Here we go again, the myth makers are at it again.
This time, it’s grow tank depth for raft systems.
The suggestion is that grow tanks should be 300mm (12″) deep…..and some of the reasons being proferred for this depth include:
-
the more water in a system the greater its stability.
- shallower tanks may heat up (or cool) down quicker.
-
shallower beds may become clogged with roots.
-
12″ is a handy number for calculating with (my personal favourite).
Since all aquaponic growing systems are actually hydroponic systems, I consulted my copy of “Hydroponic Food Production” by Howard M. Resh PhD.
As it happens, water culture was one of the earliest hydroponic methods used in commercial crop production.
Dr Resh describes an early method (circa 1970’s) that featured concrete grow troughs (painted with bituminous paint) that varied in width from 12″ - 42″ (300mm - 1650mm) and were 25′ - 100′ (7.5m to 33m) long……and 6” – 9″ (150mm – 225mm) deep. The nutrient solution in the grow troughs was 4″ – 6″ (100mm – 150mm) deep.
Unlike the raft systems of today, these troughs did not use a styrofoam raft but rather supported a tray containing the plants. Their roots were allowed to dangle in the nutrient solution.
Resh reports that, in 1977, the Japanese had about 300 hectares (about 750 acres of greenhouse-based water culture. The water troughs were made of rigid plastic and were typically 800mm wide, 3 metres long and were filled with nutrient solution to a depth of 150 – 200mm.
The troughs were fitted with a Styrofoam lid and the plants were inserted into holes in the lid. This system grew mainly tomatoes, cucumbers and salad crops.
Dr Merle Jensen (University of Arizona) developed a raceway raft system during 1981 – 82. The grow troughs that he used were 600mm (2′) wide, 200mm (8″) deep and 30m (90+ feet) long.
So, based on the above, it can be concluded that grow tanks do not need to be 300mm deep. In fact, premised on the experience of the past, most of them…..and we’re talking hundreds of hectares here……were 150mm – 200mm deep.
Now, if you have 300mm (or deeper) grow tanks, don’t despair……they’ll work fine (just like 300mm grow beds do) but don’t let anyone tell you that they have to be 300mm.
-o0o-
{ 6 comments… read them below or add one }
I find a 300mm deep growbed handy because of the stability afforded by a bigger rootbase. It’s difficult not to accidentally bump into, tug at or otherwise damage plants that grow vigorously whilst you are attending to the normal duties of running a system. That’s the only reason, though.
As for your initial points:-
-the more water in a system the greater its stability.
(more like the longer the roots are under water and the longer it takes to drain)
shallower tanks may heat up (or cool) down quicker.
(One would imagine that the GBs are shaded by vegetation fairly swiftly once planted out)
shallower beds may become clogged with roots.
(possibly true, but I’m always more worried about roots in the drain, that’s what floods my greenhouse)
12″ is a handy number for calculating with (my personal favourite).
Doncha have six fingers, dude?
Uncle Yarra……….I think 300mm grow beds are good, too. I currently have nine of them. To summarise my observations about grow beds, shallower ones will do most everything the deeper ones will do…..and they offer some advantages over the 300mm ones. Most of the reasons for suggesting that 300mm beds must (or should) be used, amount to pop science and don’t stack up in practice.
As for 12″ being a nice handy number to deal with……I think the metric system is far easier……and I’m old enough that I straddle both imperial and metric systems.
Hello Gary,
I am curious as to what the advantages are over 300mm beds and would like for you to show me where i could find them. Or could you tell me what they are.
Wouldn’t it make sense to use the beds (whether it be 150mm, 300mm, 600mm) that provide the most possible positive outcomes for you at the most cost effective price?
The reasons given by the “Fundamentalist” appear to be quite sound. Where can i find the info to refute there cases?
I would much appreciate your guidance in this as i would like to make sure that i have a balanced view of what Aquaponics is and what i really need to be made aware of before i commit any serious dollars to my self sufficient dreams.
Noah……I’ve responded to your questions on my forum……here.
Thank you for your reply gary it is much appreciated.
I apologise for all of these silly qustions however like I said in my last post I want a really balanced picture of Aquaponics.
I don’t have a copy of Dr Resh’s book and and haven’t seen Dr Jensons reports. I am curious as to whether if Dr Resh and Jenson designed their beds specifically for the purpose of their hydro system or did they use what was already available for their research?
I have read your reply via the link that you have given and was hoping to see some quoted evidence to support your stance against the “fundamentalist claims. Any one can make claims but until evidence has been shown that clearly refutes their claims it will still have some weight of credibility. It will still feed doubt to the mind of unenlightened.
You said i should be asking where can they produce the evidence to support their claims and that is true they most certainly should and I can’t wait to see it if ever. Please don’t take offense but i haven’t really seen where you have provided evidence either. There are no quoted references from people of authority or are there none to quote from?
I think I am starting to ramble on a bit and I should get some shut eye before I say something really dumb.
Thanks for your help hope to learn more soon.
Noah…..
Drs Resh and Jensen were not reporting on their own systems but rather on those in commercial use in places like the US and Japan. In some cases, these arrangements covered commercial undertakings of many hectares.
What I have said is that the suggestion that grow tanks should/must be 300mm (for the reasons that they state) is nonsense. I’ve provided references to the work of researchers like Drs Resh and Johnson which demonstrates quite clearly that grow tanks of less than 300mm were frequently used……which suggests that they worked quite satisfactorily.
To further support my view that grow beds and tanks of less than 300mm work quite satisfactorily, they have been sold by hydroponic stores for many years. They have also been used effectively by Matt and Shannida Herbert at their farm near Mudgee for longer than most (if not all) other grow beds or tanks in Australia…….and my experience supports theirs. You can see video footage of the systems that feature these beds…..here.
I belong to a US-based aquaponics listserve which has members who have also been using sub-300 grow beds…..for years.
I’m sure that, if I wanted to spend more time, I could find many more examples.
Howzat?