Gman1983
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Posts: 1
Joined: Sun Jul 10, 2022 4:02 am

How to compound a specific NPK fertiliser

Hi Everyone! I was wondering if someone could help me work out a fertiliser with
an NPK of 3-1-1?
The macro nutrients I'm using are:

Magnesium sulfate,
Potassium nitrate,
Ammonium phosphate monobasic
and ammonium nitrate.

Your help would mean a lot! ❤️

Thank you so much!!!

G

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applestar
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Posts: 30541
Joined: Thu May 01, 2008 7:21 pm
Location: Zone 6, NJ (3/M)4/E ~ 10/M(11/B)

I’m not good at this kind of math, but I believe the basic principle is to take the NPK ratio of each of your ingredients and adjust the amounts until you achieve some kind of a multiple of the ratio you want such as 3-1-1 … 12-4-4 …36-12-12 etc then reduce the total combined volume used to be appropriate for your application.

It will be kind of like adding fractions using “least common multiple”

imafan26
Mod
Posts: 13987
Joined: Tue Jan 01, 2013 8:32 am
Location: Hawaii, zone 12a 587 ft elev.

You will need to figure out the NPK of each component. Know their solubility limits. Things like epsom salt are missing NPK since the main ingredients are magnesium and sulfur. These are important micronutrients. They are only needed in small quanities and can be toxic in excess.

If you are mixing a custom mix for a particular plant, say lettuce, then look up the requirements of nutrients for lettuce and you will need to calculate the nutrients for each element including the micros in ppm.

This is a bit of math by hand but this online calculator can help with the big stuff like NPK. Blending fertilizer precisely also requires an accurate scale. It is a lot like baking. Too much or too little and the balance will be off and the results are not going to be good. It is different from cooking where a little bit of this or that can be estimated (within reasonable limits) to taste without causing a chemical imbalance.
In addition an ec meter to monitor pH, and a water analysis for your area. You will have to make adjustments to account for the solutes in your water source.

https://cropaia.com/blog/how-to-calcula ... n-formula/
https://precisionag.sites.clemson.edu/C ... fertBlend/

For specific hydroponic mixes you can use hydrobuddy which is an open source calculator specifically for hydroponic applications.

https://scienceinhydroponics.com/2016/0 ... ram-o.html

Lettuce blend works for most leafy crops.
It uses 3 basic components Master blend NPK (4-18-38)
Calcium Nitrate (15.5-0-0)
Epsom salt

The MASTERBLEND recipe is 12 grams nutrient mix, 12 grams calcium nitrate, and 6 grams of Epsom salt per 5 gallons of nutrient solution/water.

https://whyfarmit.com/hydroponic-lettuce-nutrients/



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