What is in a Fertilizer?
Analysis or Grade
By law, all products sold as fertilizer require uniform labeling guaranteeing the minimum percentage of nutrients. The three-number combination (fertilizer
grade or
analysis) on the product identifies percentages of nitrogen (N), phosphate (P2O5), and potash (K2O), respectively. For example, a 20-10-5 fertilizer contains 20% nitrogen, 10% phosphate, and 5% potash.
Note:
Phosphorus, P, is a primary nutrient in plant growth. The word
phosphate, P2O5, refers to the ionic compound containing two atoms of phosphorus with five atoms of oxygen. The
phosphorus content of fertilizers is measured in percent
phosphate.
Note:
Potassium, K, is a primary nutrient in plant growth. The word
potash, K2O, refers to the ionic compound containing two atoms of potassium with one atom of oxygen. The
potassiumcontent of fertilizers is measured in percent
potash.
The product may also identify other nutrients, such as sulfur, iron, and zinc, if the manufacturer wants to guarantee the amount. This may be done by placing a fourth number on the product label and identifying what nutrient was added in the ingredients.
http://www.ext.colostate.edu/mg/gardennotes/232.html#analysis
Formulation
The
formulation tells what specific kinds of fertilizer are in the product. Table 1 gives examples of manufactured fertilizers that could be mixed to derive any specific analysis, ratio, or brand name.
Table 1.
Examples of Manufactured Fertilizers
Product
Nitrogen %
Phosphate %
Potash %
Ammonium nitrate
34
0
0
Ammonium sulfate
21
0
0
Urea
48
0
0
Ammoniated super-phosphate
3-6
48-53
0
Di-ammonium phosphate
11
48
0
Mono-ammonium phosphate
11
48
0
Super-phosphate
0
18-50
0
Triple super phosphate
0
46
0
Potassium chloride
0
0
60
Potassium nitrate
13
0
44
Potassium sulfate
0
0
50
Potassium-magnesium sulfate
0
0
22
What else is in the fertilizer? In a manufactured fertilizer, the grade does not add up to 100% because the fertilizer also contains other elements like carbon, hydrogen, oxygen, sulfur, iron, zinc, etc. For example, ammonium nitrate (NH4+ NO3-) has a grade of 34-0-0 with 34% of the content from nitrogen and 66% from hydrogen and oxygen. Ammonium sulfate (NH4+ SO2- has a grade of 21-0-0 with 21% from the nitrogen and 79% from the hydrogen, sulfur and oxygen.
Time release or
slow release fertilizers contain coating materials or are otherwise formulated to release the nutrients over a period of time as water, heat, and/or microorganisms break down the material. [Table 2]
Table 2.
Examples of Quickly and Slowly Available Nitrogen
Quickly available nitrogenLasts 4-6 weeks
Ammonium sulfate
Ammonium nitrate
Calcium nitrate
Potassium nitrate
Urea
Slowly available nitrogenAvailable over weeks to months
Regulated by solubility or microorganism activity
Resin-coated urea
Sulfur-coated urea
Isobutylidene diurea (IBDU)
Methylene urea
Urea formaldehyde
Manure
Poultry wastes
Blood meal
In an “organic” type fertilizer, the base is decomposed or processed plant and/or animal by-products. For example, fish emulsion is ground and processed non-edible fish or fish scraps. Its nutrient content would be around 8-4-2, with 8% from nitrogen, 4% from phosphate, and 2% from potash.
Some manufactured and “organic” fertilizers contain fillers, which are used to prevent caking, control dust, derive the desired grade, or to facilitate ease of application.
Complete fertilizer is a term used to identify fertilizers that contains nitrogen, phosphorus,and potassium. In the national home garden trade, most fertilizers are complete. However, in Colorado the majority of gardens do not need phosphorus or potassium. It is advisable to avoid heavy applications of phosphate and potash when unneeded as they contribute to soil salts.
