Trying to understand NPK ratings (esp. manure)

**OllieMartin** · 14-05-2010, 02:05 PM

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

**Bigmallly** · 14-05-2010, 03:28 PM

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

What is NPK? – Understanding Fertiliser Labels | FluidsensorOnline.com

**OllieMartin** · 14-05-2010, 03:42 PM

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

**taff** · 14-05-2010, 04:28 PM

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

**OllieMartin** · 14-05-2010, 04:32 PM

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.

**Nicos** · 14-05-2010, 04:42 PM

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

**OllieMartin** · 14-05-2010, 05:02 PM

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

**Two_Sheds** · 14-05-2010, 07:36 PM

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

**Snadger** · 14-05-2010, 08:58 PM

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.........

**OllieMartin** · 14-05-2010, 09:21 PM

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?

**Snadger** · 15-05-2010, 07:47 AM

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!

**Bigmallly** · 15-05-2010, 09:18 AM

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.............

**OllieMartin** · 15-05-2010, 09:34 AM

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

**Snadger** · 15-05-2010, 10:38 PM

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!

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