Maximum Plant Uptakes for Water, Nutrients, and Oxygen

Advanced Techniques
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This is an interesting paper that discusses limiting factors across a variety of growing technique through the measurement of Radiation Use Efficiency (abbv. RUE):

Maximum Plant Uptakes for Water, Nutrients, and Oxygen Are Not Always Met by Irrigation Rate and Distribution in Water-based Cultivation Systems:

blok2017.pdf (886.4 KB) Retrieved from: https://sci-hub.tw/https://doi.org/10.3389/fpls.2017.00562

Specifically evaluated are systems that include substrate based DWC, substrateless DWC, NFT, and Aeroponics.

From their evaluation, they found:

  1. Substrate based DWC resulted in the highest RUE.
  2. Substrateless DWC resulted in a 15-17% decrease in RUE.
  3. NFT resulted in an 8% decrease in RUE.
  4. Aeoponics shows a 2% decrease in RUE.

The authors conclude:

Transport rates are expected to affect growth only when transport rates are below the maximum plant uptake. The maximum plant uptake is defined as the highest possible uptake to be expected under optimum commercial circumstances of light, carbon dioxide, temperature, water, nutrients, and oxygen.

which may seem obvious to which they comment:

Transport rate differences explain why different substrates require different irrigation strategies for optimum production.

So, while they note they differences in RUE, they also note that systems showing a decrease in RUE may simply require additional tuning of the system in order to improve transport rates under the differing conditions.

Of particular interest, at least to me, is the dissolved oxygen availability. On this topic, there is a lot of mystery and perhaps at times assumptions about aeration, dissolved oxygen limits, the supply of oxygen to the roots, and the rate of uptake of oxygen. The authors discuss this and note that oxygen availability in their experiments is at deficit relative to the maximum transport rate for each of the techniques with the possible exception of aeroponics.

Here are a couple of the references used in the above study that may be of interest regarding oxygen availability:
morard2004.pdf (533.9 KB)
morard2000.pdf (794.5 KB)
bar-yosef2013.pdf (658.7 KB)
ehret2010.pdf (169.3 KB)

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You have my attention now for sure - great find! The DO oxygenation thing is one of my current obsessions, and one of the main reasons Im doing air atomized aeroponics. Im very curious to find out what they have to say.

Now Im off to read it…

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The paper is a good to think on although some details may be up for debate. Take a look at the reference PDFs, too.

I was thinking of your system when I was reading that paper.

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Just managed a fast scan through and I agree - some of their techniques/methodology seem off to me as far as how they are doing NFT and their “deep water” pond tests. The deep water in particular is not really all that close to DWC of any form. Its really more like aqua culture.

Its still interesting, and generally confirms my thinking on aeration and DO - more is better.

I still havent looked at the reference docs.

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sorry! Posted to the wrong thread!

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They kinda have their own terminology going and I couldn’t really understand some the details on their set-up. Thanks for the feedback on that.
I’m thinking I need to look into how they’ve theoretically determined the limited vs maximum rate of oxygen uptake. It seems excessive but it does tend to play into the rationale for some of the experiments over here.

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LOL No kidding! Im still wading through the reference papers and the original paper, but one thing is clear to me.

Assuming those folks all actually know something about hydroponics, and growing in general, and that they are at least somewhat educated in those fields - in other words, that they are really experts, then its clear that we as pot growers are way out in left field! :smiley:

Like you said, the terminology they use and quite a few of the techniques they describe, are very different from what we generally do. Some of it is difficult to figure out, partly for that reason, plus the terminology seems to be different in many cases.

Its still very interesting reading. Some things are not what I expected and there seems to be some conflicting conclusions, but that may be just me misunderstanding parts of the papers.

Im going to keep wading…

Thats one of the problems Im having as well. So far I dont get where their reasoning comes from or is going with that. I have not had time to look into it at all though. They seem to assume everyone knows all about it already :slight_smile:

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Spending a bit of time looking at some more papers on rate of oxygen uptake at the roots (root respiration):

Some notes that I found interesting from the following paper, Veen, B. W. (1988). Influence of oxygen deficiency on growth and function of plant roots. Plant and Soil, 111(2), 259–266. doi:10.1007/bf02139950. veen1988.pdf (557.4 KB)

The most striking effect of reduction of oxygen supply to the roots was the increase in alkalinization of the nutrient solution by increased HCO3 production of the roots.

Reduction of the oxygen supply to 20% of the maximal respiration rate caused death of the root tips of tomato, reduction of the water uptake rate and hence wilting of the plant.

And, their experimental maximal uptake numbers:

image.png1162×251 17.2 KB

This one looks interesting, too: Changhoo CHUN, Tadashi TAKAKURA, Rate of Root Respiration of Lettuce under Various Dissolved Oxygen Concentrations in Hydroponics, Environment Control in Biology, 1994, Volume 32, Issue 2, Pages 125-135, Released June 22, 2010, Rate of Root Respiration of Lettuce under Various Dissolved Oxygen Concentrations in Hydroponics. 32_125.pdf (1.1 MB)

In hydroponic systems, aeration is usually performed in storage tanks. Bubbling, agitation or other oxygen-enrichment facilities are installed to maintain the DO concentration near the saturation concentration. However, the rapid decrease in the DO concentration as shown in Fig. 3 suggests that only raise the initial DO concentration are insufficient in providing enough oxygen for the whole growing period. Though the nutrient solution is oxygen-rich in the storage tanks, its concentration may decrease while the nutrient fluid passes through the root respiration. This could explain the nonuniform DO concentrations in the NFT beds.

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Very interesting! So a lack of O2 is another thing that will drive PH up.

Now that one is also interesting. I have not read it yet, but it sounds like they are talking about an NFT rail system - like the ones in gutters or plastic pipes - where the plants are essentially in a long line where they all see the same water one after the other. They seem to be saying that the plants that are first in line get good O2, and the ones further down the line get less and less O2. That makes sense to me.

I dont see how that would apply to most other types of hydro though - like Flood/Drain or DWC. RDWC could also suffer from the same effect to some degree though if the aeration is all in the control bucket.

So far, everything you have found indicates that maintaining good DO levels is a critical thing to keep in mind in hydro.

I cant help thinking that it has to be just as important in soil grows. The general recommendations to not over water and to have soil that has good drainage, and can breath well (good aeration) are as important as folks say.

Another excellent find!!

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