Is Pre-harvest Flushing A Myth?

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MIMedGrower

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The NPK Mistery – What Do These Numbers Mean and How are they Calculated ?
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  • The NPK Mistery – What Do These Numbers Mean and How are they Calculated ?
When you go into a forum about hobby hydroponic or soil growing one of the first things you will notice is that there is a big confusion regarding the meaning of the traditional NPK notation and the way these values are actually calculated. Some people believe this is supposed to be merely an N to P to K ratio measurement while others erroneously use ppm information directly to get their NPK fertilizer information. On today's post I want to talk about the real meaning and nature of the NPK measurement as it is used in traditional agriculture, how it is calculated and what it tells us about a fertilizer. (below a fertilizer made with pelletized nutrients in clay, traditionally described using the NPK ratio, this ratio is important because it is necessary to know how much is clay and how much is fertilizer)

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The NPK measurement was invented as a way to gauge the quality and concentration of the 3 most important nutrients relevant in agriculture within a particular solid or liquid fertilizer. These three numbers represent the percentage composition by weight of any given fertilizer, telling us its percentage composition of N as nitrogen, K as K2O and P as P2O5. The reasons why K2O and P2O5 were used to represent potassium and phosphorous instead of referring to the simple quantities of these elements are that, first of all, the traditional analysis methods used to determine K and P give the values of the oxides in a more straightforward manner and second, the actual percentages of K and P when expressed as the oxides give "good ratios for the plants in soil" when the values are close to the value of N (making comparisons easier).


It is now important to note that the NPK reading must be calculated taking into account the weight of the given nutrient within the solution and the WHOLE weight of the fertilizer used. For example if you have a liquid concentrated fertilizer that has a composition of N = 12000 ppm, K = 20000 ppm and P = 4000 ppm which was prepared with 200g of added salts. The NPK ratio of this solution would be :

Total Solution Weight = 1000g (1L of water) + 200g (added salts)

N = 12000 ppm = 12000 mg/L = 12 g/L
K = 20000 ppm = 20000 mg/L = 20 g/L
P = 4000 ppm = 4000 mg/L = 4 g/L

Percentage of Nitrogen = (12g/1200g)*100 = 1%
Percentage of K as K2O5 = (20g/1200g)*1.2046 (K to K2O conversion factor)*100 = 2%
Percentage of P as P2O5 = (4g/1200g)*2.2914 (P to P2O5 conversion factor)*100 = 0.76%

The final NPK ratio is therefore 1-0.76-2. As you see you need to know the total weight of the solution and the elemental composition in order to be able to obtain this number. It should also be clear that the traditional NPK ratio is a PERCENTAGE COMPOSITION measurement and NOT a mere comparison of the ppm concentration ratios of N, P and K. Knowing a fertilizer's NPK not only allows you to know the ratio between these three elements but it also allows you to know how much of each one is contained within the solution so that the relative strength of different fertilizers can be calculated.

The traditional NPK ratio however has very limited use in hydroponic cultivation since it was invented to gauge the quality of soil intended fertilizers. Nonetheless it can be used to compare the relative strengths of different fertilizers and the ratio of the three main nutrients within them. However it should be clear that if you want to communicate a measurement that compares ppm concentration ratios you should not refer to this as an NPK measurement since this will cause confusion against the "traditional NPK" which was explained above. In hydroponics it would be easier to talk about ratios of ppm which should be expressed as N/K-P/K-1 for example which would give us the ratio of N to K and P to K without giving information about the percentage composition of the solution.
 
G

Glow

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Oops. Here is the article


The NPK Mistery – What Do These Numbers Mean and How are they Calculated ?
  • Home
  • NPK
  • The NPK Mistery – What Do These Numbers Mean and How are they Calculated ?
When you go into a forum about hobby hydroponic or soil growing one of the first things you will notice is that there is a big confusion regarding the meaning of the traditional NPK notation and the way these values are actually calculated. Some people believe this is supposed to be merely an N to P to K ratio measurement while others erroneously use ppm information directly to get their NPK fertilizer information. On today's post I want to talk about the real meaning and nature of the NPK measurement as it is used in traditional agriculture, how it is calculated and what it tells us about a fertilizer. (below a fertilizer made with pelletized nutrients in clay, traditionally described using the NPK ratio, this ratio is important because it is necessary to know how much is clay and how much is fertilizer)

-
-
The NPK measurement was invented as a way to gauge the quality and concentration of the 3 most important nutrients relevant in agriculture within a particular solid or liquid fertilizer. These three numbers represent the percentage composition by weight of any given fertilizer, telling us its percentage composition of N as nitrogen, K as K2O and P as P2O5. The reasons why K2O and P2O5 were used to represent potassium and phosphorous instead of referring to the simple quantities of these elements are that, first of all, the traditional analysis methods used to determine K and P give the values of the oxides in a more straightforward manner and second, the actual percentages of K and P when expressed as the oxides give "good ratios for the plants in soil" when the values are close to the value of N (making comparisons easier).


It is now important to note that the NPK reading must be calculated taking into account the weight of the given nutrient within the solution and the WHOLE weight of the fertilizer used. For example if you have a liquid concentrated fertilizer that has a composition of N = 12000 ppm, K = 20000 ppm and P = 4000 ppm which was prepared with 200g of added salts. The NPK ratio of this solution would be :

Total Solution Weight = 1000g (1L of water) + 200g (added salts)

N = 12000 ppm = 12000 mg/L = 12 g/L
K = 20000 ppm = 20000 mg/L = 20 g/L
P = 4000 ppm = 4000 mg/L = 4 g/L

Percentage of Nitrogen = (12g/1200g)*100 = 1%
Percentage of K as K2O5 = (20g/1200g)*1.2046 (K to K2O conversion factor)*100 = 2%
Percentage of P as P2O5 = (4g/1200g)*2.2914 (P to P2O5 conversion factor)*100 = 0.76%

The final NPK ratio is therefore 1-0.76-2. As you see you need to know the total weight of the solution and the elemental composition in order to be able to obtain this number. It should also be clear that the traditional NPK ratio is a PERCENTAGE COMPOSITION measurement and NOT a mere comparison of the ppm concentration ratios of N, P and K. Knowing a fertilizer's NPK not only allows you to know the ratio between these three elements but it also allows you to know how much of each one is contained within the solution so that the relative strength of different fertilizers can be calculated.

The traditional NPK ratio however has very limited use in hydroponic cultivation since it was invented to gauge the quality of soil intended fertilizers. Nonetheless it can be used to compare the relative strengths of different fertilizers and the ratio of the three main nutrients within them. However it should be clear that if you want to communicate a measurement that compares ppm concentration ratios you should not refer to this as an NPK measurement since this will cause confusion against the "traditional NPK" which was explained above. In hydroponics it would be easier to talk about ratios of ppm which should be expressed as N/K-P/K-1 for example which would give us the ratio of N to K and P to K without giving information about the percentage composition of the solution.


A couple of things to be aware of with NPK ratios though is the ratio is often rounded down to the nearest whole number. Also if say your NPK ratio is 6 - 2 - 8 this is the same thing as saying 3 - 1 - 4 because while you are working with percentages first and foremost it is the ratio that is being measured. Also K as K2O and P as P2O5 is somewhat unique to North America - in other countries they use elemental percentages (i.e. K and P as elemental) so you need to check what the listing stands for. In fact I find it quite daft they use K2O and P2O5 because plants don't uptake K2O and P2O5 or for that matter this isn't how P and K is represented in a hydroponic solution. Simple rule is though use the guaranteed analysis to establish percentages and not the NPK rating. BTW generally both are a long way away from what is actually in solution because these are guaranteed minimums (what is in the product as a minimum stated level) and aren't in most cases representative of what is actually in a product re %w/v or %w/w.
 
MIMedGrower

MIMedGrower

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A couple of things to be aware of with NPK ratios though is the ratio is often rounded down to the nearest whole number. Also if say your NPK ratio is 6 - 2 - 8 this is the same thing as saying 3 - 1 - 4 because while you are working with percentages first and foremost it is the ratio that is being measured. Also K as K2O and P as P2O5 is somewhat unique to North America - in other countries they use elemental percentages (i.e. K and P as elemental) so you need to check what the listing stands for. In fact I find it quite daft they use K2O and P2O5 because plants don't uptake K2O and P2O5 or for that matter this isn't how P and K is represented in a hydroponic solution. Simple rule is though use the guaranteed analysis to establish percentages and not the NPK rating. BTW generally both are a long way away from what is actually in solution because these are guaranteed minimums (what is in the product as a minimum stated level) and aren't in most cases representative of what is actually in a product re %w/v or %w/w.


All very true. Well said.

The ag industry in north america is as screwed up as the rest of our governments regulations.

At least my truncheont measures ec.

Im working on centimeters but there are always so many of them. :-)
 
G

Glow

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All very true. Well said.

The ag industry in north america is as screwed up as the rest of our governments regulations.

At least my truncheont measures ec.

Im working on centimeters but there are always so many of them. :)

Yes I have to say that I find it very disconcerting that the US uses the antiquated and highly flawed imperial system when the rest of the planet uses a standard of measurements that make so much more sense:-) Try doing chemistry in imperial aghhh!! Or what is it with ml per gallon? Are you bloody confused man?:-) Hang on let me convert that and then we have something we can actually work with (the same unit of measurement)… Def a tad weird to work in imperial but it is what it is. Funnily enough they changed imperial to metric when I was in school so I learned the two systems and still think in feet versus cm re height. Feet strangely does make more sense (less numbers to worry about).
 
MIMedGrower

MIMedGrower

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Yes I have to say that I find it very disconcerting that the US uses the antiquated and highly flawed imperial system when the rest of the planet uses a standard of measurements that make so much more sense:) Try doing chemistry in imperial aghhh!! Or what is it with ml per gallon? Are you bloody confused man?:) Hang on let me convert that and then we have something we can actually work with (the same unit of measurement)… Def a tad weird to work in imperial but it is what it is. Funnily enough they changed imperial to metric when I was in school so I learned the two systems and still think in feet versus cm re height. Feet strangely does make more sense (less numbers to worry about).


Its the kings math man. Math fit for a king.
 
Bannacis

Bannacis

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High in K and Fe seems to be common. Ca and Mg are extremely low so Mg isn't an issue as one person claimed.
High in K and Fe seems to be common. Ca and Mg are extremely low so Mg isn't an issue as one person claimed.
not all molasses are the same... as you stated up on your cane molasses post with 204% magnesium
 
Bannacis

Bannacis

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Must be a bad batch:) Where do I say others are all wrong and they are spreading lies? I think you will find I discuss the science. I aren't particularly into opinions (opinions are like arseholes - everyone has one) The myth of flushing which I have made very clear as the myth is that the benefits of flushing have long been argued to be related to the idea that through flushing the plant is forced to use up nutrients that have accumulated in the plant tissue. I've not once commented on removing nutrients from soil which feasibly can be done albeit CEC and bulk density pose some very real issues pertaining to this.
Sorry to say that you are saying others are wrong...You are, implying by your argument of it not be a scientific test it there fore is a myth.
Growing Cannabis is easy, it needs to stay easy...When you do all this lab testing crap and trying to make it all about scientific analysis... you are making it Industrial, non natural, and to much like a government controlled resource. When you do that, your plant becomes commercial poison and unbalanced with nature...
And please do not take offense from my rambling, I understand where your coming from, but sometimes science just has it wrong. And if big companies or the Government is behind these testings then beware of the results! I know..i know... this aresholes opinion is just that... I do apologize...but i get the best responses from people when i challenge their post. lol And by all means i'm not saying my facts are true, but i have do the side by side "testing" of flushing and non flushing. mainly if you are growing True living organics (TLO) you do not need to flush. So flushing is relevant to having synthetics/edta nutrients in your soil.
 
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Glow

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You've certainly got a lot of opinions. I actually think from my side of things flushing is all flushed out:-)
 
G

Glow

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not all molasses are the same... as you stated up on your cane molasses post with 204% magnesium

No definitely... different sources will have somewhat different NPK etcs… Although did you stop to think that if you take a sample that = 100% so somehow someone has messed up horribly listing 204% ??
 
FatManatee

FatManatee

151
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A couple of things to be aware of with NPK ratios though is the ratio is often rounded down to the nearest whole number. Also if say your NPK ratio is 6 - 2 - 8 this is the same thing as saying 3 - 1 - 4 because while you are working with percentages first and foremost it is the ratio that is being measured. Also K as K2O and P as P2O5 is somewhat unique to North America - in other countries they use elemental percentages (i.e. K and P as elemental) so you need to check what the listing stands for. In fact I find it quite daft they use K2O and P2O5 because plants don't uptake K2O and P2O5 or for that matter this isn't how P and K is represented in a hydroponic solution. Simple rule is though use the guaranteed analysis to establish percentages and not the NPK rating. BTW generally both are a long way away from what is actually in solution because these are guaranteed minimums (what is in the product as a minimum stated level) and aren't in most cases representative of what is actually in a product re %w/v or %w/w.

I live in Europe, and all the nutrient bottles I have bought here have NPK value listed, and percentages. The percentages are always labeled the same as the NPK ratio in the bottle, with the exception of NPK values rounding down compared to the percentage values.
 
G

Glow

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I live in Europe, and all the nutrient bottles I have bought here have NPK value listed, and percentages. The percentages are always labeled the same as the NPK ratio in the bottle, with the exception of NPK values rounding down compared to the percentage values.

Yep it's actually wise to stick to the actual percentages when listing NPK because it also says how concentrated a product is so while from a chemistry perspective you can say write down e.g. 6 - 2 - 6 to 3 -1 - 3 and be correctly showing the ratio you've also down rated the concentration of the product. Yeah Europe has some odd labelling compliance things going on and some labels list in unusual ways. I think though the EU standardised things pretty well but back in the day you may find labels listing both elemental and oxides. One massive problem with labelling globally is that they could never agree and create a universal standard to labelling so country to country labelling can differ. Are they listing elemental there or P as P2O5 and K as K2O? I know in the hydro industry a lot of crew list as P as P2O5 and K as K2O just to satisfy US regulations so they don't have to change labels when and if they sell in the US.
 
Bulldog420

Bulldog420

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I quoted a reliable, well trusted magazine that confirms my statement. Would you like to give sources to your claim, as I can't find anything on Google that supports your statement.



Here is how NPK is calculated and what it's used for. Read the entire link if needed.



"The fertilizer numbers can be used to calculate how much of a fertilizer needs to be applied to equal 1 pound of the nutrient you are trying to add to the soil. So if the numbers on the fertilizer are 10-10-10, you can divide 100 by 10 and this will tell you that you need 10 pounds of the fertilizer to add 1 pound of the nutrient to the soil. If the fertilizer numbers were 20-20-20, you divide 100 by 20 and you know that it will take 5 pounds of the fertilizer to add 1 pound of the nutrient to the soil."
 
Bulldog420

Bulldog420

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Let me ask you guys something........ If NPK is a pure % like a food grade label........ Then why are there NPK ratios as followed? 1-2-3 and 2-4-6 and 4-8-12 and 8-16-24.......

Why wouldn't all of them just be 1-2-3? When you figure that out, you will figure out why food labels are different than NPK ratings. :smoking:
 
G

Glow

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Let me ask you guys something........ If NPK is a pure % like a food grade label........ Then why are there NPK ratios as followed? 1-2-3 and 2-4-6 and 4-8-12 and 8-16-24.......

Why wouldn't all of them just be 1-2-3? When you figure that out, you will figure out why food labels are different than NPK ratings. :smoking:

Most manufacturers will use the NPK % on the ratio but chemically speaking you can downgrade that ratio. You basically have ratio and percentages and while they can be the same thing they can also be different. Better also not to use the ratio but the information on the guaranteed minimum analysis of any product. Better yet access COA for more reliable data. Generally say though if the actual percentage that were listed on a guaranteed analysis was 5.2% it would be listed on the NPK of a front label for a hydroponic liquid fert as 5%.

And no mate you're flogging a dead horse. A percentage is always a percentage of 100%. That is an absolute and a universal standard. If you are trying to convince yourself go ahead but if you are trying to convince me and others sorry you lucked out the moment you first raised it... Nighty night.. Late here
 
FatManatee

FatManatee

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Here is how NPK is calculated and what it's used for. Read the entire link if needed.



"The fertilizer numbers can be used to calculate how much of a fertilizer needs to be applied to equal 1 pound of the nutrient you are trying to add to the soil. So if the numbers on the fertilizer are 10-10-10, you can divide 100 by 10 and this will tell you that you need 10 pounds of the fertilizer to add 1 pound of the nutrient to the soil. If the fertilizer numbers were 20-20-20, you divide 100 by 20 and you know that it will take 5 pounds of the fertilizer to add 1 pound of the nutrient to the soil."

Your source doesn't actually deny the fact that NPK values are percentages. The author just invented her own way of using the NPK values to mix nutrients in her garden, she doesn't explain what the numbers represent.

However, looking at the discussion so far, we have learned that the NPK values truly are percentages, there is a small difference between USA and EU though.

In USA
N= Percentage of all available Nitrogen
P= Percentage of P2O5
K= Percentage of K2O

In EU
N= Percentage of all available Nitrogen
P= Percentage of all available Phosphorous
K= Percentage of all available Potassium

So you were right about food labeling. In the USA if 5% Potassium is labelled on molasses, it doesn't mean that the product contains 5% of K20.

In the EU however, if food grade molasses is labelled with 2% N and 5% K, it's NPK value would be listed 2-0-5.

Man you guys really need to ditch the imperial system etc. :D
 
G

Glow

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Lol yep - why anyone would use imperial when another system of measurement is far superior is beyond me. Maybe they have a hang up on the King and their ties to ancient Britain:-) Ah so is that what he was saying 5% K in food is elemental K and 5% in a fertilizer represents K20 so 4.15% elemental K? Yeah ratios and percentages are very different things albeit a ratio can be established by percentage and represented in a percentage but ratio in a fertilizer is e.g. the N to K ratio etc. I'm sort of confused after all of that :-)
 
3 balls

3 balls

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You've certainly got a lot of opinions. I actually think from my side of things flushing is all flushed out:)
LOL, this topic just wont die. I wouldn't mind seeing your scientific knowledge being shared on some other threads. Personally I think CO2 enrichment- value of, how much, for how long, its relationships with other environmentals, etc. is the biggest mystery left in indoor gardening.
 
G

Glow

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Yes, its drifted now badly but I try to be polite and respond to things. Its just that people keep posting. Is there a CO2 thread running? I'm happy to chime in. Its not really a mystery at all these days. Chandra and others have done great studies measuring rates of photosynthesis, CO2, temperature and light.
 
Ina

Ina

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Flushing is just the term people use for describing running water for 10 - 14 or even more days in some cases so to call it running water only or flushing sort of depends on opinion - i.e. some believe they can flush inorganic nutrients out of the tissue when they can't and this is scientifically proven (albeit the flat earthers choose to scream fowl). :) Haze genetics going at the moment about 5 weeks out (haze genetics take a long long time to finish but the wait is well worth it). Stacking nicely and will keep stacking for a while yet. Oh and now I've shown you mine you need to show me yours yes :)
View attachment 852194
I saw you deleted some parts of your post,yes?:)I like it better now:)Here some of my small guerilla(my goal for now is less to no efforts and visiting)garden.I can grow only this way for now unfortunatelly.It is really unpleasant activity to be honest( for a lady to carry so much water but I just cant quit growing).I can show you some of my old indoor mixes I was making when I had the chance for small indoors(first few pics)....I grow bio with homemade or collected ferts in nature,i feed with transplanting and different soil mixes so I don't flush and I don't find it necessary...…But I was poisoning some of my plants with fresh or too much manure(I don't use manure anymore) from time to time,they were intoxicated with N and than one or two big flush(lots of water and runn off,not the long flush)were really heplfull.I'm judging by the amount of new pistils that were popping after the flush.But that was different case of flushing than the common two weeks before chop.....
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