo postulated that bacteria were actively transporting nutrients across a pH barrier. Perhaps soil biota have complex symbioses with plants that we have not yet discovered....

I think from what we have discussed in other threads the advantage of AP over HP was the complexity of the ecosytem and the resulting complex of disolved nutrients in the water. In HP the ecosystem is basically the cultivated plants and any other organism in the system that competes with the crop for whats in the nutrient solution. In AP the resulting complexity of chemicals disolved in the water is just not practical to measure or reproduce except in a "natural" AP way.

Feeding the fish adds a lot more than N to the system and fish poo supports a range of cweetures of which the nitrifying bacteria are only a small part (although crucial). Which in turn produces the complexicty of other stuff that people havn't even began to measure let alone study.