Time for all the plant experts to wade in please! I have been tinkering with a number of different media-less / media filled growing configurations of late. The ones that interested me the most in the end was partly filtered versus “dirty” NFT. The reason why this has become interesting for me relates back to the type of technology that is required to run these. Should there be some way of making “dirty” NFT work, then there should be an advantage in trying to understand what I am observing here. There is already (kind of) a precedent for thinking that “dirty”, media less culture could work – Nate Story’s towers. While this blog is not designed to suggest that people turn their backs on conventional design (What, ME suggest something like that? ), I am more than a bit interested in the implications that it could have.
While Nate’s towers obviously have the filtration angle also covered, my interest in the experiment’s outcome is related to plant morphology, and how this influences what we can do with aquaponics. What got me thinking was looking at the roots of the two sets of strawberries. I had two configurations going: The one was in a system with nitrates hovering around 14 mg/l and getting a permanent flow of water through a horizontal 110mm pipe, while the other was constructed the same but getting less nutrients and intermittent flow. The results were kind of obvious in one way but not so (to me in any case) on another level. I expected the dirty line to eventually soil the roots of the strawberries. This did not happen, but the roots of the partially filtered unit was a different story. They appear to be much finer, and permanently dirty even if you carefully try to rinse them. My reasoning is that when nutrients are sparse, the plants put a lot more energy into creating a fine root network, which in turn clogs easier with the fines still in the water. The strawberries growing in the higher nutrient stream were not that fussed, as a smaller root mass could keep them going. They therefore never made the fine root mass and as a result, the “dirty” NFT was never a serious problem for the plants. It has never been cleaned and the plants are thriving. The plants in the low nutrient (the tilapia was removed and the koi are still small) unit on the other hand are struggling a bit, to the point that I considered replacing the whole lot to see if it is not an issue with old stock. The two sets of plants are, however, from the same stock.
For me the implication here is in system design. I have always considered NFT to be a set-up that needs perfectly clear water. Now, the outcome of my little experiment has thrown me a bit. It seems as if NFT can be operated either on very clean, or very dirty water? The partially filtered water seem to be a problem in low nutrient conditions, but would perhaps also have worked well in a high nutrient environment. I’m interested in the feedback from others on the forum regarding my observations.