Comment

Comment by David Waite on August 16, 2011 at 8:40am

 I have taken readings for nitrates at both my gravel bed intakes and outlets as well as my rafts which are downstream of my rafts and the nitrates are even through out the system. My system mimics TC in that the rafts show more nutrient defeciencys than my gravel beds do. My plants personally do much better in gravel vs rafts with the exception of lettuce crops. Part of my problem is not only nutrient uptake but areation in the rafts could be improved.

Comment by TCLynx on August 15, 2011 at 8:19pm

Well the calcium carbonate is good for buffering the pH up but you may need occasionally to provide potassium instead of calcium since an over abundance of calcium can lock out potassium.

Comment by Miguel Afonso on August 15, 2011 at 7:35pm

I put a chunk of coral in my raft system, and this has settled the ph real nicely (6.8 steady).Still yet to see how this works over the long term. Apparently calcium carbonate (coral stone amongst many sources) should settle the PH in the system as it neutralizes the PH as the system tends to become more acidic. In theory this should ward of any nutrient lockout.

Comment by Sylvia Bernstein on August 15, 2011 at 7:29pm

Great idea for a group, Miguel!

Comment by TCLynx on August 15, 2011 at 7:14pm

No I don't think that putting greedy plants at the start of a raft bed or NFT is going to leave the plants further down starved.

I do think that perhaps the NFT or Raft are likely to leave plants suffering more in situations of unfavorable pH causing nutrient lock out.

Comment by Miguel Afonso on August 15, 2011 at 6:56pm

So are you saying that you think this is a concern for NFT and Raft systems?

Comment by TCLynx on August 15, 2011 at 6:49pm

No it really doesn't matter much in my experience.

There are other far more critical factors like the sun exposure or where the water inlet to the bed is and how the plant feels about wet ankles and so forth.

I have noticed that many plants seem to suffer worse deficiency problems in the raft or NFT positions in my systems as opposed to the gravel beds.  This is interesting since I've had many people insist to me that in a nutrient limited situation that the constant flow portions of a system would fair better than flood and drain but my experience seems to be showing different.  Now I suppose if solids were removed from a system and one was comparing raft or nft to flood and drain with only the water bringing nutrients then maybe the constant flow would be better but with the flood and drain gravel beds providing my solids mineralization, the gravel beds seem to do better.

Comment by Miguel Afonso on August 15, 2011 at 6:42pm

Does where you place a plant make a difference in terms of nutrient uptake. For instance I hypothesize that it is better to put your heavy feeders at the end of the system so that they do not hog the nutrients. Does this even matter in your experience? Are nutrients consistent though out the system?

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