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Duncan
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 Posted: Sat Jun 28, 2008 10:50 pm Post subject: Confused by NPK labelling |
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This is probably a dumb question but bear with me...
Mostly people tell me that NPK labelling on fertilizer refers to the
percentage concentration of the nutrients. So, simplistically, if I
buy a metric ton of 5-10-10 I get 50kg of Nitrogen, 100kg of
Phosphorous and 100kg of Potash. (I know it won>t be in elemental
form but you get the idea).
Presumably therefore if I buy 1/2 a ton of 10-20-20 I get the same
quantities of nutrient with a smaller percentage of filler. So why
not use this instead and just spread twice as thin?
One person has told me that it doesn>t work like that because the
labelling is not the real proportions. It>s an artificial scale which
takes account of the effect of the nutrients (ie including speed of
release) rather than the absolute quantity. Is this true?
Duncan |
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Dean Hoffman
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| Posted: Sun Jun 29, 2008 4:30 am Post subject: Re: Confused by NPK labelling |
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Duncan wrote:
[quote]This is probably a dumb question but bear with me...
Mostly people tell me that NPK labelling on fertilizer refers to the
percentage concentration of the nutrients. So, simplistically, if I
buy a metric ton of 5-10-10 I get 50kg of Nitrogen, 100kg of
Phosphorous and 100kg of Potash. (I know it won>t be in elemental
form but you get the idea).
Presumably therefore if I buy 1/2 a ton of 10-20-20 I get the same
quantities of nutrient with a smaller percentage of filler. So why
not use this instead and just spread twice as thin?
One person has told me that it doesn>t work like that because the
labelling is not the real proportions. It>s an artificial scale which
takes account of the effect of the nutrients (ie including speed of
release) rather than the absolute quantity. Is this true?
Duncan
[/quote]
It>s the percentage by weight.
http://tinyurl.com/58wmeb
I don>t get your source>s logic. The percentage of a given
nutrient will be constant no matter the speed of release.
Dean
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Duncan
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| Posted: Sun Jun 29, 2008 9:28 pm Post subject: Re: Confused by NPK labelling |
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On Jun 29, 1:36 am, Dean Hoffman <""dh0496\"@ine$br#as&ka.com"> wrote:
[quote] It>s the percentage by weight.
http://tinyurl.com/58wmeb
I don>t get your source>s logic. The percentage of a given
nutrient will be constant no matter the speed of release.
Dean
Thanks, the cited article supports my original contention. Namely[/quote]
that it does make sense to buy a fertilizer with a higher nutrient
content and spread it thinly, rather than using (say) 5-10-10. Not
only is it likely to be cheaper per pound of nutrient but the
transport costs will be lower and it involves less handling (ie a
spreader load will last longer). Why would anyone buy a mix with a
high filler content? It just seems like poor value for money.
Duncan |
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Dean Hoffman
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| Posted: Mon Jun 30, 2008 3:10 am Post subject: Re: Confused by NPK labelling |
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Duncan wrote:
[quote]On Jun 29, 1:36 am, Dean Hoffman <""dh0496\"@ine$br#as&ka.com"> wrote:
It>s the percentage by weight.
http://tinyurl.com/58wmeb
I don>t get your source>s logic. The percentage of a given
nutrient will be constant no matter the speed of release.
Dean
Thanks, the cited article supports my original contention. Namely
that it does make sense to buy a fertilizer with a higher nutrient
content and spread it thinly, rather than using (say) 5-10-10. Not
only is it likely to be cheaper per pound of nutrient but the
transport costs will be lower and it involves less handling (ie a
spreader load will last longer). Why would anyone buy a mix with a
high filler content? It just seems like poor value for money.
Duncan
[/quote]
I grew up on a farm but never really gave it a thought. I don>t
remember if the local coops gave one a choice.
One reason might be sprayer/applicator adjustment and calibration.
There would be more margin for error with a lower concentration of
active ingredients. The old applicators weren>t all that precise.
Now, computers monitor the applicator speed and other things to
regulate the flow on the go for NH3 and liquid fertilizers. I suspect
there might be something similar for dry fertilizer but don>t know that
for fact.
Dean
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Phred
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| Posted: Mon Jun 30, 2008 3:21 pm Post subject: Re: Confused by NPK labelling |
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In article <de0c0c5a-5766-48d4-84ec-08bf33a6883d@c58g2000hsc.googlegroups.com>, Duncan <noreply@hard-wired.co.uk> wrote:
[quote]On Jun 29, 1:36am, Dean Hoffman <""dh0496\"@ine$br#as&ka.com"> wrote:
It>s the percentage by weight.
http://tinyurl.com/58wmeb
I don>t get your source>s logic. The percentage of a given
nutrient will be constant no matter the speed of release.
Thanks, the cited article supports my original contention. Namely
that it does make sense to buy a fertilizer with a higher nutrient
content and spread it thinly, rather than using (say) 5-10-10. Not
only is it likely to be cheaper per pound of nutrient but the
transport costs will be lower and it involves less handling (ie a
spreader load will last longer). Why would anyone buy a mix with a
high filler content? It just seems like poor value for money.
[/quote]
G>day mates,
It>s not necessarily a *filler* that causes the lower nutrient content
as a percentage. It>s more likely to be the actual chemical
composition of the nutrients in the fertiliser.
Remember those ratios such as 5-10-10 are based on elemental figures
(N, P, K) or, perhaps, as oxides (e.g. P2O5). [I admit I>m not too
sure just how these values are specified in modern fertilisers,
though the label should tell you which approach has been used!]
Now, there are various chemical compounds used to supply the actual
nutrients required, and these will have differing physical properties
such as solubility (especially P compounds) and volatility (N).
Given these facts, it may well make sense to use a lower analysis
fertiliser if that means it is less soluble, for example, so less
likely to be leached right out of the system by a shower of rain.
(As an extreme example, rock phosphate is sometimes used and that
really only breaks down to release P at very low rates -- rather like
soil forming processes per se. :-)
There>s also another issue to consider and that>s the fact that high
analysis fertilisers tend to be more "caustic" and can cause damage to
seedlings, or other tender plants, even though applied at a lower rate
per acre.
After those types of issues have been considered, the "best buy" would
be a product that applies the nutrients you need at the lowest cost
per kilogram of nutrient *applied* in the field.
Cheers, Phred.
--
ppnerkDELETE@THISyahoo.com.INVALID |
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