Autopots don't need to be top fed after the wicking system is first turned on. After transplant, plants are top fed until their roots reach the bottom. When the wicking is turned on only the top 1-2cm of the rhizosphere will dry out leaving no effective salt build up that will affect the roots. As long as the roots are fully grown and the coco EC isn't high when wicking starts it doesn't cause an issue.
Autopots should not be top fed from then on to keep that top salt build up from washing into the root zone. After centimeters are dry there's no future risk of toxicity or lockout unless water is reintroduced. The only situation that can be a problem is when feeding full strength fertigation right up to the day wicking turns on and continuing to feed high EC for the days directly after as this would obviously stack the coco EC.
I got this info from Autopot so this is how it was intended to be used, at least. Just thought I'd spread what info I have. Wicking systems are a bit strange but they can have their benefits like providing constant fertigation, constant access to oxygen, and a more stable living environment for soil microbiology to set up camp. Also they're a much more sustainable way to use hydroponics than drain to waste, which I feel needs to change on the large scale due to how polluted the water and soil already is from poor agricultural practices over the years. On the small scale I doubt its a drop in the bucket, though
Autopots are certainly clever with the 2 level auto valve but some of the claims make little scientific sense to me. OctaPots are similar and just use a float valve or master float valve to keep saucers at a constant level whereas the autopot fills to an inch and then lets the water in the saucer almost completely dry before the refill water is triggered to come up to one inch. This cyclic draining encourages autopot roots to grow all the way to the bottom and with the next flooding some terrestrial roots may begin to drown. This is not likely with the Octapot system where a constant level of water prevents air loving terrestrial roots from growing where the media is simply too saturated Of course, Cannabis can adapt and grow aquatic type roots, larger smoother roots with fewer root hairs. In a way OctaPots water prune as much as Air prune. Some people add some airstones or an inverted net pot in the bottom of the grow bag to ensure even more oxygen diffision and because the AutoPot only cycles from zero to 1 inch there is probably enough oxygen as well just like with an NFT system.
However, "AutoPots should not be top fed to prevent top salt build up from washing into the root zone is not true The accumulation of salts on the soil surface will always happen eventually with sub irrigation. And if your soil is coarse enough that the autopot does not wick water all the way to the surface but leaves the top 1 to 2 cm dry does not eliminate the salt build up. In fact now a potentially toxic salt accumulation is happening but you can not see it. , Possibly the salt concentration can be so high that any root tips that come into contact will chemical prune back, but somewhere in there some roots will come into contact with a salt concentration that is both unbalanced and too hot.. The unbalanced part could lead to some lockout issues because of ph or cause some toxicities or deficiencies. The bigger problem is likely the too hot where the concentration of solutes in that zone will begin to suck the water out of the plant or at least make that water osmostically hard to uptake.
If the crop cycle were short enough, maybe the salt accumulation is not big deal, but i have had a plant alive for almost 2 years in 2 inches of constant flood water at the bottom and i can water from the top any time i want. If there is a big salt build up, one should not just water but really flush with ample volumes of water
There are several clear advantages that sub irrigation systems do provide. They will water every single mix in any size container to Container Capacity, which means that the media in that container will hold the maximum amount of water against the force of gravity. That water will be held at 0 Matric Tension which means plant roots will suck up the water with almost zero work. Of course, the choice of media will dictate how high the perched water table or saturated zone is above the container bottom. For instance a Clay soil may be saturated 3 inches above the bottom of the container so it would not be ideal to fill a 4 inch container with clay and expect to grow successfully. The perched water table in sand may be an inch above the bottom so growing in a 4 inch container might work better than clay. Nevertheless, both the clay and sand will provide the maximum amount of freely available water that each material can hold against the force of gravity.
A clever way to avoid any problem with Wet Feet in a sub irrigated setup is to use a container that is taller by at least the height of the perched water table plus the depth of the saucer or reservoir water. In my case where i used a 2 inch deep saucer, I simply used a 247 tall fabric pot instead of a short squatty pot of the same volume. One can also make sure they play with their mix until they find a mix that can wick water almost to the surface of the container mix but still have enough coarse particles to provide Air Space. Another way to moderate wicking rise and Airspace is to make a gradient mix slowly going from coarse bottom material to finer particle sizes toward the top of the container to provide more airspace to the lower, wetter parts of the soil. Placing an inverted pot or net pot wrapped in pantyhose is also a good way to displace the wettest part of any container with an air filled void which also encourages increased air exchange through the media profile and keeping the standing saucer water more aerated as well. When i get some extra money i am going to test ride both the autopot and the octapot and compare them to my own similar designs and variations.
BTW, Wicking Systems do not necessarily provide Constant access to oxygen. A fast draining mix watered from the top will actually suck in air as the water drains from the bottom. A wicking system will never suck in air, but it will also never temporarily saturate the Air Voids and will hold any media in a perpetual optimal easy water step. In my example above where i used clay sized particles, There would be a lack of oxygen whether water from above or from below. It is true that a shallow depth of water will have slightly more oxygen than a deeper depth. It is the amount of water surface area exposed to oxygen and more particularly how much oxygen can get into water voids where the grow media inside the grow bag is. Since both Ocatpots and AutoPots use breathable fabric bags there is some diffusion of oxygen, but in the bottom center of the bag where coco or coco perlite is saturated in static moving water there is considerbly less oxygen than in the surrounding water outside the pot.
Just so you can trust what I am disputing with the sales literature you were sharing. It could be said that i am one of the Pioneers of Greenhouse sub-irrigation. In fact I think i published a few years before Kratky. I literally invented Greenhouse subirrigation in 1989 [a simpler less polished version to be sure than autopots and OctaPots] and published the concept of CFI aka Constant Flood Irrigation System in HortScience in Nov 1992] I simply placed experiment plants in individual oversized saucers and used a fertilizer proportion and drop in weighted drip emitters to top off the saucers eight times a day with short enough timing to minimize the overflow waste, but the same concept. My experiment consisted of thousands of plants in over a dozen different media mixtures and this was the best way i could think of to water the plants most equivalently
