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Fertilzer Concentrations
ommthree
Posts: 314
Hi all,
I'm very confused about comparing fertilisers. The N-P-K values given are, I believe actual percentages by weight.
But for example, I have a bottle of fertiliser that claims to be 6-12-10 and then recommends a dilution of 1 to 500 leading to about 0.01% nitrogen. Conversely, human urine, I have seen quoted at 10-1-4, with a dilution of 1 to 15 recommended, which would yield 0.7% nitrogen. These numbers don't seem at all comparable.
What am I doing wrong here?
Thank you!
0
Posts
perhaps the figures relate to the fertiliser after the water is added
You aren't doing anything wrong. Given that they are very different dilutions why do you expect the numbers to be comparable?
The NPK values are the ratios to each other and nothing more. It should really be written N:P:K but this forum will mess-up certain combinations of colons and numbers and display emoticons instead, so I'll use the dash below!
For example, a 10-6-4 will have 10 parts Nitrates, 6 parts Phosphates and 4 parts Potash.
So, for solid fertilizers, 100 grams of a 10-6-4 would have 50g Nitrates, 30g Phosphates and 20g Potash.
If supplied as a liquid, 1 litre of a 12-8-10 woulld have 400ml N, 267ml P and 333ml K.
Not sure if that helps, but there you go.
Thanks all. I got it figured out. Like you say, the key point was that it's ratios. You then need to think about how much of the total material is actually part of that active portion.
It's all making sense now.
Don't know if anything in this thread may help: http://www.gardenersworld.com/forum/talkback/the-mystery-of-npk/270092.html
The simple looking N:P:K label is in fact quite complex. This link explains it in some detail http://en.wikipedia.org/wiki/Labeling_of_fertilizer but you need to know a bit of chemistry to fully understand the implications. For example potash is largely potassium chloride (as used in LoSalt for a low sodium diet) but the K number refers to the equivalent oxide K2O. That is why UK labelling carries more information including the actual elemental composition.
The RHS gives some simpler advice on labelling here https://www.rhs.org.uk/advice/profile?PID=451 . It is interesting that the so-called "balanced" fertiliser Growmore (NPK of 7:7:7) is in fact a high nitrogen fertiliser.
Basically NPK is: N=nitrogen P=phosphorous and K=potash, the three main food elements necessary for plant life. Nitrogen is required for foliage growth, phosphorous for root growth and potash for growth of flowers and fruit.
I have copied and pasted this from an old thread that DavidK did for us.
These elements can be applied in chemical or organic form…..the latter being preferred by most gardeners and the former mainly used by commercial growers.
Although there are several types in there chemical form, the most common available to us gardeners being, Sulphate of Ammonia = N (nitrogen) Superphosphates = P (phosphorus) and Sulphate of Potash = K (potash)
For an example, blood, fish & bonemeal (a favorite amongst gardeners) offers these properties.
Dried blood is a slaughter house by-product and is an excellent source of quickly available organic nitrogen, when used as a top dressing or watered in. Dried blood completely soluble and can be mixed with water and used as a liquid fertilizer.
Fish meal is a great natural fertilizer, high in phosphorous and high in organic nitrogen. Fish meal is quick acting, offering a sustained supply of nutrients.
Bone meal is used as a long-lasting source of phosphorous as well as low levels of nitrogen, potassium and calcium. The extremely slow availability of nutrients from bone meal makes it a very safe fertilizer, especially when planting of potting very young or new plants.
Sorry David I was too slow at the starting gate
Messed it up right I've even posted on the old thread..I'll get my coat