Fertilizer chemical ratio query and application rates

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Fertilizer chemical ratio query and application rates
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gray_b

Joined: 24 Jun 2011
Posts: 251
Location: Leafy Shires of the Midlands

Posted: Sat Mar 15, 14 8:45 am Post subject: Fertilizer chemical ratio query and application rates

It has always preyed on my mind about the chemical ratio of fertilizers and application rates.

I am sure many people have the same thoughts, or am I on my own.

Lets say you have Grow More 7+7+7, and if you can get fertilizer xyz at 14+14+14

Does that mean you only need apply fertilizer xyz at half the rate as Growmore.

That is, if both fertilizers are the same price, would it be more prudent to buy fertilzer xyz

Also when the packet says this is suitable for 100msq (100m to the power of 2). Is this 100m x 100m or 10m x 10m

oldish chris

Joined: 14 Jun 2006
Posts: 4148
Location: Comfortably Wet Southport

Posted: Sat Mar 15, 14 9:23 am Post subject:
the numbers refer to percentages, the small print on the back should give more details, including chemical formulae (e.g. is N provided by NH3 or NO3?) The area is likely to be square metres (surely?), 100sqM = 10x10, this way you get a big number, 100 squared is 10,000 an even bigger number.

Nick

Joined: 02 Nov 2004
Posts: 34535
Location: Hereford

Posted: Sat Mar 15, 14 9:31 am Post subject:
So, presumably, you could spread at half the rate?

gregotyn

Joined: 24 Jun 2010
Posts: 2201
Location: Llanfyllin area

Posted: Sat Mar 15, 14 9:41 am Post subject:

That sums it up perfectly, Nick.
I would, however, buy an in depth book about fertilizers or at least head to the local library where you could copy down the needs of individual crops. This way you don't waste money putting in more fertiliser than any crop needs, for example cabbages need lots of nitrogen as that helps leaf production which is the bit you want to eat. If you want to take it further then you can get a soil analysis, but for me that's a step beyond where want I go. All you need to do over the fertilizer needs of the crop is to know what type of soil you have and add a bit on or take a bit; off sandy soils need more as much fertiliser can be leached, depending on how much organic matter you have to increase the chemical activity by the current bugs in the soil. Basically sandy soils are inert and clay soils are chemically active both benefit from organic matter. there will be folks on here who can expand if you need to know more.

gray_b

Joined: 24 Jun 2011
Posts: 251
Location: Leafy Shires of the Midlands

Posted: Sat Mar 15, 14 10:42 am Post subject:

Something I did not know, and the info is taken from RHS website.

Growmore has a ratio of 7:7:7 for these materials, but is actually 7 percent nitrogen, 3.1 percent phosphorus and 5.8 percent potassium, or 7:3.1:5.8. Therefore it is a high-nitrogen feed, rather than the ‘balanced’ fertiliser commonly assumed

So you are not really buying what you think you are.

I think on application rates, 10m x 10m is more likely. Is 100m sq - (100m to the power of 2) the same as 100sq m

Any suggestions on the best place (mail order) to get a full soil analysis.

Rob R

Joined: 28 Oct 2004
Posts: 31902
Location: York

Posted: Sat Mar 15, 14 12:56 pm Post subject:

gray_b wrote:

Any suggestions on the best place (mail order) to get a full soil analysis.

SAC do all my analytics, they're efficient and reasonable.

oldish chris

Joined: 14 Jun 2006
Posts: 4148
Location: Comfortably Wet Southport

Posted: Sat Mar 15, 14 6:12 pm Post subject:

gray_b wrote:

I think on application rates, 10m x 10m is more likely. Is 100m sq - (100m to the power of 2) the same as 100sq m.

There's a hundred metres squared (100x100) and a hundred square metres (10x10)

BTW, what size area are you cultivating?

A good basic course in horticulture is the RHS General Certificate.

Mr O

Joined: 13 Feb 2005
Posts: 5512
Location: Nova Scotia, Canada

Posted: Sun Mar 16, 14 12:37 am Post subject:
Don't use any of them artificials, it will kill the bacteria and fungus in your soil that are responsible for breaking down organic matter into usable nutrients for your plants. Just add orgranic matter, high in N if possible, Horse, pig, cow manure are all good for this. Lots cheaper too.

gregotyn

Joined: 24 Jun 2010
Posts: 2201
Location: Llanfyllin area

Posted: Mon Mar 17, 14 2:40 pm Post subject:
I tend to be with you, Mr O. organic is better, not always for yield, but nearly always for taste, and helps the soil to keep fit! With regard to the % calculations, you have opened my eyes gray_b, how can they say 7.7.7. for the N,P K, if it isn't? Think I need to find out for myself- its so long since I did this at college-more than 40 years now.

Ty Gwyn

Joined: 22 Sep 2010
Posts: 4563
Location: Lampeter

Posted: Mon Mar 17, 14 2:50 pm Post subject:
I would`nt be surprised the calculation of the 7.7.7 is made up of soluble and unsoluble,with a total of 7.

oldish chris

Joined: 14 Jun 2006
Posts: 4148
Location: Comfortably Wet Southport

Posted: Mon Mar 17, 14 6:04 pm Post subject:

Ty Gwyn wrote:

I would`nt be surprised the calculation of the 7.7.7 is made up of soluble and unsoluble,with a total of 7.

All soluble. However, to the lay person, the label 7:7:7 can be misleading. The first seven refers to the percentage of the product that is Nitrogen. Can't find out what the actual chemical is, most likely ammonium sulphate, but it could be sodium nitrate (Chile saltpetre) or urea. The second digit is phosphorous, probably calcium hydrogen phosphate ("super phosphate") however, it is calculated as if it were phosphorus pentoxide, so that 7% of the product is P2O5. The third number is potassium, calculated as percent potassium oxide (which is definitely isn't - probably potassium sulphate).

The problem with being soluble is that one good deluge (unlikely in the UK) and it is all washed away. This is why some of us prefer the organic alternatives, such as Fish, Blood and Bone.

Ty Gwyn

Joined: 22 Sep 2010
Posts: 4563
Location: Lampeter

Posted: Mon Mar 17, 14 8:28 pm Post subject:
The Potassium is most likely Potassium Chloride which is mined in greater quantities than Potassium Sulphate,which is a weaker grade of Potassium.

oldish chris

Joined: 14 Jun 2006
Posts: 4148
Location: Comfortably Wet Southport

Posted: Mon Mar 17, 14 9:24 pm Post subject:

Ty Gwyn wrote:

The Potassium is most likely Potassium Chloride which is mined in greater quantities than Potassium Sulphate,which is a weaker grade of Potassium.

Yes, thank-you. We amateurs usually buy it as sulphate of Potash (£3/kilo from Wilko's).

BTW - you wouldn't happen to know which form of nitrogen is used in Growmore would you? (Just curious, I have my own supply of Urea

)

Ty Gwyn

Joined: 22 Sep 2010
Posts: 4563
Location: Lampeter

Posted: Mon Mar 17, 14 10:21 pm Post subject:

No idea what they use in Growmore,the NPK could be made up of several sources.

Regarding the Calcium Phosphate,which is insoluble and in-fact is Ground Rock Phosphate,

Super Phosphate is produced by treating Rock Phosphate with Sulphuric Acid,which is then soluble.

Nitrate of Potash is Saltpetre.

Mistake above by myself,
Sulphate of Potash-Magnesium is the weaker variety of Potash,
Potassium Sulphate is made by treating Potassium Chloride with Sulphuric Acid or by a crystallisation process which reduces the salt content of the Chloride.

Mistress Rose

Joined: 21 Jul 2011
Posts: 15600

Posted: Tue Mar 18, 14 7:53 am Post subject:

Generally nitrates or ammonium salts are very soluble, so as you say, they will go straight into the ground. Potassium salts are generally quite soluble, so potassium sulphate the best for long term as it is going to be among the least soluble. Phosphates are not that soluble so will stay in the ground longest.

If you have a wood fire, keep the ash dry, then use it as top dressing for tomatoes of other things that like potash. The name potash shows how it was originally made; ash.

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