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Trying to understand NPK ratings (esp. manure)

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  • Trying to understand NPK ratings (esp. manure)

    I'm trying to get my head around NPK ratings (yes ,for the website!), and it generally makes sense, but I've come across a discrepancy regarding their use.

    Having read the Wikipedia article on it:
    Originally posted by Wikipedia
    ...an 18−51−20 fertilizer contains by weight:

    18% elemental (N)
    22% elemental (P), and
    16% elemental (K)
    So because N is the only factor that doesn't need converting (as it is not in an oxide form unlike the other two), this example suggests that the fertilizer contains 18% N and the other elements are converted from their oxide states into an elemental form.
    Q1: So when buying fertilizer, do we have to mentally convert the P and K content?
    (Apparently UK fertilizers can show the elemental ratio, but in brackets afterwards)

    Also, having browsed the internet for nutritional values of various manures I have found that sheep manure is reported as both 18-11-26 and 0.7-0.3-0.9.
    So if nitrogen is the % by weight I would think that 0.7% N is more likely than a massive 18% N..
    Q2: Which do I believe?
    And
    Q3: What's the difference in the way they're reporting these figures?
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  • #2
    Hmmm, just realised that 0.7-0.3-0.9 is approximately equal to 18-11-26 as a ratio, but how do we know if a bottle of liquid fertilizer is made entirely out of N, P and K, or if it only has trace amounts? Surely a ratio is just proportionate to each other unless it contained a "all other materials" comparison
    Current Executive Board Members at Ollietopia Inc:
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    RedThorn - Chief Interrobang Officer
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    WikiGardener a subsidiary of Ollietopia Inc.

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    • #3
      I lost the will to live around 2pm Ollie but I hope this helps.

      What is NPK? – Understanding Fertiliser Labels | FluidsensorOnline.com
      sigpic“Gorillas are very intelligent, but they don't have to be as delicate as chimps -- they can just smash open the termite nest,”
      --------------------------------------------------------------------
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      • #4
        Thanks it did help a lot.
        So the NPK 18-11-26 is probably just a ratio and doesn't reflect the % mass of a sample of that manure, where as the 0.7-0.3-0.9 probably does.

        Cheers, hope the will to live comes back before an opportunity to end it all arrised
        Current Executive Board Members at Ollietopia Inc:
        Snadger - Director of Poetry
        RedThorn - Chief Interrobang Officer
        Pumpkin Becki - Head of Dremel Multi-Tool Sales & Marketing and Management Support
        Jeanied - Olliecentric Eulogy Minister
        piskieinboots - Ambassador of 2-word Media Reviews

        WikiGardener a subsidiary of Ollietopia Inc.

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        • #5
          you could always not buy it, and use comfrey, nettles and manure instead?

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          • #6
            Originally posted by taff View Post
            you could always not buy it, and use comfrey, nettles and manure instead?
            I'm a shoe-string gardener, I don't buy things I can pinch off my friend who keeps horses for free

            Besides, I'm collating the infromation to try and make a definitive list of Soil Conditioners, their uses and nutrient contents on the website.
            Current Executive Board Members at Ollietopia Inc:
            Snadger - Director of Poetry
            RedThorn - Chief Interrobang Officer
            Pumpkin Becki - Head of Dremel Multi-Tool Sales & Marketing and Management Support
            Jeanied - Olliecentric Eulogy Minister
            piskieinboots - Ambassador of 2-word Media Reviews

            WikiGardener a subsidiary of Ollietopia Inc.

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            • #7
              Originally posted by taff View Post
              you could always not buy it, and use comfrey, nettles and manure instead?
              I think it's a bit of research for the excellent site he's creating

              I've never truely understood it to be honest apart from where each bit is aiming for in the plant!


              Here's how I remember it if it's any help Ollie...

              http://www.growfruitandveg.co.uk/gra...p-k_14880.html
              "Nicos, Queen of Gooooogle" and... GYO's own Miss Marple

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              • #8
                Originally posted by Nicos View Post
                I think it's a bit of research for the excellent site he's creating

                I've never truely understood it to be honest apart from where each bit is aiming for in the plant!


                Here's how I remember it if it's any help Ollie...

                http://www.growfruitandveg.co.uk/gra...p-k_14880.html
                Thanks, I already had a read of that one

                tbh it looks like the NPK of manures varies wildly depending on how old the animal is, what sex it is, what it's reared for, what it's fed on, what's mixed with the manure (bedding) and how they run the tests on the ingredients. So I'm just going to have to go for ball-park figures, it's that or show a minimum and maximum for each which would end up looking something like: 0.7-18-0.3-11-.09-26 and would be as much use as a wet fart in a windy teacup...er...yea
                Current Executive Board Members at Ollietopia Inc:
                Snadger - Director of Poetry
                RedThorn - Chief Interrobang Officer
                Pumpkin Becki - Head of Dremel Multi-Tool Sales & Marketing and Management Support
                Jeanied - Olliecentric Eulogy Minister
                piskieinboots - Ambassador of 2-word Media Reviews

                WikiGardener a subsidiary of Ollietopia Inc.

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                • #9
                  Originally posted by OllieMartin View Post
                  tbh it looks like the NPK of manures varies wildly depending on how old the animal is, what sex it is, what it's reared for, what it's fed on, what's mixed with the manure
                  Yep!
                  I think of manure as more of a soil improver than a fertiliser (feed). For those without horses, or money, there is comfrey (or borage): more nutritious than farmyard manure
                  All gardeners know better than other gardeners." -- Chinese Proverb.

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                  • #10
                    Originally posted by OllieMartin View Post
                    Thanks it did help a lot.
                    So the NPK 18-11-26 is probably just a ratio and doesn't reflect the % mass of a sample of that manure, where as the 0.7-0.3-0.9 probably does.

                    Cheers, hope the will to live comes back before an opportunity to end it all arrised
                    It is a ratio..............Carlsberg don't make manure, but if they did.........
                    My Majesty made for him a garden anew in order
                    to present to him vegetables and all beautiful flowers.- Offerings of Thutmose III to Amon-Ra (1500 BCE)

                    Diversify & prosper


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                    • #11
                      Originally posted by Snadger View Post
                      It is a ratio..............Carlsberg don't make manure, but if they did.........
                      Except if it is ONLY a ratio then that creates the following problem:

                      Fertiliser 1 has an NPK of 1-1-1
                      Fertiliser 2 has an NPK of 5-4-4

                      You'd assume that Fertiliser 2 is better/stronger/has more nutrients in it, but:
                      If it's JUST a ratio, then who says the 5-4-4 doesn't make up 1% of the fertiliser and the rest is just water, and Fertiliser 1 is 33% N, 33% P, 33% K and 1% water making it actually stronger.

                      There surely has to be some indicator to suggest how much (by mass or volume) that N, P & K actually take up.

                      D'ya get meh?
                      Current Executive Board Members at Ollietopia Inc:
                      Snadger - Director of Poetry
                      RedThorn - Chief Interrobang Officer
                      Pumpkin Becki - Head of Dremel Multi-Tool Sales & Marketing and Management Support
                      Jeanied - Olliecentric Eulogy Minister
                      piskieinboots - Ambassador of 2-word Media Reviews

                      WikiGardener a subsidiary of Ollietopia Inc.

                      Comment


                      • #12
                        Originally posted by OllieMartin View Post
                        Except if it is ONLY a ratio then that creates the following problem:

                        Fertiliser 1 has an NPK of 1-1-1
                        Fertiliser 2 has an NPK of 5-4-4

                        You'd assume that Fertiliser 2 is better/stronger/has more nutrients in it, but:
                        If it's JUST a ratio, then who says the 5-4-4 doesn't make up 1% of the fertiliser and the rest is just water, and Fertiliser 1 is 33% N, 33% P, 33% K and 1% water making it actually stronger.

                        There surely has to be some indicator to suggest how much (by mass or volume) that N, P & K actually take up.

                        D'ya get meh?
                        Erm........I think so? I see where you're coming from but lets get this out of the way first. The 0.7-0.3-0.9 you quoted earlier will still be a ratio of 7-3-9 in my opinion.
                        As far as I know, most fertilisers have 'carriers' which are inert materials the nutrients are impregnated into. The ratio will be as stipulated but the weight of each element, in a granular or powder fertiliser should also be stipulated on the packaging. This means that if you do a soil analysis and the results indicate you nead 'X' ammount of a single nutrient applied over a season, you should be able to calculate dozage per application to give you the required ammount annually?
                        I aint no mathematician, but thats the way I see it anyway!
                        My Majesty made for him a garden anew in order
                        to present to him vegetables and all beautiful flowers.- Offerings of Thutmose III to Amon-Ra (1500 BCE)

                        Diversify & prosper


                        Comment


                        • #13
                          Originally posted by OllieMartin View Post
                          something like: 0.7-18-0.3-11-.09-26 and would be as much use as a wet fart in a windy teacup...er...yea
                          If all else fails, they look like good lottery numbers.............
                          sigpic“Gorillas are very intelligent, but they don't have to be as delicate as chimps -- they can just smash open the termite nest,”
                          --------------------------------------------------------------------
                          Official Member Of The Nutters Club - Rwanda Branch.
                          -------------------------------------------------------------------
                          Sent from my ZX Spectrum with no predictive text..........
                          -----------------------------------------------------------
                          KOYS - King Of Yellow Stickers..............

                          Comment


                          • #14
                            Originally posted by Snadger View Post
                            Erm........I think so? I see where you're coming from but lets get this out of the way first. The 0.7-0.3-0.9 you quoted earlier will still be a ratio of 7-3-9 in my opinion.
                            As far as I know, most fertilisers have 'carriers' which are inert materials the nutrients are impregnated into. The ratio will be as stipulated but the weight of each element, in a granular or powder fertiliser should also be stipulated on the packaging. This means that if you do a soil analysis and the results indicate you nead 'X' ammount of a single nutrient applied over a season, you should be able to calculate dozage per application to give you the required ammount annually?
                            I aint no mathematician, but thats the way I see it anyway!
                            Okay that does explain it for labelled fertilisers (thank you).
                            But how do we know how good a manure is, even if we have a vague idea of its NPK?
                            I agree, I thought 0.7-0.3-0.9 = 7-3-9!

                            I did find this comprehensive list:
                            Ohio Livestock Manure Management Guide, Bulletin 604-06
                            But it still seems they've done the maths wrong (although more likely I have)
                            E.g. They say a "lactating cow producing 90lb milk a day":
                            Produces 153lb faeces containing just over 1lb of Nitrogen.
                            They also say that is "5.4% N db" (whatever "db" is)
                            But I calculate that as 0.65% N

                            Still not totally happy
                            Current Executive Board Members at Ollietopia Inc:
                            Snadger - Director of Poetry
                            RedThorn - Chief Interrobang Officer
                            Pumpkin Becki - Head of Dremel Multi-Tool Sales & Marketing and Management Support
                            Jeanied - Olliecentric Eulogy Minister
                            piskieinboots - Ambassador of 2-word Media Reviews

                            WikiGardener a subsidiary of Ollietopia Inc.

                            Comment


                            • #15
                              How about this then?

                              If a 100-pound bag of fertilizer has an N-P-K ratio of 5-7-4, it contains 5 pounds of nitrate, 7 pounds of phosphate (which contains phosphorous), 4 pounds of potash (which contains potassium) and 84 pounds of filler.

                              As far as I know, cow manure, which is mainly used as a soil improver rather than a fertiliser is roughly 1-1-1 so a 100-pound bag would add 97 pounds of bulk and 3 pounds of fertiliser.

                              So methinks the ratio AND percentages ARE linked.

                              I must admit, being the saddo that I am, I find this quite interesting!
                              Last edited by Snadger; 15-05-2010, 09:46 PM.
                              My Majesty made for him a garden anew in order
                              to present to him vegetables and all beautiful flowers.- Offerings of Thutmose III to Amon-Ra (1500 BCE)

                              Diversify & prosper


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