Soil ppm
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Emilya Green
Well-Known Member
how exactly are you measuring soil ppm?? Do you realize that if you grind up your soil into micro bits that the ppm would start to approach infinity? PPM in soil has no practical meaning.
I have been wondering about the messages lately form people growing in soil mixes who are asking how to measure the PPM or who have already "measured soil PPM" and want to know how to interpret the number.
Questions run in cycles. We see a bunch of questions on the same topic and then it dies off and a new topic pops up.
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- #5
No. There is something named the law of conservation of mass. If there is 10 grams of iron, then there still is 10 grams of iron if you grind it to dust.
Only black holes have infinite mass
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- #6
Well. Explain better. I just wanna know what the ideal osmotic pressure is for the roots to uptake nutes.
But I think that is something beyond your education.
Yes, it might be.
I was just commenting on the increase in the number of questions from people growing in soil who want to know about their PPM number. They want to know what it is supposed to be, or if the number they came up with means anything, or if the number means they have a healthy soil.
How does the mixture of soil and demiwater and then the PPM measurement compensate for the continued dissolving of minerals. The method has to compensate for the constant eating of organic materials by the the micro-organisms.
Emilya Green
Well-Known Member
parts per million and mass are two completely different things. I said that the parts per million can approach infinity in soil, depending on how fine you want to grind it up. Mass has nothing to do with this, no matter how much education you might have.
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Im sorry man. I had just finished working and was a little bit cranky. I needed a good smoke
But yeah. PPM is the already dissolved free ions that is available to the roots. I dont think slow releasers have a lot of influence on the average ppm at that certain timeframe. They release too slow. And there exist an equilibrium between all particles in the solution.
But I havent either got the education. Lol. So I refer to this document. Soil test methods from the southeastern united states. Chapter 4.1 page 91. Introduction to soil extractable plant nutrient.
or better this one with actual methods. Soil testing methods by the united nations on page 44
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- #10
ppm= mg/L
There is no such thing as 100000000000000000000000000 mg/L (mg iron in a litre) No matter how much you grind it
Started looking the two over. Going to save the links to the hard-drive. Good reading so far.
Emilya Green
Well-Known Member
it means parts of a contaminant per million. If you need to know exactly how much of something is in a mix, it can be measured approximately and extrapolated by using weight as a reference, since the atomic weight of the pure water and the contaminant are known, you can figure out the actual number of particles (molecules) per million or billion for that matter, is in the mix. We commonly use general measurements by saying a mix one part of this with 3 parts of that, making the ppm number more of a percentage of the total than anything else. If you know the mix is 1 part soil and 3 parts water and you know the total weight, you can figure out exactly how many water molecules are there and how much soil is there...but what if you have a 1:3 mix and one small component of the 1 portion weighs 10x what the water weighs? How can you tell how much of that mg/L is that particular contaminant simply by weight? Soil is comprised of at least 19 elements, each with different weights, so you may be able to tell me using your general measurement how much is water and how much is other stuff, but without next looking at the molecular weight of each component and figuring out how many molecules (particles) there are, you really have no idea. Take a look at your county water report, where they tell you how many ppm of each contaminant is in there. That actually is a very complicated analysis, and certainly not done just by weighing the water.
Try an experiment. Take 1L of water and measure its ppm. Stick a piece of glass in there and measure the ppm again. By your general measurement, you can easily see that by weight there is 1 part glass and 3 parts water there. Measuring the ppm with your meter can't show the change... there is 1 large part per billion of contaminant in that container. Now grind that glass up, right down to its molecules. Silicate and carbon and whatever else you get, and mix it into the water. Now measure it with your ppm meter. It is the same added weight, but a drastically different measured ppm. The difference? The number of particles per million of contaminants in the water.
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1 liter of pure water is 1 kg. So 1 ppm = 1 mg of charged particles (since conductivity is measured) /1 kg pure water (which does not conduct electricity) =1 mg/L
If your rod weighs a gram and you add water until 1 liter it will occupy the same space as when its powder since glass keeps the same density. So volume wise and mass wise the ppm stays the same.
PPM is not a SI unit. It needs to be defined first i guess. You go for mass, volume, ratio. Its all possible. But in general in horticulture they use mine definition of mg/kg(L). A volume of soil contains a certain amount of something. A liter of soil can contains 5 % N. One liter soil weighs 0,6 kilo which is 5% N. Which is 0,03 kilo N in one liter soil = 30000 mg/L =30000 ppm N. But not all of this N is extractable or free.
What I actually was asking was the ppm of the extractable nutrients in soil since these are available to the plant.
Emilya Green
Well-Known Member
I have never studied botany or large farming, so there are many things and ways of doing things that I have never even considered. My fields are Physics, Computer Science and Economics, so I do come at things a little differently. I am glad to hear that for the field farmer it is as easy as this, but I suspect that the container farmer is not going to find it as simple to implement. I hope you figure out how to make this work in your garden... I want to learn from you.
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And yeah. What do i mean with soil ppm. With or without water. The nutrients in the soil water. Which is important. If this concentration gets to high the potential gradient switches and water gets sucked out of the plant. If the plant drinks soil water, the concentration of nutrients and particles increase and it get more difficult to uptake nutrients into the roots because of the concentration gradient. The roots compensate by producing sugars in the roots. This costs energy and thus costs yield.
So good control of the concentration levels in the soil is a pro. And concentration is measured as ppm= mg/L
I hope im right. I should murder myself otherwise
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- #16
The reason imasking is because im trying to figure out how much a plant is eating in total during its lifetime.Is this a good representation of soil ppm during an 84 week (3 week veg, 9 week bloom) grow.
If I integrate the equation for this graph I get a total of 98 grams nutrients / L. (about average of 1150 ppm in 84 days)
b and a = max and min y values. i and j are midpoints of the s curves on the x axis. M and n are the slopes of the curves. And P is the ratio of the two curves y length.
Anyway. I got about 98 grams/ liter soil of nutrients. (thats for a 20 L pot 20*98 = 1,98 kilo of nutrients)
A rule of thump is that a plant consistst of 4% nitrogen. For a 2 kilo plant thats 80 grams of N. Which it can only get from eating.
Yeah. Dont know where im going exactly. Nevermind
i think you have the idea, @prankster.
Since you have cited some ag resources, you can see how its done as a paste, slurry, or pourthrough. Most casual growers dont need much analysis, if using a known substrate, some balanced nutrients, and quality water.
You are correct in that a soil paste test will give you the ec of the total dissolved solids, (including the available nutrients but also including non nutrient ions) and ppm in this context is mass / mass ratio of reagent to solution. And the ec that we care about is as an indicator of osmotic pressure which regulates water uptake.
If you want to know how much of a particular nutrient was absorbed it will be impossible to compute from soil analysis. You would need to treat the plant as a completely closed system and measure all the inputs and outputs - complete nutrient analysis of the substrate before and after, analysis of the atmosphere (nitrification causes loss of N to the air), all the runoff, etc. Thats like Nasa level analysis. The most straightforward way to get that is a tissue sample analysis.
Is that graph your measured substrate ppm? That seems high to me.
Since you have cited some ag resources, you can see how its done as a paste, slurry, or pourthrough. Most casual growers dont need much analysis, if using a known substrate, some balanced nutrients, and quality water.
You are correct in that a soil paste test will give you the ec of the total dissolved solids, (including the available nutrients but also including non nutrient ions) and ppm in this context is mass / mass ratio of reagent to solution. And the ec that we care about is as an indicator of osmotic pressure which regulates water uptake.
If you want to know how much of a particular nutrient was absorbed it will be impossible to compute from soil analysis. You would need to treat the plant as a completely closed system and measure all the inputs and outputs - complete nutrient analysis of the substrate before and after, analysis of the atmosphere (nitrification causes loss of N to the air), all the runoff, etc. Thats like Nasa level analysis. The most straightforward way to get that is a tissue sample analysis.
Is that graph your measured substrate ppm? That seems high to me.
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- #18
I was hoping that some research had been done on some university since its legal these days. But yeah. Research takes time. Some paper will pop up someday I hope.
Yeah. That graph is actually the ec of the solution of fertilizer given to a soilles medium. I agree. Its high. Based it on a formulation of salts calculated by myself. To get the right ratios it became a littlebit to concentrated i guess. I believe the upper limit is about 1800 ppm before it starts to suck water out of the plant.
This isnt new, but here is some analysis you may like @prankster. I am not a big fan of these products, but the data are interesting.
its a tissue analysis of cannabis at veg and flower, with the theme “why do so many nutrient lines provide so much P in flower?”
and the raw data
its a tissue analysis of cannabis at veg and flower, with the theme “why do so many nutrient lines provide so much P in flower?”
The Real BigMike
True Confessions of a Cannabis Entrepreneur Subscribe to BigMike’s Email Newsletter…… chock-full of unconventional wisdom on cannabis, business, and
www.growersunderground.com
Wayyy tooo complicated for my hazed out brain, think I will stick to DWC, lmao.
