Labeling of fertilizer
Encyclopedia
The labeling of fertilizers varies by country in terms of analysis methodology and subsequently nutrient labeling, and minimum nutrient requirements.
For example, the fertilizer potash
is a naturally occurring mineral composed of nearly pure potassium chloride
(KCl). As such, its composition is 1:1 potassium to chloride or 52% potassium and 48% chlorine by weight (owing to differences in molecular weight between the elements). Traditional analysis of 100g. of KCl would yield 60g. K2O. The percentage yield of K2O from the original 100g. of fertilizer is the number shown on the label. A potash fertilizer would thus be labeled 0-0-60, not 0-0-52.
Many articles on the internet will have the wrong succession. It should always be nitrogen, phosphorus and potassium. Lawn specialists and farmers plan their entire growing season with the analysis in that order. If, for some odd reason, it was not in that order, crops and lawns could be ruined. Always look for NPK.
Fertilizer is described in this way dating back to Liebig in the 19th century due to the methods he used then to compare and evaluate fertilizers
Nitrogen values represent actual nitrogen content so these numbers do not need to be converted.
Using these conversion factors we determine that 18−51−20 fertilizer contains (by weight):
In the UK, fertilizer labeling regulations allow for reporting elemental mass fractions of phosphorus and potassium. The regulations stipulate this should be done in parentheses after standard NPK values.
Macronutrient fertilizers
Macronutrient fertilizers are labeled with an NPK analysis and also "N-P-K-S" in Australia. However, these numbers do not directly represent the source composition or absolute nutrient content of the fertilizer--macronutrient fertilizers are not labeled by content but according to traditional analysis.For example, the fertilizer potash
Potash
Potash is the common name for various mined and manufactured salts that contain potassium in water-soluble form. In some rare cases, potash can be formed with traces of organic materials such as plant remains, and this was the major historical source for it before the industrial era...
is a naturally occurring mineral composed of nearly pure potassium chloride
Potassium chloride
The chemical compound potassium chloride is a metal halide salt composed of potassium and chlorine. In its pure state, it is odorless and has a white or colorless vitreous crystal appearance, with a crystal structure that cleaves easily in three directions. Potassium chloride crystals are...
(KCl). As such, its composition is 1:1 potassium to chloride or 52% potassium and 48% chlorine by weight (owing to differences in molecular weight between the elements). Traditional analysis of 100g. of KCl would yield 60g. K2O. The percentage yield of K2O from the original 100g. of fertilizer is the number shown on the label. A potash fertilizer would thus be labeled 0-0-60, not 0-0-52.
Many articles on the internet will have the wrong succession. It should always be nitrogen, phosphorus and potassium. Lawn specialists and farmers plan their entire growing season with the analysis in that order. If, for some odd reason, it was not in that order, crops and lawns could be ruined. Always look for NPK.
Fertilizer is described in this way dating back to Liebig in the 19th century due to the methods he used then to compare and evaluate fertilizers
Converting nutrient analysis to composition
P2O5 consists of 57.4% oxygen and 43.6% elemental phosphorus. The percentage ([mass fraction]) of elemental phosphorus is 43.6% so P= 0.43 x P2O5. K2O consists of 17% oxygen and 83% elemental potassium. The percentage (mass fraction) of elemental potassium is 83% so K = 0.83 x K2O.Nitrogen values represent actual nitrogen content so these numbers do not need to be converted.
Using these conversion factors we determine that 18−51−20 fertilizer contains (by weight):
- 18% elemental (N)
- 22% elemental (P)
- 16% elemental (K)
In the UK, fertilizer labeling regulations allow for reporting elemental mass fractions of phosphorus and potassium. The regulations stipulate this should be done in parentheses after standard NPK values.
Other fertilizer designations
Fertilizer containing only the three primary macronutrients can be referred to as artificial or straight. Compound fertilizers are N-P-K fertilizers with other elements purposely intermixed. For example, a mainly nitrogenous fertilizer mix would be described as a nitrogen fertilizer.See also
- FertilizerFertilizerFertilizer is any organic or inorganic material of natural or synthetic origin that is added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use...
- NPK values for commercial fertilizers