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Sometimes a fertilizer ratio is specified on soil test reports or in fertilizer recommendation sheets. The fertilizer ratio indicates the proportion of nitrogen, phosphate, and potash in the fertilizer product, and is determined by dividing each of the three numbers in the fertilizer grade (listed on the container) by the lowest number in the grade. For example, when each number in a fertilizer grade of 18-6-6 is divided by 6 (the lowest number in the grade), the proportion is determined as: three parts nitrogen to one part phosphate, to one part potash. Thus, the fertilizer has a 3-1-1 ratio.
If your soil test report recommends applying 1.5 lb of nitrogen, 0.5 lb of phosphate, and 0.5 lb of potash per sq ft, you should apply a fertilizer with a ratio of 3-1-1 since you need three times as much nitrogen as phosphate and three times as much nitrogen as potash. The simplest method of determining a ratio is to divide the weights of nitrogen, phosphate, and potash listed on the soil test report by the lowest weight of the three.
To determine a fertilizer ratio for a soil test recommendation of 1.5 lb of nitrogen, 0.5 lb of phosphate, and 0.5 lb of potash, divide the weight of each of the three nutrients (1.5 lb, 0.5 lb, 0.5 lb) listed on the report by the lowest nutrient weight (0.5 lb in this case).
1.5 ÷ 0.5 = 3
0.5 ÷ 0.5 = 1
0.5 ÷ 0.5 = 1
Thus, the fertilizer ratio that best fits this recommendation is 3-1-1. As demonstrated in the first paragraph, you can match the fertilizer ratio for this recommendation with a fertilizer grade by dividing each number in the fertilizer grade by the lowest number in the grade.
As you can see from these three examples, fertilizer grades for certain products do not always match the exact fertilizer ratio you are searching for. Thus, the goal is to find a product with a grade that is as close as possible to the specified ratio.
Growers sometimes ask me how come that potassium nitrate 13-0-46 = 59% and not 100%.
Let's start with a basic explanation about the NPK nutrients and their percentages (%) in fertilizer formulae.
Fertilizer's formula usually refers to the content of nutrients in their oxide forms (N-P2O5-K2O).
In Scandinavia, Australia and South Africa it is more common to refer to elemental forms (N-P-K).
For example:
The nutritional composition of Multi-K' Classic is 13-0-46.
This means that the fertilizer contains
13% nitrogen (N)
0 % phosphorus oxide (P2O5) = 0% phosphorus (P)
46% potassium oxide (K2O) = 38.3% potassium (K)
So how do we sum to 100%?
Here we have to consider the actual form of the nutrients in the fertilizer:
In mineral fertilizers, nitrogen may be present as ammonium, nitrate or amide (urea), phosphorus is present mainly as phosphate, and potassium is present as K+ ion.
The following table shows the ratios between elements, oxides, and the forms mentioned above.
Ammonium
NH4 =
N x 1.28
Nitrate
NO3 =
N x 4.43
For more wholesale npk 15-5-20 fertilizerinformation, please contact us. We will provide professional answers.
Amide
(NH2)2CO=
N x 2.14
Phosphate
H2PO4=
P x 2.68
P2O5 x1.15
Potassium
K =
K x1
K2O x 0.83
Use the
conversion calculator
to calculate nutrient quantities in their oxide and elemental forms.
Now, 13% N as NO3 means that the product contains 13x4.43= 57.6% NO3
and 46% K2O are 46/1.2= 38.3% K.
These sum up to 57.6+38.3=95.9%
Not 100% yet'.
The difference is attributed to
Actual analysis which is somewhat higher than 13-0-46
Presence of moisture and trace impurities in the product
Note that Multi-K' GG, Multi-K' pHast and Multi-K' Reci contain higher rates of nutrients, and less impurities.
Contact us to discuss your requirements of urea ammonium sulphate. Our experienced sales team can help you identify the options that best suit your needs.