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| why do growbeds have to be drained in flood and drain? http://byap.backyardmagazines.com/forum/viewtopic.php?f=3&t=2251 |
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| Author: | little_froggi [ Oct 18th, '07, 08:50 ] |
| Post subject: | why do growbeds have to be drained in flood and drain? |
I did a FFA presentation on AP at Puyallup Fair last month. Everything went good until the judge asked me why the plants can't just sit in growbeds full of water all the growbeds. I tried to explain and I said something like the plants need to breathe. I need a good scientific explanation of why flood and drain systems need to drain. Besides this irritating question, I had alot of fun w/ my presentation. I would've got a blue ribbon if I was wearing an FFA scarf  .
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| Author: | Dave Donley [ Oct 18th, '07, 09:11 ] |
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The water would become deoxygenated if it just sat in the gravel, leading to anaerobic conditions, root rot, etc. If the water were anaerobic the nitrification of ammonia to nitrate would cease because the bacteria that do this are aerobic ones. You might get bad stuff created by anaerobic bacteria in the beds (hydrogen sulfide?). The plants wouldn't be happy, unless they liked living in swamps or marshes. |
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| Author: | monya [ Oct 18th, '07, 09:24 ] |
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why do growbeds have to be drained in flood and drain? because then it would just be called flood, and that doesn't sound right 
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| Author: | RupertofOZ [ Oct 18th, '07, 09:31 ] |
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Yep as DD says...... 
Think about a natural system.... it rains, then it (drains) dries out, allowing the oxygenating lateral roots (near the surface) to obtain the oxygen needed to photosynthesis the nitrates etc..... If after rain it doesn't dry out.... you have a flood.... Like Monya says.... just doesn't sound right 
And your plants wont last long if they're covered by water....
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| Author: | mrgrackletx [ Oct 18th, '07, 09:39 ] |
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but the plants would do ok if they where submerged in oxygenated water 100% of the time... right? as long as the water is oxygenated and flowing it should be fine, no? |
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| Author: | RupertofOZ [ Oct 18th, '07, 09:44 ] |
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High flow, highly oxygenated continuous flow systems are a proven method... like the Virgin Islands systems.... and some hydroponic style operations But its really only the roots that are submerged. The rest of the plant needs to be able to transpire, respire etc to photosynthesis properly... The only plants that really grow totally submerged are seaweeds etc
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| Author: | steve [ Oct 18th, '07, 15:26 ] |
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Quote: but the plants would do ok if they where submerged in oxygenated water 100% of the time... right? as long as the water is oxygenated and flowing it should be fine, no?
Yep, as rupe said UVI does it that way, as did an australian PhD student. and of course there is the old DWC. O2 is the KEY, flooding and draining ensures good root O2. A few of the systems i've helped with are a NFT/DWC hybrid, roots continuously submerged with high water flow over them |
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| Author: | bundaberg kid [ Oct 18th, '07, 16:50 ] |
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root rot? |
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| Author: | bio-farmer [ Oct 18th, '07, 17:44 ] |
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chuck a few air stones at the bottom of the growbed before you fill with gravel then you have a dwc f&d combo. from what i've seen dwc far out performs f&d for production in hydroponics. i don't see why the same wouldn't apply to aquaponics. having said this f&d is far easier to setup commercially then dwc. i imagine its more efficient for energy consumption as well. i am going to experiment with airstones in beds on a very slow drain. i will time it so that just as the water in the beds finish draining the pump will turn back on. this way the water is circulated and anaerobic spots avoided. my theory is the more contact the plants roots have with both air and nutrient rich water the better. the DO levels will be no where near as high if there is not at least a slow drain. circulation is the key there imo. |
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| Author: | steve [ Oct 18th, '07, 17:48 ] |
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Quote: having said this f&d is far easier to setup commercially then dwc
willow and UVI basically use DWC |
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| Author: | bio-farmer [ Oct 18th, '07, 18:47 ] |
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got a link to their setups steve? |
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| Author: | RupertofOZ [ Oct 18th, '07, 18:55 ] |
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Here's the UVI setup.... http://rps.uvi.edu/AES/Aquaculture/aquaponics.html Willow sold all his stuff up recently I believe. |
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| Author: | steve [ Oct 18th, '07, 19:06 ] |
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he still consults 
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| Author: | bio-farmer [ Oct 18th, '07, 21:18 ] |
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thanks for that. some interesting stuff there. |
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