Dissolved Oxygen

DoVVn_CaSt · 09-16-2005, 10:02 PM

Ive been struggling lately with the issue of dissolved oxygen.How important is it?Which systems is it more important in.What exactly is the role of dissolved oxygen?I wanted to share my findings.

From what Ive read the main way plants recieve oxygen is through the air.DO is necessary anytime the roots are submersed in water.And they must be submersed in water at times to access nutrients.If possible,you would want air contact with the roots 100 percent of the time.The problem with this is that it restricts nutrient availability since the roots usually arent in contact with water if in contact with air.

You can see that systems like DWC would rely heavily on Do since the roots are constantly submerged.The amount of oxygen is also limited by the fact that water cannot hold large amounts of oxygen at the temps necessary for plant growth.And,current methods of water oxygenation arent completely effective.

Systems such as aero rely less on DO which is what makes it so effective.The plants roots are allowed maximum contacct with air while being allowed maximum contact with water at the same time.

Systems such as flood and drain attempt to balance water and air access by alternating them.

There really isnt much info about the role of DO so you have to read everything you can about hydro and put all the pieces together.I did come across this article and it really cleared up this issue for me.Its the clearest portrait of the role of DO that Ive come across in about 8 months of reading.It starts out quite slow but, keep reading.It has some very interesting info about different systems and how DO relates to them.

Quote:

Oxygen Life began in the oceans, first in simple forms, algae for example, and later evolving into more complex forms. Common to practically all forms of life on Earth today, is the need for oxygen.

In aquatic environments-oceans, lakes, rivers, etc., most life must draw their oxygen out of tile water, which contains dissolved oxygen. For example, fish take water in through their gills to extract oxygen. Terrestrial animals have lungs that can draw oxygen in with air. In both cases, the oxygen is essential for life, though the mechanism for deriving oxygen is quite different: gills versus lungs.

In the atmosphere, oxygen content is fairly constant, about 18 percent. But in water the oxygen content can vary greatly. This is because oxygen dissolves into water at different rates depending upon variables like temperature and pressure. Put simply, the colder the water, the more dissolved oxygen it can hold and conversely, the warmer the water, the less oxygen it can hold.

Refer to the chart on page 21 for a graphic description of oxygen solubility in water according to temperature. Notice that at 590F (15?C) water cannot contain more than 10.05 ppm dissolved oxygen. Now notice that at 86?F (30?C) water cannot contain more than 7.51 ppm dissolved oxygen. Therefore, organisms that benefit from high dissolved oxygen levels will suffer in warm water.

The value of high oxygen levels in life-containing water is well demonstrated by comparing the richness of life in Arctic waters to that found in tropical waters. In Arctic waters, huge populations of plankton provide fish, sea mammals and a myriad of other life forms with food. This is possible because of the very high levels of dissolved oxygen in the cold Arctic waters.

Warm tropical waters cannot hold high levels of dissolved oxygen, so only those life forms, which have adapted to lower levels of dissolved oxygen can thrive. Tropical oceans are sometimes described as "underwater deserts" because of the limited life forms they support.

The effect temperature and pressure have on the solubility of gases is best described with the carbonated drink example. When you open a bottle of soda or beer, bubbles of carbon dioxide (CO2) begin to form and rise as the compound is released from the bottle. This is the result of a drop in pressure that occurs when the bottle is opened. If the liquid is very cold, the gas release will be slow, but if it is warm and shaken before opening, the CO2, will surge from the open bottle.

Oxygen behaves very much in the manner as CO2 does with regard to solubility in water-according to temperature and pressure. Water at a temperature of 65?F (18?C) has an oxygen capacity twice that of water at 85?F (29?C).

It is important to also understand that temperature and pressure are not the only factors that can limit dissolved oxygen content in water. As organisms draw oxygen from water, it must be replaced as quickly as they extract it. In aquariums, it is common practice to bubble air through the water to charge it with oxygen. This is not an especially powerful way to add oxygen to water, but it works with fish tanks that hold only a small amount of fish in many liters of water. A far more effective way to charge water with oxygen is to spray the water through the air, which many hydroponic growers do to supply their rapidly growing plants with the large amount of oxygen they need to remain healthy.

Plants Plants can derive oxygen from air or water. In nature, plant roots receive water saturated with oxygen following a rainfall. As the soil begins to dry, air permeates so the roots can breathe and absorb oxygen. During watering, the roots receive both moisture and dissolved minerals. If plants are over-watered, their roots sit in soggy, saturated soil and they can die of oxygen deficiency. Over watering is one of the most common causes of houseplant death.

Some plants have adapted to be able to survive in deficient or stagnant water such as water lilies, rice and some carnivorous plants. Most other plants have a much lower tolerance for oxygen deficiency and cannot sit in over-saturated water for very long.
Hydroponics

If a plant's roots are suspended in water, it will absorb oxygen rapidly. If the oxygen content of the water is inadequate, the plant growth will slow in proportion to oxygen availability. Thus the trick is to co-ordinate the supply of water, nutrient and oxygen with the crops' needs according to other environmental factors like temperature of air and water, CO2 levels, ventilation, humidity, moisture capacity of the rooting media, size and type of crop, and day length. This can be difficult in some extreme conditions, but when applied properly the results can be quite dramatic. Hydroponic growers stimulate plant growth by controlling the amount of water, minerals and oxygen in the nutrient solution. These growers work within a narrow realm between irrigating their crop and allowing oxygen into the root zone. Ebb and flow hydroponic systems are based upon the natural principle of irrigation and oxygenation of plant roots. Mineral-rich water is pumped into gravel-filled beds in which the crop is planted. The irrigation ceases and the water quickly drains away. Oxygen follows and fills the gravel bed, allowing the roots to breathe. The roots release CO2, and absorb oxygen. Then the irrigation is repeated and drained away again, basically emulating nature but very quickly. This basic hydroponic method is very reliable; it has been used for decades with different medias such as gravel, sand, wood chips, sawdust, perlite and Rock Wool.

The down side of ebb and flow hydroponics is that the crop is provided with moisture and mineral nutrients at alternating times from oxygen. In other words, when the roots are breathing, they are not being provided with a constant stream of moisture and nutrients. If the media is too absorbent, then the irrigation cycles must be infrequent to allow time for oxygen to penetrate the roots.

"Constant drip" is a more recent irrigation method designed to level out the availability of moisture, minerals and oxygen. Mineral-rich water is constantly provided in a slow drip to plants that grow in a rapidly draining media. The idea is to maintain a constant balance of moisture and minerals without drowning the crop. It can be somewhat tricky to consistently provide a perfect balance. On a hot summer's day, a large plant can transpire a lot of moisture, so water must be provided at a far higher rate than would be required on a cooler day for a small plant.

In recent decades, the leaders in the development of hydroponic technology have moved into "water-culture" methods and away from rooting media. The first and certainly one of the best recognized is the Nutrient Film Technique (N.F.T.), developed in England in the sixties and seventies and made famous by Dr. Alan Cooper. A breakthrough in its day, N.F.T. was based upon the principle of a very thin film of nutrient-rich water flowing slowly over plant roots held within a plastic envelope. The idea is that the nutrient film provides both moisture and nutrients while above it the roots receive a constant supply of oxygen. Today N.F.T. is widely used and well respected by commercial growers and scientific researchers throughout the world. The only drawback is that there is a fairly critical balance between the right amount of moisture and air required in the rooting envelope. If the film is too deep, then the plants will suffer from oxygen deficiency that can lead to root disease. On the other hand, if the pump fails and the film of moisture is interrupted, even for a relatively brief time, the crop can be lost. Because of this drawback, a more reliable and less risky method of water-culture was sought, so "Aeroponics" arose. Aeroponic systems provide roots with a spray of nutrient rich water. Generally, the plant is supported with its roots dangling in the air. A fine mist of nutrient solution is constantly or intermittently sprayed over the roots. This is a great method as long as there is no failure in the pumping system or clogging of spray nozzles...still not completely forgiving or reliable and generally expensive and tricky to set up and run.

The next generation of water cultivation methods was "aero-hydroponics," in which the root zone is divided into two sections. The root tips are immersed in a constantly flowing stream of nutrient solution while the upper roots hang in an air gap and are sprayed or misted with nutrient solution to provide optimum oxygen levels. This is a superb method since a pump failure does not result in water loss to the roots. Generally, aero-hydroponics is more forgiving than the other water-culture methods. Rather than causing dehydration of the crop, pump failure will result in oxygen deficiency from which most crops can recover without a disaster, provided the pump is fixed quickly.

The common link in all of these methods of hydroponic plant cultivation can be found in the oxygen content of the water. As you now understand, warm nutrient is somewhat oxygen deficient, which can have a lot of meaning for a hydroponic grower. Many root diseases, including fungus infestations can proliferate in oxygen deficient environments. I first realized the magnitude of this phenomenon when I observed Pythium destroying crops in Holland growing in Rock Wool. In this case the oxygen deficiency started when the Rock Wool was over-watered. The plants were growing in a saturated sponge. As the Rock Wool dried out, the situation improved, but the next watering led to saturation again. The problem was compounded by the presence of fungus gnats, which seemed to be the vector, or source, of the Pythium. One thing led to another until ultimately, the crop was lost. From this model we learned the importance of deeply analysing problems to learn from experience. Gnat larvae ate and damaged the plants' roots; oxygen deficient conditions caused by high temperature and over-watering stimulated Pythium and the Pythium entered the impaired roots to destroy the crop. In nature, many variables can interact, causing wonderful-or horrible- things to happen. When the plants grow well, there is a lot more things going on than you realize. Similarly, when things go wrong you must look deeper than the obvious to find answers. By better understanding the physical chemistry of water, you can obtain a deeper and richer comprehension of the many phenomena to observe while growing plants.

HydroSan · 09-17-2005, 03:21 AM

Hi DnC

They're saying Aero arose because pumps might fail in NFT?

so aero pumps are less likely to fail then

never mind, just thought it was funny

Quote:

NFT...if the pump fails and the film of moisture is interrupted, even for a relatively brief time, the crop can be lost. Because of this drawback, a more reliable and less risky method of water-culture was sought, so "Aeroponics" arose.

I think the bit you're missing is the fact that aero was developed to gain the maxium DO available - O2 exchange only happens in the surface tension zone, more so when that zone is in flux. NFT takes advantage of this as it has a huge surface area both in the channels/tray and on the res, so maximum exchange potential for the system. If you think of aero in terms of water capacity and surface area of that water whilst it's in spray form, you can see just how massive the surface area would be compared to any other standing res

Hence the smaller the droplet size in aero, the better. Shira developed the 5 micron atomized droplet thing for just this reason

Thinking in terms of getting maximum AIR to the roots is counter productive IMO, as the grower needs to supply O2/DO, and all the nutrients at the same time, hence timing the spray jets is counter productive IMO, I would run them 24/7 so nutrients are available at all times.

San

DoVVn_CaSt · 09-17-2005, 08:02 AM

I respect your opinion San.You've brought up some interesting points.

Im not gonna read to much into what they said about aero and the reasons why aero came along.It could be that the reason they wanted to develop a new system was because of the shortcomings of NFT(being prone to failure) but,upon experimenting it led them to aero even though it can be just as prone to failure.Even though the aim may have been to overcome being prone to failure,they couldnt overlook the obvious advantages to aeroponics.Im sure aero would have come along regardless.I dunno,just my thinking.

As for aero putting more DO into solution,I think your right to a point.But,there are alot of ways to saturate a solution with oxygen.I think its possible to get the same DO levels in other systems if the right method is employed.People use sprayers in non aero systems to achieve this.

Heres a question for ya.Lets say dissolved oxygen is the best way to supply oxygen to the plant roots.The thing that keeps telling me that cant be true is the fact that not one hydroponic system has the roots completely submerged in water(DWC is almost completely submerged).You would think that the best way to get oxygen to the roots would be to submerge them in water if thats where the oxygen came from.With DWC you see alot of people having problems with root rot.And it isnt the fastest system either.There are plenty of ways to get adequate DO into a DWC system yet it still isnt the best hydroponics sytem(in terms of speed).Now the difference between Aero and DWC isnt DO(since you could create the same DO conditions in the res for both and aero would still outgrow DWC)its the amount of air contact with the roots.Sure those sprayers help put DO into the water but,theres a saturation point where the water will hold no more oxygen and its the same point as the DWC system has.Same can be said for ebb and flow.If it was all about the DO then you could saturate the solution with oxygen and then run the pump continuously.I dont think theres many people who would agree thats the way to go.NFT,for example,you could completely flood the roots with oxygen saturated water and they should get all the oxygen they need,right?It seems the whole setup of NFT would be against DO being the primary provider of oxygen since the roots are sitting in a thin layer of water and 90 percent of the roots are suspended in air.Thats alot of roots being left out.

What I do agree on is that anytime the roots come into contact with water,DO is vitally important since they are cut off from the air at that point(aero is somewhat different because its design allows both at the same time,air and water contact).

Another thing about ebb and flow.DO is almost useless in this type of system.The pump floods the tray and oxygen and nutrient rich water is supplied to the roots for about 15 minutes.As soon as that pump turns off,it takes minutes for all of the DO in the medium to be used up.Its then about 3-4 hours until it gets a fresh supply of DO yet ebb and flow is one of the most successful hydroponic methods there is.More successful than DWC Id say.It is almost independent of DO yet it blows soil away.The reason for this is the air contact with the roots is so much greater.It has zero to do with DO since just as in soil,the DO is used up in minutes.I will say that for those 15-20 minutes where the tray is flooded,DO is vital since otherwise the roots would be starved of oxygen.

So,Id like your input about what Ive said.This is a very interesting subject to me because there isnt much clearly written about the subject.

Beener · 09-17-2005, 08:45 AM

Quote:

Originally Posted by DoVVn_CaSt

I respect your opinion San.You've brought up some interesting points.

Im not gonna read to much into what they said about aero and the reasons why aero came along.It could be that the reason they wanted to develop a new system was because of the shortcomings of NFT(being prone to failure) but,upon experimenting it led them to aero even though it can be just as prone to failure.Even though the aim may have been to overcome being prone to failure,they couldnt overlook the obvious advantages to aeroponics.Im sure aero would have come along regardless.I dunno,just my thinking.

Heres a question for ya.Lets say dissolved oxygen is the best way to supply oxygen to the plant roots.The thing that keeps telling me that cant be true is the fact that not one hydroponic system has the roots completely submerged in water(DWC is almost completely submerged).You would think that the best way to get oxygen to the roots would be to submerge them in water if thats where the oxygen came from.With DWC you see alot of people having problems with root rot.And it isnt the fastest system either.There are plenty of ways to get adequate DO into a DWC system yet it still isnt the best hydroponics sytem(in terms of speed).Now the difference between Aero and DWC isnt DO(since you could create the same DO conditions in the res for both and aero would still outgrow DWC)its the amount of air contact with the roots.Sure those sprayers help put DO into the water but,theres a saturation point where the water will hold no more oxygen and its the same point as the DWC system has.Same can be said for ebb and flow.If it was all about the DO then you could saturate the solution with oxygen and then run the pump continuously.I dont think theres many people who would agree thats the way to go.NFT,for example,you could completely flood the roots with oxygen saturated water and they should get all the oxygen they need,right?It seems the whole setup of NFT would be against DO being the primary provider of oxygen since the roots are sitting in a thin layer of water and 90 percent of the roots are suspended in air.Thats alot of roots being left out.

What I do agree on is that anytime the roots come into contact with water,DO is vitally important since they are cut off from the air at that point(aero is somewhat different because its design allows both at the same time,air and water contact).

So,Id like your input about what Ive said.This is a very interesting subject to me because there isnt much clearly written about the subject.

Hi DoVVn_CaSt I've been following your conversation. I'd like to add my

Quote:

Lets say dissolved oxygen is the best way to supply oxygen to the plant roots.The thing that keeps telling me that cant be true is the fact that not one hydroponic system has the roots completely submerged in water(DWC is almost completely submerged).

I run a "deep flood technique" system (my own design). The DFT is a constant recirculating system. The solution level in my flood chamber is @ the net pot bottom. The Rockwool is on the bottom of the pots. My root systems are constantly submerged. Only when I change out the rez, do they see any time out of solution.

Without question...you can witness dramatic growth rate changes by manipulating the solution air flow. As I was building and testing, I increased the air supply to the rez solution a few times. Each time I made an increase, there was a dramatic upswing in processing rate.

The more air introduced, the more nutes that were used, the more growth that was experienced....... A good freshly aerated solution, and strong flow throughout the root zone, also help combat root disease and fungus etc. Aerobic microbes are our friends in as much as anaerobic microbes are not. Keeping the solution aerated, helps sustain the population aerobic micro-organisms. Not only do aerobic microbes play a large part in disease and pest control, but they also function as a vital part in the plant feeding process.

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If it was all about the DO then you could saturate the solution with oxygen and then run the pump continuously.I dont think theres many people who would agree thats the way to go.

Well....that's exactly what we (try) to do. The keyword here is "saturation". What is the max D/O at point of saturation? Can "max" or "saturation" be easily acheived? At any rate...it takes an outside source to provide the air. So, to answer that statement - yes, if your solution is saturated with D/O, then you'd only need to run a pump. But the point is...you'd need more than just a pump, to "saturate" the solution in the first place.

DoVVn_CaSt · 09-17-2005, 09:27 AM

Beener2969,thanks for your input.

Quote:

I run a "deep flood technique" system (my own design). The DFT is a constant recirculating system. The solution level in my flood chamber is @ the net pot bottom. The Rockwool is on the bottom of the pots. My root systems are constantly submerged. Only when I change out the rez, do they see any time out of solution.

Without question...you can witness dramatic growth rate changes by manipulating the solution air flow. As I was building and testing, I increased the air supply to the rez solution a few times. Each time I made an increase, there was a dramatic upswing in processing rate.

The more air introduced, the more nutes that were used, the more growth that was experienced....... A good freshly aerated solution, and strong flow throughout the root zone, also help combat root disease and fungus etc. Aerobic microbes are our friends in as much as anaerobic microbes are not. Keeping the solution aerated, helps sustain the population aerobic micro-organisms. Not only do aerobic microbes play a large part in disease and pest control, but they also function as a vital part in the plant feeding process.

I have no doubt that with that type of system DO is vital.Basically what my objective is in all of this was to find out what source of oxygen is the best for plants.Either DO in the nutrient solution or from the air.

How do you aerate your solution?Are your roots always white and healthy?

Quote:

Well....that's exactly what we (try) to do. The keyword here is "saturation". What is the max D/O at point of saturation? Can "max" or "saturation" be easily acheived? At any rate...it takes an outside source to provide the air. So, to answer that statement - yes, if your solution is saturated with D/O, then you'd only need to run a pump. But the point is...you'd need more than just a pump, to "saturate" the solution in the first place.

Yea,I dont think any current method is able to saturate the solution beyond 80 percent(besides using pure oxygen).I understand that you could run the pump continuously with a high level of oxygenated solution.My question is,why dont more systems employ this?Systems that employ this are almost nonexistent(aero is the only one I know of that constantly has the entire root mass supplied with solution).My understanding of DWC is that the roots arent completely submerged.The plant is put into its container with the roots just above the bubbling water and allowed to grow into the solution.Some of the mass is still in the air.Im not familiar with deep flood technique.Im curious as to how fast it is compared to ebb and flow.

We know that plants can be grown on just DO alone.My main concern is which is faster.A plant that derives its oxygen mainly from DO or one that derives it mainly from the air.Systems such as ebb and flow use the air as their main source of oxygen and closely mimick soil except for the ability of ebb and flows medium to hold more oxygen than soil.Aero on the other hand has no medium,allowing maximum air contact.Combine this with high levels of DO and a mist delivery system that allows constant delivery of nutrients without overwatering.I believe that the greater air contact is what makes aero succeed.Other wise you could just use any old system with high levels of DO and have the same results.

HydroSan · 09-18-2005, 02:49 AM

Comparing systems/methods is a little confusing to the central subject IMO- E.G. as you say, alot of folks get root rot in DWC, now in theory it is possible to saturate the solution with DO as much in DWC as in any system, but theory does not match practice as it is hard to replenish it as efficiently, and harder to control temps, besides the design works on different principles that try to mimic soil moisture levels, with air roots at the top and deep water roots too. The differences between aero and DWC are too numerous to mention besides not being DO, or the ammount of air contact - it's a far too simplistic view and ignors all the other drawbacks of DWC, making any conclusions about DO or air to the roots tenuous at the very least.

Saying that in E&F "As soon as that pump turns off,it takes minutes for all of the DO in the medium to be used up." is very misleading IMO, have you any data that compares DO levels in different mediums? because IMO it is the moisture to air ratios in the medium that is important here. Remember that a good medium is like a sponge holding alot of air aswell as the water

Canna recently stated that optimal moisture content is 50 - 60% (the old horticultural norm was 80% ) which clearly leaves 40 - 50% air in the medium - back to surface area inside the medium and greater exchange for a more open medium as it has greater surface area.

Quote:

NFT,for example,you could completely flood the roots with oxygen saturated water and they should get all the oxygen they need,right?It seems the whole setup of NFT would be against DO being the primary provider of oxygen since the roots are sitting in a thin layer of water and 90 percent of the roots are suspended in air.Thats alot of roots being left out.

You've never seen NFT in real life mate

I'd say 90% of the roots are in solution 24/7. The rootmat evolves in NFT, plants are placed directly onto a capilary mat which is constantly filmed with solution, roots grow through and over this mat receiving a constant thin film (think surface area exchange again, but all over the roots/rootmat - the exchange happens all the time) 90% of the roots have a thin film over them. Now then, the other 10% of roots grow above the rootmat, some grow almost vertical for about 10mm directly into the air, these are the air roots (as opposed to water roots) they can only survive in the 10mm above the solution as they also need alot of moisture to prevent them drying out, if they grow more than 10mm above the solution, there is insufficient moisture/humidity the end of the root browns off and dies. (I can show pics of this if you are interested)

Maybe we need to look at the root (hehe) of the problem, different types of roots?

You've seen air roots right? roots covered in teeny tiny hairs measured in microns - these roots can't be efficient in water as there is no air, nothing to fluff them up and increase the surface area of the root (like a wet dogs tail) so, air roots must be in air 24/7 to be 100% efficient IMO. If I flooded the trays in my NFT system too deep, i.e. deep enough to cover these air roots (regardless of DO content) they are not going to work very well, I've never actually done this and recorded how long it takes for the air roots to grow up into that 10mm zone again, but there has to be a time element, and you have to be limiting O2 takeup during that time, unless (pause for the crowd) there's sufficient DO in the solution

Lets look at aero cloners for a moment - the spray is turned on 24/7 once roots appear from the 1" cubes - before one turns the spray on, one can clearly see a mass of air roots covering the new rootball - with the spray on, these air roots all go 'wet dogs tail' again - back to using DO instead or air.

The only time I can say I've seen efficient 'wet' air roots is with the addition of H2O2 - the rootball looks amazing, all fluffy, yet all wet too - clearly this is about maxium O2 levels in solution, chemically enhanced O2 levels above any DO content possible make it possible for air roots to work efficiently when wet too.

How long does it take air roots to re-grow (or dry sufficiently to work properly) once the spray is turned to it's off cycle in your aero system? I'll be interested to find this out

Quote:

which is faster.A plant that derives its oxygen mainly from DO or one that derives it mainly from the air

I think all the best systems are designed to take advantage of both

The most efficient system would be one that keeps moisture/humidity levels in the rootzone high enough to prevent root death, and low enough to prevent the air roots becomming saturated with moisture to the point where the hairs lay flat. If you want one of those, search on 'foggerponics' and write a big cheque to Shira

San

DoVVn_CaSt · 09-18-2005, 09:47 AM

Quote:

You've never seen NFT in real life mate

I'd say 90% of the roots are in solution 24/7. The rootmat evolves in NFT, plants are placed directly onto a capilary mat which is constantly filmed with solution, roots grow through and over this mat receiving a constant thin film (think surface area exchange again, but all over the roots/rootmat - the exchange happens all the time) 90% of the roots have a thin film over them. Now then, the other 10% of roots grow above the rootmat, some grow almost vertical for about 10mm directly into the air, these are the air roots (as opposed to water roots) they can only survive in the 10mm above the solution as they also need alot of moisture to prevent them drying out, if they grow more than 10mm above the solution, there is insufficient moisture/humidity the end of the root browns off and dies. (I can show pics of this if you are interested)

Your right,Ive never seen NFT up close.I assumed by its definition that since it was a thin film of solution that it would be hard to get large amounts of roots into it.

Quote:

You've seen air roots right? roots covered in teeny tiny hairs measured in microns - these roots can't be efficient in water as there is no air, nothing to fluff them up and increase the surface area of the root (like a wet dogs tail) so, air roots must be in air 24/7 to be 100% efficient IMO. If I flooded the trays in my NFT system too deep, i.e. deep enough to cover these air roots (regardless of DO content) they are not going to work very well, I've never actually done this and recorded how long it takes for the air roots to grow up into that 10mm zone again, but there has to be a time element, and you have to be limiting O2 takeup during that time, unless (pause for the crowd) there's sufficient DO in the solution

Lets look at aero cloners for a moment - the spray is turned on 24/7 once roots appear from the 1" cubes - before one turns the spray on, one can clearly see a mass of air roots covering the new rootball - with the spray on, these air roots all go 'wet dogs tail' again - back to using DO instead or air.

The only time I can say I've seen efficient 'wet' air roots is with the addition of H2O2 - the rootball looks amazing, all fluffy, yet all wet too - clearly this is about maxium O2 levels in solution, chemically enhanced O2 levels above any DO content possible make it possible for air roots to work efficiently when wet too.

How long does it take air roots to re-grow (or dry sufficiently to work properly) once the spray is turned to it's off cycle in your aero system? I'll be interested to find this out

Hmm.I wasnt aware there are specialized roots for taking in oxygen from the air.Or are you saying that the root structure changes depending on the source of the O2?More fine hairs for absorbing oxygen from the air?Interesting.

Quote:

I think all the best systems are designed to take advantage of both

The most efficient system would be one that keeps moisture/humidity levels in the rootzone high enough to prevent root death, and low enough to prevent the air roots becomming saturated with moisture to the point where the hairs lay flat. If you want one of those, search on 'foggerponics' and write a big cheque to Shira

That I agree with.Its hard to express in words what you are thinking sometimes.I think theres alot of misinterpreting going on.I have ben doing more reading about aero.I found this article on another site.Im not sure of the source but,it gave me a different view of aeroponics.Take a look.Notice how he says that aero isnt about DO.

Quote:

Basics:
10 Rules of TAG(True Aero Growing)

1. PSI > 30, 50=Ideal
2. Interval cycling 20-30 seconds on, 3-4 minutes off (Dark periods may extend dry periods).
3.Average droplet size 50µ (micron) nozzles (acceptable ranges 30-80µ) with flows < 2 gph preferably .5-1gph with screen filters of 150 and up.
4.Target root temperatures maintained at 68F. (Mature clones lower temps/younger prefer warmer) Temperatures should never exceed 74F (Dangerous).
5. The greater the aerospace around the root zones the better—lateral root development equals bud thickness and development your goal are pom pom roots.
6. Nutrient strengths for TAG are 50% that of DWC. Most strains burn above 1000 ppms ideal ph is 5.8.
7. The use of a beneficial such as HydroGuard is highly recommended.
8. Always have a back up pump or system for failure—always!
9. Root zones should be completely dark and sealed from any UV penetration.
10.Always use RO water and premix nutrients before adding to systems to prevent chemicals from coming out of solution and clogging nozzles.

Now a more indepth if you like...

Compendium for TAG (True Aero Growing)

The principles of aeroponics differ considerably from other methods of plant propagation. Several factors influence the rapid absorption and accelerated grow that can be expected when rig designs are brought closer to the True Aero Environment. TAE

These factors establish a the optimal TAE.

This environment consists of these requirements:

Ideal rooting environments should be unrestricted with enough volume to allow every square cm of root zone to become completely coated with a micro-fine mist of 50µ average population nutrient solution every 3 to 4 minutes in under 60 seconds (preferably 20-30 second misting cycles).

Root Zone Temperatures are found to be ideally suited at approximately 68-72F for maximum efficiency, though younger plants grow faster at higher temperatures and older ones at lower—these extremes are not conducive to the microculture necessary to support the root colonies and risk of possible bad bacterial infections. The use of HG or any AM inoculant is advised and recommended.
Ideal root temperature has been established at 68F as being TAT. (Target Aero Temperature)
Root zone temperatures should see very little temperature fluctuation and absolutely no light penetration if possible. Anything above 75F should be considered dangerous to the health and well being of your plants and HydroGuard or other benefical is highly recommended. Beneficials are recommended in general as the speed and growth in a TAE is exceptional and the rooting environment needs as much support as possible to keep up with increasing growth demands.

A basic understanding of certain principles are necessary for all TAGers. These concern uptake of nutrition and supplimentation as the rapidly accelerated growth available in TAGing requires accurate and relatively precise balances of major life processes.

Here are some that will help the beginning TAGer understand the importance and value of precision delivery.

The basic principles
of aeroponic delivery are the rapid exchange of gases between the membranes of the root subculture and the plant roots. Application of a micro-fine nutrient film that is readily absorbed and evaporated before the next aerosol cycle is the goal.

The need for 50µ-target size for micro droplets is based on the findings by researchers that the average tube opening on the root hairs is approximate 20-50µ or within a range from 5-100µ.

The specific reason for this importance is as follows:

Aero isn't about DO. There really isn't that much in True aero, as I've mentioned. It has to do with uniformity of droplet size.
The mist that is created by these nozzles is micro fine and all the drops are pretty much the same size and an ideal size for optimum uptake.
You have a hundred different size balls that you are trying to get through a screen with holes that only fit things the size of a ping pong ball or smaller. Your standard mister is going to have like a 50/50 mix of sizes and the bigger ones have to hang out until something comes along to break it into several smaller balls kind of like the game 'asteroids' if you remember it.
True aero is a spray of balls that are all the size of ping pong balls or smaller, so everything goes right through the screen without having to wait to be broken up into smaller pieces.
That is what is happening on a microscopic level at your root level. The need for O2 is that it breaks down those H20 molecules and helps tear apart CO2 the O's are all what they call 'Free Radical' Meaning they bond with anything immediately. It is called Oxidation. That is why your blood is red, oxidized iron in your blood. It is how hemoglobin is created. All cells respire gases...it is smaller than water vapor or even the molecules themselves. O2 is a gas, CO2 is a gas, Nitrogen is a gas, Hydrogen is a gas these are all gases that when combined together to make a 'big ball' make water H20 or CO2 or any of the elements you are feeding your plant.

The first picture is a close-up of a lotus leaf, an example of a super-hydrophobic plant. The roughness of the leaf surface results from the coexistence of bumps about 10 µm(10 microns) wide and hollow channels of about 1 µm(micron) in diameter. The entire surface is covered by a layer of wax that makes it hydrophobic. The ability of the leaf to repel water is enhanced by the surface roughness. (Picture credit: W Barthlott)

That said:

Nozzles are geared towards irrigation and as such utilize a vortex flow, which means that the droplet size does not change with pressure but is indeed from 5 to 200 microns. The majority of the droplet population is about 100 microns, however there is a broad-spectrum of sizes.

PSI/Dan foggers will create 'true' aero fogging at around 50 to 80 microns, but doesn’t have consistent droplet sizes below 50. The best you could do would be a fogger nozzle with populations between 20-50 microns which are the Bio-Control nozzles.

Why Atomize?
Imagine two droplets of the same size, one droplet you break up [atomize] into 1000 smaller droplets and the other you leave alone. If you measure the surface area of each "small droplet" and add them up, the result will be more than the total surface area of single large droplet. Simply put, the smaller the droplet size, the more surface area you'll have at a given flow rate. More surface area translates into more efficient heat transfer, surface contact or reaction within a gas stream.

All mediums get in the way of gas exchange and mediumless growing is preferred.

Spray mist less than 20 microns tend to remain in the air as a fog and are not readily absorbed by the roots. The ideal mist size range for most plant species is 30 - 80 microns. Within this range the mist makes the most contact with the roots.

Inclines are necessary with most tubes to ensure adequate drainage.

One can reasonably expect 45% faster veg times when the TAE is achieved.

Third in importance for maximum efficiency is cycle timing of nutrient delivery, i.e. the on/off cycle.

Optimal industry standards for TAGing are 20-30 seconds of delivery to 180-240 seconds off depending on environment. Most rely on the 30/3 cycle of 30 seconds on 3 minutes off. This appears to be the maximum effective rate lessening in effectiveness as intervals become longer.

15-minute timers are not to be used in TAG as they overly saturate and dry too long for an effective TAE.

Ideal environments for TAG roots are light proof and completely opaque. Heat and light issues at root zones are the number 1 complication with aeroponic rigs designed without adequate space or drainage.

Nutrient Strengths are still under debate at this time. Current conventions are as follows as a basic guideline for TAGing.

Seedlings and fresh clones: 200-300 ppm
Max Vegetative: 450-500 ppm
Max flowering: 950-1050 ppm

It is to my personal understanding that I believe these numbers could be much higher once nutrient profiles are established for the growth cycle of this plant. There appears to be increased issues with P/K uptake during all phases do to lockout more than over fertilization.

HydroSan · 09-19-2005, 10:39 AM

Quote:

Its hard to express in words what you are thinking sometimes.I think theres alot of misinterpreting going on

yer not wrong there mate

bear with me while I try, air roots,water roots and even freaking dog tails

Quote:

Hmm.I wasnt aware there are specialized roots for taking in oxygen from the air.Or are you saying that the root structure changes depending on the source of the O2?

I supose it depends how you want to look at it

I woulda said it doesn't depend so much on the source of O2, but more on the moisture concentration

once the moisture concentration is too high, the root hairs get flattened, yeah, think root hairs

saying 'air' roots and 'water' roots isn't quite accurate, it's my way of trying to differentiate between a fluffy dogs tail with a huge surface area (adding the surface are of individual hairs together) or a wet dogs tail where the surface area is only length x width2 - the greater the surface area the more absorbtion potential for each root

So, it makes sence that the most efficient roots have the biggest surface area, that means lots and lots of teeny tiny root hairs, this is what I mean by 'air roots'

because, if you think about it, these hairs ain't gonna be much use if water is holding them flat against the root, roots constantly immersed in water don't seem to have them - go back to the aero cloner scenareo, lots of hairs standing up from each root, turn on the spray - no hairs (dry tail - wet tail)

You might think these root hairs are for direct O2 absorbtion from the air, but you have to consider that air alone cannot support them, it has to be moisture rich air, (or a medium - dirt in nature) the moisture contains the nutrients, so I would say they are not strictly 'air roots' but specialised root hairs that absorb the plants requirements including O2 and nutrients, not strictly limited to O2

The article you posted is contradictory IMO.

Quote:

3.Average droplet size 50µ (micron) nozzles (acceptable ranges 30-80µ) ........The need for 50µ-target size for micro droplets is based on the findings by researchers that the average tube opening on the root hairs is approximate 20-50µ or within a range from 5-100µ........The ideal mist size range for most plant species is 30 - 80 microns. Within this range the mist makes the most contact with the roots......The majority of the droplet population is about 100 microns...

They say it's important to aim for a 50u droplet size based on 'findings' they say their droplet size averages at 50u ....then say the majority of the droplet population is 100u

it looks like BS to sell their stuff

Quote:

Spray mist less than 20 microns tend to remain in the air as a fog and are not readily absorbed by the roots.

This is blatent BS and flies in the face of foggerponics, check out shira's page, those guys are well published Israili scientists....

Quote:

Originally Posted by Shira's page

What we refer to in the growing industry as ‘Dry Water’ is actually a dry fog that behaves as a fluid in its gaseous phase. The fog, which is produced by an ultrasonic fog generator, is actually less than 5 micron droplets; very ‘dry’ when you compare it to atmospheric fog which is anywhere from 12 to 15 micron droplets. The ultrasonic fog generators used to produce the dry ice like effect in decorative fountains is around 20 microns and definitely not adequate for growing applications .

A silent storm is brewing over the outstanding results growers are seeing when their plants get fogged. A grower who recently switched from a conventional aeroponic system to the fog method of feeding was amazed by the simplicity of fogging “It’s such an easy and efficient way to grow. My plants thrive in this clean, almost sterile environment. My garden hasn’t been troubled by whiteflies or spidermites, a constant battle in my regular aeroponic garden.”

The ‘dry water’ or ‘fog’ produced by an ultrasonic fog generator has so many applications for horticultural use. The fog (less than 5 microns in size) or fluid in a gaseous state is capable of deep penetration of minute spaces. This eliminates the "free water" which contributes to contamination, disease and pollution of solutions using traditional methods in agricultural applications. By adding easily soluble substances to the water, the user can carry out chemical or nutrient treatments which help to provide an improved product.

Aeorponics is considered the purest form of plant cultivation. Oxygen and nutrients are delivered to the plant’s root zone in ideal proportions creating an atmosphere for vigorous and healthy growth

In the traditional aeroponic garden, roots are fed nutrient through a continuous fine mist while they are suspended in the air. A series of spray heads are connected to a high powered pump that runs on continuous cycles to keep roots moist. Because a very fine mist is required, about 20 micron droplets, the misting nozzles or spray heads in an aeroponic garden often clog with the salts and calcium contained in the nutrients. Trying to maintain an aeroponic system can be a constant source of frustration for the grower. If a sprayer becomes clogged it must be cleaned quickly as plants will suffer immediately from deprivation of oxygen and moisture.

These guys are saying 20u droplets are too big, they aim for <5u, your quote above says most of thiers are 100u, see what i mean

If the droplet size is greater than 5u (or thereabouts) the root hairs can't stand up, the moisture gathers into 'free water', so unless you're fogging them with this very expensive bit of kit, you might as well leave your 100u sprayers going 24/7 because it's unlikely the root hairs will dry out enough to benefit from a dry period IMO. Even Shira say it's a 'continuous fine mist'

I alway thought aero sprays were timed because of a heat issue with the pumps, and I remain convinced it's the only time you should cycle them

There's some root pics on shiras page too, check em out and see how yours compare, and see how long it takes root hairs to stand back up when you cycle the spray off too, should help see where I'm comming from

San

BaadPuTthyKat · 09-19-2005, 12:44 PM

I can say after experimenting with the cheaper foggers (Arnold L. hs done this too), that they tamper with the nutrient pH, in some way. I didn't persist until plant damage occurred, but hve also experimented with these in their own 'water bucket', & ducted the high RH mist to roots & leaves successfully. The leaves have a tendancy to burn, with constant fog around, but otherwise it works OK. To be sure, the 5micron units are necessary for proper aero...

Also, those air roots in NFT....I had home built system, I sometimes had a root caused back up of nutrient solution, late in the grow. The air roots grew as needed, within a day, if the nutrient levels down the channels had risen. I didn't notice any serious detrimental effect on growth, but my DO levels were very good. Air pump & a ~ 6" drop back into the res..Switching to cycled nutrient feeding fixed the problem, & worked fine once there was a good root mat...

HydroSan · 09-20-2005, 02:28 AM

From http://www.botany.uwc.ac.za/ecotree/root/rootA.htm

snip

Cells of the young epidermis (cells making up the new root) in the region of maturation give rise to the root hairs. These are formed by extensions of the cell wall of the epidermal cells and protrude into the surrounding soil. When plants are grown in moist air, the hairs form long slender tubes but in the soil they are greatly contorted as they must grow between the soil particles. The root hairs are not separate from the epidermal cells, but form a single cells. As the cell wall extension moves out from the epidermal cell into surrounding soil, the nucleus of the cell moves to the tip of the new root hair along with much of the cytoplasm. An epidermal cell with a mature root hair thus has a large central vacuole. The cell walls of the epidermal cell and its root hair are thin, thus not inhibiting the uptake of water and dissolved salts by the epidermal cell.

Root hairs greatly increase the area of the root which is exposed to the soil and through which water and dissolved nutrients can move into the root. They are ephemeral however, and only last a few day or weeks before they wither and die. New root hairs are constantly being formed at the anterior end of the region of maturation as it is pushed forward by the growing root and those further back die. In this way the new root hairs are constantly coming into contact with fresh soil. Most plants produce roots hairs, however they are absent in certain firs and redwood species and some aquatic plants. Root hair development is suppressed when some land plants are grown with their root suspended in water (hydroponically) and their growth is negatively influenced by high soil nutrient concentrations and high and low soil temperatures.

Check the link for some great pics showing root hair formation

BPK - I sometimes get that 'root dam' effect, I find that the smallest clones are best placed at the drain end of the tray, larger clones always outgrow their smaller counterparts, so with the biggest root systems at the higher end it happens alot less, I still do a daily check just incase, and I'm usually taking roots out the drains anyway

the difference between smallest and largest clone is only 2", but by the end of the run the difference can be as much as 50% so it's easy to see how I worked it out

San

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