Mixing Fertilizers “From Scratch” – Different Materials Available

Q.   I am unable to get the exact fertilisers in order to blend the standard weekly feed fertiliser.  Instead of ammonium nitrate I have calcium ammonium nitrate{27-o-o), instead of manganese sulphate  I have manganese chloride instead of sodium molybdate I have ammonium molybdate, and instead of potassium chloride I have potassium nitrate (13-0-46).  The other salts I have are diammonium phospate, Magnesium sulphate boric acid, zinc sulphate, copper sulphate iron sulphate VII.  I have limestone  and another blend of limestone  called CalMag.{20% Ca  and 12%Mg}.  Please show  me how to blend these to get maximum results for  my  crops.
 
A.  People sometimes can’t find exactly the same blends of nitrogen, phosphorus, and potassium as we state in the books.  For most smaller family gardens it’s just much easier to buy something like 16-16-16 (or 13-13-13, 20-20-20, etc.) and get the Micro-Nutrient packets from the Foundation website (Store, Fertilizers).  This works fine when you only will be using 50-100# in a year.
 
However, for those who grow a big garden it may be very worthwhile to buy the separate compounds, as well as the ‘”trace” or micro-nutrient separately, and mix them yourselves.  If you’re doing this, just email us and we’ll help you with the combinations and amounts to use, in order to end up with a balanced fertilizer formula.  The process is as follows:
 
What you want to achieve to begin with is an NPK ratio of 110, 60, 110.  This is the amount of actual nitrogen, phosphate, and potash needed to feed an acre of field crops.  To do this you will list the compounds you have available – as I have done below – then you figure how many pounds of each you must buy to end up with the 110,60,110.  Since the phosphate and potash are only in one item, you will figure how much you need of each of them first.
 
Using 130.5# of diamonium phosphate gives you the 60# of phosphate you need (60 divided by .46), and it also “throws in” 23.5# of nitrogen.  Using 239# of potassium nitrate gives you the 110# of potash you need (110 divided by .46), and it provides a bonus of 31# of nitrogen.  So, you only need an additional 55.5# of nitrogen, and this is achieved by using 205.5# of the calcium ammonium nitrate (55.5 divided by .27).  Does everyone see how this is done?  Now you can all be experts and mix your own fertilizers, if you ever have the need.  I recommend you save this post, or print it and put it in one of your gardening books, for later reference when needed.
 
Of course if you want a smaller batch, you will reduce all three items, while keeping the same ratios.
 
Compound Ratios    Amt to Use        N Provided        P Provided        K Provided

 

27-0-0                        205.5                  55.5                        0                        0

 

18-46-0                      130.5                   23.5                      60                        0

 

13-0-46                      239.0                   31.0                        0                    110

 

                                  575                   110                         60                    110

 

Next you add the following:

 

Mag sulfate                100.00
 
Borax                            6.25
 
Manganese                    3.75
 
Zinc                               7.50
 
Iron-chelated                   1.25
 
Copper                           1.25
 
Molybdenum                     .63
 
Pre-mix the micro’s with 30# of one of the NPK compounds, so they will mix much quicker into the big batch.  Mix the Mag. Sulfate in as the last ingredient.  Only make enough fertilizer for 2-3 weeks’ use.  Otherwise the mix may get wet, due to the presence of water in several of the compounds (Mag Sulfate has 7 parts water!).
 
If you really need to mix a large batch to last longer, email or call me and we will teach you how to do it without getting it wet.
 
Regarding the best source of calcium to use for your Pre-Plant mix, if you receive more than 20″ of annual rainfall you will use agricultural lime or Dolomite lime (also called CalMag).  The Dolomite lime gives you extra magnesium, and if the price is comparable, this is the best.  If you receive less than 20″ of annual rainfall, you should use gypsum for your calcium source.