Backyard Aquaponics
A place to discuss aquaponics

Hello

I see a lot of references to AP using "one-tenth the water of conventional growing" or "AP is ten times more efficient that soil growing". I am curious to know more about this and in particular how these figures are derived.

Water usage in agriculture has four main components:
1. Losses in transporting water to the plant
2. Water percolating past the rootzone and draining to the subsoil
3. Water evaporating from the soil surface
4. Water transpired by the plant

Items 1-3 are generally unproductive and can be minimised in conventional farming. For example, #1 is minimised by drip irrigation or low pressure sprinklers, #2 is minimised by matching water application to water demand by either soil moisture sensors or watering according to meteorological data and #3 can be minimised by mulching and drip irrigation. It is important to note that some of these losses will occur in aquaponics also - for example #1 will occur from evaporation from the fish pond, #2 will occur if sodium builds in the water and the water has to be dumped (this is the reason why some percolation is often necessary in irrigated agriculture since sodium needs to be flushed from the rootzone), and #3 will occur from the gravel surface.

I can't see that factors 1-3 are necessarily ten times worse in conventional agriculture than they are in aquaponics and even if they were, factors 1-3 are still less than the actual transpiration by the plant which accounts for the bulk of the water usage. The transpiration in aquaponics is likely to be higher than in soil grown plants since aquaponics plants will never experience water stress and thus will never close their stomata to limit their water losses.

I am keen to hear of any research or comments on this.

(sorry if this has been covered, but I could not find anything when I searched).

Regards

Sorry I must admit that I read it somewhere but I have never challenged "the claim"... so in responding to your questions, I am not sure whether "the claim" is in relation to both agriculture and aquaculture (ie fish and vege farming)...

But I seriously think that you will need to consider the fish farming or growing out aspect of aquaponics instead of just the vege farming or growing aspect like you have stated...

Typically in the aquarium trade, a 10-20% water change per week (or fortnight) is required to ensure prolonged fish health, and possibly more when you are growing out fishes for maximum growth... so say 20% of water change per week for a 1000L tank... 200L per week dumped...

With the concept of aquaponics this water change would not be necessary... so you have just saved 20% if not more... I am sure those with the information of aquaculture can provide better figures on what water changes are required for a backyard fish farming.

And if the claim has not taken into consideration the aquaculture side of things, then it would be less than 1/10...

Gumby,

You just need to look at the water use in a hydroponic setup to get an idea of efficiency.
Check out this submission to the Productivity Commission of Australia:
http://www.pc.gov.au/__data/assets/pdf_ ... sub046.pdf

In my view aquaponics is even better than hydroponics from a water usage point of view because you don't need to dump all the solution every couple of weeks. That's assuming you are getting the same production from an aquaponics setup compared to a hydroponic setup, to which most mature APers will testify.

And then considering the fish side of things, in aquaponics you are not exchanging 20% of the fish tank water each week either.

It's all good.
Pete

I wouldnt worry about water Gumby, youre made out of plasticine and that tends to be pretty water reppellent
( sorry couldnt help it )

Beeing into aqua for over three years it isent 10 times better there are so many factors that need to be taken into account
For starters could you link me to those statements that said its 10 times better or tell us who said it
there are a lot of shonks out there trying to make a quid

I cant vouch for the 10 times better clame but I have heard it from many sorces. I do know that AP is much more effecient than normal farming, just not how much more.

#1 there is alot less piping required in AP than regular farming because of the compactness of the systems.
#2 Water is continually recurculated in the system so the only losses are basiscly due to #1.
#3 Water will evaporate but with so much less surface area there will be less loss. Also plants shade almost all the grow space so there is less evaporation and water is generally kept below the surface of the gorw media. More like watering direct to the roots.
#4 Plants will transpire the same.

I beg to differ on that account. Plants that are water stressed (ie. lack of available water) have a tendency to shut down their Stoma and transpire less. AP planets do not have this need because of constant access to water.

However it could be said that to compare the growth rate vs water usage between AP and normal agriculture they must have the same needs. So under those rules, your quote would stand.

Hi Gumby
I often see such figures bandied around and have even quoted them myself although I often quote 20% because of our hot dry desert climate, but like you I would like to know where this figure was derived and how scientific and sound the research.
I have been curious to how much water I am actually using in my AP system and have started searching for a suitable water meter and in the process of digging up around all buried plumbing joins and double checking for leaks, although fairly confident of my plumbing skills I want to discount losses from leaks before monitoring the system for true water usage, I intend to keep a record of this for the next 12 months so will keep you posted.

First before going into the numbers, keep in mind.
When many people make these claims (the first ones to make the big claims, not those of us simply repeating) they often exaggerate. I hate that people tend to do this, I would prefer that people make very reasonable claims so that it would be reasonable for real systems to live up to those claims. But anyway.

I expect the claims would be basing the "traditional agriculture" as the most water wasteful huge sprinklers running every other day during the hottest part of the day rain or shine wind or no. The losses from using overhead sprinklers are huge. The water savings from simply switching to micro sprinklers or drip irrigation is amazing so if you switch to a loss less method of delivering the water to the plants, you get even better. Remember that when people compare stuff to being better on water than dirt gardening they are generally comparing to big sprinklers.
Anyway, Aquaponics is gonna save huge on number 1.
Aquaponics is also going to save on 2 since they water can't percolate away, it is a recirculating system. You mention needing to have some leaching to avoid salt buildup, well in aquaponics we are not using chemical salts to fertilize the plants so we don't have to rinse or leach them away. There are only rare occasions that one might need to use large amounts of salt in an established system and even then large water changes are usually not needed unless something goes really wrong.
Number 3, evaporation from the soil surface, well since the surface of the gravel doesn't get wet it isn't as big an evaporation source as one might think. The evaporation from the fish tank where there is water splashing or bubbling would be a source of evaporation but it isn't as extreme as what evaporates from the soil surface of a whole garden or field after sprinkler irrigation.

Of course number 4 is gonna be the biggest source of water loss to an Aquaponics system of course the humidified air in the micro-climate created by the AP system and the transpiring plants will also help to reduce additional water loss from evaporation since humid air doesn't suck up more water as easily as dry air. Comparing water stressed plants not transpiring as much to well watered plants in an AP system kinda skips the whole production side since most water stressed plants don't produce as well.

So, I can't really answer about the exact amount of water savings from using AP since it will really depend alot on exactly what kind of agriculture and method you are gonna compare to and where it is.

Yes, but this clay horse is an inquisitive one

Thank you all for your input, I will reply more specifically to the points raised later but I wish to reply to queries about the sources of this information

"Research has shown that an aquaponic system uses about 1/10th of the water used to grow vegetables in the ground." from http://www.byapmagazine.com/BYAP_Magazine_Issue1.pdf

I have also seen these in two books I recently read, one from NSW and one from Perth.

There is also a mention of this on some other forum users homepages but I assume they have just repeated the info from somewhere else.

Regards

A typical soil vege garden would be watered for about 10 mins per day...

Sprinklers can use as much as 1,000 litres of water per hour and your hosepipe can spew as much as 18 litres of water a minute.

So using a sprinkler for 10 mins would use about 166L... and a hose about 180L....

And most people would water at least once a day, 3-4 times each week... a total average usage of about 664 -720L+ per week...

And 90% of that water applied.... just drains down beyond plant roots...

Typically an aquaponics system might require a 10% top up... maybe twice a week.... in extremely hot weather...

And that's purely (or at least 90%+) due to plant transpiration.... as would occur in a soil garden anyway...

But with neglible evaporative losses in comparison to those from soil surface.... and none from "run to waste" drainage....

For a 1000L tank, which could easily support 4-6sq mtrs of growing space.... that's about 200L per week....

It really is a no-brainer... by pure logic...

There is... and I'll find the link later... a definitive study that showed the 10% usage...

P.S ... I think the 10% figure was also derived from an estimate of the amount of water (proportionally) that plants lose through transpiration... hence, as AP recycles all other water... and transpiration is the only loss factor....

It was suggested that aquaponics effectively only used 1/10th of the water a soil garden would...

Here's one study.... http://www.pc.gov.au/__data/assets/pdf_ ... sub046.pdf

And an article by Geoff Wilson ... http://www.aquaponicsjournal.com/articl ... terUse.htm

That suggests that AP uses about 50% of the water a similar hydroponics operation would use....

And quotes some data from UVI...

I think another factor which is pointed out in that first linked article is that plants produce higher yield. So if you get a crop from seed to harvest size in 6 weeks in AP rather than 8 weeks in the ground then you save 2 weeks worth of watering.