Here is an idea that I believe if done PROPERLY could be used in an AP system with fish…[edit* as of this writing, it has been used in dozens of systems with fish]. I first described what I've done in Wil’s ‘Medicinal Plants Any Luck’ discussion (there is some encouraging feedback from people I respect there, and other ideas we bounced around which might be worth checking out)…
The deal here was that once my AP system is up and running, I wanted be able to cater to the needs of specific plants that may have nutritional requirements that a brand new system might not be able to provide (so called ‘heavy feeders' like tomatoes, corn, cucumbers, for instance). Patience, I've been told, is not one of my strong suits. And I don't want big huge tomato plants with no tomatoes, or even no flowers, stuck in a nitrate induced perpetual vegetative twilight-zone of just green leafy growth. Yet pouring different nutrients, or nutrient products into your AP system (like P-K, “bloom/flower” type products) may not be advisable for a number of reasons discussed at length elsewhere. So what I did was the following…
Research shows that plants in nature tend to specialize the function of their roots. To make a long story short, we’ll divide the rhizosphere into two categories: upper roots, and lower roots. The upper roots tend to spread throughout the top soil specializing in seeking and up-taking nutrients, while the lower roots go downward seeking out moisture, specializing in water up-take. Using this concept I’ve taken five 13cm net pots (for hot peppers, but you can go larger for tom’s etc…) and set them up in the following way...
Fill the bottom half of the net pot with hydroton (rinsed, presoaked). Put a thin layer (5-10mm thick) of rockwool on top of the hydroton. (I have a rockwool cube and a sharp ceramic knife, so this was easy, but you can tear of pieces with your fingers as well). The whole purpose for the rockwool is to act as a barrier between the upper and lower zone of your net pot, so make sure all the hydroton is covered.
Fill the remainder of the net-pot with a mixture 13/perlite, 1/3 vermiculite, 1/3 cocco coir. To this mixture I added about 10% worm castings a handful of hydroton, to help with compaction, and about 5% Zeolite (I might forgo the Zeolite in an AP set-up though).
Then I poured water into this top portion and noted when water started leaking down into the hydroton. This way you will know what the absorption capacity of the upper layer is. Later when feeding your plants use slightly less than this ultimate holding capacity amount. Three small weekly feedings is probably better than one large one. This is an extra pot that I took a picture of...
If you had some screen material you could line the inside wall with it, but probably not necessary.
I planted my 3 Habeneros and 2 Hungarian Wax into the net pots. They have been placed into an aerated DWC bin. The reservoir holds only water (no nutes) and the roots have begun to dangle in it. There is about a 1" air-space between where the rockwool layer is and the top of the water, so that the upper layer doen't get too moist from over-wicking. This air space might also help with oxygenation of some of the roots.
Every third day or so I feed a solution of liquid home made nutes (but you could use whatever type you wanted, orgaic hydro store bought, mineral salts etc)…I pour only enough solution as the top mixture will hold so as not to contaminate the reservoir (or an AP system) with nutrients. They are growing like mad thus far.
In an AP setting the bottom roots would be exposed to both moisture and mostly nitrates, while the upper to whatever you wanted (though I imagine and K, Mg and P...would be among the prime candidates...and perhaps P if your system is real, real new.but P shouldn't ever really be a problem in a well fed AP system).
As long as you didn't over saturate with your solution while top feeding your plants, you should be able to keep any nutrient contaminants out of your AP system. Another benefit, would be less root mass to deal with in your grow bed (which is where this idea evolved from anyways).... I had originally planned on using 'huge' net-pot-bucket-with-drilled-out-holes filled with hydroton to help contain some of the root mass of the tomato plants, and make it easier too get it out of the grow bed when the time came. Reclaiming and re-using the hydroton would also be simple. Since I am relying on my 8 IBC media beds to pre-filter the DWC troughs, the last thing I need is a root bound anaerobic bed to deal with because of a couple of tomato plants. This method can address both the nutrient issue, and may help keep the more monstrous roots contained and more manageable. (Less maintenance to the grow bed).
Twice during the course of one week I used 'mineral salts' and an EC meter for before and after EC measurements. There was no contamination of the reservoir. As long as the amount of liquid you pour can be absorbed by the 'top' layer, it seems that you should be alright. Now my guess is that there would probably be a bit of 'leeching' over time, but who cares? It would just be a tiny bit of P, K or micro/trace element most people add those on purpose anyways (with the exception of maybe P).
I was able to measure contamination levels when I purposely tried to contaminate by adding (measurable/mineral nutes), more solution than the 'top' layer could absorb.
It really shouldn't matter if the bed is flood and drain or constant flood... and with DWC, I suppose as long as the bucket wasn't sitting on the bottom of the trough, you'd be OK. I'd imagine you'd it'd be better, if not exactly necessary, to lift the bucket off the bottom (with a couple of bricks or however) to give the roots some room grow. But then you could just drill some holes on the sides of the bucket (the part under water) too. But really media bed was my intended app.
Root development in the "water" zone was just ridiculous (I might have pics somewhere), looked like Laura Prepon having a 'bad hair day' when I pulled them out...just a huge tangled mass of red-ish blonde roots....
My conclusions were that this worked really friggin well for what I wanted. Jon Parr has and is using this method now in his AP system and stated in other threads that he was/is really happy with how it works and 'will be using this method for his fruiting plants from here on out'...a while ago I asked him if this was still the case, his answer was yes.
Vlad. Curious what your conclusion to this experiment was. Where you able to measure any contamination levels in the reservoir? How was your root development in each zone longer term, specifically the "water" zone?
If doing this with something larger (tomatoes) and applying to an AP system, were you thinking a dual zone net pots which were only half buried in a flood/drain media bed or something like a constant height, post media bed DWC/trough?
Of course there will be a small amount of leeching. I was mostly just curious about some unknown wicking action where the minerals might be trying to diffuse against the net flow of water or if there was issues with wicking in general or condensation that caused dripping and contamination. It was unlikely but just wanted to confirm :)
I was only thinking of burying the buckets partly to better anchor them but i guess the roots will take care of that eventually. Do you know if Jon bothered to add a media bottom to the buckets at all or just full out plant them in a potting mix and drop them in the media beds with some extra drainage/root holes?
I agree with elevating the buckets in a DWC scenario. I was thinking more like your experiment but in a trough like this below, but i guess its just over complicating. Just make a tough, fill with media, drop buckets ontop and be done with it.
Great thanks for the info Jon!
Interesting theory regarding the anaerobic action being beneficial. Not exactly sure on the chemistry why that would be true, but that's something that would be really interesting to test out in a side by side comparison.
As for the toms that makes a lot of sense. Not an obvious place to think about applying "less is more". I wonder how far you can get away with dehydrating a media bed and not killing off the bacteria colony in it.
Jon, I saw from another thread your comment regarding the anaerobic action being specific to mineralization of solids. That makes sense :)
I was thinking with this dual root zone method and tomatoes, if one was to maintain a secondary media bed which was not as reliable as a bio filter to an AP system but ran as a secondary timed system which provide a limited soaking time and even dryout periods (like 15minutes every 2 hours and no floods overnight). if you could strict to water uptake enough to still be "dehydrating" to the plants but keep the biofilter alive and have it effective and so the nute root zones moisture was negligible besides aiding in nute uptake. Maybe this would provide a balance between you're already dual zoned toms and the soil variety?
Finally plopped the cucumbers in the GH system...I've got two different varieties of gynoecious (all-female) and parthenocarpic (grows fruit without pollination) cucumbers that I’m growing dual root-zone style in the AP GH.
Yeah, it went from real cold to real hot (way to hot for this time of year) in about a week and a half. It's been near 40C in the GH everyday for a while now. The weather is supposed to cool down a bit and normalize after next week, which ill be nice. Here is the same cuke today (2 and a half days later... Wed. May 1st)
If anyone cares…the main stem of this herbaceous and annual plant begins growing erect but soon after assumes a prostrate trailing habit and grows like a vine over the ground. The branching is of the sympodial type (i.e., a lateral bud at each node grows and displaces the main growing point, the latter assuming a position on the opposite side of the leaf). From the nodes of the main axis originate primary laterals, each of which can have their(secondary) laterals, and so on...So I'm not about to let them just sprawl around wherever they want to. As far as I'm concerned, you should always prune cukes to a single main stem, then choose a pruning strategy specific to the dimensions (height and ventilation being the biggies) of your physical grow space and the conditions you are able to provide the plant with (light, nutrients, temps, blabla...). I'm not looking to get 20 or 30 crummy cucumbers off of each plant, I'm looking to get 120-130 off of each plant ...And the only way to do that is by providing a support structure and a good pruning technique...(presuming all those other prerequisites i.e nutrients, water and light and all that other good stuff is at least somewhat under control).
It sure seems like I get a heck of a lot more out of the same plants, in the same system, with the same inputs, when I take the time to learn about how they grow. i.e the way in which you'd prune tomatoes is different from the way you prune peppers...which is different from the way you'd prune cucumbers etc...because they each grow somewhat differently.