Floating raft

[Houliham]

I have a raft system and a chop system. The chop system is taking off with the lettuce. The raft system's lettuce is growing real slow and is starting to get little black dots on the leaves. Any suggestions?

[keith_r]

are you adding air to the raft tanks?

[Houliham]

yes there a have bubble stones.

[urbanfarmer]

You don't need to add air to your floating raft system if you're growing lettuce!

[davidstcldfl]

You don't need to add air to your floating raft system if you're growing lettuce!

Wow, this is a first Urbanfarmer....that is, I disagree with your advice to some degree. Of course there are lots of variables....how much water, how many plants, tempt of water, length of the raft beds, ect.
I have seen pictures of other people's raft systems...it was obvious 'where' the air stones were located, because there was a noticeable size difference in the lettuce plants. They were much larger near the air stones.
In general, it's better to have more air then not. Especially now that the water is getting warmer.

Houliham, I too have a mixed system, my lettuce does grow faster in the gravel beds then in the rafts. I guess because of the concentration of nutes in the 'sludge' building up in there .
The growth of the lettuce in the rafts has improved as the system has matured. I do add a little liquid iron...I also use Maxicrop with iron.
I find the lettuce does better when the PH is just under 7...6.8 seems to be good for my system's lettuce.
Sorry, not sure what your black spots are...? I haven't had that issue.

[keith_r]

if the roots in the raft are dark colored or black, it's root rot, and the roots need more oxygen..
raft systems definitely need oxygenation!

[urbanfarmer]

Good, I was hoping to turn a few heads (pun intended)! I recently sat through a lecture with Dr. Tyson. He's a hort science guy from UF and the Director of the Orange County extension. He stated that floating raft systems didn't need added oxygen; so, of course I had to question him. He proceeded to display pictures of different farms that raise crops hydroponically without any aerators. The local farmers here in Florida grow with no aerators or pumps!!! Their yields are not affected, and they have found that they don't get any difference by adding these devices. I was as shocked as you were, but not is it only scientific fact, but many many farmers are doing this here in central Florida!!!

He did state not ALL vegetables and fruits can be grown like that. It is possible to have a specific species of lettuce that can't grow in there, but in general he did state lettuce can and will grow without added oxygen or a reduction in yield. Also, the accepted way to grow plants that want more oxygen is not to add aerators, but to provide a gap between the water and the roots at the top.

University of Florida raft system example: http://edis.ifas.ufl.edu/hs184

[davidstcldfl]

Wow...that's interesting U. F. I wonder if there is some difference between the hydro and the AP systems ...? I wonder how often in the hydro, they change water (keeping the DO up)...?...don't they have issues with some kind of bad bacteria attacking the roots....?
I wonder how many 'actually tried it' both ways....or are they just doing what others are doing ?
Did he happen to give you any links to some documentation ?

I took some lettuces to the flea markey in a small floating raft set up. The 1st weekend, I had no air ( or water movement) and the roots started getting dark by the end of the 1st day. The 2nd weekend, I had a small air pump and a few stones...the roots/plants seemed better. The water wasn't very deep. Not exactly 'scientific', but the results where obvious. The air temps were about the same both weekends.

I'm waiting for permission to post a picture....it shows an AP trough of lettuce ( in rafts) and the lettuce over the air stones are much larger then the rest. ( I don't know what the flow rates were, or the PH and other factors of the water in the picture)

Here's 2 links to a news letter from Friendly's Aquaponics, in regards to what they have found about added air in their AP systems... scroll down and look for 'Aeration In Aquaponics Systems'
http://hosted.verticalresponse.com/5273 ... 51f16240b/
http://hosted.verticalresponse.com/5273 ... 51f16240b/

Friendly's is doing tests on reducing the water 'flow' through the troughs and increasing the DO instead. They think there is less power needed to add air VS. the power to move the water. (Of course, there are lots of variables on the different pump ratings) Every little reduction in power counts...especially for what they pay in HI.

[urbanfarmer]

I haven't looked for anything specific because so many hydroponic/aquaponic farms are apparently doing it this way. I believe the trick is adding a gap that's few inches between the bottom of the raft and the top of the water for oxygen hungry plants (this is why I have seen in EDIS articles). I haven't really looked into it because he was more than confident about it and he showed so many examples of farms that did this and have been doing it for years if not decades. Also, we have a local restaurant called Scorpio's and they have this exact setup outside with basil and lettuce (in front of the restaurant). I looked, and they don't even have a gap under the raft and they go from seed to harvest without adding any oxygen. It's just a barrel with water and a styro raft on top. They also have this setup at the demo garden at the Orange County extension, and it's growing great: http://edis.ifas.ufl.edu/hs184

I don't put much faith in companies that sell training and materials for the same system designs they are supposedly "researching"... seems like a conflict of interest at a minimum... To be honest, I think any of these companies that charge $1500 for a 4 day seminar for training on aquaponics could care less about the quality of the material they put out. There is plenty of scientific information out there, and there's no reason why they make up concepts or explanations for things instead of doing the research and presenting the facts... you definitely don't get what you pay for. Not a fan of Friendly's to say the least... Anyway... I digress.

I think more information needs to come out in a practical format so people have the right facts about aquaponics. Knowledge on how to feed yourself and your family should not be sold to the public for a profit... ESPECIALLY if it's not right... OK, I'm off topic... sorry... this is just a real issue that peeves me off, and I'm so glad we have a forum like DIYAP to help people out, out of the good of our hearts and not to fill our wallets...

[davidstcldfl]

Your right, most of the AP experts selling stuff/systems are...well, questionable. I've read enough about Friendly's set ups and have actually looked at one of their commercial set ups over in Brooksville FL. Pretty impressive.
I know the owners....I can hook you up with a free tour of the one in Brooksville...so you can check it out first hand...? Since your in the Master Gardener's program, 'maybe' they'd even let you 'sit in on' the next commercial classes in Oct.

Sure, Friendly's AP are making money by doing the classes, but they are also making money with their AP set up. If it doesn't produce, they don't make money. ( un-like science that has a budget that they 'must spend to get more'...on whatever they are trying to prove :P )

For sake of argument, lets say their system does work....
you pay them 1500 for the 4 days,all the books,the plans, and the hands on training......or....
you do like I did, sit in front of the computer for countless hours trying to find info, hopefully from some one that actually knows....then you try this and that, till you get it right. Thank the Lord, I did get lots of good help here and got to see a few systems in person (which only made me want to spend 'more' time changinfg stuff...lol) Your paying, one way or another.... :P

Back to adding more air....

If the bottom of the raft isn't in the water...you lose some good surface area for the bacteria to grow on. The Dr's idea of having 2 sheets of styro, with the hole in the top one being bigger and filled with vermiculite (or was it perlite...maybe hydrotron would work too) sounds like it would be a great way to give more air to the plants ( I think he was talking about tomatoes)



here's a picture of spinach grown in a test by A.U. The left has added air...the right doesn't.