When handling and evaluating analyses of tap water, fertilizers and nutrient solutions, misunderstandings and mistakes with serious consequences often occur. The reason for this are the sometimes considerable differences in the product declaration/analysis, especially in the units of measurement used. The main problem is that the values mentioned are often given in elementary form, especially in North America and the UK, while in Germany and the EU the corresponding oxide form is much more common. However, many manufacturers based in the EU also use the units of measurement common in North America and Great Britain. This is where things get complicated for the consumer, since products and their declarations cannot easily be compared with one another. The exchange of information between gardeners, e.g. in forums (especially at international level) is full of misunderstandings.
In order to avoid problems of this kind, one should always pay close attention to the form of the respective nutrient. If in doubt, it is always worth checking again before making any adjustments to the nutrient solution.
Here is an overview of the most important conversion factors:
Calcium
Calcium (Ca) zu Calciumoxide (CaO): 1,399
Calcium Oxide (CaO) and Calcium (Ca): 0.7147
Magnesium
Magnesium (Mg) to Magnesium Oxide (MgO): 1.658
Magnesium Oxide (MgO) to Magnesium (Mg): 0.6032
Phosphor
Phosphorus (P) to phosphorus pentoxide (P2THE5): 2,2914
Phosphorpentoxid (P2THE5) to phosphorus (P): 0.4364
Potassium
Potassium (K) to Potassium Oxide (K2O): 1.205
Potassium oxide (K2O) to potassium (K): 0.8302
sulfur
Sulfur (S) to sulfur dioxide (SO2): 1,998
Sulfur dioxide (SO2) to sulfur (S): 0.501
Sulfur (S) to sulfur trioxide (SO3): 2,497
Sulfur trioxide (SO3) to sulfur (S): 0.4
Sulfur (S) to sulfate (SO4): 2,996
Sulfat (SO4) to sulfur (S): 0.334
nitrogen
Nitrate (NO3) to nitrogen (N): 0.226
Ammonium (NH4) to nitrogen (N): 0.777
