Scientific methods for determining plant nutrient uptake in hydroponic systems?

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ThePundertaker

Member
So we're all probably familiar with the many charts circulating the internet that shows how nutrient uptake is affected by pH range. We're also all equipped with EC/TDS meters to know the total concentration of nutes in the liquid. But my interest is in how one would determine the 'ideal' nutrient ratios for a given strain, even if there are different ideal ratios at different points in the life cycle.

My question is: how would one rigorously determine the exact ratios that a given plant was uptaking nutrients from a liquid solution?

For example, if I filled my reservoir with a certain N-P-K ratio, is there a way I can measure the change to that ratio after a time period, and thus fine tune it? Probably some relevant scientific methods out there I don't know of...

(By the way, I'm familiar with the Lucas formula. However, I'm also aware that this formula is decades old, and probably was determined through trial and error rather than direct measurements of individual nutrients.)

What I'm imagining is the ability to hone in on a near-exact feeding ratio for a given strain at each phase in its growth, leading to the following benefits:
  • Maximizing cost efficiency of used nutrients (no wasted/drained nutes)
  • Optimizing plant nutrient uptake and growth rate
  • Increase the success of a no-change RDWC build by avoiding a toxic buildup of unconsumed nutrients
 
ruwtz

ruwtz

Well-Known Member
Tissue analysis will tell you what the plant is up taking and where there might be tox or deficiency.

Testing the res would require various different and expensive instruments to measure the various elements. Not practical for home growers, but a lab can do a water analysis for you from a sample.

I too have been working hard trying to fine tune the right nutrient profile through adjustments of elemental salts, but lets be honest this is not an exact science and more trial and error. A deficiency, for instance, has likely been present for a while before it reveals itself in leaf symptoms or stunted growth.

Ultimately this can all be a bit of a rabbits hole, I feel, and it drags you in fast if you are that way inclined. It is worth remembering that plant food falls relatively low on the list of priorities to dial in when maximizing quality/yield. Light, temperature, air quality (including CO2) and water (including humidity control) are worth everyone's effort well before fussing with nutritional precision.

Thats not to say it isn't important, but it can be overthought if you already have the basics down. This is why you'll find most people saying any decent nute line will do, because ultimately this is true.

To answer your last points, you can maximize cost efficiencies by buying dry ferts in bulk, by running less nutes overall (intense light + higher transpiration, for instance, means more water volume uptake requiring lower EC), and controlling runoff if in soil/soilless.

FWIW, i have my own nute profile i'm working to in third run now, together with a DIY line of salts for max control. Happy to share here if you're interested.
 
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vostok

vostok

Well-Known Member
look to whats missing in the rez

over a given period

including evaporation and current climate

good luck
 
Kingrow1

Kingrow1

Well-Known Member
Perfection is way harder than just growing, tissue analysis machines if your anal and youll probably end up with a dissertations worth of notes maybe even a lifetimes worth.
 
Richard Drysift

Richard Drysift

Well-Known Member
Plants have evolved over millennia to take what they need as needed from the earth but in hydroponic systems you are basically force feeding your plants by giving them everything all the time whether they need it or not. A natural soil food web dispenses only what the plant exchanges cations for. So if you grow in soil and simply water your plants your are already optimizing nutrient uptake....
 
Budley Doright

Budley Doright

Well-Known Member
"My question is: how would one rigorously determine the exact ratios that a given plant was uptaking nutrients from a liquid solution?"
You can't unless you have access to a lab, you would need to do a before and after analysis of the water and measure all components ...... keep us posted :).

 
T

ThePundertaker

Member
KryptoBud said:
They make meters to measure different ions individually, not sure about an all in one. If one is made this place will have it, be prepared to drop some$$$$$$$$$$$$$$$$$
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This is an awesome source, thanks for the link!



ruwtz said:
Tissue analysis will tell you what the plant is up taking and where there might be tox or deficiency.

FWIW, i have my own nute profile i'm working to in third run now, together with a DIY line of salts for max control. Happy to share here if you're interested.
Click to expand...
For sure, if you're willing to post. Knowledge is power!

I know it's a potential rabbits hole... It's just one more area to optimize. But hey, we do it for the love the science/art, right?
 
ruwtz

ruwtz

Well-Known Member
I made this little table and its constantly adjusting, but so far so good on the second run. I hope it makes sense to unfamiliar eyes.

At the top here is a list of the salts I use, all built around a base of Peters 5-11-26 + cal-nit. These columns show the elemental ppm's at 1g/gal.

Then there's my veg profile, which I ramp up to by week 3 or 4 (typical veg is 7wks). Only other additives are kelp (for aminos and cytokinins) and fulvic/humic (chelates) and Hydroguard (start to finish).

The grey bar shows the profile i'm aiming for, mostly based off of some intensive work I found by some awesome nute nerds @icmag. They really got down into the functions of ratios between NO3:NH4 and K:Ca:Mg and others, which is why you will see me running MAP in early bloom - see below.

Screen Shot 2017-02-01 at 12.00.32.png

Profiles for bloom, split into three phases of growth.

Screen Shot 2017-02-01 at 12.00.27.png

Major changes across the phases are: MAP early for flower setting and roots, then MKP as P booster at peak, then finishing with K-sulfate for the potassium and terpene boost.

I do run humates in bloom but not kelp except for transition. I'm finding it gets a little crazy after that.

I run all these salts from concentrated stocks and i've worked out application rates (ie. ml's per gal) to consistently deliver the above ppms and without having to EC everything whilst loading the res.

I'm still playing with final res dilutions to compliment fertigation rates and transpiration in a hot room (83F with CO2) under 34w/sqft DE fixtures. This is especially important in the second half of flowering in order to avoid problems. As an example i've been having mad foxtailing most likely due to excessive P whilst running Mammoth P: those guys claim you can roll back nutes by up to 25% to account for the increased uptake.

Obviously everything is rolled back incrementally in the week of finishing, but green til the end and no flush.

As I say this is a work in progress in a new room with nothing really dialed in. I don't claim this to be optimal but it is working well. This is about as precise as I want to be with it at this stage.
 
The_Enthusiast

The_Enthusiast

Active Member
ruwtz - are you sure different "npk ratios" and formulas are important in "different" weeks of bloom?

Most other plants in greenhouse have only "one" bloom formula/recommendation

I used to run different week formulas but after few years of experience - switched to single bloom formula - and results are - nice.

Here is my "newer" formula for 50% RO 50% Tap water:
pt 1.png
And here is - the how it's made:
pt 2.png

The values in the second table are with included "impurities". And Micro Combi is Haifa Micro Combi (micronutrients)

After all that I get around 1.9 EC and around 5.8 PH

I let EC drift up to 2.2 EC. PH is so stable i can leave it for a week and return to +/- 0.1 PH (around 150L reservoir for a 600W system)

As far as nutrient solution - you have opto refractormeters (i can post a link if you want it) from HANNA INSTRUMENTS.
I'm planing to buy one when the opportunity arises it costs about 1000-1500€ with reagents.
 
ruwtz

ruwtz

Well-Known Member
The_Enthusiast said:
ruwtz - are you sure different "npk ratios" and formulas are important in "different" weeks of bloom?

Most other plants in greenhouse have only "one" bloom formula/recommendation
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Good question, to which the short answer is probably no and i'm fiddling way too much!

However it is true that a plant requires elements in varying quantities at different times, and so my thinking here is that there is benefit to be had in articulating this manually, especially in soilless like coco with its low cation exchange capacity (relative to, say, organic soil where the plant takes up only what it needs when it needs it).

I also think there's benefit in preparing for specific foreseeable nutritional requirements at the growth phases. Flower setting, for example, is a key turning point for the plant. Does upping the ratio of ammoniacal nitrogen really affect this process? Do we really need to bump P in peak bloom? If so, by how much? Is that extra K late on helping the plant to finish green and healthy?

I'm trying to learn the answers for myself.

I'm trying work within a certain amount of predictability with plants we have learned to understand very well: clones of clones of plants that have been grown several times over, demonstrating the same nutritional requirement at near identical stages.

The pros will always say to feed a plant what it needs when it needs it, which requires a very keen diagnostic eye, and besides we know that a def or tox has been around for a while before it presents itself as a symptom in the leaf etc.

This way is adequate, and obviously gives results (all else being equal), and so is good enough. There may be no such thing as a perfect nute profile, but hey its fun trying. :bigjoint:

I like this discussion.
 
T

ThePundertaker

Member
ruwtz said:
I made this little table and its constantly adjusting, but so far so good on the second run. I hope it makes sense to unfamiliar eyes.
Click to expand...
Thanks ruwtz, very informative!

Have you looked at the cost effectiveness of these formulas vs popular commercial ones? I'm wondering if the low price of the bulk salts would compensate for the variety of ingredients and work that needs to be done (once all the research is complete and the formula is dialed in that is). For example, I just spent about $80 with tax for 1 gal containers of the GH's Flora trio.


Jay80'sbaby said:
Is this ready for to be cut down? Need help
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Make a separate post for your question dude, we are talking about nutrient uptake here.
 
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